Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session R44: Quantum Information and ThermodynamicsFocus

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Sponsoring Units: GQI Chair: Mohammad Ansari, Delft University of Technology Room: 347 
Thursday, March 17, 2016 8:00AM  8:36AM 
R44.00001: Quantum thermodynamics for arbitrarily small devices Invited Speaker: Stephanie Wehner Quantum thermodynamics for arbitrarily small devices. [Preview Abstract] 
Thursday, March 17, 2016 8:36AM  8:48AM 
R44.00002: The maximum efficiency of nano heat engines depends on more than temperature Mischa Woods, Nelly Ng, Stephanie Wehner Sadi Carnotâ€™s theorem regarding the maximum efficiency of heat engines is considered to be of fundamental importance in the theory of heat engines and thermodynamics. Here, we show that at the nano and quantum scale, this law needs to be revised in the sense that more information about the bath other than its temperature is required to decide whether maximum efficiency can be achieved. In particular, we derive new fundamental limitations of the efficiency of heat engines at the nano and quantum scale that show that the Carnot efficiency can only be achieved under special circumstances, and we derive a new maximum efficiency for others. A preprint can be found here arXiv:1506.02322 [quantph] [Preview Abstract] 
Thursday, March 17, 2016 8:48AM  9:00AM 
R44.00003: Exceeding the Carnot efficiency Nelly Huei Ying Ng, Mischa Woods, Stephanie Wehner A suitable way of quantifying work for microscopic quantum systems has been constantly debated in the field of quantum thermodynamics. One natural approach is to measure the average increase in energy of an ancillary system, called the battery, after a work extraction protocol. The quality of work extracted is usually argued to be good by quantifying higher moments of the energy distribution, or by restricting the amount of entropy to be low. This limits the amount of heat contribution to the energy extracted, but does not completely prevent it. We show that if one allows for a definition of work that tolerates a nonnegligible entropy increase in the battery, then a small scale heat engine (with a similar set up to that of arXiv:1506.02322) can possibly exceed the Carnot efficiency. This can be done without using any additional resources such as coherence or correlations, and furthermore can be achieved by using finitesize quantum heat baths as well. [Preview Abstract] 
Thursday, March 17, 2016 9:00AM  9:12AM 
R44.00004: Autonomous quantum thermal machines and quantum to classical energy flow Max Frenzel, David Jennings, Terry Rudolph We address the issue of autonomous quantum thermal machines that are tailored to achieve some specific thermodynamic primitive, such as work extraction in the presence of a thermal environment, while having minimal or no control from the macroscopic regime. Beyond experimental implementations, this provides an arena in which to address certain foundational aspects such as the role of coherence in thermodynamics, the use of clock degrees of freedom and the simulation of local timedependent Hamiltonians in a particular quantum subsystem. For smallscale systems additional issues arise. Firstly, it is not clear to what degree genuine ordered thermodynamic work has been extracted, and secondly nontrivial backactions on the thermal machine must be accounted for. We find that both these aspects can be resolved through a judicious choice of quantum measurements that magnify thermodynamic properties up the ladder of lengthscales, while simultaneously stabilizing the quantum thermal machine. Within this framework we show that thermodynamic reversibility is obtained in a particular Zeno limit, and finally illustrate these concepts with a concrete example involving spinsystems. [Preview Abstract] 
Thursday, March 17, 2016 9:12AM  9:24AM 
R44.00005: Stochastic Independence as a Resource for SmallScale Thermodynamics Matteo Lostaglio, Markus P. Mueller, Michele Pastena It is wellknown in thermodynamics that the creation of correlations costs work. It seems then a truism that if a thermodynamic transformation $A \rightarrow B$ is impossible, so will be any transformation that in sending $A$ to $B$ also correlates among them some auxiliary systems $C$. Surprisingly, we show that this is not the case for nonequilibrium thermodynamics of microscopic systems. On the contrary, the creation of correlations greatly extends the set of accessible states, to the point that we can perform on individual systems and in a single shot any transformation that would otherwise be possible only if the number of systems involved was very large. We also show that one only ever needs to create a vanishingly small amount of correlations (as measured by mutual information) among a small number of auxiliary systems (never more than three). The many, severe constraints of microscopic thermodynamics are reduced to the sole requirement that the nonequilibrium free energy decreases in the transformation. This shows that, in principle, reliable extraction of work equal to the free energy of a system can be performed by microscopic engines. [Preview Abstract] 
Thursday, March 17, 2016 9:24AM  9:36AM 
R44.00006: Quantum coherence, timetranslation symmetry and thermodynamics Kamil Korzekwa, Matteo Lostaglio, David Jennings, Terry Rudolph The first law of thermodynamics imposes not just a constraint on the energy content of systems in extreme quantum regimes but also symmetry constraints related to the thermodynamic processing of quantum coherence. We show that this thermodynamic symmetry decomposes any quantum state into mode operators that quantify the coherence present in the state. We then establish general upper and lower bounds for the evolution of quantum coherence under arbitrary thermal operations, valid for any temperature. We identify primitive coherence manipulations and show that the transfer of coherence between energy levels manifests irreversibility not captured by free energy. Moreover, the recently developed thermomajorization relations on blockdiagonal quantum states are observed to be special cases of this symmetry analysis. [Preview Abstract] 
