Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C50: Many-Body Localization in Atomic Systems IFocus
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Sponsoring Units: DAMOP Chair: Bela Bauer, Microsoft Station Q Room: Hilton Baltimore Holiday Ballroom 1 |
Monday, March 14, 2016 2:30PM - 3:06PM |
C50.00001: Suppression and Revival of Weak Localization of Ultra-Cold Atoms by Manipulation of Time-Reversal Symmetry Invited Speaker: Alain Aspect In the early 1980's, observation of a magneto-resistance anomaly in metallic thin films was attributed to the phenomenon of weak localization of electrons and to time-reversal symmetry breaking due to a magnetic field acting upon charged particles. We have observed weak localization of ultra-cold atoms in a 2D configuration, placed in a disordered potential created by a laser speckle. In order to manipulate time-reversal symmetry with our neutral atoms, we take advantage of the slow evolution of our system, and we observe the suppression and revival of weak localization when time reversal symmetry is cancelled and reestablished. References: K. Muller, J. Richard, V. V. Volchkov, V. Denechaud, P. Bouyer, A. Aspect, and V. Josse, "Suppression and Revival of Weak Localization through Control of Time-Reversal Symmetry," Physical Review Letters 114 (20) (2015) and references in. [Preview Abstract] |
Monday, March 14, 2016 3:06PM - 3:18PM |
C50.00002: Using subadditivity to reason about many-body localization on single disorder realizations. Bryan Clark, Xiongjie Yu, David J. Luitz In the many-body localized (MBL) phase, the interplay of interactions and disorder prevents thermalization. Typically to reason about the many-body localized phase we average over many disorder realizations. It is interesting to ask in what ways we can we talk about MBL transitions for single disorder patterns. We show that subadditivity gives us a mechanism to make sense of MBL transitions on single disorder realizations and report what this implies for the average over disorder. [Preview Abstract] |
Monday, March 14, 2016 3:18PM - 3:30PM |
C50.00003: Many-Body Localization and Quantum Nonergodicity in a Model with a Single-Particle Mobility Edge Xiaopeng Li, Sriram Ganeshan, J.H. Pixley We investigate many-body localization in the presence of a single-particle mobility edge. By considering an interacting deterministic model with an incommensurate potential in one dimension we find that the single-particle mobility edge in the noninteracting system leads to a many-body mobility edge in the corresponding interacting system for certain parameter regimes. Using exact diagonalization, we probe the mobility edge via energy resolved entanglement entropy (EE) and study the energy resolved applicability (or failure) of the eigenstate thermalization hypothesis (ETH). Our numerical results indicate that the transition separating area and volume law scaling of the EE does not coincide with the nonthermal to thermal transition. Consequently, there exists an extended nonergodic phase for an intermediate energy window where the many-body eigenstates violate the ETH while manifesting volume law EE scaling. We also establish that the model possesses an infinite temperature many-body localization transition despite the existence of a single-particle mobility edge. We propose a practical scheme to test our predictions in atomic optical lattice experiments which can directly probe the effects of the mobility edge. [Preview Abstract] |
Monday, March 14, 2016 3:30PM - 3:42PM |
C50.00004: Early Breakdown of Area-Law Entanglement at the Many-Body Delocalization Transition Trithep Devakul, Rajiv Singh We introduce the numerical linked cluster expansion as a controlled numerical tool for the study of the many-body localization transition in a disordered system with continuous nonperturbative disorder. Our approach works directly in the thermodynamic limit, in any spatial dimension, and does not rely on any finite size scaling procedure. We study the onset of many-body delocalization through the breakdown of area-law entanglement in a generic many-body eigenstate. By looking for initial signs of an instability of the localized phase, we obtain a value for the critical disorder, which we believe should be a lower bound for the true value, that is higher than current best estimates from finite size studies. This implies that most current methods tend to overestimate the extent of the localized phase due to finite size effects making the localized phase appear stable at small length scales. We also study the mobility edge in these systems as a function of energy density, and we find that our conclusion is the same at all examined energies. Work based on Phys. Rev. Lett. 115, 187201. [Preview Abstract] |
Monday, March 14, 2016 3:42PM - 3:54PM |
