2,223 research outputs found
Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath
The interrelationship between the non-Markovian stochastic Schr\"odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.Comment: 19 pages, typos corrected, references adde
The Accuracy of Perturbative Master Equations
We consider open quantum systems with dynamics described by master equations
that have perturbative expansions in the system-environment interaction. We
show that, contrary to intuition, full-time solutions of order-2n accuracy
require an order-(2n+2) master equation. We give two examples of such
inaccuracies in the solutions to an order-2n master equation: order-2n
inaccuracies in the steady state of the system and order-2n positivity
violations, and we show how these arise in a specific example for which exact
solutions are available. This result has a wide-ranging impact on the validity
of coupling (or friction) sensitive results derived from second-order
convolutionless, Nakajima-Zwanzig, Redfield, and Born-Markov master equations.Comment: 6 pages, 0 figures; v2 updated references; v3 updated references,
extension to full-time and nonlocal regime
Asymmetric quantum dot in microcavity as a nonlinear optical element
We have investigated theoretically the interaction between individual quantum
dot with broken inversion symmetry and electromagnetic field of a single-mode
quantum microcavity. It is shown that in the strong coupling regime the system
demonstrates nonlinear optical properties and can serve as emitter of the
terahertz radiation at Rabi frequency of the system. Analytical results for
simplest physical situations are obtained and numerical quantum approach for
calculating emission spectrum is developed.Comment: Article is accepted to Phys. Rev. A (7 pages, 5 figures
Material studies related to lunar surface exploration, volume 3 Final report, 6 Mar. 1967 - 30 Jun. 1968
Mechanical properties of lunar soils related to lunar exploratio
Predictability sieve, pointer states, and the classicality of quantum trajectories
We study various measures of classicality of the states of open quantum
systems subject to decoherence. Classical states are expected to be stable in
spite of decoherence, and are thought to leave conspicuous imprints on the
environment. Here these expected features of environment-induced superselection
(einselection) are quantified using four different criteria: predictability
sieve (which selects states that produce least entropy), purification time
(which looks for states that are the easiest to find out from the imprint they
leave on the environment), efficiency threshold (which finds states that can be
deduced from measurements on a smallest fraction of the environment), and
purity loss time (that looks for states for which it takes the longest to lose
a set fraction of their initial purity). We show that when pointer states --
the most predictable states of an open quantum system selected by the
predictability sieve -- are well defined, all four criteria agree that they are
indeed the most classical states. We illustrate this with two examples: an
underdamped harmonic oscillator, for which coherent states are unanimously
chosen by all criteria, and a free particle undergoing quantum Brownian motion,
for which most criteria select almost identical Gaussian states (although, in
this case, predictability sieve does not select well defined pointer states.)Comment: 10 pages, 13 figure
Matrix Product Density Operators: Simulation of finite-T and dissipative systems
We show how to simulate numerically both the evolution of 1D quantum systems
under dissipation as well as in thermal equilibrium. The method applies to both
finite and inhomogeneous systems and it is based on two ideas: (a) a
representation for density operators which extends that of matrix product
states to mixed states; (b) an algorithm to approximate the evolution (in real
or imaginary time) of such states which is variational (and thus optimal) in
nature.Comment: See also M. Zwolak et al. cond-mat/040644
Spontaneous Collapse of Unstable Quantum Superposition State: A Single-Particle Model of Modified Quantum Dynamics
We propose a modified dynamics of quantum mechanics, in which classical
mechanics of a point mass derives intrinsically in a massive limit of a
single-particle model. On the premise that a position basis plays a special
role in wavefunction collapse, we deduce to formalize spontaneous localization
of wavefunction on the analogy drawn from thermodynamics, in which a
characteristic energy scale and a time scale are introduced to separate quantum
and classical regimes.Comment: 2figs., contribution to Xth ICQO 200
Corrigendum to 'Longitudinal prevalence, faecal shedding and molecular characterization of Campylobacter spp. and Salmonella enterica in sheep' [The Veterinary Journal 202 (2014) 250-254]
Prevalence, faecal shedding and genetic characterisation of Yersinia spp. in sheep across four states of Australia
Objectives
To develop molecular tools for the investigation of the prevalence, species and faecal shedding of Yersinia in sheep.
Methods
A quantitative PCR (qPCR) targeting the β subunit of the Yersinia spp. RNA polymerase gene was developed and validated. The prevalence of pathogenic Y. enterocolitica was determined by screening for the virulent yst gene. These qPCR assays were used to determine Yersinia spp. prevalence and faecal shedding concentration from 3412 faecal samples collected from approximately 1189 lambs (100–180 lambs/flock) on eight farms across Australia. This was a longitudinal study, with sheep sampled on three occasions (weaning, post-weaning and pre-slaughter). A subset of up to five positive samples from each sampling on each farm (n = 111) was sequenced.
Results
Yersinia spp. (including both pathogenic and non-pathogenic species) were identified in all flocks, with 60.7% of lambs shedding Yersinia spp. on at least one sampling occasion. Point prevalence ranged from 4% to 91% across farms and sampling occasions. Median Yersinia spp. bacterial concentration was 1.1 × 106, 2.8 × 106 and 5.6 × 105 organisms/g faeces at weaning, post-weaning and pre-slaughter, respectively, across all farms. Pathogenic Y. enterocolitica was identified in all eight flocks sampled, with 14.8% of lambs shedding pathogenic Y. enterocolitica on at least one sampling occasion.
Conclusion
Yersinia spp. and pathogenic Y. enterocolitica in particular were commonly identified in a sample of Australian sheep flocks using molecular techniques. Further studies into associations between faecal shedding of pathogenic Yersinia spp. and sheep productivity or clinical disease may utilise qPCR in conjunction with other diagnostic tools
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