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1.  Lu, WT; Zeng, Weiqiao; Sridhar, S Duality between quantum and classical dynamics for integrable billiards (Journal Article) In: Physical Review E, 73 (4), pp. 046201, 2006. @article{lu2006duality, title = {Duality between quantum and classical dynamics for integrable billiards}, author = {WT Lu and Weiqiao Zeng and S Sridhar}, year = {2006}, date = {20060101}, journal = {Physical Review E}, volume = {73}, number = {4}, pages = {046201}, publisher = {APS}, abstract = {We establish a duality between the quantum wave vector spectrum and the eigenmodes of the classical Liouvillian dynamics for integrable billiards. Signatures of the classical eigenmodes appear as peaks in the correlation function of the quantum wave vector spectrum. A semiclassical derivation and numerical calculations are presented in support of the results. These classical eigenmodes can be observed in physical experiments through the autocorrelation of the transmission coefficient of waves in quantum billiards. Exact classical trace formulas of the resolvent are derived for the rectangle, equilateral triangle, and circle billiards. We also establish a correspondence between the classical periodic orbit length spectrum and the quantum spectrum for integrable polygonal billiards.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We establish a duality between the quantum wave vector spectrum and the eigenmodes of the classical Liouvillian dynamics for integrable billiards. Signatures of the classical eigenmodes appear as peaks in the correlation function of the quantum wave vector spectrum. A semiclassical derivation and numerical calculations are presented in support of the results. These classical eigenmodes can be observed in physical experiments through the autocorrelation of the transmission coefficient of waves in quantum billiards. Exact classical trace formulas of the resolvent are derived for the rectangle, equilateral triangle, and circle billiards. We also establish a correspondence between the classical periodic orbit length spectrum and the quantum spectrum for integrable polygonal billiards. 
2.  Lu, WT; Sridhar, S Long range correlations among the eigenvalues of polygonal billiards and Riemann zeros (Journal Article) In: APS, 2004 , pp. D19–004, 2004. @article{lu2004long, title = {Long range correlations among the eigenvalues of polygonal billiards and Riemann zeros}, author = {WT Lu and S Sridhar}, year = {2004}, date = {20040101}, journal = {APS}, volume = {2004}, pages = {D19004}, abstract = {The momentum eigenvalue spectrum of polygonal billiards is shown to display a remarkable invariance when analyzed in terms of the spectral autocorrelation. The autocorrelation of any spectral window is encoded with the lowest eigenvalues. Thus a resurgence of the lowlying eigenstates occurs throughout the entire spectrum. We show that this can be understood in terms of the trace formula if the periodic orbits are stable, as occurs in integrable and pseudointegrable polygonal billiards. The same resurgence also occurs in the nontrivial zeros of the Riemann zeta function, albeit with negative amplitude. The analytical arguments are supported by numerical calculations. Work supported by NSF.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The momentum eigenvalue spectrum of polygonal billiards is shown to display a remarkable invariance when analyzed in terms of the spectral autocorrelation. The autocorrelation of any spectral window is encoded with the lowest eigenvalues. Thus a resurgence of the lowlying eigenstates occurs throughout the entire spectrum. We show that this can be understood in terms of the trace formula if the periodic orbits are stable, as occurs in integrable and pseudointegrable polygonal billiards. The same resurgence also occurs in the nontrivial zeros of the Riemann zeta function, albeit with negative amplitude. The analytical arguments are supported by numerical calculations. Work supported by NSF. 
3.  Lu, WT; Sridhar, S Correlations among the Riemann zeros: Invariance, resurgence, prophecy and selfduality (Journal Article) In: arXiv preprint nlin/0405058, 2004. @article{lu2004correlations, title = {Correlations among the Riemann zeros: Invariance, resurgence, prophecy and selfduality}, author = {WT Lu and S Sridhar}, year = {2004}, date = {20040101}, journal = {arXiv preprint nlin/0405058}, abstract = {We present a conjecture describing new long range correlations among the Riemann zeros leading to 3 principal features:(i) The spectral autocorrelation is invariant wrt the averaging window.(ii) Resurgence occurs wherein the lowest zeros appear in all autocorrelations.(iii) Suitably defined correlations lead to predictions (prophecy) of new zeros. This conjecture is supported by analytical arguments and confirmed by numerical calculations using 10^{22} zeros computed by Odlyzko. The results lead to a selfduality of the Riemann spectrum similar to the quantumclassical duality observed in billiards.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a conjecture describing new long range correlations among the Riemann zeros leading to 3 principal features:(i) The spectral autocorrelation is invariant wrt the averaging window.(ii) Resurgence occurs wherein the lowest zeros appear in all autocorrelations.(iii) Suitably defined correlations lead to predictions (prophecy) of new zeros. This conjecture is supported by analytical arguments and confirmed by numerical calculations using 10^{22} zeros computed by Odlyzko. The results lead to a selfduality of the Riemann spectrum similar to the quantumclassical duality observed in billiards. 
4.  Lu, WT; Sokoloff, JB; Sridhar, S Classical physics, including nonlinear media and photonic materialsRefraction of electromagnetic energy for wave packets incident on a negativeindex medium is always negative (Journal Article) In: Physical ReviewSection EStatistical Nonlinear and Soft Matter Physics, 69 (2), pp. 26604–26604, 2004. (BibTeX) @article{lu2004classical, title = {Classical physics, including nonlinear media and photonic materialsRefraction of electromagnetic energy for wave packets incident on a negativeindex medium is always negative}, author = {WT Lu and JB Sokoloff and S Sridhar}, year = {2004}, date = {20040101}, journal = {Physical ReviewSection EStatistical Nonlinear and Soft Matter Physics}, volume = {69}, number = {2}, pages = {2660426604}, publisher = {Melville, NY: Published by the American Physical Society through the~…}, keywords = {}, pubstate = {published}, tppubtype = {article} } 
5.  Wentao, Lu T; Sridhar, Srinivas; Zworski, Maciej Fractal Weyl laws for chaotic open systems (Journal Article) In: 2003. @article{wenfractal, title = {Fractal Weyl laws for chaotic open systems}, author = {Lu T Wentao and Srinivas Sridhar and Maciej Zworski}, year = {2003}, date = {20031008}, abstract = {We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems. 
6.  Pradhan, Prabhakar; Lu, Wentao T; Sridhar, S Statistics of the Eigenfunctions of Chaotic and Disordered Quantum Systems: A Disordered Tight Binding Model Calculation (Inproceedings) In: APS Meeting Abstracts, 2003. @inproceedings{pradhan2003statistics, title = {Statistics of the Eigenfunctions of Chaotic and Disordered Quantum Systems: A Disordered Tight Binding Model Calculation}, author = {Prabhakar Pradhan and Wentao T Lu and S Sridhar}, year = {2003}, date = {20030101}, booktitle = {APS Meeting Abstracts}, abstract = {We analyze the statistical properties of the eigenfunctions of the Anderson disordered tight binding Hamiltonian, for an electron in closed 2D, chaotic and disordered systems. For chaotic systems, the inverse participation ratio (IPR) that measures the amount of localization of an eigenstate, has a narrow and symmetric distribution peaked around IPR = 3, as predicted by random matrix theory. For disordered systems, the distribution is asymmetric and peaks at IPR > 3. As a function of energy, the IPR distribution decays as a power law with exponent 1/2 at low energies (i.e. more localized state), and saturates at IPR =3 (delocalized state) for larger energies. The spatial intensity autocorrelations of the eigenfunctions are strong for a more localized state at short distances, and they decay via a Friedel oscillation, as predicted by nonlinear sigma models, with a decay length scale corresponding to the localization length. For weak to moderate disorder in 2D, our numerical calculations are consistent with the random matrix theory, nonlinear sigma models, and also with our previous experimental results for 2D quantum chaotic and disordered systems.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } We analyze the statistical properties of the eigenfunctions of the Anderson disordered tight binding Hamiltonian, for an electron in closed 2D, chaotic and disordered systems. For chaotic systems, the inverse participation ratio (IPR) that measures the amount of localization of an eigenstate, has a narrow and symmetric distribution peaked around IPR = 3, as predicted by random matrix theory. For disordered systems, the distribution is asymmetric and peaks at IPR > 3. As a function of energy, the IPR distribution decays as a power law with exponent 1/2 at low energies (i.e. more localized state), and saturates at IPR =3 (delocalized state) for larger energies. The spatial intensity autocorrelations of the eigenfunctions are strong for a more localized state at short distances, and they decay via a Friedel oscillation, as predicted by nonlinear sigma models, with a decay length scale corresponding to the localization length. For weak to moderate disorder in 2D, our numerical calculations are consistent with the random matrix theory, nonlinear sigma models, and also with our previous experimental results for 2D quantum chaotic and disordered systems. 
7.  Lu, WT; Sridhar, Srinivas; Zworski, Maciej Fractal Weyl laws for chaotic open systems (Journal Article) In: Physical review letters, 91 (15), pp. 154101, 2003. @article{lu2003fractal, title = {Fractal Weyl laws for chaotic open systems}, author = {WT Lu and Srinivas Sridhar and Maciej Zworski}, year = {2003}, date = {20030101}, journal = {Physical review letters}, volume = {91}, number = {15}, pages = {154101}, publisher = {APS}, abstract = {We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems. 
8.  Sato, Daisuke; Lu, Wentao; Pradhan, Prabhakar; Sridhar, Srinivas Spectral statistics of microwave disordered billiards (Inproceedings) In: APS Meeting Abstracts, 2003. @inproceedings{sato2003spectral, title = {Spectral statistics of microwave disordered billiards}, author = {Daisuke Sato and Wentao Lu and Prabhakar Pradhan and Srinivas Sridhar}, year = {2003}, date = {20030101}, booktitle = {APS Meeting Abstracts}, abstract = {Using a new algorithm to analyze experimental microwave spectra, we are able to accurately obtain nearly 1000 eigenvalues for microwave disordered billiards with no missing energy level. The cumulative level density N (E) of all billiards is in good agreement with the Weyl formula. We also determine statistical measures such as P (s), Delta_3, R_2, Y_2, Sigma_2, and study their dependence on the mean free path and localization length. The experimental results are compared with the supersymmetry sigma model and tight binding calculations. Work supported by NSF0098801.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Using a new algorithm to analyze experimental microwave spectra, we are able to accurately obtain nearly 1000 eigenvalues for microwave disordered billiards with no missing energy level. The cumulative level density N (E) of all billiards is in good agreement with the Weyl formula. We also determine statistical measures such as P (s), Delta_3, R_2, Y_2, Sigma_2, and study their dependence on the mean free path and localization length. The experimental results are compared with the supersymmetry sigma model and tight binding calculations. Work supported by NSF0098801. 
9.  Dhar, Abhishek; Rao, Madhusudhana D; Sridhar, S; others, Isospectrality in chaotic billiards (Journal Article) In: Physical Review E, 68 (2), pp. 026208, 2003. @article{dhar2003isospectrality, title = {Isospectrality in chaotic billiards}, author = {Abhishek Dhar and Madhusudhana D Rao and S Sridhar and others}, year = {2003}, date = {20030101}, journal = {Physical Review E}, volume = {68}, number = {2}, pages = {026208}, publisher = {APS}, abstract = {We consider a modification of isospectral cavities whereby the classical dynamics changes from pseudointegrable to chaotic. We construct an example where we can prove that isospectrality is retained. We then demonstrate this explicitly in microwave resonators.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We consider a modification of isospectral cavities whereby the classical dynamics changes from pseudointegrable to chaotic. We construct an example where we can prove that isospectrality is retained. We then demonstrate this explicitly in microwave resonators. 
10.  Sridhar, S; Lu, WT Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments (Journal Article) In: Journal of statistical physics, 108 (56), pp. 755–765, 2002. @article{sridhar2002sinai, title = {Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments}, author = {S Sridhar and WT Lu}, year = {2002}, date = {20020101}, journal = {Journal of statistical physics}, volume = {108}, number = {56}, pages = {755765}, publisher = {Kluwer Academic PublishersPlenum Publishers}, abstract = {We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as “scars” in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as “scars” in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards. 
11.  Pradhan, Prabhakar; Sridhar, S From chaos to disorder: Statistics of the eigenfunctions of microwave cavities (Journal Article) In: Pramana, 58 (2), pp. 333–341, 2002. @article{pradhan2002chaos, title = {From chaos to disorder: Statistics of the eigenfunctions of microwave cavities}, author = {Prabhakar Pradhan and S Sridhar}, year = {2002}, date = {20020101}, journal = {Pramana}, volume = {58}, number = {2}, pages = {333341}, publisher = {Springer India}, abstract = {We study the statistics of the experimental eigenfunctions of chaotic and disordered microwave billiards in terms of the moments of their spatial distributions, such as the inverse participation ratio (IPR) and densitydensity autocorrelation. A path from chaos to disorder is described in terms of increasing IPR. In the chaotic, ballistic limit, the data correspond well with universal results from random matrix theory. Deviations from universal distributions are observed due to disorder induced localization, and for the weakly disordered case the data are welldescribed by including finite conductance and mean free path contributions in the framework of nonlinear sigma models of supersymmetry.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the statistics of the experimental eigenfunctions of chaotic and disordered microwave billiards in terms of the moments of their spatial distributions, such as the inverse participation ratio (IPR) and densitydensity autocorrelation. A path from chaos to disorder is described in terms of increasing IPR. In the chaotic, ballistic limit, the data correspond well with universal results from random matrix theory. Deviations from universal distributions are observed due to disorder induced localization, and for the weakly disordered case the data are welldescribed by including finite conductance and mean free path contributions in the framework of nonlinear sigma models of supersymmetry. 
12.  Sridhar, S; Lu, WT Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments. eprint (Journal Article) In: 2002. @article{sridhar2002sinaib, title = {Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments. eprint}, author = {S Sridhar and WT Lu}, year = {2002}, date = {20020101}, abstract = {We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as ‘‘scars’’in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as ‘‘scars’’in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards. 
13.  Sinai, Ya G; Young, LaiSang; Sridhar, S; Lu, WT; van Beijeren, Henk; Dorfman, JR; Jakšic, V; Pillet, CA; Gallavotti, G; Lebowitz, JL; others, Some IllFormulated Problems on Regular and Messy Behavior in Statistical Mechanics and Smooth Dynamics for Which I Would Like the Advice of Yasha Sinai David Ruelle What, in My Opinion, David Ruelle Should Do in the Coming Years (Journal Article) In: Journal of Statistical Physics, 108 (3/4), 2002. (BibTeX) @article{sinai2002some, title = {Some IllFormulated Problems on Regular and Messy Behavior in Statistical Mechanics and Smooth Dynamics for Which I Would Like the Advice of Yasha Sinai David Ruelle What, in My Opinion, David Ruelle Should Do in the Coming Years}, author = {Ya G Sinai and LaiSang Young and S Sridhar and WT Lu and Henk van Beijeren and JR Dorfman and V Jakšic and CA Pillet and G Gallavotti and JL Lebowitz and others}, year = {2002}, date = {20020101}, journal = {Journal of Statistical Physics}, volume = {108}, number = {3/4}, keywords = {}, pubstate = {published}, tppubtype = {article} } 
14.  Lu, WT; Sridhar, S; others, Spectra and wave functions of open chaotic billiards (Inproceedings) In: APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts, 2002. @inproceedings{lu2002spectra, title = {Spectra and wave functions of open chaotic billiards}, author = {WT Lu and S Sridhar and others}, year = {2002}, date = {20020101}, booktitle = {APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts}, abstract = {The quantum spectra and wave functions of the ndisk open chaotic system are studied. The spectra consist of quantum resonances which are calculated in period orbit theory and measured in microwave experiments. The correlation of quantum resonances leads to the classical RuellePollicott resonances. The scattering wave functions are studied numerically and experimentally. Scars are observed and wave function statistics are analyzed. Spectra and wave functions of divided phase space billiard are also studied. Work supported by NSFPHY0098801}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } The quantum spectra and wave functions of the ndisk open chaotic system are studied. The spectra consist of quantum resonances which are calculated in period orbit theory and measured in microwave experiments. The correlation of quantum resonances leads to the classical RuellePollicott resonances. The scattering wave functions are studied numerically and experimentally. Scars are observed and wave function statistics are analyzed. Spectra and wave functions of divided phase space billiard are also studied. Work supported by NSFPHY0098801 
15.  Sridhar, Srinivas Quantum Chaos in Microwave Billiards (Inproceedings) In: APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts, 2002. @inproceedings{sridhar2002quantum, title = {Quantum Chaos in Microwave Billiards}, author = {Srinivas Sridhar}, year = {2002}, date = {20020101}, booktitle = {APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts}, abstract = {I discuss some recent themes from microwave experiments designed to explore issues in Quantum Chaos. The experiments measure spectra and eigenfunctions of model geometries in the form of closed and open billiards. The microwave billiards provide a nearly ideal laboratory realization of a particle in hardwall 2D potentials, suitable for exploring the quantumclassical correspondence in chaotic systems, and capture the essential features of diverse situations in atomic and optical physics. The experiments reveal universal features of spectral and eigenfunction statistics that are well described by random matrix theory. Nonuniversal features are also observed, particularly periodic orbit contributions such as scars in eigenfunctions. A systematic trend from chaos to disorder is studied in disordered billiards, where quantum diffusion and interference lead to localization and nonuniversal behavior of density … }, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } I discuss some recent themes from microwave experiments designed to explore issues in Quantum Chaos. The experiments measure spectra and eigenfunctions of model geometries in the form of closed and open billiards. The microwave billiards provide a nearly ideal laboratory realization of a particle in hardwall 2D potentials, suitable for exploring the quantumclassical correspondence in chaotic systems, and capture the essential features of diverse situations in atomic and optical physics. The experiments reveal universal features of spectral and eigenfunction statistics that are well described by random matrix theory. Nonuniversal features are also observed, particularly periodic orbit contributions such as scars in eigenfunctions. A systematic trend from chaos to disorder is studied in disordered billiards, where quantum diffusion and interference lead to localization and nonuniversal behavior of density … 
16.  Lu, Wentao T; Prance, Kristi; Pradhan, Prabhakar; Sridhar, S Quantum correlations and classical resonances in an open chaotic system (Journal Article) In: Physica Scripta, 2001 (T90), pp. 238, 2001. @article{lu2001quantum, title = {Quantum correlations and classical resonances in an open chaotic system}, author = {Wentao T Lu and Kristi Prance and Prabhakar Pradhan and S Sridhar}, year = {2001}, date = {20010101}, journal = {Physica Scripta}, volume = {2001}, number = {T90}, pages = {238}, publisher = {IOP Publishing}, abstract = {We show that the autocorrelation of quantum spectra of an open chaotic system is well described by the classical RuellePollicott resonances of the associated chaotic strange repeller. This correspondence is demonstrated utilizing microwave experiments on 2D ndisk billiard geometries, by determination of the wavevector autocorrelation C (κ) from the experimental quantum spectra S 21 (k). The correspondence is also established via" numerical experiments" that simulate S 21 (k) and C (κ) using periodic orbit calculations of the quantum and classical resonances. Semiclassical arguments that relate quantum and classical correlation functions in terms of fluctuations of the density of states and correlations of particle density are also examined and support the experimental results. The results establish a correspondence between quantum spectral correlations and classical decay modes in an open system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that the autocorrelation of quantum spectra of an open chaotic system is well described by the classical RuellePollicott resonances of the associated chaotic strange repeller. This correspondence is demonstrated utilizing microwave experiments on 2D ndisk billiard geometries, by determination of the wavevector autocorrelation C (κ) from the experimental quantum spectra S 21 (k). The correspondence is also established via" numerical experiments" that simulate S 21 (k) and C (κ) using periodic orbit calculations of the quantum and classical resonances. Semiclassical arguments that relate quantum and classical correlation functions in terms of fluctuations of the density of states and correlations of particle density are also examined and support the experimental results. The results establish a correspondence between quantum spectral correlations and classical decay modes in an open system. 
17.  Sridhar, S Quantum resonances and decay of a fractal repeller observed using microwaves (Inproceedings) In: APS Meeting Abstracts, 2000. @inproceedings{sridhar2000quantum, title = {Quantum resonances and decay of a fractal repeller observed using microwaves}, author = {S Sridhar}, year = {2000}, date = {20000101}, booktitle = {APS Meeting Abstracts}, abstract = {We describe an experimental realization of the wellknown problem of ndisk scattering, which may be regarded as the "hydrogen atom" of chaotic scattering. This model geometry is related to diverse areas such as open systems, semiconductor microstructures and photodissociation. In the experiment, the quantum resonances of classically chaotic ndisk geometries were studied utilizing thin 2D microwave geometries. The transmission spectrum probes the stationary Green's function of the system, and yields both frequencies and widths of the lowlying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. In the microwave experiments the wave vector correlations can be directly studied, and hence these are an interesting complement to ballistic transport in semiconductor microstructures in which correlations in the magnetotransport are obtained. The long time or small energy behavior of the wavevector autocorrelation gives information about the quantum decay rate, which is in good agreement with that obtained from classical scattering theory. For intermediate energies, nonuniversal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits. W.T. Lu, M. Rose, K. Pance and S.Sridhar, Phys. Rev. Lett., vol 82, pp. 5233 (1999). W.T. Lu, L. Viola, K.Pance, M. Rose and S.Sridhar, Phys. Rev. E (submitted)}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } We describe an experimental realization of the wellknown problem of ndisk scattering, which may be regarded as the "hydrogen atom" of chaotic scattering. This model geometry is related to diverse areas such as open systems, semiconductor microstructures and photodissociation. In the experiment, the quantum resonances of classically chaotic ndisk geometries were studied utilizing thin 2D microwave geometries. The transmission spectrum probes the stationary Green's function of the system, and yields both frequencies and widths of the lowlying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. In the microwave experiments the wave vector correlations can be directly studied, and hence these are an interesting complement to ballistic transport in semiconductor microstructures in which correlations in the magnetotransport are obtained. The long time or small energy behavior of the wavevector autocorrelation gives information about the quantum decay rate, which is in good agreement with that obtained from classical scattering theory. For intermediate energies, nonuniversal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits. W.T. Lu, M. Rose, K. Pance and S.Sridhar, Phys. Rev. Lett., vol 82, pp. 5233 (1999). W.T. Lu, L. Viola, K.Pance, M. Rose and S.Sridhar, Phys. Rev. E (submitted) 
18.  Sridhar, S Quantum chaos, localization and tunnelling: microwave experiments on model geometries (Journal Article) In: Philosophical Magazine B, 80 (12), pp. 2129–2141, 2000. @article{sridhar2000quantumb, title = {Quantum chaos, localization and tunnelling: microwave experiments on model geometries}, author = {S Sridhar}, year = {2000}, date = {20000101}, journal = {Philosophical Magazine B}, volume = {80}, number = {12}, pages = {21292141}, publisher = {Taylor & Francis}, abstract = {Microwave experiments using twodimensional billiard geometries are a precise test of basic issues in quantum chaos, localization and tunnelling. In closed chaotic geometries, analysis of eigenvalue statistics yields good agreement with randommatrix theory. A unique aspect of the experiments is the ability to measure eigenfunctions directly. The influence of periodic orbit scarring in chaotic eigenfunctions is directly demonstrated. Disordered microwave billiards are a textbook model system for studying the quantum properties of a single particle in a disordered potential. Localization is directly observed in eigenfunctions of the disordered billiards. Statistical properties of disordered eigenfunctions deviate from universal behaviour due to localization. These statistical properties are in good agreement with predictions from nonlinearsigma models, although many challenges for further theoretical understanding remain. The experiments can also probe open systems, in terms of the quantum resonances and escape rate of a fractal repeller. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Microwave experiments using twodimensional billiard geometries are a precise test of basic issues in quantum chaos, localization and tunnelling. In closed chaotic geometries, analysis of eigenvalue statistics yields good agreement with randommatrix theory. A unique aspect of the experiments is the ability to measure eigenfunctions directly. The influence of periodic orbit scarring in chaotic eigenfunctions is directly demonstrated. Disordered microwave billiards are a textbook model system for studying the quantum properties of a single particle in a disordered potential. Localization is directly observed in eigenfunctions of the disordered billiards. Statistical properties of disordered eigenfunctions deviate from universal behaviour due to localization. These statistical properties are in good agreement with predictions from nonlinearsigma models, although many challenges for further theoretical understanding remain. The experiments can also probe open systems, in terms of the quantum resonances and escape rate of a fractal repeller. 
19.  Pance, Kristi; Lu, Wentao; Sridhar, S Quantum fingerprints of classical ruellepollicott resonances (Journal Article) In: Physical review letters, 85 (13), pp. 2737, 2000. @article{pance2000quantum, title = {Quantum fingerprints of classical ruellepollicott resonances}, author = {Kristi Pance and Wentao Lu and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physical review letters}, volume = {85}, number = {13}, pages = {2737}, publisher = {American Physical Society}, abstract = {Quantum and classical correlations are studied experimentally in model ndisk microwave billiards. The wave vector κ autocorrelation C (κ) of the quantum spectrum displays nonuniversal oscillations for large κ, comparable to the universal random matrix theory behavior observed for small κ. The nonuniversal behavior is shown to be completely determined by the classical RuellePollicott resonances, arising from the complex eigenvalues of the PerronFrobenius operator, and calculated using periodic orbit theory. This work establishes a fundamental connection between the quantum and classical correlations of an open system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Quantum and classical correlations are studied experimentally in model ndisk microwave billiards. The wave vector κ autocorrelation C (κ) of the quantum spectrum displays nonuniversal oscillations for large κ, comparable to the universal random matrix theory behavior observed for small κ. The nonuniversal behavior is shown to be completely determined by the classical RuellePollicott resonances, arising from the complex eigenvalues of the PerronFrobenius operator, and calculated using periodic orbit theory. This work establishes a fundamental connection between the quantum and classical correlations of an open system. 
20.  Pradhan, Prabhakar; Sridhar, S Correlations due to localization in quantum eigenfunctions of disordered microwave cavities (Journal Article) In: Physical review letters, 85 (11), pp. 2360, 2000. @article{pradhan2000correlations, title = {Correlations due to localization in quantum eigenfunctions of disordered microwave cavities}, author = {Prabhakar Pradhan and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physical review letters}, volume = {85}, number = {11}, pages = {2360}, publisher = {APS}, abstract = {Statistical properties of experimental eigenfunctions of quantum chaotic and disordered microwave cavities are shown to demonstrate nonuniversal correlations due to localization. Varying energy E and mean free path l enable us to experimentally tune from localized to delocalized states. Large leveltolevel inverse participation ratio (I 2) fluctuations are observed for the disordered billiards, whose distribution is strongly asymmetric about< I 2>. The spatial density autocorrelations of eigenfunctions are shown to spatially decay exponentially and the decay lengths are experimentally determined. All the results are quantitatively consistent with calculations based upon nonlinear sigma models.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Statistical properties of experimental eigenfunctions of quantum chaotic and disordered microwave cavities are shown to demonstrate nonuniversal correlations due to localization. Varying energy E and mean free path l enable us to experimentally tune from localized to delocalized states. Large leveltolevel inverse participation ratio (I 2) fluctuations are observed for the disordered billiards, whose distribution is strongly asymmetric about< I 2>. The spatial density autocorrelations of eigenfunctions are shown to spatially decay exponentially and the decay lengths are experimentally determined. All the results are quantitatively consistent with calculations based upon nonlinear sigma models. 
2006 

