2,935 research outputs found
Thermodynamic length for far from equilibrium quantum systems
We consider a closed quantum system, initially at thermal equilibrium, driven
by arbitrary external parameters. We derive a lower bound on the entropy
production which we express in terms of the Bures angle between the
nonequilibrium and the corresponding equilibrium state of the system. The Bures
angle is an angle between mixed quantum states and defines a thermodynamic
length valid arbitrarily far from equilibrium. As an illustration, we treat the
case of a time-dependent harmonic oscillator for which we obtain analytic
expressions for generic driving protocols.Comment: 8 pages, 3 figure
Performance of superadiabatic quantum machines
We investigate the performance of a quantum thermal machine operating in
finite time based on shortcut-to-adiabaticity techniques. We compute efficiency
and power for a quantum harmonic Otto engine by taking the energetic cost of
the superadiabatic driving explicitly into account. We further derive generic
upper bounds on both quantities, valid for any heat engine cycle, using the
notion of quantum speed limits for driven systems. We demonstrate that these
quantum bounds are tighter than those stemming from the second law of
thermodynamics.Comment: 8 pages, 5 figure
Quantum speed limit for non-Markovian dynamics
We derive a Margolus-Levitin type bound on the minimal evolution time of an
arbitrarily driven open quantum system. We express this quantum speed limit
time in terms of the operator norm of the nonunitary generator of the dynamics.
We apply these results to the damped Jaynes-Cummings model and demonstrate that
the corresponding bound is tight. We further show that non-Markovian effects
can speed up quantum evolution and therefore lead to a smaller quantum speed
limit time.Comment: 5 pages, 2 figures; Corrected inconsistency in the derivation;
improved bound
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