6,233 research outputs found
Microscopic description of dissipative dynamics of a level crossing transition
We analyze the effect of a dissipative bosonic environment on the
Landau-Zener-Stuckelberg-Majorana (LZSM) level crossing model by using a
microscopic approach to derive the relevant master equation. For an environment
at zero temperature and weak dissipation our microscopic approach confirms the
independence of the survival probability on the decay rate that has been
predicted earlier by the simple phenomenological LZSM model. For strong decay
the microscopic approach predicts a notable increase of the survival
probability, which signals dynamical decoupling of the initial state. Unlike
the phenomenological model our approach makes it possible to study the
dependence of the system dynamics on the temperature of the environment. In the
limit of very high temperature we find that the dynamics is characterized by a
very strong dynamical decoupling of the initial state - temperature-induced
quantum Zeno effect.Comment: 6 pages, 4 figure
Spin-1/2 sub-dynamics nested in the quantum dynamics of two coupled qutrits
In this paper we investigate the quantum dynamics of two spin-1 systems,
and , adopting a generalized
-nonconserving Heisenberg model. We
show that, due to its symmetry property, the nine-dimensional dynamics of the
two qutrits exactly decouples into the direct sum of two sub-dynamics living in
two orthogonal four- and five-dimensional subspaces. Such a reduction is
further strengthened by our central result consisting in the fact that in the
four-dimensional dynamically invariant subspace, the two qutrits quantum
dynamics, with no approximations, is equivalent to that of two non interacting
spin 1/2's. The interpretative advantages stemming from such a remarkable and
non-intuitive nesting are systematically exploited and various intriguing
features consequently emerging in the dynamics of the two qutrits are deeply
scrutinised. The possibility of exploiting the dynamical reduction brought to
light in this paper for exactly treating as well time-dependent versions of our
Hamiltonian model is briefly discussed.Comment: 14 pages, 11 figures; Last two authors name corrected, corrected
typos, Fig. 11 changed (same result
Definition of smolder experiments for Spacelab
The feasibility of conducting experiments in space on smoldering combustion was studied to conceptually design specific smoldering experiments to be conducted in the Shuttle/Spacelab System. Design information for identified experiment critical components is provided. The analytical and experimental basis for conducting research on smoldering phenomena in space was established. Physical descriptions of the various competing processes pertaining to smoldering combustion were identified. The need for space research was defined based on limitations of existing knowledge and limitations of ground-based reduced-gravity experimental facilities
Stimulated Raman adiabatic passage in an open quantum system: Master equation approach
A master equation approach to the study of environmental effects in the
adiabatic population transfer in three-state systems is presented. A systematic
comparison with the non-Hermitian Hamiltonian approach [N. V. Vitanov and S.
Stenholm, Phys. Rev. A {\bf 56}, 1463 (1997)] shows that in the weak coupling
limit the two treatments lead to essentially the same results. Instead, in the
strong damping limit the predictions are quite different: in particular the
counterintuitive sequences in the STIRAP scheme turn out to be much more
efficient than expected before. This point is explained in terms of quantum
Zeno dynamics.Comment: 11 pages, 4 figure
Nonequilibrium Casimir-Polder Force in Non-Stationary Systems
Recently the Casmir-Polder force felt by an atom near a substrate under
nonequilibrium stationary conditions has been studied theoretically with
macroscopic quantum electrodyanamics (MQED) and verified experimentally with
cold atoms. We give a quantum field theory derivation of the Langevin equation
describing the atom's motion based on the influence functional method valid for
fully nonequilibrium (nonstationary) conditions. The noise associated with the
quantum field derived from first principles is generally colored and nonlocal,
which is at variance with the `local source hypothesis' of MQED's
generalization to nonequilibrium conditions. Precision measurements on the
shape deformation of an atomic gas as a function of its distance from a mirror
would provide a direct check of our predictions based on this Langevin
equation.Comment: Rewritten Introduction and Abstract in v2 with a slightly altered
title to place a sharper focus of our goals and a clearer distinction of what
the influence functional method can achieve beyond the macroscopic QED
approach. The rest of the paper and the results remain the sam
Polyelectrolyte Multilayering on a Charged Planar Surface
The adsorption of highly \textit{oppositely} charged flexible
polyelectrolytes (PEs) on a charged planar substrate is investigated by means
of Monte Carlo (MC) simulations. We study in detail the equilibrium structure
of the first few PE layers. The influence of the chain length and of a (extra)
non-electrostatic short range attraction between the polycations and the
negatively charged substrate is considered. We show that the stability as well
as the microstructure of the PE layers are especially sensitive to the strength
of this latter interaction. Qualitative agreement is reached with some recent
experiments.Comment: 28 pages; 11 (main) Figs - Revtex4 - Higher resolution Figs can be
obtained upon request. To appear in Macromolecule
Ion pairing in model electrolytes: A study via three particle correlation functions
A novel integral equations approach is applied for studying ion pairing in
the restricted primitive model (RPM) electrolyte, i. e., the three point
extension (TPE) to the Ornstein-Zernike integral equations. In the TPE
approach, the three-particle correlation functions are obtained. The TPE results are compared to molecular
dynamics (MD) simulations and other theories. Good agreement between TPE and MD
is observed for a wide range of parameters, particularly where standard
integral equations theories fail, i. e., low salt concentration and high ionic
valence. Our results support the formation of ion pairs and aligned ion
complexes.Comment: 43 pages (including 18 EPS figs) - RevTeX 4 - J. Chem. Phys. (in
press
âEsprit de corpsâ: Towards collaborative integration of pharmacists and nurses into antimicrobial stewardship programmes in South Africa
With the global threat of antimicrobial resistance now more emergent than ever, there should be wider collaboration between members of the multidisciplinary healthcare team. This article proposes possible ways of engagement between the pharmacist, nurse and doctor. The pharmacist and nurse are placed in an ideal position through united efforts (camaraderie) to redirect healthcare towards improved patient outcomes while also reducing antimicrobial resistance
Zeno-like phenomena in STIRAP processes
The presence of a continuous measurement quantum Zeno effect in a Stimulated Rapid Adiabatic Passage is studied, exploring in detail a sort of self-competition of the damping, which drives the system toward a loss of population and, at the same time, realizes the conditions to optimize the adiabatic passag
ArDM: a ton-scale liquid Argon experiment for direct detection of Dark Matter in the Universe
The ArDM project aims at developing and operating large noble liquid
detectors to search for direct evidence of Weakly Interacting Massive Particle
(WIMP) as Dark Matter in the Universe. The initial goal is to design, assemble
and operate a 1 ton liquid Argon prototype to demonstrate the
feasibility of a ton-scale experiment with the required performance to
efficiently detect and sufficiently discriminate backgrounds for a successful
WIMP detection. Our design addresses the possibility to detect independently
ionization and scintillation signals. In this paper, we describe this goal and
the conceptual design of the detector.Comment: 5 pages, 3 figures, Talk given at IXth international conference on
Topics in Astroparticle and Underground Physics (TAUP05), Zaragoza, (Spain
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