Thursday, March 17, 2016 9:36AM  9:48AM 
R44.00007: Quantum work statistics of charged Dirac particles in timedependent fields Sebastian Deffner, Avadh Saxena The quantum Jarzynski equality is an important theorem of modern quantum thermodynamics. We show that the Jarzynski equality readily generalizes to relativistic quantum mechanics described by the Dirac equation. After establishing the conceptual framework we solve a pedagogical, yet experimentally relevant, system analytically. As a main result we obtain the exact quantum work distributions for charged particles traveling through a timedependent vector potential evolving under Schr\"odinger as well as under Dirac dynamics, and for which the Jarzynski equality is verified. Special emphasis is put on the conceptual and technical subtleties arising from relativistic quantum mechanics. [Preview Abstract] 
Thursday, March 17, 2016 9:48AM  10:24AM 
R44.00008: The second law of quantum thermodynamics as an equality Invited Speaker: Jonathan Oppenheim The traditional second law of thermodynamics says that the average amount of work required to change one state into another while in contact with a heat reservoir, must be at least as large as the change in free energy of the system. Here, we consider a finegrained notion of the free energy, and show that in terms of it, the second law can be written as an equality. We also obtain a generalisation of the Jarzynski fluctuation theorem which holds for arbitrary initial states, not just the case of an initial thermal state. We derive a generalisation of Gibbsstochasticity, a condition originally found in the approach to thermodynamics inspired by quantum information theory. This generalisation directly incorporates the case of fluctuating work and serves as a parent equation which can be used to derive the second law equality and the generalisation of the Jarzynski equation. We further show that each of these three generalisations can be seen as the quasiclassical limit of three fully quantum identities. This allows for more general and fully quantum fluctuation relations from the information theoretic approach to quantum thermodynamics. [Preview Abstract] 
Thursday, March 17, 2016 10:24AM  10:36AM 
R44.00009: Recoverability in quantum information theory Mark Wilde The fact that the quantum relative entropy is nonincreasing with respect to quantum physical evolutions lies at the core of many optimality theorems in quantum information theory and has applications in other areas of physics. In this work, we establish improvements of this entropy inequality in the form of physically meaningful remainder terms. One of the main results can be summarized informally as follows: if the decrease in quantum relative entropy between two quantum states after a quantum physical evolution is relatively small, then it is possible to perform a recovery operation, such that one can perfectly recover one state while approximately recovering the other. This can be interpreted as quantifying how well one can reverse a quantum physical evolution. Our proof method is elementary, relying on the method of complex interpolation, basic linear algebra, and the recently introduced Renyi generalization of a relative entropy difference. The theorem has a number of applications in quantum information theory, which have to do with providing physically meaningful improvements to many known entropy inequalities. This is based on arXiv:1505.04661, now accepted for publication in Proceedings of the Royal Society A. [Preview Abstract] 
Thursday, March 17, 2016 10:36AM  10:48AM 
R44.00010: Quantum Decoherence at Finite Temperatures: Theory and Computations M.A. Novotny, Fengping Jin, Seiji Miyashita, Shengjun Yuan, Hans De Raedt, Kristel Michielsen The decoherence of a finite quantum system $S$ coupled to a finite quantum environment $E$ is considered, where the entirety $S$$+$$E$ is a closed quantum system. The entirety is prepared in a canonical thermal state at a finite temperature. By applying perturbation theory, we find closed form expressions for measures of decoherence and thermalization of $S$ in terms of the free energies of $S$ and $E$. Hence we have quantified how difficult it is to decohere a particular finite quantum system $S$ at a fixed temperature, the result being a function of the free energy of $S$. We have also quantified how potent a particular finite Hilbert space environment $E$ at a fixed temperature is at decohering a generic quantum system. To test these predictions, we performed both real and imaginary time calculations for the Schr{\"o}dinger equation for an entirety with up to 40 quantum spins. The largescale calculations (vectors in Hilbert space with length up to $2^{40}$$\approx$$10^{12}$) validate our predictions for all temperatures. Preprint arXiv:1502.03996. [Preview Abstract] 
Thursday, March 17, 2016 10:48AM  11:00AM 
R44.00011: Dynamical and thermodynamical control of open quantum Brownian motion Francesco Petruccione, Ilya Sinayskiy Open quantum Brownian motion was introduced as a new type of quantum Brownian motion for Brownian particles with internal quantum degrees of freedom. Recently, an example of the microscopic derivation of open quantum Brownian motion has been presented [I. Sinayskiy and F. Petruccione, Phys. Scr. T165, 014017 (2015)]. The microscopic derivation allows to relate the dynamical properties of open Quantum Brownian motion and the thermodynamical properties of the environment. In the present work, we study the possibility of control of the external degrees of freedom of the "walker" (position) by manipulating the internal one, e.g. spin, polarization, occupation numbers. In the particular example of the known microscopic derivation the connection between dynamics of the "walker" and thermodynamical parameters of the system is established. For the system of open Brownian walkers coupled to the same environment controllable creation of quantum correlations is investigated. [Preview Abstract] 
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