190 research outputs found
Energetic fluctuations in an open quantum process
Relations similar to work and exchange fluctuations have been recently
derived for open systems dynamically evolving in the presence of an ancilla.
Extending these relations and constructing a non-equilibrium Helmholtz equation
we derive a general expression for the energetic and entropic changes of an
open quantum system undergoing a nontrivial evolution. The expressions depend
only on the state of the system and the dynamical map generating the evolution.
Furthermore our formalism makes no assumption on either the nature or dimension
of the ancilla. Our results are expected to find application in understanding
the energetics of complex quantum systems undergoing open dynamics.Comment: 5 pages and 3 figure
Total correlations of the diagonal ensemble as a generic indicator for ergodicity breaking in quantum systems
The diagonal ensemble is the infinite time average of a quantum state
following unitary dynamics. In analogy to the time average of a classical phase
space dynamics, it is intimately related to the ergodic properties of the
quantum system giving information on the spreading of the initial state in the
eigenstates of the Hamiltonian. In this work we apply a concept from quantum
information, known as total correlations, to the diagonal ensemble. Forming an
upper-bound on the multipartite entanglement, it quantifies the combination of
both classical and quantum correlations in a mixed state. We generalize the
total correlations of the diagonal ensemble to more general -Renyi
entropies and focus on the the cases and with further
numerical extensions in mind. Here we show that the total correlations of the
diagonal ensemble is a generic indicator of ergodicity breaking, displaying a
sub-extensive behaviour when the system is ergodic. We demonstrate this by
investigating its scaling in a range of spin chain models focusing not only on
the cases of integrability breaking but also emphasize its role in
understanding the transition from an ergodic to a many body localized phase in
systems with disorder or quasi-periodicity.Comment: v3: several minor improvement
A non-equilibrium quantum Landauer principle
Using the operational framework of completely positive, trace preserving
operations and thermodynamic fluctuation relations, we derive a lower bound for
the heat exchange in a Landauer erasure process on a quantum system. Our bound
comes from a non-phenomenological derivation of the Landauer principle which
holds for generic non-equilibrium dynamics. Furthermore the bound depends on
the non-unitality of dynamics, giving it a physical significance that differs
from other derivations. We apply our framework to the model of a spin-1/2
system coupled to an interacting spin chain at finite temperature.Comment: 4 pages, 2 figures, RevTeX4-1; Accepted for publication in Phys. Rev.
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Daemonic Ergotropy: Enhanced Work Extraction from Quantum Correlations
We investigate how the presence of quantum correlations can influence work
extraction in closed quantum systems, establishing a new link between the field
of quantum non-equilibrium thermodynamics and the one of quantum information
theory. We consider a bipartite quantum system and we show that it is possible
to optimise the process of work extraction, thanks to the correlations between
the two parts of the system, by using an appropriate feedback protocol based on
the concept of ergotropy. We prove that the maximum gain in the extracted work
is related to the existence of quantum correlations between the two parts,
quantified by either quantum discord or, for pure states, entanglement. We then
illustrate our general findings on a simple physical situation consisting of a
qubit system.Comment: 7 pages, 3 figures; RevTeX
Heat current rectification and mobility edges
We investigate how the presence of a single-particle mobility edge in a
system can generate strong heat current rectification. Specifically, we study a
quadratic bosonic chain subject to a quasi-periodic potential and coupled at
its boundaries to spin baths of differing temperature. We find that
rectification increases by orders of magnitude depending on the spatial
position in the chain of localized eigenstates above the mobility edge. The
largest enhancements occur when the coupling of one bath to the system is
dominated by a localized eigenstate, while the other bath couples to numerous
delocalized eigenstates. By tuning the parameters of the quasi-periodic
potential it is thus possible to vary the amplitude, and even invert the
direction, of the rectification.Comment: 5+3 pages 4+4 figure
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