Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L52: Statistics of Ensemble Quantum Systems |
Hide Abstracts |
Sponsoring Units: GQI GSNP Chair: Oren Raz, University of Maryland, College Park Room: 399 |
Wednesday, March 15, 2017 11:15AM - 11:27AM |
L52.00001: Dependence of dissipation on the initial distribution over states Artemy Kolchinsky, David H. Wolpert We consider a driven nonequilibrium system. There is a large literature on how the amount of work dissipated during such driving varies with changes to the driving process, for a fixed initial distribution over microstates. We instead analyze how the amount of work dissipated for a fixed driving process varies with changes to the initial distribution over microstates. We show that the dissipated work for a given initial distribution has a simple information-theoretic form that depends only on the initial and final distributions, and reflects the logical irreversibility of the process. Our results hold under very general conditions, independent of how long the process takes, whether it obeys local detailed balance, etc. We also consider the case where the process induces dynamics over a space of coarse-grained macrostates that implement some specified computation (i.e., a specified map from initial "input" macrostates to ending "output" macrostates). We show that our formulas for extra dissipated work still hold, only now stated in terms of distributions over the macrostates of the computer, and that this extra dissipated work reflects changes to the distribution of a computer's inputs. It is a novel thermodynamic cost of computation, in addition to the well-known Landauer's cost. [Preview Abstract] |
Wednesday, March 15, 2017 11:27AM - 11:39AM |
L52.00002: Quantum information processing by a continuous Maxwell demon Josey Stevens, Sebastian Deffner Quantum computing is believed to be fundamentally superior to classical computing; however quantifying the specific thermodynamic advantage has been elusive. Experimentally motivated, we generalize previous minimal models of discrete demons to continuous state space. Analyzing our model allows one to quantify the thermodynamic resources necessary to process quantum information. By further invoking the semi-classical limit we compare the quantum demon with its classical analogue. Finally, this model also serves as a starting point to study open quantum systems. [Preview Abstract] |
Wednesday, March 15, 2017 11:39AM - 11:51AM |
L52.00003: Partial erasure of a bit: Direct measurement of Shannon’s entropy function using a feedback trap John Bechhoefer, Momcilo Gavrilov, Raphael Chetrite In 1961, Landauer proposed that erasing one bit of information should require a work of $kT \ln 2$ per bit erased. Standard \textit{gedanken} and recent actual experiments have demonstrated how to erase a single bit. Here, using a feedback trap to place a colloidal particle in a controllable virtual potential, we show how to erase part of a bit, finding that the minimum average work $W/kT$ required is consistent with $\ln 2 - H(p)$, where $H(p) = -p \, \ln p - (1-p) \, \ln (1-p)$ is the Shannon entropy function for two states, with $p$ the nonequilibrium probability to be in one of the states. While the Shannon entropy has long been hypothesized to be the appropriate definition for nonequilibrium systems, we directly confirm by experiment its functional form and relation to work. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L52.00004: A new and trustworthy formalism to compute entropy in quantum systems Mohammad Ansari Entropy is nonlinear in density matrix and as such its evaluation in open quantum system has not been fully understood. Recently a quantum formalism was proposed by Ansari and Nazarov\footnote{M.H. Ansari and Y. V. Nazarov, Phys. Rev. B 91, 104303 (2015)} that evaluates entropy using parallel time evolutions of multiple worlds. We can use this formalism to evaluate entropy flow in a photovoltaic cells coupled to thermal reservoirs and cavity modes. Recently we studied the full counting statistics of energy transfers in such systems\footnote{M.H. Ansari and Y. V. Nazarov, Phys. Rev. B 91, 174307 (2015)}. This rigorously proves a nontrivial correspondence between energy exchanges and entropy changes in quantum systems, which only in systems without entanglement can be simplified to the textbook second law of thermodynamics. We evaluate the flow of entropy using this formalism. In the presence of entanglement, however, interestingly much less information is exchanged than what we expected. This increases the upper limit capacity for information transfer and its conversion to energy for next generation devices in mesoscopic physics. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L52.00005: Ergodicity-breaking eigenstates in quantum spin glasses Christopher Baldwin, Christopher Laumann, Arijeet Pal, Antonello Scardicchio The two high-temperature eigenstate phases that have been most well-studied are the eigenstate-thermalized (ETH) and many-body localized (MBL) phases. In this talk, I discuss how eigenstates of the quantum p-spin models, which are the canonical models of mean-field spin-glass theory, do not fit into either category. In particular, I describe how the structure and organization of these eigenstates resembles the thermodynamics of classical spin glasses. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L52.00006: Direct control of transitions between different mode-locking states of a fiber laser Fatih Ilday, Tesfay Teamir, Roman Iegorov, Ghaith Makey Mode-locking corresponds to a far-from-equilibrium steady state of a laser, whereby extremely short pulses can be produced. Capability to directly control mode-locking states can be used to improve laser performance with numerous applications, as well as shed light on their far-from-equilibrium physics using the laser as an experimental platform. Here, we demonstrate direct control of the mode-locking state using spectral pulse shaping by incorporating a spatial light modulator at a Fourier plane inside the cavity of an Yb-doped fiber laser. We show that we can halt and restart mode-locking, suppress instabilities, induce controlled reversible and irreversible transitions between mode-locking states, and perform advanced pulse shaping on pulses as short as 40 fs. This capability can be used to experimentally investigate bifurcations, reversible and irreversible transitions, by selecting, steering, and even competing various mode-locking states. Such studies can explore collective dynamics of dissipative soliton molecules, and ultimately test emerging theories about far-from-equilibrium physics, where there is an acute lack of experimental systems that are sufficiently well controlled. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L52.00007: Non-adiabatic effect on spin pumping Kazunari Hashimoto, Gen Tatara, Chikako Uchiyama The spin pumping is a standard method to generate spin polarized electron current (spin current) in ferromagnetic-normal metal junctions. Typically, spin current is considered to be induced by precession of the magnetization in the ferromagnetic layer into the normal metal. Most of theoretical studies of the spin pumping are performed in an adiabatic regime where precession of magnetization is sufficiently slow compared to system relaxation time. However, since the magnetization precesses with finite frequency (several gigaherz) in actual experiments, it is necessary to study validity of adiabatic approximation. For this purpose, we investigate non-adiabatic effect on spin pumping by analyzing electron dynamics due to precession of the magnetization. To this end, we introduce a minimum model of the spin pumping, which consists of a magnetic quantum dot contacting with an electron lead, and analyze it by means of the full counting statistics. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L52.00008: Minimizing losses by variational counter-diabatic driving Dries Sels, Anatoli Polkovnikov Despite the time-reversal symmetry of the microscopic dynamics of isolated systems, losses are ubiquitous in any process that tries to manipulate them. Whether it's the heat produced in a car engine or the decoherence of a qubit, all losses arise from our lack of control on the microscopic degrees of freedom of the system. Counter-diabatic driving protocols were proposed as a means to do fast changes in the Hamiltonian without exciting transitions. Such driving in principle allows one to realize arbitrarily fast annealing protocols or implement fast dissipationless driving, circumventing standard adiabatic limitations requiring infinitesimally slow rates. These ideas were tested and used both experimentally and theoretically in small systems, but in larger chaotic systems it is known that exact counter-diabatic protocols do not exist. Here we will present a simple variational approach allowing one to find best physical counter-diabatic protocols. We will show that, while they do not get rid of all transitions, the variational protocols are able to significantly reduce the induced fluctuations in the system. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L52.00009: Controlling stochastic non -- linear systems: ``universal'' strategies. Giuseppe Forte, Dervis Can Vural Reaction networks describe a broad range of physical, chemical, biological, ecological and social phenomena. Reactions are defined in terms of a set of rules that define what species turn into what others upon collision, and are well approximated by coupled Langevin equations in the high-concentration limit. In this work,~we focus on the control of stochastic reaction networks of the Langevin type. We derive an exact formula that allows us controlling a generic stochastic system subject to generic cost functionals, and illustrate our formula with special cases. Perhaps more interestingly than our general result, we find that under certain limits, the optimal protocol assumes a ``universal'' form, i. e. it does not depend explicitly on the details of the cost functional. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L52.00010: Relaxation in a two-body Fermi-Pasta-Ulam system in the canonical ensemble Surajit Sen, Tyler Barrett The study of the dynamics of the Fermi-Pasta-Ulam (FPU) chain remains a challenging problem. Inspired by the recent work of Onorato et al. (PNAS 112, 4208 (2015)) on thermalization in the FPU system, we report a study of relaxation processes in a two-body FPU system in the canonical ensemble. The studies have been carried out using the Recurrence Relations Method introduced by Zwanzig, Mori, Lee and others. We have obtained exact analytical expressions for the first thirteen levels of the continued fraction representation of the Laplace transformed velocity autocorrelation function of the system. Using simple and reasonable extrapolation schemes and known limits we are able to estimate the relaxation behavior of the oscillators in the two-body FPU system and recover the expected