C50.00005: Exponential Orthogonality Catastrophe in Single-Particle and Many-Body Localized Systems Dong-Ling Deng, J. H. Pixley, Xiaopeng Li We investigate the statistical orthogonality catastrophe (StOC) in single-particle and many-body localized systems by studying the response of the many-body ground state to a local quench. Using scaling arguments and exact numerical calculations, we establish that the StOC gives rise to a wave function overlap between the pre- and post-quench ground states that has an \emph{exponential} decay with the system size, in sharp contrast to the well-known power law Anderson orthogonality catastrophe in metallic systems. This exponential decay arises from a statistical charge transfer process where a particle can be effectively ``transported'' to an arbitrary lattice site. We show that in a many-body localized phase, this non-local transport and the associated exponential StOC phenomenon persist in the presence of interactions. We study the possible experimental consequences of the exponential StOC on the Loschmidt echo and spectral function, establishing that this phenomenon might be observable in cold atomic experiments through Ramsey interference and radio-frequency spectroscopy. [Preview Abstract] |
Monday, March 14, 2016 3:54PM - 4:06PM |
C50.00006: Many-body localization effects in a disordered system coupled to a delocalized chain Katharine Hyatt, James R. Garrison, Bela Bauer The possibility of closed quantum systems that robustly violate quantum statistical mechanics has received a tremendous amount of interest in recent years. Using both numerical and analytical techniques, it has been established that weakly interacting disordered systems can be brought into a many-body localized regime, where the system does not conduct and does not equilibrate even for arbitrarily long times. The starting point for such a phase is usually taken to be an Anderson insulator where in the limit of vanishing interactions, all degrees of freedom of the system are localized. Here, we revisit this problem in a model where in the non-interacting limit, some degrees of freedom are localized while others remain delocalized. Such a system can be viewed as a model for a many-body localized system brought into contact with a small bath of a comparable number of degrees of freedom. We numerically study the effect of interactions on this system and find that generically, the entire system delocalizes. However, we find certain parameter regimes where results are consistent with localization of the entire system, an effect recently termed many-body proximity effect. [Preview Abstract] |
Monday, March 14, 2016 4:06PM - 4:18PM |
C50.00007: Fractional transport and photonic sub-diffusion in aperiodic dielectric metamaterials Luca Dal Negro, Yu Wang, Sandeep Inampudi Using rigorous transfer matrix theory and full-vector Finite Difference Time Domain (FDTD) simulations in combination with Wavelet Transform Modulus Maxima analysis of multifractal spectra, we demonstrate all-dielectric aperiodic metamaterial structures that exhibit sub-diffusive photon transport properties that are widely tunable across the near-infrared spectral range. The proposed approach leverages the unprecedented spectral scalability offered by aperiodic photonic systems and demonstrates the possibility of achieving logarithmic Sinai sub-diffusion of photons for the first time. In particular we will show that the control of multifractal energy spectra and critical modes in aperiodic metamaterials with nanoscale dielectric components enables tuning of anomalous optical transport from sub- to super-diffusive dynamics, in close analogy with the electron dynamics in quasi-periodic potentials. Fractional diffusion equations models will be introduced for the efficient modeling of photon sub-diffusive processes in metamaterials and applications to diffraction-free propagation in aperiodic media will be provided. The ability to tailor photon transport phenomena in metamaterials with properties originating from aperiodic geometrical correlations can lead to novel functionalities and active devices that rely on anomalous photon sub-diffusion to control beam collimation and non-resonantly enhance light-matter interaction across multiple spectral bands. [Preview Abstract] |
Monday, March 14, 2016 4:18PM - 4:30PM |
C50.00008: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 4:30PM - 4:42PM |
C50.00009: Transport of Light in disordered random media Regine Frank, Andreas Lubatsch The Anderson transition was originally proposed for electrons, however it has been soon searched for all kinds of waves in disordered media. This physics became extremely interesting with the application of high amplitude excitations, where the medium is supposed to respond with non-linear effects. In theory it is ever since a challenge to treat large random ensembles numerically, even if the medium is completely non-resonant or passive. We discuss in this talk transport of light with respect to a quantum field theoretical approach and we explain through comparison to other existing theories, what the advantages of state of the art theory in that field is, and why it is exciting. [Preview Abstract] |
Monday, March 14, 2016 4:42PM - 4:54PM |
