4,342 research outputs found
Heisenberg picture operators in the stochastic wave function approach to open quantum systems
A fast simulation algorithm for the calculation of multitime correlation
functions of open quantum systems is presented. It is demonstrated that any
stochastic process which ``unravels'' the quantum Master equation can be used
for the calculation of matrix elements of reduced Heisenberg picture operators,
and thus for the calculation of multitime correlation functions, by extending
the stochastic process to a doubled Hilbert space. The numerical performance of
the stochastic simulation algorithm is investigated by means of a standard
example.Comment: RevTex, 5 pages, 2 figures, uses multico
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
The Quest for Purchasing Power Parity with a Series-specific Unit Root Test Using Panel Data
A unit root testing procedure is presented that exploits the well-established power advantages of panel estimation while rectifying a deficiency in other panel unit root tests. This procedure, which takes into account contemporaneous cross-correlation and heterogeneous serial correlation of the regression residuals, allows determination of which members of the panel reject the null hypothesis of a unit root and which do not. Applying the procedure to real exchange rates yields results that are in broad agreement with those obtained from single-equation unit root tests. There is little evidence that a unit root can be rejected in dollar-based real exchange rates for the floating rate period.Marketing,
Entropy production and information fluctuations along quantum trajectories
Employing the stochastic wave function method, we study quantum features of
stochastic entropy production in nonequilibrium processes of open systems. It
is demonstarted that continuous measurements on the environment introduce an
additional, non-thermal contribution to the entropy flux, which is shown to be
a direct consequence of quantum fluctuations. These features lead to a quantum
definition of single trajectory entropy contributions, which accounts for the
difference between classical and quantum trajectories and results in a quantum
correction to the standard form of the integral fluctuation theorem.Comment: 9 pages, 5 figure
Initial correlations in open system's dynamics: The Jaynes-Cummings model
Employing the trace distance as a measure for the distinguishability of
quantum states, we study the influence of initial correlations on the dynamics
of open systems. We concentrate on the Jaynes-Cummings model for which the
knowledge of the exact joint dynamics of system and reservoir allows the
treatment of initial states with arbitrary correlations. As a measure for the
correlations in the initial state we consider the trace distance between the
system-environment state and the product of its marginal states. In particular,
we examine the correlations contained in the thermal equilibrium state for the
total system, analyze their dependence on the temperature and on the coupling
strength, and demonstrate their connection to the entanglement properties of
the eigenstates of the Hamiltonian. A detailed study of the time dependence of
the distinguishability of the open system states evolving from the thermal
equilibrium state and its corresponding uncorrelated product state shows that
the open system dynamically uncovers typical features of the initial
correlations.Comment: 12 pages, 7 figure
Cross border Classical Swine Fever control: Improving Dutch and German crisis management systems by an integrated public-private approach
The objective of this research approach is to analyse in which ways crisis management measures against Classical Swine Fever (CSF) can be improved by a public private cross border model. A core activity contains the analysis of information and communication systems: In a case study it has been empirically analysed if a sufficient supply of public and private information enables crisis managers at both sides of the Dutch-German border area to take decisions about CSF control more efficient. At the end of this approach a new crisis management model had been developed. One of the most important aspects thereby is the assessment of data: (1) within private quality management systems in normal times according to the benefit for public management tasks in times of crisis and (2) within public crisis management systems according to the benefit for cross-border CSF-control activities. To this effect two different methodological approaches have been combined within the model: (1) a method to identify and illustrate public actors and their options in crisis management decision making and (2) a system of communication and information exchange between public and private as well as Dutch and German actors (engage& exchange model) which permit to collect and to evaluate data in addition for a predefined time period are activated
The equilibrium states of open quantum systems in the strong coupling regime
In this work we investigate the late-time stationary states of open quantum
systems coupled to a thermal reservoir in the strong coupling regime. In
general such systems do not necessarily relax to a Boltzmann distribution if
the coupling to the thermal reservoir is non-vanishing or equivalently if the
relaxation timescales are finite. Using a variety of non-equilibrium formalisms
valid for non-Markovian processes, we show that starting from a product state
of the closed system = system + environment, with the environment in its
thermal state, the open system which results from coarse graining the
environment will evolve towards an equilibrium state at late-times. This state
can be expressed as the reduced state of the closed system thermal state at the
temperature of the environment. For a linear (harmonic) system and environment,
which is exactly solvable, we are able to show in a rigorous way that all
multi-time correlations of the open system evolve towards those of the closed
system thermal state. Multi-time correlations are especially relevant in the
non-Markovian regime, since they cannot be generated by the dynamics of the
single-time correlations. For more general systems, which cannot be exactly
solved, we are able to provide a general proof that all single-time
correlations of the open system evolve to those of the closed system thermal
state, to first order in the relaxation rates. For the special case of a
zero-temperature reservoir, we are able to explicitly construct the reduced
closed system thermal state in terms of the environmental correlations.Comment: 20 pages, 2 figure
Magnetism of the LTT phase of Eu doped La_{2-x}Sr_xCuO_4
The ESR signal of Gd spin probes (0.5 at %) as well as the static normal
state susceptibility of Eu (J(Eu^{3+})=0) doped La_{2-x-y}Sr_xEu_yCuO_4 reveal
pronounced changes of the Cu magnetism at the structural transition from the
orthorhombic to the low temperature tetragonal phase for all
non-superconducting compositions. Both a jumplike decrease of \chi as well as
the ESR data show an increase of the in-plane magnetic correlation length in
the LTT phase. From the Gd^{3+} ESR linewidth we find that for specific Eu and
Sr concentrations in the LTT phase the correlation length increases up to more
than 100 lattice constants and the fluctuation frequency of the CuO_2 spin
system slows down to 10^{10}- 10^{11}sec^{-1}. However, there is no static
order above T ~ 8K in contrast to the LTT phase of Nd doped La_{2-x}Sr_xCuO_4
with pinned stripe correlations.Comment: 7 pages, RevTex, 3 eps figures. To appear in the Proceedings of the
International Conference "Stripes, Lattice Instabilities and High Tc
Superconductivity", (Rome, Dec. 1996
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