Chains of Quasi-Classical Informations for Bipartite Correlations and the Role of Twin Observables

Having the quantum correlations in a general bipartite state in mind, the information accessible by simultaneous measurement on both subsystems is shown never to exceed the information accessible by measurement on one subsystem, which, in turn is proved not to exceed the von Neumann mutual information. A particular pair of (opposite- subsystem) observables are shown to be responsible both for the amount of quasi-classical correlations and for that of the purely quantum entanglement in the pure-state case: the former via simultaneous subsystem measurements, and the latter through the entropy of coherence or of incompatibility, which is defined for the general case. The observables at issue are so-called twin observables. A general definition of the latter is given in terms of their detailed properties.Comment: 7 pages, Latex2e, selected for the December 2002 issue of the Virtual Journal of Quantum Informatio

On Conserved Current in Markovian Open Quantum Systems

We reexamine the markovian approximation of local current in open quantum systems, discussed recently by Gebauer and Car. Our derivation is more transparent, the proof of current conservation becomes explicit and easy.Comment: 3 page

Correlations in optically-controlled quantum emitters

We address the problem of optically controlling and quantifying the dissipative dynamics of quantum and classical correlations in a set-up of individual quantum emitters under external laser excitation. We show that both types of correlations, the former measured by the quantum discord, are present in the system's evolution even though the emitters may exhibit an early stage disentanglement. In the absence of external laser pumping,we demonstrate analytically, for a set of suitable initial states, that there is an entropy bound for which quantum discord and entanglement of the emitters are always greater than classical correlations, thus disproving an early conjecture that classical correlations are greater than quantum correlations. Furthermore, we show that quantum correlations can also be greater than classical correlations when the system is driven by a laser field. For scenarios where the emitters' quantum correlations are below their classical counterparts, an optimization of the evolution of the quantum correlations can be carried out by appropriately tailoring the amplitude of the laser field and the emitters' dipole-dipole interaction. We stress the importance of using the entanglement of formation, rather than the concurrence, as the entanglement measure, since the latter can grow beyond the total correlations and thus give incorrect results on the actual system's degree of entanglement.Comment: 11 pages, 10 figures, this version contains minor modifications; to appear in Phys. Rev.

The fidelity of general bosonic channels with pure state input

We first derive for the general form of the fidelity for various bosonic channels. Thereby we give the fidelity of different quantum bosonic channel, possibly with product input and entangled input respectively, as examples. The properties of the fidelity are carefully examined.Comment: 3 pages, comments welcom

Pure Stationary States of Open Quantum Systems

Using Liouville space and superoperator formalism we consider pure stationary states of open and dissipative quantum systems. We discuss stationary states of open quantum systems, which coincide with stationary states of closed quantum systems. Open quantum systems with pure stationary states of linear oscillator are suggested. We consider stationary states for the Lindblad equation. We discuss bifurcations of pure stationary states for open quantum systems which are quantum analogs of classical dynamical bifurcations.Comment: 7p., REVTeX

Nonequilibrium entropy production for open quantum systems

We consider open quantum systems weakly coupled to a heat reservoir and driven by arbitrary time-dependent parameters. We derive exact microscopic expressions for the nonequilibrium entropy production and entropy production rate, valid arbitrarily far from equilibrium. By using the two-point energy measurement statistics for system and reservoir, we further obtain a quantum generalization of the integrated fluctuation theorem put forward by Seifert [PRL 95, 040602 (2005)].Comment: 4 pages, 1 figur

Relational physics with real rods and clocks and the measurement problem of quantum mechanics

The use of real clocks and measuring rods in quantum mechanics implies a natural loss of unitarity in the description of the theory. We briefly review this point and then discuss the implications it has for the measurement problem in quantum mechanics. The intrinsic loss of coherence allows to circumvent some of the usual objections to the measurement process as due to environmental decoherence.Comment: 19 pages, RevTex, no figure

Steady state entanglement in open and noisy quantum systems at high temperature

We show that quantum mechanical entanglement can prevail even in noisy open quantum systems at high temperature and far from thermodynamical equilibrium, despite the deteriorating effect of decoherence. The system consists of a number N of interacting quantum particles, and it can interact and exchange particles with some environment. The effect of decoherence is counteracted by a simple mechanism, where system particles are randomly reset to some standard initial state, e.g. by replacing them with particles from the environment. We present a master equation that describes this process, which we can solve analytically for small N. If we vary the interaction strength and the reset against decoherence rate, we find a threshold below which the equilibrium state is classically correlated, and above which there is a parameter region with genuine entanglement.Comment: 5 pages, 3 figure

Asymptotics of Quantum Relative Entropy From Representation Theoretical Viewpoint

In this paper it was proved that the quantum relative entropy $D(\sigma \| \rho)$ can be asymptotically attained by Kullback Leibler divergences of probabilities given by a certain sequence of POVMs. The sequence of POVMs depends on $\rho$, but is independent of the choice of $\sigma$.Comment: LaTeX2e. 8 pages. The title was changed from "Asymptotic Attainment for Quantum Relative Entropy

A multi-site, double-blind, placebo-controlled pilot clinical trial to evaluate the efficacy of buspirone as a relapse-prevention treatment for cocaine dependence

Objective—To evaluate the potential efficacy of buspirone as a relapse-prevention treatment for cocaine dependence. Method—A randomized, double-blind, placebo-controlled, 16-week pilot trial conducted at six clinical sites between August 2012 and June 2013. Adult crack cocaine users meeting DSM-IVTR criteria for current cocaine dependence scheduled to be in inpatient/residential substance use disorder (SUD) treatment for 12–19 days when randomized, and planning to enroll in local outpatient treatment through the end of the active treatment phase were randomized to buspirone titrated to 60 mg/day (n=35) or to placebo (n=27). All participants received psychosocial treatment as usually provided by the SUD treatment programs in which they were enrolled. Outcome measures included maximum days of continuous cocaine abstinence (primary), proportion of cocaine use days, and days-to-first-cocaine-use during the outpatient treatment phase (study weeks 4–15) as assessed by self-report and urine drug screens. Results—There were no significant treatment effects on maximum continuous days of cocaine abstinence or days to first cocaine use. In the females (n=23), there was a significant treatment-bytime interaction effect (X2 (1)=6.06, p=.01), reflecting an increase in cocaine use by the buspirone, relative to placebo, participants early in the outpatient treatment phase. A similar effect was not detected in the male participants (n=39; X2 (1)=0.14, p=.70). Conclusions—The results suggest that buspirone is unlikely to have a beneficial effect on preventing relapse to cocaine use and that buspirone for cocaine-dependent women may worsen their cocaine-use outcomes. Trial Registration—Clinical Trials.gov http://www.clinicaltrials.gov; Identifier: NCT0164115