1,720,966 research outputs found
Fluctuation theorems and expected utility hypothesis
Full text linkThe expected utility hypothesis is a popular concept in economics that is
useful for making decisions when the payoff is uncertain. In this paper, we
investigate the implications of a fluctuation theorem in the theory of expected
utility. In particular, we wonder whether entropy could serve as a guideline
for gambling. We prove the existence of a bound involving the certainty
equivalent which depends on the entropy produced. Then, we examine the
dependence of the certainty equivalent on the entropy by looking at specific
situations, in particular the work extraction from a nonequilibrium initial
state.Comment: 5 pages, 3 figures, comments welcom
Work fluctuation theorems with initial quantum coherence
Full text linkFluctuation theorems are fundamental results in nonequilibrium thermodynamics beyond the linear response regime. Among these, the paradigmatic Tasaki-Crooks fluctuation theorem relates the statistics of the works done in a forward out-of-equilibrium quantum process and in a corresponding backward one. In particular, the initial states of the two processes are thermal states and thus incoherent in the energy basis. Here we aim to investigate the role of initial quantum coherence in work fluctuation theorems, by considering a quasiprobability distribution of work. To do this, we formulate and examine the implications of a detailed fluctuation theorem, which reproduces the Tasaki-Crooks fluctuation theorem in the absence of initial quantum coherence
Role of quantum correlations in daemonic expected utility
Full text linkFluctuations can challenge the possibility of improving work extraction from quantum correlations. This uncertainty in the work extraction process can be addressed by resorting to the expected utility hypothesis, which can provide an optimal method for work extraction. We study a bipartite quantum system and examine the role of quantum correlations in a daemonic work extraction performed by certain local operations and classical communication. Specifically, we demonstrate and explain how, depending on the so-called absolute risk aversion, a non -neutral risk agent, influenced by fluctuations, views quantum correlations differently from a neutral risk agent that is affected solely by the average work
Quasiprobability distribution of work in the quantum Ising model
Full text linkA complete understanding of the statistics of the work done by quenching a
parameter of a quantum many-body system is still lacking in the presence of an
initial quantum coherence in the energy basis. In this case, the work can be
represented by a class of quasiprobability distributions. Here, we try to
clarify the genuinely quantum features of the process by studying the work
quasiprobability for an Ising model in a transverse field. We consider both a
global and a local quench, by focusing mainly on the thermodynamic limit. We
find that, while for a global quench there is a symmetric non-contextual
representation with a Gaussian probability distribution of work, for a local
quench we can get quantum contextuality as signaled by a negative fourth moment
of the work. Furthermore, we examine the critical features related to a quantum
phase transition and the role of the initial quantum coherence as useful
resource.Comment: 15 pages, 4 figures. Comments welcom
Optimal work extraction from quantum batteries based on the expected utility hypothesis
Full text linkWork extraction in quantum finite systems is an important issue in quantum thermodynamics. The optimal work extracted is called ergotropy, and it is achieved by maximizing the average work extracted over all the unitary cycles. However, an agent that is non-neutral to risk is affected by fluctuations and should extract work by following the expected utility hypothesis. Thus, we investigate the optimal work extraction performed by a risk non-neutral agent by maximizing the average utility function over all the unitary cycles. We mainly focus on initial states that are incoherent with respect to the energy basis, achieving a probability distribution of work. In this case we show how the optimal work extraction will be performed with an incoherent unitary transformation, namely a permutation of the energy basis, which depends on the risk aversion of the agent. We give several examples, in particular also the work extraction from an ensemble of quantum batteries is examined. Furthermore, we also investigate how work extraction is affected by the presence of initial quantum coherence in the energy basis by considering a quasiprobability distribution of work
Anomalous universal adiabatic dynamics: The case of the Fredkin model
Full text linkWhen a system is driven across a second-order quantum phase transition, the
number of defects which are produced scales with the speed of the variation of
the tuning parameter according to a universal law described by the Kibble-Zurek
mechanism. We study a possible breakdown of this prediction proving that the
number of defects can exhibit another universal scaling law which is still
related only to the critical exponents and , but differs from the
Kibble-Zurek result. Finally we provide an example, the deformed Fredkin spin
chain, where this violation of the standard adiabatic dynamics can occur.Comment: 5 pages, 5 figure
Normal and superconducting currents through the Sachdev-Ye-Kitaev model
Full text linkWe study the current driven by an applied voltage as a function of time
through the Sachdev-Ye-Kitaev model when coupled to two normal or
superconducting reservoirs. For normal leads, in the strong coupling limit and
for small bias, the current through the Sachdev-Ye-Kitaev model, described by a
quartic interaction term, reaches monotonically the stationarity, in contrast
to the case of a disordered quadratic interaction where the current has a peak
before reaching the stationary phase. For superconducting leads the currents
have oscillations whose frequencies are determined by the gap and the voltage,
and are suppressed in the strong coupling limit. Moreover, due to different
short time scales between the normal and the oscillating part of the
superconducting current, a peak appears before reaching the stationarity.Comment: 9 pages, 6 figure
Topological phases in the presence of disorder and longer-range couplings
Full text linkWe study the combined effects of disorder and range of the couplings on the
phase diagram of one-dimensional topological superconductors. We consider an
extended version of the Kitaev chain where hopping and pairing terms couple
many sites. Deriving the conditions for the existence of Majorana zero modes,
we show that either the range and the on-site disorder can greatly enhance the
topological phases characterized by the appearance of one or many Majorana
modes localized at the edges. We consider both a discrete and a continuous
disorder distribution. Moreover we discuss the role of correlated disorder
which might further widen the topological regions. Finally we show that in the
purely long-range regime and in the presence of disorder, the spatial decay of
the edge modes remains either algebraic or exponential, with eventually a
modified localization length, as in the absence of disorder.Comment: 14 pages, 11 figure
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