40.  Lu, WT; Zeng, Weiqiao; Sridhar, S Duality between quantum and classical dynamics for integrable billiards Journal Article Physical Review E, 73 (4), pp. 046201, 2006. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2006duality, title = {Duality between quantum and classical dynamics for integrable billiards}, author = {WT Lu and Weiqiao Zeng and S Sridhar}, year = {2006}, date = {20060101}, journal = {Physical Review E}, volume = {73}, number = {4}, pages = {046201}, publisher = {APS}, abstract = {We establish a duality between the quantum wave vector spectrum and the eigenmodes of the classical Liouvillian dynamics for integrable billiards. Signatures of the classical eigenmodes appear as peaks in the correlation function of the quantum wave vector spectrum. A semiclassical derivation and numerical calculations are presented in support of the results. These classical eigenmodes can be observed in physical experiments through the autocorrelation of the transmission coefficient of waves in quantum billiards. Exact classical trace formulas of the resolvent are derived for the rectangle, equilateral triangle, and circle billiards. We also establish a correspondence between the classical periodic orbit length spectrum and the quantum spectrum for integrable polygonal billiards.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We establish a duality between the quantum wave vector spectrum and the eigenmodes of the classical Liouvillian dynamics for integrable billiards. Signatures of the classical eigenmodes appear as peaks in the correlation function of the quantum wave vector spectrum. A semiclassical derivation and numerical calculations are presented in support of the results. These classical eigenmodes can be observed in physical experiments through the autocorrelation of the transmission coefficient of waves in quantum billiards. Exact classical trace formulas of the resolvent are derived for the rectangle, equilateral triangle, and circle billiards. We also establish a correspondence between the classical periodic orbit length spectrum and the quantum spectrum for integrable polygonal billiards. 
2004 

