37,737 research outputs found
Quantum Equivalence and Quantum Signatures in Heat Engines
Quantum heat engines (QHE) are thermal machines where the working substance
is quantum. In the extreme case the working medium can be a single particle or
a few level quantum system. The study of QHE has shown a remarkable similarity
with the standard thermodynamical models, thus raising the issue what is
quantum in quantum thermodynamics. Our main result is thermodynamical
equivalence of all engine type in the quantum regime of small action. They have
the same power, the same heat, the same efficiency, and they even have the same
relaxation rates and relaxation modes. Furthermore, it is shown that QHE have
quantum-thermodynamic signature, i.e thermodynamic measurements can confirm the
presence of quantum coherence in the device. The coherent work extraction
mechanism enables power outputs that greatly exceed the power of stochastic
(dephased) engines.Comment: v2 contains style and figures improvements. Subsection III.D was
adde
Experimental demonstration of quantum effects in the operation of microscopic heat engines
The heat engine, a machine that extracts useful work from thermal sources, is
one of the basic theoretical constructs and fundamental applications of
classical thermodynamics. The classical description of a heat engine does not
include coherence in its microscopic degrees of freedom. By contrast, a quantum
heat engine might possess coherence between its internal states. Although the
Carnot efficiency cannot be surpassed, and coherence can be performance
degrading in certain conditions, it was recently predicted that even when using
only thermal resources, internal coherence can enable a quantum heat engine to
produce more power than any classical heat engine using the same resources.
Such a power boost therefore constitutes a quantum thermodynamic signature. It
has also been shown that the presence of coherence results in the thermodynamic
equivalence of different quantum heat engine types, an effect with no classical
counterpart. Microscopic heat machines have been recently implemented with
trapped ions, and proposals for heat machines using superconducting circuits
and optomechanics have been made. When operated with standard thermal baths,
however, the machines implemented so far have not demonstrated any inherently
quantum feature in their thermodynamic quantities. Here we implement two types
of quantum heat engines by use of an ensemble of nitrogen-vacancy centres in
diamond, and experimentally demonstrate both the coherence power boost and the
equivalence of different heat-engine types. This constitutes the first
observation of quantum thermodynamic signatures in heat machines
Swift heat transfer by fast-forward driving in open quantum systems
Typically, time-dependent thermodynamic protocols need to run asymptotically
slowly in order to avoid dissipative losses. By adapting ideas from
counter-diabatic driving and Floquet engineering to open systems, we develop
fast-forward protocols for swiftly thermalizing a system oscillator locally
coupled to an optical phonon bath. These protocols control the system frequency
and the system-bath coupling to induce a resonant state exchange between the
system and the bath. We apply the fast-forward protocols to realize a fast
approximate Otto engine operating at high power near the Carnot Efficiency. Our
results suggest design principles for swift cooling protocols in coupled
many-body systems.Comment: 16 pages, 10 figure
Nonequilibrium thermodynamics as a gauge theory
We assume that markovian dynamics on a finite graph enjoys a gauge symmetry
under local scalings of the probability density, derive the transformation law
for the transition rates and interpret the thermodynamic force as a gauge
potential. A widely accepted expression for the total entropy production of a
system arises as the simplest gauge-invariant completion of the time derivative
of Gibbs's entropy. We show that transition rates can be given a simple
physical characterization in terms of locally-detailed-balanced heat
reservoirs. It follows that Clausius's measure of irreversibility along a
cyclic transformation is a geometric phase. In this picture, the gauge symmetry
arises as the arbitrariness in the choice of a prior probability. Thermostatics
depends on the information that is disposable to an observer; thermodynamics
does not.Comment: 6 pages. Non-fatal errors in eq.(6), eq.(26) and eq.(31) have been
amende
Stability of Spatio-Temporal Structures in a Lattice Model of Pulse-Coupled Oscillators
We analyze the collective behavior of a lattice model of pulse-coupled
oscillators. By studying the intrinsic dynamics of each member of the
population and their mutual interactions we observe the emergence of either
spatio-temporal structures or synchronized regimes. We perform a linear
stability analysis of these structures.Comment: 15 pages, 2 PostScript available upon request at
[email protected], Accepted in Physica
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