6 research outputs found
Non-Markovianity and negative entropy production rates
Entropy production plays a fundamental role in nonequilibrium thermodynamics
to quantify the irreversibility of open systems. Its positivity can be ensured
for a wide class of setups, but the entropy production rate can become negative
sometimes. This is often taken as an indicator of non-Markovian dynamics. We
make this link precise by showing under which conditions a negative entropy
production rate implies non-Markovian dynamics and when it does not. This is
established within a unified language for two setups: (i) the dynamics
resulting from a coarse-grained description of a system in contact with a
single heat bath described by a Markovian master equation and (ii) the
classical Hamiltonian dynamics of a driven system, which is coupled arbitrary
strongly to a single heat bath. The quantum version of the latter result is
shown not to hold despite the fact that the integrated thermodynamic
description is formally equivalent to the classical case. The instantaneous
steady state of a non-Markovian dynamics plays an important element in our
study. Our key contribution is to provide a consistent theoretical framework to
study the finite-time thermodynamics of a large class of dynamics with a
precise link to its non-Markovianity.Comment: Changed intro and summary; 21 pages incl. 7 figures plus references
and appendi
On work and heat in time-dependent strong coupling
This paper revisits the classical problem of representing a thermal bath interacting with a system as a large collection of harmonic oscillators initially in thermal equilibrium. As is well known, the system then obeys an equation, which in the bulk and in the suitable limit tends to the Kramers-Langevin equation of physical kinetics. I consider time-dependent system-bath coupling and show that this leads to an additional harmonic force acting on the system. When the coupling is switched on and switched off rapidly, the force has delta-function support at the initial and final time. I further show that the work and heat functionals as recently defined in stochastic thermodynamics at strong coupling contain additional terms depending on the time derivative of the system-bath coupling. I discuss these terms and show that while they can be very large if the system-bath coupling changes quickly, they only give a finite contribution to the work that enters in Jarzynski's equality. I also discuss that these corrections to standard work and heat functionals provide an explanation for non-standard terms in the change of the von Neumann entropy of a quantum bath interacting with a quantum system found in an earlier contribution (Aurell and Eichhorn, 2015).Peer reviewe