39.  Lu, WT; Sridhar, S Long range correlations among the eigenvalues of polygonal billiards and Riemann zeros Journal Article APS, 2004 , pp. D19–004, 2004. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2004long, title = {Long range correlations among the eigenvalues of polygonal billiards and Riemann zeros}, author = {WT Lu and S Sridhar}, year = {2004}, date = {20040101}, journal = {APS}, volume = {2004}, pages = {D19004}, abstract = {The momentum eigenvalue spectrum of polygonal billiards is shown to display a remarkable invariance when analyzed in terms of the spectral autocorrelation. The autocorrelation of any spectral window is encoded with the lowest eigenvalues. Thus a resurgence of the lowlying eigenstates occurs throughout the entire spectrum. We show that this can be understood in terms of the trace formula if the periodic orbits are stable, as occurs in integrable and pseudointegrable polygonal billiards. The same resurgence also occurs in the nontrivial zeros of the Riemann zeta function, albeit with negative amplitude. The analytical arguments are supported by numerical calculations. Work supported by NSF.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } The momentum eigenvalue spectrum of polygonal billiards is shown to display a remarkable invariance when analyzed in terms of the spectral autocorrelation. The autocorrelation of any spectral window is encoded with the lowest eigenvalues. Thus a resurgence of the lowlying eigenstates occurs throughout the entire spectrum. We show that this can be understood in terms of the trace formula if the periodic orbits are stable, as occurs in integrable and pseudointegrable polygonal billiards. The same resurgence also occurs in the nontrivial zeros of the Riemann zeta function, albeit with negative amplitude. The analytical arguments are supported by numerical calculations. Work supported by NSF. 
38.  Lu, WT; Sridhar, S Correlations among the Riemann zeros: Invariance, resurgence, prophecy and selfduality Journal Article arXiv preprint nlin/0405058, 2004. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2004correlations, title = {Correlations among the Riemann zeros: Invariance, resurgence, prophecy and selfduality}, author = {WT Lu and S Sridhar}, year = {2004}, date = {20040101}, journal = {arXiv preprint nlin/0405058}, abstract = {We present a conjecture describing new long range correlations among the Riemann zeros leading to 3 principal features:(i) The spectral autocorrelation is invariant wrt the averaging window.(ii) Resurgence occurs wherein the lowest zeros appear in all autocorrelations.(iii) Suitably defined correlations lead to predictions (prophecy) of new zeros. This conjecture is supported by analytical arguments and confirmed by numerical calculations using 10^{22} zeros computed by Odlyzko. The results lead to a selfduality of the Riemann spectrum similar to the quantumclassical duality observed in billiards.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We present a conjecture describing new long range correlations among the Riemann zeros leading to 3 principal features:(i) The spectral autocorrelation is invariant wrt the averaging window.(ii) Resurgence occurs wherein the lowest zeros appear in all autocorrelations.(iii) Suitably defined correlations lead to predictions (prophecy) of new zeros. This conjecture is supported by analytical arguments and confirmed by numerical calculations using 10^{22} zeros computed by Odlyzko. The results lead to a selfduality of the Riemann spectrum similar to the quantumclassical duality observed in billiards. 
37.  Lu, WT; Sokoloff, JB; Sridhar, S Classical physics, including nonlinear media and photonic materialsRefraction of electromagnetic energy for wave packets incident on a negativeindex medium is always negative Journal Article Physical ReviewSection EStatistical Nonlinear and Soft Matter Physics, 69 (2), pp. 26604–26604, 2004. BibTeX  Tags: Quantum Chaos @article{lu2004classical, title = {Classical physics, including nonlinear media and photonic materialsRefraction of electromagnetic energy for wave packets incident on a negativeindex medium is always negative}, author = {WT Lu and JB Sokoloff and S Sridhar}, year = {2004}, date = {20040101}, journal = {Physical ReviewSection EStatistical Nonlinear and Soft Matter Physics}, volume = {69}, number = {2}, pages = {2660426604}, publisher = {Melville, NY: Published by the American Physical Society through the~…}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } 
2003 