C50.00010: Many body localization in the presence of a single particle mobility edge Subroto Mukerjee, Ranjan Modak In one dimension, noninteracting particles can undergo a localization-delocalization transition in a quasiperiodic potential. Recent studies have suggested that this transition transforms into a many body localization transition upon the introduction of interactions. It has also been shown that mobility edges can appear in the single particle spectrum for certain types of quasiperiodic potentials. Here we investigate the effect of interactions in models with such mobility edges. Employing the technique of exact diagonalization for finite-sized systems, we calculate the level spacing distribution, time evolution of entanglement entropy, optical conductivity and return probability to characterize the nature of localization. The localization that develops in the presence of interactions in these systems appears to be different from regular Many-Body Localization (MBL) in that the growth of entanglement entropy with time is linear (like in a thermal phase) but saturates to a value much smaller than the thermal value (like for MBL). All other diagnostics seem consistent with regular MBL. [Preview Abstract] |
Monday, March 14, 2016 4:54PM - 5:06PM |
C50.00011: Energy Dependence and Scaling Property of Localization Length near a Gapped Flat Band Li Ge, Hakan Tureci Using a tight-binding model for a one-dimensional Lieb lattice, we show that the localization length near a gapped flat band behaves differently from the typical Urbach tail in a band gap: instead of reducing monotonically as the energy E moves away from the flat band energy Ef, the presence of the flat band causes a nonmonotonic energy dependence of the localization length. This energy dependence follows a scaling property when the energy is within the spread (W) of uniformly distributed diagonal disorder, i.e. the localization length is only a function of (E-Ef)/W. Several other lattices are compared to distinguish the effect of the flat band on the localization length, where we eliminate, shift, or duplicate the flat band, without changing the dispersion relations of other bands. Using the top right element of the Green's matrix, we derive an analytical relation between the density of states and the localization length, which shines light on these properties of the latter, including a summation rule for its inverse. [Preview Abstract] |
Monday, March 14, 2016 5:06PM - 5:18PM |
C50.00012: Spatial and temporal localization of light in two dimensions Romain Bachelard Despite decades of active research, punctuated by several contradictory experimental and theoretical claims, the mere existence of Anderson localization of light, a regime where light cannot propagate due to interference effects between randomly distributed scatterers, has not been demonstrated yet. Recent theoretical works suggest that the vectorial nature of light might actually prohibit localization. We here present a study on the scattering of light in two dimensions, a regime where both scalar or as a vectorial electromagnetic waves coexist. The scaling analysis reveals that although both kinds of wave present long-lived subradiant modes, only scalar ones do localize, supporting the theoretical claim in 3D. Yet we also observe a lack of correlation between lifetimes and localization length, calling for a differentiation between temporal (subradiant) and spatial (Anderson) localization. Finally, we discuss the implication of localization, following the original idea that the localization of the modes induces a metal to insulator transition, bringing transport to a halt. Indeed, in the case of light, the scattering is characterized by the presence of a few long-range (superradiant) modes, which appear to alter dramatically the transport properties. [Preview Abstract] |
Monday, March 14, 2016 5:18PM - 5:30PM |
C50.00013: Anderson Localization in Degenerate Spin-Orbit Coupled Fermi Gas with Disorder Sheng Liu, Xiangfa Zhou, Guangcan Guo, Yongsheng Zhang Competition between superconductivity and disorder plays an essential role in undenstanding the metal-insulator transition. Based on the Bogoliubov-de Gennes equation, we studied an $s$-wave superconductor with both spin-orbit coupling and disorder are presented . With increasing the strength of disorder, the mean superconducting order parameter will vanish while the energy gap will persist which indicates that the system undergoes a transition from a superconducting state to a insulating state which can be conformed by calculating the inverse participation ratio. We also find that, if the strength of disorder is small, the superconducting order parameter and energy gap will decrease if we increase the strength of spin-orbit coupling and Zeeman field. In the large disorder limits, increasing the strength of spin-orbit coupling will increase the mean superconducting order parameter. This phenomena shows that the system is more insensitive to disorder if the spin-orbit coupling is presented. Numerical computing also shows that the whole system breaks up into several {\it superconducting islands} instead of being superconductive. [Preview Abstract] |
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