behavior in the harmonic limit. Generalizations of the calculations to larger systems will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L52.00011: Intermittent Fermi-Pasta-Ulam Dynamics at Equilibrium David Campbell, Carlo Danieli, Sergej Flach The equilibrium value of an observable defines a manifold in the phase space of an ergodic and equipartitioned many-body syste. A typical trajectory pierces that manifold infinitely often as time goes to infinity. We use these piercings to measure both the relaxation time of the lowest frequency eigenmode of the Fermi-Pasta-Ulam chain, as well as the fluctuations of the subsequent dynamics in equilibrium. We show that previously obtained scaling laws for equipartition times are modified at low energy density due to an unexpected slowing down of the relaxation. The dynamics in equilibrium is characterized by a power-law distribution of excursion times far off equilibrium, with diverging variance. The long excursions arise from sticky dynamics close to regular orbits in the phase space. Our method is generalizable to large classes of many-body systems. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L52.00012: Small systems of Duffing oscillators and the Fermi-Pasta-Ulam-Tsingou system – An examination of the possible reasons for the unusual stability of localized nonlinear excitations in these systems Rahul Kashyap, Alexandra Westley, Surajit Sen |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L52.00013: Abstract Withdrawn The first numerical experiment by Fermi, Pasta, Ulam and Tsingou in 1955 observed recurrence in an array of non-linear systems. This has led to a large number of nonlinear numerical experiments with various new results from a chain of ideal oscillators. FPUT arrays consists of linear oscillators connected nonlinearly which leads to recurrence of energy mode with time. However, if such a system were to be physically constructed, inherent process variations would introduce a manufacturing tolerance into the parameters of the system. This abstract reports investigation into the effects of these tolerances on the FPU matrices. It has been observed that tolerance in the oscillators can degrade the observance of recurrence and with a chain of even 64 oscillators, recurrence cannot be observed with tolerances more than 10\%. It has also been observed that linear oscillators’ tolerances have more effects on recurrence than those of the nonlinear coupling. Even with very small tolerances of $\pm$ 1\% on the linear components, one start to observe variations in the quality and magnitude of the recurrence and at $\pm$ 5\%, recurrence is starting to break down. |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L52.00014: Entanglement properties of Floquet Chern insulators Daniel Yates, Yonah Lemonik, Aditi Mitra Results are presented for the entanglement entropy and spectrum of half-filled graphene following the switch on of a circularly polarized laser. The laser parameters are chosen to correspond to several different Floquet Chern insulator phases. The entanglement properties of the unitarily evolved wavefunctions are compared with the state where one of the Floquet bands is completely occupied. The true states show a volume law for the entanglement, whereas the Floquet states show an area law. Qualitative differences are found in the entanglement properties of the off-resonant and on-resonant laser. Edge states are found in the entanglement spectrum corresponding to certain physical edge states expected in a Chern insulator. However, some edge states that would be expected from the Floquet band structure are missing from the entanglement spectrum. An analytic theory is developed for the long time structure of the entanglement spectrum. It is argued that only edge states corresponding to off-resonant processes appear in the entanglement spectrum. [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L52.00015: Observation of quantum limit of anyonic Heat Flow Mitali Banerjee, Moty Heiblum, Amir Rosenblatt, Yuval Oreg, Dima Feldman, Ady Stern, Vladimir Umansky Quantum mechanics sets a bound on information flow, and thus also a bound on heat flow. Indeed, the heat conductance of a ballistic one-dimensional channel was predicted to be a universal quantity (depending only on universal constants), called the `quantum limit of heat conductance'; namely, ($\pi^{\mathrm{2}}$k$_{\mathrm{B}}^{\mathrm{2}}$T)/3h [1]. Note that this constant does not depend on the charge, the statistics, or the interaction strength of the heat-carrying particles. This had been verified experimentally for weakly interacting phonons [2], photons [3] and electronic Fermi-liquids [4]. Here, we report the first observation of quantized heat flow in a strongly interacting system of 2D electrons in the fractional quantum Hall regime. We observed such quantization in the particle-like 1/3 state and in several hole-like states with fillings between 1/2 and 1. Since the heat in these fractional states is carried by fractionally charged and neutral quasiparticles, the observed quantization is relevant for both, independent on their anyonic statistics [5]. [1] J. B. Pendry, J. Phys. A 16, 2161 (1983) [2] K. Schwab et al., Nature 404, 974 (2000). [3] M. Meschke et al., Nature 444, 187 (2006). [4] S. Jezouin et al., Science 342, 601(2013). [5] C. L. Kane et al., Phys. Rev. B 55, 15852 (1997). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2020 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700