36.  Wentao, Lu T; Sridhar, Srinivas; Zworski, Maciej Fractal Weyl laws for chaotic open systems Journal Article 2003. Abstract  BibTeX  Tags: Quantum Chaos @article{wenfractal, title = {Fractal Weyl laws for chaotic open systems}, author = {Lu T Wentao and Srinivas Sridhar and Maciej Zworski}, year = {2003}, date = {20031008}, abstract = {We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems. 
35.  Pradhan, Prabhakar; Lu, Wentao T; Sridhar, S Statistics of the Eigenfunctions of Chaotic and Disordered Quantum Systems: A Disordered Tight Binding Model Calculation Inproceedings APS Meeting Abstracts, 2003. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{pradhan2003statistics, title = {Statistics of the Eigenfunctions of Chaotic and Disordered Quantum Systems: A Disordered Tight Binding Model Calculation}, author = {Prabhakar Pradhan and Wentao T Lu and S Sridhar}, year = {2003}, date = {20030101}, booktitle = {APS Meeting Abstracts}, abstract = {We analyze the statistical properties of the eigenfunctions of the Anderson disordered tight binding Hamiltonian, for an electron in closed 2D, chaotic and disordered systems. For chaotic systems, the inverse participation ratio (IPR) that measures the amount of localization of an eigenstate, has a narrow and symmetric distribution peaked around IPR = 3, as predicted by random matrix theory. For disordered systems, the distribution is asymmetric and peaks at IPR > 3. As a function of energy, the IPR distribution decays as a power law with exponent 1/2 at low energies (i.e. more localized state), and saturates at IPR =3 (delocalized state) for larger energies. The spatial intensity autocorrelations of the eigenfunctions are strong for a more localized state at short distances, and they decay via a Friedel oscillation, as predicted by nonlinear sigma models, with a decay length scale corresponding to the localization length. For weak to moderate disorder in 2D, our numerical calculations are consistent with the random matrix theory, nonlinear sigma models, and also with our previous experimental results for 2D quantum chaotic and disordered systems.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } We analyze the statistical properties of the eigenfunctions of the Anderson disordered tight binding Hamiltonian, for an electron in closed 2D, chaotic and disordered systems. For chaotic systems, the inverse participation ratio (IPR) that measures the amount of localization of an eigenstate, has a narrow and symmetric distribution peaked around IPR = 3, as predicted by random matrix theory. For disordered systems, the distribution is asymmetric and peaks at IPR > 3. As a function of energy, the IPR distribution decays as a power law with exponent 1/2 at low energies (i.e. more localized state), and saturates at IPR =3 (delocalized state) for larger energies. The spatial intensity autocorrelations of the eigenfunctions are strong for a more localized state at short distances, and they decay via a Friedel oscillation, as predicted by nonlinear sigma models, with a decay length scale corresponding to the localization length. For weak to moderate disorder in 2D, our numerical calculations are consistent with the random matrix theory, nonlinear sigma models, and also with our previous experimental results for 2D quantum chaotic and disordered systems. 
34.  Lu, WT; Sridhar, Srinivas; Zworski, Maciej Fractal Weyl laws for chaotic open systems Journal Article Physical review letters, 91 (15), pp. 154101, 2003. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2003fractal, title = {Fractal Weyl laws for chaotic open systems}, author = {WT Lu and Srinivas Sridhar and Maciej Zworski}, year = {2003}, date = {20030101}, journal = {Physical review letters}, volume = {91}, number = {15}, pages = {154101}, publisher = {APS}, abstract = {We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems. 
33.  Sato, Daisuke; Lu, Wentao; Pradhan, Prabhakar; Sridhar, Srinivas Spectral statistics of microwave disordered billiards Inproceedings APS Meeting Abstracts, 2003. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{sato2003spectral, title = {Spectral statistics of microwave disordered billiards}, author = {Daisuke Sato and Wentao Lu and Prabhakar Pradhan and Srinivas Sridhar}, year = {2003}, date = {20030101}, booktitle = {APS Meeting Abstracts}, abstract = {Using a new algorithm to analyze experimental microwave spectra, we are able to accurately obtain nearly 1000 eigenvalues for microwave disordered billiards with no missing energy level. The cumulative level density N (E) of all billiards is in good agreement with the Weyl formula. We also determine statistical measures such as P (s), Delta_3, R_2, Y_2, Sigma_2, and study their dependence on the mean free path and localization length. The experimental results are compared with the supersymmetry sigma model and tight binding calculations. Work supported by NSF0098801.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } Using a new algorithm to analyze experimental microwave spectra, we are able to accurately obtain nearly 1000 eigenvalues for microwave disordered billiards with no missing energy level. The cumulative level density N (E) of all billiards is in good agreement with the Weyl formula. We also determine statistical measures such as P (s), Delta_3, R_2, Y_2, Sigma_2, and study their dependence on the mean free path and localization length. The experimental results are compared with the supersymmetry sigma model and tight binding calculations. Work supported by NSF0098801. 
32.  Dhar, Abhishek; Rao, Madhusudhana D; Sridhar, S; others, Isospectrality in chaotic billiards Journal Article Physical Review E, 68 (2), pp. 026208, 2003. Abstract  BibTeX  Tags: Quantum Chaos @article{dhar2003isospectrality, title = {Isospectrality in chaotic billiards}, author = {Abhishek Dhar and Madhusudhana D Rao and S Sridhar and others}, year = {2003}, date = {20030101}, journal = {Physical Review E}, volume = {68}, number = {2}, pages = {026208}, publisher = {APS}, abstract = {We consider a modification of isospectral cavities whereby the classical dynamics changes from pseudointegrable to chaotic. We construct an example where we can prove that isospectrality is retained. We then demonstrate this explicitly in microwave resonators.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We consider a modification of isospectral cavities whereby the classical dynamics changes from pseudointegrable to chaotic. We construct an example where we can prove that isospectrality is retained. We then demonstrate this explicitly in microwave resonators. 
2002 

