5,617 research outputs found
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
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
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
‘Esprit de corps’: 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
Two-qubit entanglement generation through non-Hermitian Hamiltonians induced by repeated measurements on an ancilla
In contrast to classical systems, actual implementation of non-Hermitian
Hamiltonian dynamics for quantum systems is a challenge because the processes
of energy gain and dissipation are based on the underlying Hermitian
system-environment dynamics that is trace preserving. Recently, a scheme for
engineering non-Hermitian Hamiltonians as a result of repetitive measurements
on an anicillary qubit has been proposed. The induced conditional dynamics of
the main system is described by the effective non-Hermitian Hamiltonian arisng
from the procedure. In this paper we demonstrate the effectiveness of such a
protocol by applying it to physically relevant multi-spin models, showing that
the effective non-Hermitian Hamiltonian drives the system to a maximally
entangled stationary state. In addition, we report a new recipe to construct a
physical scenario where the quantum dynamics of a physical system represented
by a given non-Hermitian Hamiltonian model may be simulated. The physical
implications and the broad scope potential applications of such a scheme are
highlighted
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
Two-qubit entanglement generation through non-hermitian hamiltonians induced by repeated measurements on an ancilla
In contrast to classical systems, actual implementation of non-Hermitian Hamiltonian dynamics for quantum systems is a challenge because the processes of energy gain and dissipation are based on the underlying Hermitian system–environment dynamics, which are trace preserving. Recently, a scheme for engineering non-Hermitian Hamiltonians as a result of repetitive measurements on an ancillary qubit has been proposed. The induced conditional dynamics of the main system is described by the effective non-Hermitian Hamiltonian arising from the procedure. In this paper, we demonstrate the effectiveness of such a protocol by applying it to physically relevant multi-spin models, showing that the effective non-Hermitian Hamiltonian drives the system to a maximally entangled stationary state. In addition, we report a new recipe to construct a physical scenario where the quantum dynamics of a physical system represented by a given non-Hermitian Hamiltonian model may be simulated. The physical implications and the broad scope potential applications of such a scheme are highlighted
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
Dzyaloshinskii-Moriya and dipole-dipole interactions affect coupling-based Landau-Majorana-Stückelberg-Zener transitions
It has been theoretically demonstrated that two spins (qubits or qutrits), coupled by exchange interaction only, undergo a coupling-based joint Landau-Majorana-Stuckelberg-Zener (LMSZ) transition when a linear ramp acts on one of the two spins. Such a transition, under appropriate conditions on the parameters, drives the two-spin system toward a maximally entangled state. In this paper, effects on the quantum dynamics of the two qudits, stemming from the Dzyaloshinskii-Moriya (DM) and dipole-dipole (d-d) interactions, are investigated qualitatively and quantitatively. The enriched Hamiltonian model of the two spins shares with the previous microscopic one the same C2 symmetry which once more brings about an exact treatment of the new quantum dynamical problem. This paper transparently reveals that the DM and d-d interactions generate independent, enhancing or hindering, modifications in the dynamical behavior predicted for the two spins coupled exclusively by the exchange interaction. It is worthwhile to notice that, on the basis of the theory here developed, the measurement of the time evolution of the magnetization in a controlled LMSZ scenario can furnish information on the relative weights of the three kinds of couplings describing the spin system. This possibility is very important since it allows us in principle to legitimate the choice of the microscopic model to be adopted in a given physical scenario
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