5,615 research outputs found
Witness for initial system-environment correlations in open system dynamics
We study the evolution of a general open quantum system when the system and
its environment are initially correlated. We show that the trace distance
between two states of the open system can increase above its initial value, and
derive tight upper bounds for the growth of the distinguishability of open
system states. This represents a generalization of the contraction property of
quantum dynamical maps. The obtained inequalities can be interpreted in terms
of the exchange of information between the system and the environment, and lead
to a witness for system-environment correlations which can be determined
through measurements on the open system alone.Comment: 4 pages, 1 figur
New applications for phosphoric acid fuel cells
New applications for phosphoric acid fuel cells were identified and evaluated. Candidates considered included all possibilities except grid connected electric utility applications, on site total energy systems, industrial cogeneration, opportunistic use of waste hydrogen, space and military applications, and applications smaller than 10 kW. Applications identified were screened, with the most promising subjected to technical and economic evaluation using a fuel cell and conventional power system data base developed in the study. The most promising applications appear to be the underground mine locomotive and the railroad locomotive. Also interesting are power for robotic submersibles and Arctic villages. The mine locomotive is particularly attractive since it is expected that the fuel cell could command a very high price and still be competitive with the conventionally used battery system. The railroad locomotive's attractiveness results from the (smaller) premium price which the fuel cell could command over the conventional diesel electric system based on its superior fuel efficiency, and on the large size of this market and the accompanying opportunities for manufacturing economy
Initial state preparation with dynamically generated system-environment correlations
The dependence of the dynamics of open quantum systems upon initial
correlations between the system and environment is an utterly important yet
poorly understood subject. For technical convenience most prior studies assume
factorizable initial states where the system and its environments are
uncorrelated, but these conditions are not very realistic and give rise to
peculiar behaviors. One distinct feature is the rapid build up or a sudden jolt
of physical quantities immediately after the system is brought in contact with
its environments. The ultimate cause of this is an initial imbalance between
system-environment correlations and coupling. In this note we demonstrate
explicitly how to avoid these unphysical behaviors by proper adjustments of
correlations and/or the coupling, for setups of both theoretical and
experimental interest. We provide simple analytical results in terms of
quantities that appear in linear (as opposed to affine) master equations
derived for factorized initial states.Comment: 6 pages, 2 figure
Problems of operationalizing the concept of a cost-of-living index
The aim of our paper is to discuss the problems of operationalizing the concept of a .cost-of-living-index. (COLI). For this purpose we are first undertaking a theoretical analysis of Diewert’s theory of superlative index numbers as one possible approach to approximate a COLI. We show that Diewert.s superlative index approach is arguable in many points and that the approach requires restrictive assumptions which are not likely to be met in observed households behaviour. To get a better idea about the deviation of observed households behaviour from the neoclassical assumptions about utility maximizing behaviour, we are estimating an Almost Ideal Demand System and a Quadratic Almost Ideal Demand System with cross section micro data from the German income and expenditure survey. Using the results of the demand system estimations we calculate COLIs and compare them with superlative index numbers and the Laspeyres price index.cost-of-living index; superlative index numbers; Diewert; demand systems
PT-symmetric quantum Liouvillian dynamics
We discuss a combination of unitary and anti-unitary symmetry of quantum
Liouvillian dynamics, in the context of open quantum systems, which implies a
D2 symmetry of the complex Liovillean spectrum. For sufficiently weak
system-bath coupling it implies a uniform decay rate for all coherences, i.e.