31.  Sridhar, S; Lu, WT Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments Journal Article Journal of statistical physics, 108 (56), pp. 755–765, 2002. Abstract  BibTeX  Tags: Quantum Chaos @article{sridhar2002sinai, title = {Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments}, author = {S Sridhar and WT Lu}, year = {2002}, date = {20020101}, journal = {Journal of statistical physics}, volume = {108}, number = {56}, pages = {755765}, publisher = {Kluwer Academic PublishersPlenum Publishers}, abstract = {We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as “scars” in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as “scars” in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards. 
30.  Pradhan, Prabhakar; Sridhar, S From chaos to disorder: Statistics of the eigenfunctions of microwave cavities Journal Article Pramana, 58 (2), pp. 333–341, 2002. Abstract  BibTeX  Tags: Quantum Chaos @article{pradhan2002chaos, title = {From chaos to disorder: Statistics of the eigenfunctions of microwave cavities}, author = {Prabhakar Pradhan and S Sridhar}, year = {2002}, date = {20020101}, journal = {Pramana}, volume = {58}, number = {2}, pages = {333341}, publisher = {Springer India}, abstract = {We study the statistics of the experimental eigenfunctions of chaotic and disordered microwave billiards in terms of the moments of their spatial distributions, such as the inverse participation ratio (IPR) and densitydensity autocorrelation. A path from chaos to disorder is described in terms of increasing IPR. In the chaotic, ballistic limit, the data correspond well with universal results from random matrix theory. Deviations from universal distributions are observed due to disorder induced localization, and for the weakly disordered case the data are welldescribed by including finite conductance and mean free path contributions in the framework of nonlinear sigma models of supersymmetry.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We study the statistics of the experimental eigenfunctions of chaotic and disordered microwave billiards in terms of the moments of their spatial distributions, such as the inverse participation ratio (IPR) and densitydensity autocorrelation. A path from chaos to disorder is described in terms of increasing IPR. In the chaotic, ballistic limit, the data correspond well with universal results from random matrix theory. Deviations from universal distributions are observed due to disorder induced localization, and for the weakly disordered case the data are welldescribed by including finite conductance and mean free path contributions in the framework of nonlinear sigma models of supersymmetry. 
29.  Sridhar, S; Lu, WT Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments. eprint Journal Article 2002. Abstract  BibTeX  Tags: Quantum Chaos @article{sridhar2002sinaib, title = {Sinai billiards, Ruelle zetafunctions and Ruelle resonances: microwave experiments. eprint}, author = {S Sridhar and WT Lu}, year = {2002}, date = {20020101}, abstract = {We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as ‘‘scars’’in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We discuss the impact of recent developments in the theory of chaotic dynamical systems, particularly the results of Sinai and Ruelle, on microwave experiments designed to study quantum chaos. The properties of closed Sinai billiard microwave cavities are discussed in terms of universal predictions from random matrix theory, as well as periodic orbit contributions which manifest as ‘‘scars’’in eigenfunctions. The semiclassical and classical Ruelle zetafunctions lead to quantum and classical resonances, both of which are observed in microwave experiments on ndisk hyperbolic billiards. 
28.  Sinai, Ya G; Young, LaiSang; Sridhar, S; Lu, WT; van Beijeren, Henk; Dorfman, JR; Jakšic, V; Pillet, CA; Gallavotti, G; Lebowitz, JL; others, Some IllFormulated Problems on Regular and Messy Behavior in Statistical Mechanics and Smooth Dynamics for Which I Would Like the Advice of Yasha Sinai David Ruelle What, in My Opinion, David Ruelle Should Do in the Coming Years Journal Article Journal of Statistical Physics, 108 (3/4), 2002. BibTeX  Tags: Quantum Chaos @article{sinai2002some, title = {Some IllFormulated Problems on Regular and Messy Behavior in Statistical Mechanics and Smooth Dynamics for Which I Would Like the Advice of Yasha Sinai David Ruelle What, in My Opinion, David Ruelle Should Do in the Coming Years}, author = {Ya G Sinai and LaiSang Young and S Sridhar and WT Lu and Henk van Beijeren and JR Dorfman and V Jakšic and CA Pillet and G Gallavotti and JL Lebowitz and others}, year = {2002}, date = {20020101}, journal = {Journal of Statistical Physics}, volume = {108}, number = {3/4}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } 
27.  Lu, WT; Sridhar, S; others, Spectra and wave functions of open chaotic billiards Inproceedings APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts, 2002. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{lu2002spectra, title = {Spectra and wave functions of open chaotic billiards}, author = {WT Lu and S Sridhar and others}, year = {2002}, date = {20020101}, booktitle = {APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts}, abstract = {The quantum spectra and wave functions of the ndisk open chaotic system are studied. The spectra consist of quantum resonances which are calculated in period orbit theory and measured in microwave experiments. The correlation of quantum resonances leads to the classical RuellePollicott resonances. The scattering wave functions are studied numerically and experimentally. Scars are observed and wave function statistics are analyzed. Spectra and wave functions of divided phase space billiard are also studied. Work supported by NSFPHY0098801}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } The quantum spectra and wave functions of the ndisk open chaotic system are studied. The spectra consist of quantum resonances which are calculated in period orbit theory and measured in microwave experiments. The correlation of quantum resonances leads to the classical RuellePollicott resonances. The scattering wave functions are studied numerically and experimentally. Scars are observed and wave function statistics are analyzed. Spectra and wave functions of divided phase space billiard are also studied. Work supported by NSFPHY0098801 
26.  Sridhar, Srinivas Quantum Chaos in Microwave Billiards Inproceedings APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts, 2002. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{sridhar2002quantum, title = {Quantum Chaos in Microwave Billiards}, author = {Srinivas Sridhar}, year = {2002}, date = {20020101}, booktitle = {APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts}, abstract = {I discuss some recent themes from microwave experiments designed to explore issues in Quantum Chaos. The experiments measure spectra and eigenfunctions of model geometries in the form of closed and open billiards. The microwave billiards provide a nearly ideal laboratory realization of a particle in hardwall 2D potentials, suitable for exploring the quantumclassical correspondence in chaotic systems, and capture the essential features of diverse situations in atomic and optical physics. The experiments reveal universal features of spectral and eigenfunction statistics that are well described by random matrix theory. Nonuniversal features are also observed, particularly periodic orbit contributions such as scars in eigenfunctions. A systematic trend from chaos to disorder is studied in disordered billiards, where quantum diffusion and interference lead to localization and nonuniversal behavior of density … }, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } I discuss some recent themes from microwave experiments designed to explore issues in Quantum Chaos. The experiments measure spectra and eigenfunctions of model geometries in the form of closed and open billiards. The microwave billiards provide a nearly ideal laboratory realization of a particle in hardwall 2D potentials, suitable for exploring the quantumclassical correspondence in chaotic systems, and capture the essential features of diverse situations in atomic and optical physics. The experiments reveal universal features of spectral and eigenfunction statistics that are well described by random matrix theory. Nonuniversal features are also observed, particularly periodic orbit contributions such as scars in eigenfunctions. A systematic trend from chaos to disorder is studied in disordered billiards, where quantum diffusion and interference lead to localization and nonuniversal behavior of density … 
2001 

25.  Lu, Wentao T; Prance, Kristi; Pradhan, Prabhakar; Sridhar, S Quantum correlations and classical resonances in an open chaotic system Journal Article Physica Scripta, 2001 (T90), pp. 238, 2001. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2001quantum, title = {Quantum correlations and classical resonances in an open chaotic system}, author = {Wentao T Lu and Kristi Prance and Prabhakar Pradhan and S Sridhar}, year = {2001}, date = {20010101}, journal = {Physica Scripta}, volume = {2001}, number = {T90}, pages = {238}, publisher = {IOP Publishing}, abstract = {We show that the autocorrelation of quantum spectra of an open chaotic system is well described by the classical RuellePollicott resonances of the associated chaotic strange repeller. This correspondence is demonstrated utilizing microwave experiments on 2D ndisk billiard geometries, by determination of the wavevector autocorrelation C (κ) from the experimental quantum spectra S 21 (k). The correspondence is also established via" numerical experiments" that simulate S 21 (k) and C (κ) using periodic orbit calculations of the quantum and classical resonances. Semiclassical arguments that relate quantum and classical correlation functions in terms of fluctuations of the density of states and correlations of particle density are also examined and support the experimental results. The results establish a correspondence between quantum spectral correlations and classical decay modes in an open system.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We show that the autocorrelation of quantum spectra of an open chaotic system is well described by the classical RuellePollicott resonances of the associated chaotic strange repeller. This correspondence is demonstrated utilizing microwave experiments on 2D ndisk billiard geometries, by determination of the wavevector autocorrelation C (κ) from the experimental quantum spectra S 21 (k). The correspondence is also established via" numerical experiments" that simulate S 21 (k) and C (κ) using periodic orbit calculations of the quantum and classical resonances. Semiclassical arguments that relate quantum and classical correlation functions in terms of fluctuations of the density of states and correlations of particle density are also examined and support the experimental results. The results establish a correspondence between quantum spectral correlations and classical decay modes in an open system. 
2000 

