6,378 research outputs found
Autonomous thermal machine for amplification and control of energetic coherence
We present a model for an autonomous quantum thermal machine comprised of two
qubits capable of manipulating and even amplifying the local coherence in a
non-degenerate external system. The machine uses only thermal resources,
namely, contact with two heat baths at different temperatures, and the external
system has a non-zero initial amount of coherence. The method we propose allows
for an interconversion between energy, both work and heat, and coherence in an
autonomous configuration working in out-of-equilibrium conditions. This model
raises interesting questions about the role of fundamental limitations on
transformations involving coherence and opens up new possibilities in the
manipulation of coherence by autonomous thermal machines.Comment: v1: 5 + 3 pages, 2 figures. v2: Restructured version with several new
results and a new appendix, 11 + 14 pages, 4 + 3 figures. v3: Improved and
corrected version with new discussions, 8 + 8 pages, 4 + 3 figure
Separability Criteria and Entanglement Measures for Pure States of N Identical Fermions
The study of the entanglement properties of systems of N fermions has
attracted considerable interest during the last few years. Various separability
criteria for pure states of N identical fermions have been recently discussed
but, excepting the case of two-fermions systems, these criteria are difficult
to implement and of limited value from the practical point of view. Here we
advance simple necessary and sufficient separability criteria for pure states
of N identical fermions. We found that to be identified as separable a state
has to comply with one single identity involving either the purity or the von
Neumann entropy of the single-particle reduced density matrix. These criteria,
based on the verification of only one identity, are drastically simpler than
the criteria discussed in the recent literature. We also derive two
inequalities verified respectively by the purity and the entropy of the single
particle, reduced density matrix, that lead to natural entanglement measures
for N-fermion pure states. Our present considerations are related to some
classical results from the Hartree-Fock theory, which are here discussed from a
different point of view in order to clarify some important points concerning
the separability of fermionic pure states.Comment: 6 pages, 0 figure
Simple relationship between the virial-route hypernetted-chain and the compressibility-route Percus--Yevick values of the fourth virial coefficient
As is well known, approximate integral equations for liquids, such as the
hypernetted chain (HNC) and Percus--Yevick (PY) theories, are in general
thermodynamically inconsistent in the sense that the macroscopic properties
obtained from the spatial correlation functions depend on the route followed.
In particular, the values of the fourth virial coefficient predicted by
the HNC and PY approximations via the virial route differ from those obtained
via the compressibility route. Despite this, it is shown in this paper that the
value of obtained from the virial route in the HNC theory is exactly
three halves the value obtained from the compressibility route in the PY
theory, irrespective of the interaction potential (whether isotropic or not),
the number of components, and the dimensionality of the system. This simple
relationship is confirmed in one-component systems by analytical results for
the one-dimensional penetrable-square-well model and the three-dimensional
penetrable-sphere model, as well as by numerical results for the
one-dimensional Lennard--Jones model, the one-dimensional Gaussian core model,
and the three-dimensional square-well model.Comment: 8 pages; 4 figures; v2: slight change of title; proof extended to
multicomponent fluid
Nonequilibrium potential and fluctuation theorems for quantum maps
We derive a general fluctuation theorem for quantum maps. The theorem applies
to a broad class of quantum dynamics, such as unitary evolution, decoherence,
thermalization, and other types of evolution for quantum open systems. The
theorem reproduces well-known fluctuation theorems in a single and simplified
framework and extends the Hatano-Sasa theorem to quantum nonequilibrium
processes. Moreover, it helps to elucidate the physical nature of the
environment inducing a given dynamics in an open quantum system.Comment: 10 page
Quantum fluctuation theorems for arbitrary environments: adiabatic and non-adiabatic entropy production
We analyze the production of entropy along non-equilibrium processes in
quantum systems coupled to generic environments. First, we show that the
entropy production due to final measurements and the loss of correlations obeys
a fluctuation theorem in detailed and integral forms. Second, we discuss the
decomposition of the entropy production into two positive contributions,
adiabatic and non-adiabatic, based on the existence of invariant states of the
local dynamics. Fluctuation theorems for both contributions hold only for
evolutions verifying a specific condition of quantum origin. We illustrate our
results with three relevant examples of quantum thermodynamic processes far
from equilibrium.Comment: 20 pages + 6 of appendices; 7 figures; v2: New example added (example
A) and some minor corrections; accepted in Phys. Rev.
Complexity analysis of Klein-Gordon single-particle systems
The Fisher-Shannon complexity is used to quantitatively estimate the
contribution of relativistic effects to on the internal disorder of
Klein-Gordon single-particle Coulomb systems which is manifest in the rich
variety of three-dimensional geometries of its corresponding quantum-mechanical
probability density. It is observed that, contrary to the non-relativistic
case, the Fisher-Shannon complexity of these relativistic systems does depend
on the potential strength (nuclear charge). This is numerically illustrated for
pionic atoms. Moreover, its variation with the quantum numbers (n, l, m) is
analysed in various ground and excited states. It is found that the
relativistic effects enhance when n and/or l are decreasing.Comment: 4 pages, 3 figures, Accepted in EPL (Europhysics Letters
Information theory of quantum systems with some hydrogenic applications
The information-theoretic representation of quantum systems, which
complements the familiar energy description of the density-functional and
wave-function-based theories, is here discussed. According to it, the internal
disorder of the quantum-mechanical non-relativistic systems can be quantified
by various single (Fisher information, Shannon entropy) and composite (e.g.
Cramer-Rao, LMC shape and Fisher-Shannon complexity) functionals of the
Schr\"odinger probability density. First, we examine these concepts and its
application to quantum systems with central potentials. Then, we calculate
these measures for hydrogenic systems, emphasizing their predictive power for
various physical phenomena. Finally, some recent open problems are pointed out.Comment: 9 pages, 3 figure
Evaluating the process for deceased organ donation: a programme theory approach
– Organ donation and transplantation services represent a microcosm of modern healthcare organisations. They are complex adaptive systems. They face perpetual problems of matching supply and demand. They operate under fierce time and resource constraints. And yet they have received relatively little attention from a systems perspective. The purpose of this paper is to consider some of the fundamental issues in evaluating, improving and policy reform in such complex systems
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