off-diagonal elements of the system's density matrix taken in the eigenbasis of
the Hamiltonian. As an example we discuss symmetrically boundary driven open
XXZ spin 1/2 chains.Comment: Note [18] added with respect to a published version, explaining the
symmetry of the matrix V [eq. (14)
Probing multipartite entanglement in a coupled Jaynes-Cummings system
We show how to probe multipartite entanglement in coupled Jaynes-Cummings
cells where the degrees of freedom are the electronic energies of each of the
atoms in separate single-mode cavities plus the single-mode fields
themselves. Specifically we propose probing the combined system as though it is
a dielectric medium. The spectral properties and transition rates directly
reveal multipartite entanglement signatures. It is found that the Hilbert space
of the cell system can be confined to the totally symmetric subspace of two
states only that are maximally-entangled W states with 2N degrees of freedom
Phenomenological memory-kernel master equations and time-dependent Markovian processes
Do phenomenological master equations with memory kernel always describe a
non-Markovian quantum dynamics characterized by reverse flow of information? Is
the integration over the past states of the system an unmistakable signature of
non-Markovianity? We show by a counterexample that this is not always the case.
We consider two commonly used phenomenological integro-differential master
equations describing the dynamics of a spin 1/2 in a thermal bath. By using a
recently introduced measure to quantify non-Markovianity [H.-P. Breuer, E.-M.
Laine, and J. Piilo, Phys. Rev. Lett. 103, 210401 (2009)] we demonstrate that
as far as the equations retain their physical sense, the key feature of
non-Markovian behavior does not appear in the considered memory kernel master
equations. Namely, there is no reverse flow of information from the environment
to the open system. Therefore, the assumption that the integration over a
memory kernel always leads to a non-Markovian dynamics turns out to be
vulnerable to phenomenological approximations. Instead, the considered
phenomenological equations are able to describe time-dependent and
uni-directional information flow from the system to the reservoir associated to
time-dependent Markovian processes.Comment: 5 pages, no figure
Jump-diffusion unravelling of a non Markovian generalized Lindblad master equation
The "correlated-projection technique" has been successfully applied to derive
a large class of highly non Markovian dynamics, the so called non Markovian
generalized Lindblad type equations or Lindblad rate equations. In this
article, general unravellings are presented for these equations, described in
terms of jump-diffusion stochastic differential equations for wave functions.
We show also that the proposed unravelling can be interpreted in terms of
measurements continuous in time, but with some conceptual restrictions. The
main point in the measurement interpretation is that the structure itself of
the underlying mathematical theory poses restrictions on what can be considered
as observable and what is not; such restrictions can be seen as the effect of
some kind of superselection rule. Finally, we develop a concrete example and we
discuss possible effects on the heterodyne spectrum of a two-level system due
to a structured thermal-like bath with memory.Comment: 23 page
Irreversible photon transfer in an ensemble of -type atoms and photon diode
We show that a pair of quantized cavity modes interacting with a spectrally
broadened ensemble of Lambda-type atoms is analogous to an ensemble of two
level systems coupled to a bosonic reservoir. This provides the possibility for
an irreversible photon transfer between photon modes. The density of states as
well as the quantum state of the reservoir can be engineered allowing the
observation of effects such as the quantum Zeno- and anti-Zeno effect, the
destructive interference of decay channels and the decay in a squeezed vacuum.
As a particular application we discuss a photon diode, i.e. a device which
directs a single photon from anyone of two input ports to a common output port.Comment: 5 pages, 2 figure
Reduced density matrix hybrid approach: Application to electronic energy transfer
Electronic energy transfer in the condensed phase, such as that occurring in
photosynthetic complexes, frequently occurs in regimes where the energy scales
of the system and environment are similar. This situation provides a challenge
to theoretical investigation since most approaches are accurate only when a
certain energetic parameter is small compared to others in the problem. Here we
show that in these difficult regimes, the Ehrenfest approach provides a good
starting point for a dynamical description of the energy transfer process due
to its ability to accurately treat coupling to slow environmental modes. To
further improve on the accuracy of the Ehrenfest approach, we use our reduced
density matrix hybrid framework to treat the faster environmental modes quantum
mechanically, at the level of a perturbative master equation. This combined
approach is shown to provide an efficient and quantitative description of
electronic energy transfer in a model dimer and the Fenna-Matthews-Olson
complex and is used to investigate the effect of environmental preparation on
the resulting dynamics.Comment: 11 pages, 8 figure
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