24.  Sridhar, S Quantum resonances and decay of a fractal repeller observed using microwaves Inproceedings APS Meeting Abstracts, 2000. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{sridhar2000quantum, title = {Quantum resonances and decay of a fractal repeller observed using microwaves}, author = {S Sridhar}, year = {2000}, date = {20000101}, booktitle = {APS Meeting Abstracts}, abstract = {We describe an experimental realization of the wellknown problem of ndisk scattering, which may be regarded as the "hydrogen atom" of chaotic scattering. This model geometry is related to diverse areas such as open systems, semiconductor microstructures and photodissociation. In the experiment, the quantum resonances of classically chaotic ndisk geometries were studied utilizing thin 2D microwave geometries. The transmission spectrum probes the stationary Green's function of the system, and yields both frequencies and widths of the lowlying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. In the microwave experiments the wave vector correlations can be directly studied, and hence these are an interesting complement to ballistic transport in semiconductor microstructures in which correlations in the magnetotransport are obtained. The long time or small energy behavior of the wavevector autocorrelation gives information about the quantum decay rate, which is in good agreement with that obtained from classical scattering theory. For intermediate energies, nonuniversal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits. W.T. Lu, M. Rose, K. Pance and S.Sridhar, Phys. Rev. Lett., vol 82, pp. 5233 (1999). W.T. Lu, L. Viola, K.Pance, M. Rose and S.Sridhar, Phys. Rev. E (submitted)}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } We describe an experimental realization of the wellknown problem of ndisk scattering, which may be regarded as the "hydrogen atom" of chaotic scattering. This model geometry is related to diverse areas such as open systems, semiconductor microstructures and photodissociation. In the experiment, the quantum resonances of classically chaotic ndisk geometries were studied utilizing thin 2D microwave geometries. The transmission spectrum probes the stationary Green's function of the system, and yields both frequencies and widths of the lowlying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. In the microwave experiments the wave vector correlations can be directly studied, and hence these are an interesting complement to ballistic transport in semiconductor microstructures in which correlations in the magnetotransport are obtained. The long time or small energy behavior of the wavevector autocorrelation gives information about the quantum decay rate, which is in good agreement with that obtained from classical scattering theory. For intermediate energies, nonuniversal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits. W.T. Lu, M. Rose, K. Pance and S.Sridhar, Phys. Rev. Lett., vol 82, pp. 5233 (1999). W.T. Lu, L. Viola, K.Pance, M. Rose and S.Sridhar, Phys. Rev. E (submitted) 
23.  Sridhar, S Quantum chaos, localization and tunnelling: microwave experiments on model geometries Journal Article Philosophical Magazine B, 80 (12), pp. 2129–2141, 2000. Abstract  BibTeX  Tags: Quantum Chaos @article{sridhar2000quantumb, title = {Quantum chaos, localization and tunnelling: microwave experiments on model geometries}, author = {S Sridhar}, year = {2000}, date = {20000101}, journal = {Philosophical Magazine B}, volume = {80}, number = {12}, pages = {21292141}, publisher = {Taylor & Francis}, abstract = {Microwave experiments using twodimensional billiard geometries are a precise test of basic issues in quantum chaos, localization and tunnelling. In closed chaotic geometries, analysis of eigenvalue statistics yields good agreement with randommatrix theory. A unique aspect of the experiments is the ability to measure eigenfunctions directly. The influence of periodic orbit scarring in chaotic eigenfunctions is directly demonstrated. Disordered microwave billiards are a textbook model system for studying the quantum properties of a single particle in a disordered potential. Localization is directly observed in eigenfunctions of the disordered billiards. Statistical properties of disordered eigenfunctions deviate from universal behaviour due to localization. These statistical properties are in good agreement with predictions from nonlinearsigma models, although many challenges for further theoretical understanding remain. The experiments can also probe open systems, in terms of the quantum resonances and escape rate of a fractal repeller. }, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } Microwave experiments using twodimensional billiard geometries are a precise test of basic issues in quantum chaos, localization and tunnelling. In closed chaotic geometries, analysis of eigenvalue statistics yields good agreement with randommatrix theory. A unique aspect of the experiments is the ability to measure eigenfunctions directly. The influence of periodic orbit scarring in chaotic eigenfunctions is directly demonstrated. Disordered microwave billiards are a textbook model system for studying the quantum properties of a single particle in a disordered potential. Localization is directly observed in eigenfunctions of the disordered billiards. Statistical properties of disordered eigenfunctions deviate from universal behaviour due to localization. These statistical properties are in good agreement with predictions from nonlinearsigma models, although many challenges for further theoretical understanding remain. The experiments can also probe open systems, in terms of the quantum resonances and escape rate of a fractal repeller. 
22.  Pance, Kristi; Lu, Wentao; Sridhar, S Quantum fingerprints of classical ruellepollicott resonances Journal Article Physical review letters, 85 (13), pp. 2737, 2000. Abstract  BibTeX  Tags: Quantum Chaos @article{pance2000quantum, title = {Quantum fingerprints of classical ruellepollicott resonances}, author = {Kristi Pance and Wentao Lu and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physical review letters}, volume = {85}, number = {13}, pages = {2737}, publisher = {American Physical Society}, abstract = {Quantum and classical correlations are studied experimentally in model ndisk microwave billiards. The wave vector κ autocorrelation C (κ) of the quantum spectrum displays nonuniversal oscillations for large κ, comparable to the universal random matrix theory behavior observed for small κ. The nonuniversal behavior is shown to be completely determined by the classical RuellePollicott resonances, arising from the complex eigenvalues of the PerronFrobenius operator, and calculated using periodic orbit theory. This work establishes a fundamental connection between the quantum and classical correlations of an open system.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } Quantum and classical correlations are studied experimentally in model ndisk microwave billiards. The wave vector κ autocorrelation C (κ) of the quantum spectrum displays nonuniversal oscillations for large κ, comparable to the universal random matrix theory behavior observed for small κ. The nonuniversal behavior is shown to be completely determined by the classical RuellePollicott resonances, arising from the complex eigenvalues of the PerronFrobenius operator, and calculated using periodic orbit theory. This work establishes a fundamental connection between the quantum and classical correlations of an open system. 
21.  Pradhan, Prabhakar; Sridhar, S Correlations due to localization in quantum eigenfunctions of disordered microwave cavities Journal Article Physical review letters, 85 (11), pp. 2360, 2000. Abstract  BibTeX  Tags: Quantum Chaos @article{pradhan2000correlations, title = {Correlations due to localization in quantum eigenfunctions of disordered microwave cavities}, author = {Prabhakar Pradhan and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physical review letters}, volume = {85}, number = {11}, pages = {2360}, publisher = {APS}, abstract = {Statistical properties of experimental eigenfunctions of quantum chaotic and disordered microwave cavities are shown to demonstrate nonuniversal correlations due to localization. Varying energy E and mean free path l enable us to experimentally tune from localized to delocalized states. Large leveltolevel inverse participation ratio (I 2) fluctuations are observed for the disordered billiards, whose distribution is strongly asymmetric about< I 2>. The spatial density autocorrelations of eigenfunctions are shown to spatially decay exponentially and the decay lengths are experimentally determined. All the results are quantitatively consistent with calculations based upon nonlinear sigma models.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } Statistical properties of experimental eigenfunctions of quantum chaotic and disordered microwave cavities are shown to demonstrate nonuniversal correlations due to localization. Varying energy E and mean free path l enable us to experimentally tune from localized to delocalized states. Large leveltolevel inverse participation ratio (I 2) fluctuations are observed for the disordered billiards, whose distribution is strongly asymmetric about< I 2>. The spatial density autocorrelations of eigenfunctions are shown to spatially decay exponentially and the decay lengths are experimentally determined. All the results are quantitatively consistent with calculations based upon nonlinear sigma models. 
20.  Pradhan, Prabhakar; Pance, Kristi; Rose, Michael; Sridhar, S From Localization to Chaos in experimental eigenfunctions of disordered microwave cavities Inproceedings APS Meeting Abstracts, 2000. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{pradhan2000localization, title = {From Localization to Chaos in experimental eigenfunctions of disordered microwave cavities}, author = {Prabhakar Pradhan and Kristi Pance and Michael Rose and S Sridhar}, year = {2000}, date = {20000101}, booktitle = {APS Meeting Abstracts}, abstract = {We analyze eigenfunctions of disordered billiards obtained experimentally using microwave cavities, in terms of density correlations and moment distributions. Deviations from universal distributions are observed due to disorder induced localization. Leveltolevel Inverse Participation Ratio (IPR I_2) fluctuations are observed and analyzed. Varying frequency (f) enables us to experimentally tune from localized to delocalized states, and this path for I_2 (f) follows a power law decay with exponent 1/2 above the cutoff frequency. In chaotic billiards, I 2 has a mean value close to that of the universal 2dimensional (2D) limiting value of 3.0, with small leveltolevel fluctuations resulting in a symmetric distribution about< I_2>. In disordered billiards not only is the mean value of I_2>> 3.0, but the fluctuations are also much greater. The IPR distribution for the disordered billiards is asymmetric about< I_2>, and is quantitatively …}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } We analyze eigenfunctions of disordered billiards obtained experimentally using microwave cavities, in terms of density correlations and moment distributions. Deviations from universal distributions are observed due to disorder induced localization. Leveltolevel Inverse Participation Ratio (IPR I_2) fluctuations are observed and analyzed. Varying frequency (f) enables us to experimentally tune from localized to delocalized states, and this path for I_2 (f) follows a power law decay with exponent 1/2 above the cutoff frequency. In chaotic billiards, I 2 has a mean value close to that of the universal 2dimensional (2D) limiting value of 3.0, with small leveltolevel fluctuations resulting in a symmetric distribution about< I_2>. In disordered billiards not only is the mean value of I_2>> 3.0, but the fluctuations are also much greater. The IPR distribution for the disordered billiards is asymmetric about< I_2>, and is quantitatively … 
19.  Lu, Wentao; Viola, Lorenza; Pance, Kristi; Rose, Michael; Sridhar, S Microwave study of quantum ndisk scattering Journal Article Physical Review E, 61 (4), pp. 3652, 2000. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2000microwave, title = {Microwave study of quantum ndisk scattering}, author = {Wentao Lu and Lorenza Viola and Kristi Pance and Michael Rose and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physical Review E}, volume = {61}, number = {4}, pages = {3652}, publisher = {APS}, abstract = {We describe a wavemechanical implementation of classically chaotic ndisk scattering based on thin twodimensional microwave cavities. Two, three, and fourdisk scatterings are investigated in detail. The experiments, which are able to probe the stationary Green’s function of the system, yield both frequencies and widths of the lowlying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. Wavevector autocorrelation functions are analyzed for various scattering geometries, the small wavevector behavior allowing one to extract the escape rate from the quantum repeller. Quantitative agreement is found with the value predicted from classical scattering theory. For intermediate energies, nonuniversal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We describe a wavemechanical implementation of classically chaotic ndisk scattering based on thin twodimensional microwave cavities. Two, three, and fourdisk scatterings are investigated in detail. The experiments, which are able to probe the stationary Green’s function of the system, yield both frequencies and widths of the lowlying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. Wavevector autocorrelation functions are analyzed for various scattering geometries, the small wavevector behavior allowing one to extract the escape rate from the quantum repeller. Quantitative agreement is found with the value predicted from classical scattering theory. For intermediate energies, nonuniversal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits. 
18.  Pance, Kristi; Viola, Lorenza; Sridhar, S Tunneling proximity resonances: interplay between symmetry and dissipation Journal Article Physics Letters A, 268 (46), pp. 399–405, 2000. Abstract  BibTeX  Tags: Quantum Chaos @article{pance2000tunneling, title = {Tunneling proximity resonances: interplay between symmetry and dissipation}, author = {Kristi Pance and Lorenza Viola and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physics Letters A}, volume = {268}, number = {46}, pages = {399405}, publisher = {NorthHolland}, abstract = {We report the first observation of boundstate proximity resonances in coupled dielectric resonators. The proximity resonances arise from the combined action of symmetry and dissipation. We argue that the large ratio between the widths is a distinctive signature of the multidimensional nature of the system. Our experiments shed light on the properties of 2D tunneling in the presence of a dissipative environment.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We report the first observation of boundstate proximity resonances in coupled dielectric resonators. The proximity resonances arise from the combined action of symmetry and dissipation. We argue that the large ratio between the widths is a distinctive signature of the multidimensional nature of the system. Our experiments shed light on the properties of 2D tunneling in the presence of a dissipative environment. 
17.  Lu, Wentao; Viola, Lorenza; Pance, Kristi; Rose, Michael; Sridhar, S Erratum: Microwave study of quantum ndisk scattering [Phys. Rev. E 61, 3652 (2000)] Journal Article Physical Review E, 62 (3), pp. 4478, 2000. Abstract  BibTeX  Tags: Quantum Chaos @article{lu2000erratum, title = {Erratum: Microwave study of quantum ndisk scattering [Phys. Rev. E 61, 3652 (2000)]}, author = {Wentao Lu and Lorenza Viola and Kristi Pance and Michael Rose and S Sridhar}, year = {2000}, date = {20000101}, journal = {Physical Review E}, volume = {62}, number = {3}, pages = {4478}, publisher = {APS}, abstract = {ISSN 24700053 (online), 24700045 (print). ©2019 American Physical Society. All rights reserved. Physical Review E™ is a trademark of the American Physical Society, registered in the United States, Canada, European Union, and Japan. The APS Physics logo and Physics logo are trademarks of the American Physical Society. Information about registration may be found here. Use of the American Physical Society websites and journals implies that the user has read and agrees to our Terms and Conditions and any applicable Subscription Agreement.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } ISSN 24700053 (online), 24700045 (print). ©2019 American Physical Society. All rights reserved. Physical Review E™ is a trademark of the American Physical Society, registered in the United States, Canada, European Union, and Japan. The APS Physics logo and Physics logo are trademarks of the American Physical Society. Information about registration may be found here. Use of the American Physical Society websites and journals implies that the user has read and agrees to our Terms and Conditions and any applicable Subscription Agreement. 
1999 

16.  Lu, Wentao; Rose, M; Pance, K; Sridhar, S Quantum resonances and decay of a chaotic fractal repeller observed using microwaves Journal Article Physical review letters, 82 (26), pp. 5233, 1999. Abstract  BibTeX  Tags: Quantum Chaos @article{lu1999quantum, title = {Quantum resonances and decay of a chaotic fractal repeller observed using microwaves}, author = {Wentao Lu and M Rose and K Pance and S Sridhar}, year = {1999}, date = {19990101}, journal = {Physical review letters}, volume = {82}, number = {26}, pages = {5233}, publisher = {APS}, abstract = {The quantum resonances of classically chaotic ndisk geometries were studied experimentally utilizing thin 2D microwave geometries. The experiments yield the frequencies and widths of lowlying resonances, which are compared with semiclassical calculations. The long time or small energy behavior of the wavevector autocorrelation gives information about the quantum decay rate, which is in good agreement with that obtained from classical scattering theory. The intermediate energy behavior shows nonuniversal oscillations determined by periodic orbits.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } The quantum resonances of classically chaotic ndisk geometries were studied experimentally utilizing thin 2D microwave geometries. The experiments yield the frequencies and widths of lowlying resonances, which are compared with semiclassical calculations. The long time or small energy behavior of the wavevector autocorrelation gives information about the quantum decay rate, which is in good agreement with that obtained from classical scattering theory. The intermediate energy behavior shows nonuniversal oscillations determined by periodic orbits. 
1998 

