31 research outputs found
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
Performance of shortcut-to-adiabaticity quantum engines
We consider a paradigmatic quantum harmonic Otto engine operating in finite
time. We investigate its performance when shortcut-to-adiabaticity techniques
are used to speed up its cycle. We compute efficiency and power by taking the
energetic cost of the shortcut driving explicitly into account. We analyze in
detail three different shortcut methods, counterdiabatic driving, local
counterdiabatic driving and inverse engineering. We demonstrate that all three
lead to a simultaneous increase of efficiency and power for fast cycles, thus
outperforming traditional heat engines.Comment: 6 page
Quantum state engineering by shortcuts-to-adiabaticity in interacting spin-boson systems
We present a fast and robust framework to prepare non-classical states of a
bosonic mode exploiting a coherent exchange of excitations with a two-level
system ruled by a Jaynes-Cummings interaction mechanism. Our protocol, which is
built on shortcuts to adiabaticity, allows for the generation of arbitrary Fock
states of the bosonic mode, as well as coherent quantum superpositions of a
Schr\"odinger cat-like form. In addition, we show how to obtain a class of
photon-shifted states where the vacuum population is removed, a result akin to
photon addition, but displaying more non-classicality than standard
photon-added states. Owing to the ubiquity of the spin-boson interaction that
we consider, our proposal is amenable for implementations in state-of-the-art
experiments.Comment: 11 pages, 10 figure
Shortcut-to-adiabaticity Otto engine: A twist to finite-time thermodynamics
We consider a finite-time Otto engine operating on a quantum harmonic
oscillator and driven by shortcut-to-adiabaticity (STA) techniques to speed up
its cycle. We study its efficiency and power when internal friction,
time-averaged work, and work fluctuations are used as quantitative figures of
merit, showing that time-averaged efficiency and power are useful cost
functions for the characterization of the performance of the engine. We then
use the minimum allowed time for validity of STA protocol relation to establish
a physically relevant bound to the efficiency at maximum power of the
STA-driven cycle.Comment: 6 page
Efficiency of heat engines coupled to nonequilibrium reservoirs
We consider quantum heat engines that operate between nonequilibrium
stationary reservoirs. We evaluate their maximum efficiency from the positivity
of the entropy production and show that it can be expressed in terms of an
effective temperature that depends on the nature of the reservoirs. We further
compute the efficiency at maximum power for different kinds of engineered
reservoirs and derive a nonequilibrium generalization of the Clausius statement
of the second law.Comment: 6 pages, 1 figur
Implications of non-Markovian dynamics on information-driven engine
The understanding of memory effects arising from the interaction between
system and environment is a key for engineering quantum thermodynamic devices
beyond the standard Markovian limit. We study the performance of
measurement-based thermal machine whose working medium dynamics is subject to
backflow of information from the reservoir via collision based model. In this
study, the non-Markovian effect is introduced by allowing for additional
unitary interactions between the environments. We present two strategies of
realizing non-Markovian dynamics and study their influence on the performance
of the engine. Moreover, the role of system-environment memory effects on the
engine work extraction and information gain through measurement can be
beneficial in short time.Comment: 8 page
Exponential precision by reaching a quantum critical point
Quantum metrology shows that by exploiting nonclassical resources it is
possible to overcome the fundamental limit of precision found for classical
parameter-estimation protocols. The scaling of the quantum Fisher information
-- which provides an upper bound to the achievable precision -- with respect to
the protocol duration is then of primarily importance to assess its
performances. In classical protocols the quantum Fisher information scales
linearly with time, while typical quantum-enhanced strategies achieve a
quadratic (Heisenberg) or even higher-order polynomial scalings. Here we report
a protocol that is capable of surpassing the polynomial scaling, and yields an
exponential advantage. Such exponential advantage is achieved by approaching,
but without crossing, the critical point of a quantum phase transition of a
fully-connected model in the thermodynamic limit. The exponential advantage
stems from the breakdown of the adiabatic condition close to a critical point.
As we demonstrate, this exponential scaling is well captured by the new bound
derived in arXiv:2110.04144, which in turn allows us to obtain approximate
analytical expressions for the quantum Fisher information that agree with exact
numerical simulations. In addition, we discuss the limitations to the
exponential scaling when considering a finite-size system as well as its
robustness against decoherence effects. Hence, our findings unveil a novel
quantum metrological protocol whose precision scaling goes beyond the
paradigmatic Heisenberg limit with respect to the protocol duration.Comment: 12 pages, 4 figures; comments welcome