9,254 research outputs found
Unitary decoupling treatment of a quadratic bimodal CQED model
We consider a two-photon quantum model of radiation-matter interaction
between a single two-level atom and a degenerate bimodal high-Q cavity field.
Within this tripartite system the explicit construction of two collective
radiation modes, one of which freely evolving and the other one quadratically
coupled to the matter subsystem, is reported. Meaning and advantages of such a
decoupling treatment are carefully discussed.Comment: accepted for publication in Physica Script
Elementary symmetric functions of two solvents of a quadratic matrix equation
Quadratic matrix equations occur in a variety of applications. In this paper
we introduce new permutationally invariant functions of two solvents of the n
quadratic matrix equation X^2- L1X - L0 = 0, playing the role of the two
elementary symmetric functions of the two roots of a quadratic scalar equation.
Our results rely on the connection existing between the QME and the theory of
linear second order difference equations with noncommutative coefficients. An
application of our results to a simple physical problem is briefly discussed.Comment: 20 page
Interaction-free evolving states of a bipartite system
We show that two interacting physical systems may admit entangled pure or non
separable mixed states evolving in time as if the mutual interaction
hamiltonian were absent. In this paper we define these states Interaction Free
Evolving (IFE) states and characterize their existence for a generic binary
system described by a time independent Hamiltonian. A comparison between IFE
subspace and the decoherence free subspace is reported. The set of all pure IFE
states is explicitly constructed for a non homogeneous spin star system model.Comment: submitted to Phys. Rev.
Geometric phase accumulation-based effects in the quantum dynamics of an anisotropically trapped ion
New physical effects in the dynamics of an ion confined in an anisotropic
two-dimensional Paul trap are reported. The link between the occurrence of such
manifestations and the accumulation of geometric phase stemming from the
intrinsic or controlled lack of symmetry in the trap is brought to light. The
possibility of observing in laboratory these anisotropy-based phenomena is
briefly discussed.Comment: 10 pages. Acta Physica Hungarica B 200
Zeno Dynamics and High-Temperature Master Equations Beyond Secular Approximation
Complete positivity of a class of maps generated by master equations derived
beyond the secular approximation is discussed. The connection between such
class of evolutions and physical properties of the system is analyzed in depth.
It is also shown that under suitable hypotheses a Zeno dynamics can be induced
because of the high temperature of the bath.Comment: 9 pages, 2 figure
W-like states of N uncoupled spins 1/2
The exact dynamics of a disordered spin star system, describing a central
spin coupled to N distinguishable and non interacting spins 1/2, is reported.
Exploiting their interaction with the central single spin system, we present
possible conditional schemes for the generation of W-like states, as well as of
well-defined angular momentum states, of the N uncoupled spins. We provide in
addition a way to estimate the coupling intensity between each of the N spins
and the central one. Finally the feasibility of our procedure is briefly
discussed.Comment: 8 pages, 2 figures, accepted for publication in European Physical
Journal Special Topic
Entanglement sudden death and sudden birth in two uncoupled spins
We investigate the entanglement evolution of two qubits interacting with a
common environment trough an Heisenberg XX mechanism. We reveal the possibility
of realizing the phenomenon of entanglement sudden death as well as the
entanglement sudden birth acting on the environment. Such analysis is of
maximal interest at the light of the large applications that spin systems have
in quantum information theory
High Efficiency Detection of Argon Scintillation Light of 128nm Using LAAPDs
The possibility of efficient collection and detection of vacuum ultraviolet
light as emitted by argon, krypton, and xenon gas is studied. Absolute quantum
efficiencies of large area avalanche photodiodes (LAAPDs) are derived at these
wavelengths. VUV light of wavelengths down to the 128nm of Ar emission is shown
to be detectable with silicon avalanche photodiodes at quantum efficiencies
above 42%. Flexible Mylar foil overcoated with Al+MgF is measured to have a
specular reflectivity of 91% at argon emission wavelength. Low-pressure
argon gas is shown to emit significant amounts of non-UV radiation. The average
energy expenditure for the creation of non-UV photons in argon gas at this
pressure is measured to be below 378 eV.Comment: 5 pages, 4 figures, Talk given at IEEE 2005 Nuclear Science Symposium
and Medical Imaging Conference, Puerto Ric
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
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