15.  Sridhar, S Wave Chaos and Localization in Closed Billiards and Open Scattering Systems: Microwave Experiments Inproceedings APS March Meeting Abstracts, 1998. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{sridhar1998wave, title = {Wave Chaos and Localization in Closed Billiards and Open Scattering Systems: Microwave Experiments}, author = {S Sridhar}, year = {1998}, date = {19980101}, booktitle = {APS March Meeting Abstracts}, abstract = {Microwave experiments are described, which are designed to study the signatures of chaos and localization on the quantum properties of model 2D closed (billiard) and open scattering geometries. A special advantage of the experiments is the ability to directly measure eigenfunctions. In chaotic billiards, the eigenfunctions display universal density distributions and density autocorrelations, in agreement with expressions derived from random matrix theory and from a 0D nonlinear sigma model of supersymmetry. In contrast, wavefunctions in disordered billiards show deviations from universality due to Anderson localization. The systematics of the distribution functions and inverse participation ratios are studied as a function of frequency and localization length. While results in the regime of incipient localization appear to be successfully described by leading expansions of nonlinear sigma models of supersymmetry …}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } Microwave experiments are described, which are designed to study the signatures of chaos and localization on the quantum properties of model 2D closed (billiard) and open scattering geometries. A special advantage of the experiments is the ability to directly measure eigenfunctions. In chaotic billiards, the eigenfunctions display universal density distributions and density autocorrelations, in agreement with expressions derived from random matrix theory and from a 0D nonlinear sigma model of supersymmetry. In contrast, wavefunctions in disordered billiards show deviations from universality due to Anderson localization. The systematics of the distribution functions and inverse participation ratios are studied as a function of frequency and localization length. While results in the regime of incipient localization appear to be successfully described by leading expansions of nonlinear sigma models of supersymmetry … 
1997 

14.  Kudrolli, A; Sridhar, S Experiments on quantum chaos using microwave cavities: Results for the pseudointegrable Lbilliard Journal Article Pramana, 48 (2), pp. 459–467, 1997. Abstract  BibTeX  Tags: Quantum Chaos @article{kudrolli1997experiments, title = {Experiments on quantum chaos using microwave cavities: Results for the pseudointegrable Lbilliard}, author = {A Kudrolli and S Sridhar}, year = {1997}, date = {19970101}, journal = {Pramana}, volume = {48}, number = {2}, pages = {459467}, publisher = {Springer India}, abstract = {We describe microwave experiments used to study billiard geometries as model problems of nonintegrability in quantum or wave mechanics. The experiments can study arbitrary 2D geometries, including chaotic and even disordered billiards. Detailed results on an Lshaped pseudointegrable billiard are discussed as an example. The eigenvalue statistics are welldescribed by empirical formulae incorporating the fraction of phase space that is nonintegrable. The eigenfunctions are directly measured, and their statistical properties are shown to be influenced by nonisolated periodic orbits, similar to that for the chaotic Sinai billiard. These periodic orbits are directly observed in the Fourier transform of the eigenvalue spectrum.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We describe microwave experiments used to study billiard geometries as model problems of nonintegrability in quantum or wave mechanics. The experiments can study arbitrary 2D geometries, including chaotic and even disordered billiards. Detailed results on an Lshaped pseudointegrable billiard are discussed as an example. The eigenvalue statistics are welldescribed by empirical formulae incorporating the fraction of phase space that is nonintegrable. The eigenfunctions are directly measured, and their statistical properties are shown to be influenced by nonisolated periodic orbits, similar to that for the chaotic Sinai billiard. These periodic orbits are directly observed in the Fourier transform of the eigenvalue spectrum. 
1996 

13.  Jacobs, T; Willemsen, Balam A; Sridhar, S Quantitative analysis of nonlinear microwave surface impedance from nonLorentzian resonances of high Q resonators Journal Article Review of scientific instruments, 67 (10), pp. 3757–3758, 1996. BibTeX  Tags: Quantum Chaos @article{jacobs1996quantitative, title = {Quantitative analysis of nonlinear microwave surface impedance from nonLorentzian resonances of high Q resonators}, author = {T Jacobs and Balam A Willemsen and S Sridhar}, year = {1996}, date = {19960101}, journal = {Review of scientific instruments}, volume = {67}, number = {10}, pages = {37573758}, publisher = {American Institute of Physics}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } 
12.  Kudrolli, A; Sridhar, S Comment on “Gaussian Orthogonal Ensemble Statistics in a Microwave Stadium Billiard with Chaotic Dynamics: PorterThomas Distribution and Algebraic Decay of Time Correlations” Journal Article Physical review letters, 76 (16), pp. 3036, 1996. Abstract  BibTeX  Tags: Quantum Chaos @article{kudrolli1996comment, title = {Comment on “Gaussian Orthogonal Ensemble Statistics in a Microwave Stadium Billiard with Chaotic Dynamics: PorterThomas Distribution and Algebraic Decay of Time Correlations”}, author = {A Kudrolli and S Sridhar}, year = {1996}, date = {19960101}, journal = {Physical review letters}, volume = {76}, number = {16}, pages = {3036}, publisher = {American Physical Society}, abstract = {A Comment on the Letter by H. Alt et al., Phys. Rev. Lett. 74, 62 (1995). Received 2 March 1995 DOI:https://doi.org/10.1103/PhysRevLett.76.3036 ©1996 American Physical Society}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } A Comment on the Letter by H. Alt et al., Phys. Rev. Lett. 74, 62 (1995). Received 2 March 1995 DOI:https://doi.org/10.1103/PhysRevLett.76.3036 ©1996 American Physical Society 
1995 

11.  Kudrolli, A; Kidambi, V; Sridhar, S Experimental studies of chaos and localization in quantum wave functions Journal Article Physical review letters, 75 (5), pp. 822, 1995. Abstract  BibTeX  Tags: Quantum Chaos @article{kudrolli1995experimental, title = {Experimental studies of chaos and localization in quantum wave functions}, author = {A Kudrolli and V Kidambi and S Sridhar}, year = {1995}, date = {19950101}, journal = {Physical review letters}, volume = {75}, number = {5}, pages = {822}, publisher = {APS}, abstract = {Wave functions in chaotic and disordered quantum billiards are studied experimentally using thin microwave cavities. The chaotic wave functions display universal density distributions and density autocorrelations in agreement with expressions derived from a 0D nonlinear σ model of supersymmetry, which coincides with random matrix theory. In contrast, disordered wave functions show deviations from this universal behavior due to Anderson localization. A systematic behavior of the distribution function is studied as a function of the localization length, and can be understood in the framework of a 1D version of the nonlinear σ model.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } Wave functions in chaotic and disordered quantum billiards are studied experimentally using thin microwave cavities. The chaotic wave functions display universal density distributions and density autocorrelations in agreement with expressions derived from a 0D nonlinear σ model of supersymmetry, which coincides with random matrix theory. In contrast, disordered wave functions show deviations from this universal behavior due to Anderson localization. A systematic behavior of the distribution function is studied as a function of the localization length, and can be understood in the framework of a 1D version of the nonlinear σ model. 
10.  Prigodin, VN; Taniguchi, Nobuhiko; Kudrolli, A; Kidambi, V; Sridhar, S Spatial correlation in quantum chaotic systems with timereversal symmetry: Theory and experiment Journal Article Physical review letters, 75 (12), pp. 2392, 1995. Abstract  BibTeX  Tags: Quantum Chaos @article{prigodin1995spatial, title = {Spatial correlation in quantum chaotic systems with timereversal symmetry: Theory and experiment}, author = {VN Prigodin and Nobuhiko Taniguchi and A Kudrolli and V Kidambi and S Sridhar}, year = {1995}, date = {19950101}, journal = {Physical review letters}, volume = {75}, number = {12}, pages = {2392}, publisher = {American Physical Society}, abstract = {The correlation between the values of wave functions at two different spatial points is examined for chaotic systems with timereversal symmetry. Employing a supermatrix method, we find that there exist longrange Friedel oscillations of the wave function density for a given eigenstate, although the background wave function density fluctuates strongly. We show that for large fluctuations, once the value of the wave function at one point is known, its spatial dependence becomes highly predictable for increasingly large space around this point. These results are compared with the experimental wave functions obtained from billiardshaped microwave cavities, and very good agreement is demonstrated.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } The correlation between the values of wave functions at two different spatial points is examined for chaotic systems with timereversal symmetry. Employing a supermatrix method, we find that there exist longrange Friedel oscillations of the wave function density for a given eigenstate, although the background wave function density fluctuates strongly. We show that for large fluctuations, once the value of the wave function at one point is known, its spatial dependence becomes highly predictable for increasingly large space around this point. These results are compared with the experimental wave functions obtained from billiardshaped microwave cavities, and very good agreement is demonstrated. 
9.  Kudrolli, A; Sridhar, S QUANTUM CHAOS EXPERIMENTS USING MICROWAVE CAVITIES Inproceedings Proceedings Of The 2nd Experimental Chaos Conference, pp. 184, World Scientific 1995. Abstract  BibTeX  Tags: Quantum Chaos @inproceedings{kudrolli1995quantum, title = {QUANTUM CHAOS EXPERIMENTS USING MICROWAVE CAVITIES}, author = {A Kudrolli and S Sridhar}, year = {1995}, date = {19950101}, booktitle = {Proceedings Of The 2nd Experimental Chaos Conference}, pages = {184}, organization = {World Scientific}, abstract = {We describe experiments using thin microwave cavities to test issues in Quantum Chaos. The experiments exploit the correspondence of the scalar HelmholtzMaxwell and the timeindependent Schrodinger equations. The eigenvalues and eigenfunctions of cavities with crosssections in the form of chaotic billiards are obtained experimentally. In certain geometries the eigenvalue statistics are in complete agreement with Random Matrix theory. Scars are visible in some eigenfunctions, although a general rule for their obseiVation is not yet available.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {inproceedings} } We describe experiments using thin microwave cavities to test issues in Quantum Chaos. The experiments exploit the correspondence of the scalar HelmholtzMaxwell and the timeindependent Schrodinger equations. The eigenvalues and eigenfunctions of cavities with crosssections in the form of chaotic billiards are obtained experimentally. In certain geometries the eigenvalue statistics are in complete agreement with Random Matrix theory. Scars are visible in some eigenfunctions, although a general rule for their obseiVation is not yet available. 
8.  Sridhar, S Cavities of Chaos Journal Article SCIENCE NEWSWASHINGTON, 147 , pp. 264–264, 1995. BibTeX  Tags: Quantum Chaos @article{sridhar1995cavities, title = {Cavities of Chaos}, author = {S Sridhar}, year = {1995}, date = {19950101}, journal = {SCIENCE NEWSWASHINGTON}, volume = {147}, pages = {264264}, publisher = {SCIENCE NEWS}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } 
1994 

7.  Kudrolli, A; Sridhar, S; Pandey, Akhilesh; Ramaswamy, Ramakrishna Signatures of chaos in quantum billiards: Microwave experiments Journal Article Physical Review E, 49 (1), pp. R11, 1994. Abstract  BibTeX  Tags: Quantum Chaos @article{kudrolli1994signatures, title = {Signatures of chaos in quantum billiards: Microwave experiments}, author = {A Kudrolli and S Sridhar and Akhilesh Pandey and Ramakrishna Ramaswamy}, year = {1994}, date = {19940101}, journal = {Physical Review E}, volume = {49}, number = {1}, pages = {R11}, publisher = {APS}, abstract = {The signatures of classical chaos and the role of periodic orbits in the wavemechanical eigenvalue spectra of twodimensional billiards are studied experimentally in microwave cavities. The survival probability for all the chaotic cavity data shows a ‘‘correlation hole,’’in agreement with theory, that is absent for the integrable cavity. The spectral rigidity Δ 3 (L), which is a measure of longrange correlation, is shown to be particularly sensitive to the presence of marginally stable periodic orbits. Agreement with randommatrix theory is achieved only after excluding such orbits, which we do by constructing a special geometry, the Sinai stadium. Pseudointegrable geometries are also studied, and are found to display intermediate behavior.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } The signatures of classical chaos and the role of periodic orbits in the wavemechanical eigenvalue spectra of twodimensional billiards are studied experimentally in microwave cavities. The survival probability for all the chaotic cavity data shows a ‘‘correlation hole,’’in agreement with theory, that is absent for the integrable cavity. The spectral rigidity Δ 3 (L), which is a measure of longrange correlation, is shown to be particularly sensitive to the presence of marginally stable periodic orbits. Agreement with randommatrix theory is achieved only after excluding such orbits, which we do by constructing a special geometry, the Sinai stadium. Pseudointegrable geometries are also studied, and are found to display intermediate behavior. 
1993 

6.  Sridhar, S Quantum Dynamics of Chaotic Systems Journal Article 1993. BibTeX  Tags: Quantum Chaos @article{sridhar1993quantum, title = {Quantum Dynamics of Chaotic Systems}, author = {S Sridhar}, year = {1993}, date = {19930101}, publisher = {Gordon and Breach, Amsterdam}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } 
5.  Sridhar, S; Hogenboom, D; Kudrolli, A Experimental eigenvalue spectra of “rough” and multiplyconnected billiards,” Journal Article Quantum Dynamics of Chaotic Systems, eds. Yuan, JM, Feng, DH & Zaslavsky, GM (Gordon and Breach, Amsterdam), pp. 297–304, 1993. Abstract  BibTeX  Tags: Quantum Chaos @article{sridhar1993exper, title = {Experimental eigenvalue spectra of “rough” and multiplyconnected billiards,”}, author = {S Sridhar and D Hogenboom and A Kudrolli}, year = {1993}, date = {19930101}, journal = {Quantum Dynamics of Chaotic Systems, eds. Yuan, JM, Feng, DH & Zaslavsky, GM (Gordon and Breach, Amsterdam)}, pages = {297304}, abstract = {We use microwave cavities to study the spectra of billiards with" rough" perimeters, or which ara multiply connectedWhile simple boundaries show cumulative level densities N (E) which are in good agreement with the Weyl formula, qualitative departures are observed at low energieswhen the perimeter is" roughened" by increasing the ratio of perimeter L to area A, and when obstacles are introduced to make the billiard multiply connected. Thus the Weyl formula even including perimeter corrections is not a good yardstick at low energies which probe internal length scales, interestingly, in the case of a multiplyconnected billiard with a periodic array of obstacles, large" gaps" are observed in the discrete spectrum, somewhat like a solidstate lattice of finite size. The gaps persist when disorder¿ î introduced, Le. in the analog of a solidstate glass. The influence of the shape of a planar domain on the eigenvalue …}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We use microwave cavities to study the spectra of billiards with" rough" perimeters, or which ara multiply connectedWhile simple boundaries show cumulative level densities N (E) which are in good agreement with the Weyl formula, qualitative departures are observed at low energieswhen the perimeter is" roughened" by increasing the ratio of perimeter L to area A, and when obstacles are introduced to make the billiard multiply connected. Thus the Weyl formula even including perimeter corrections is not a good yardstick at low energies which probe internal length scales, interestingly, in the case of a multiplyconnected billiard with a periodic array of obstacles, large" gaps" are observed in the discrete spectrum, somewhat like a solidstate lattice of finite size. The gaps persist when disorder¿ î introduced, Le. in the analog of a solidstate glass. The influence of the shape of a planar domain on the eigenvalue … 
1992 

4.  Sridhar, S; Heller, EJ Physical and numerical experiments on the wave mechanics of classically chaotic systems Journal Article Physical Review A, 46 (4), pp. R1728, 1992. Abstract  BibTeX  Tags: Quantum Chaos @article{sridhar1992physical, title = {Physical and numerical experiments on the wave mechanics of classically chaotic systems}, author = {S Sridhar and EJ Heller}, year = {1992}, date = {19920101}, journal = {Physical Review A}, volume = {46}, number = {4}, pages = {R1728}, publisher = {American Physical Society}, abstract = {We study chaotic quantum billiards using both microwave cavities and numerical simulations. For the same geometry, viz., a Sinai billiard, agreement to remarkable precision is found for both the eigenvalue magnitudes and the spatial detail of the eigenfunctions. The association of the eigenfunctions with classical periodic orbits is demonstrated, and scarred states are identified. Desymmetrizing the Sinai billiard by slightly moving the central disk is shown to lead to strong localization of the eigenfunction. The calculated eigenstates of the symmetric billiard show an evenand oddparity pair whose linear combination gives the localized state.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We study chaotic quantum billiards using both microwave cavities and numerical simulations. For the same geometry, viz., a Sinai billiard, agreement to remarkable precision is found for both the eigenvalue magnitudes and the spatial detail of the eigenfunctions. The association of the eigenfunctions with classical periodic orbits is demonstrated, and scarred states are identified. Desymmetrizing the Sinai billiard by slightly moving the central disk is shown to lead to strong localization of the eigenfunction. The calculated eigenstates of the symmetric billiard show an evenand oddparity pair whose linear combination gives the localized state. 
3.  Sridhar, S; Hogenboom, DO; Willemsen, Balam A Microwave experiments on chaotic billiards Journal Article Journal of statistical physics, 68 (12), pp. 239–258, 1992. Abstract  BibTeX  Tags: Quantum Chaos @article{sridhar1992microwave, title = {Microwave experiments on chaotic billiards}, author = {S Sridhar and DO Hogenboom and Balam A Willemsen}, year = {1992}, date = {19920101}, journal = {Journal of statistical physics}, volume = {68}, number = {12}, pages = {239258}, publisher = {Kluwer Academic PublishersPlenum Publishers}, abstract = {We describe experiments using billiardshaped microwave cavities, to test ideas in quantum chaos. The experimental method for observing cavity resonances to obtain the eigenvalues, and the advantages and limitations of the techniques, including the influence of absorption, are discussed. An experimental technique to obtain a 2D mapping of the wavefunction is described. Results are displayed for 36 of the lowlying wavefunctions of a Sinai billiard cavity consisting of a central disc in a rectangular enclosure. The wavefunctions demonstrate the influence of classical periodic orbits (PO), of which there are two types: nonisolated PO, which avoid the central disc, and isolated PO, which hit the central disc. Scarred states, including those associated with isolated PO, are directly observed.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } We describe experiments using billiardshaped microwave cavities, to test ideas in quantum chaos. The experimental method for observing cavity resonances to obtain the eigenvalues, and the advantages and limitations of the techniques, including the influence of absorption, are discussed. An experimental technique to obtain a 2D mapping of the wavefunction is described. Results are displayed for 36 of the lowlying wavefunctions of a Sinai billiard cavity consisting of a central disc in a rectangular enclosure. The wavefunctions demonstrate the influence of classical periodic orbits (PO), of which there are two types: nonisolated PO, which avoid the central disc, and isolated PO, which hit the central disc. Scarred states, including those associated with isolated PO, are directly observed. 
0000 

2.  Sridhar, S; Parimi, PV; Lu, WT; Vodo, P; Derov, John S; Hanscom, AFRL; Bedford, MA Negative Refraction and Imaging in Photonic Crystals Journal Article 0000. Abstract  BibTeX  Tags: Quantum Chaos @article{sridharnegative, title = {Negative Refraction and Imaging in Photonic Crystals}, author = {S Sridhar and PV Parimi and WT Lu and P Vodo and John S Derov and AFRL Hanscom and MA Bedford}, abstract = {Negative refraction and lefthanded electromagnetism in a photonic crystal are demonstrated in waveguide and free space experiments at microwave frequencies. Precision control to achieve tailormade refractive indices has been achieved. The negative refraction in these photonic crystals is shown to lead to imaging by a flat lens. We have also developed a generalized theory of flat lens imaging. These results promise potential applications in a variety of optical and microwave systems for communications and imaging.}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } Negative refraction and lefthanded electromagnetism in a photonic crystal are demonstrated in waveguide and free space experiments at microwave frequencies. Precision control to achieve tailormade refractive indices has been achieved. The negative refraction in these photonic crystals is shown to lead to imaging by a flat lens. We have also developed a generalized theory of flat lens imaging. These results promise potential applications in a variety of optical and microwave systems for communications and imaging. 
1.  Harika, K; Swetha, BV; Renuka, B; Rao, Lakshman D; Sridhar, S Analysis of Different Multiplication Algorithms & FPGA Implementation Journal Article IOSR Journal of VLSI and Signal Processing (IOSRJVSP), 4 (2), pp. 29–35, 0000. BibTeX  Tags: Quantum Chaos @article{harika4analysis, title = {Analysis of Different Multiplication Algorithms & FPGA Implementation}, author = {K Harika and BV Swetha and B Renuka and Lakshman D Rao and S Sridhar}, journal = {IOSR Journal of VLSI and Signal Processing (IOSRJVSP)}, volume = {4}, number = {2}, pages = {2935}, keywords = {Quantum Chaos}, pubstate = {published}, tppubtype = {article} } 