767 research outputs found
Microscopic models of quantum jump super-operators
We discuss the quantum jump operation in an open system, and show that jump
super-operators related to a system under measurement can be derived from the
interaction of that system with a quantum measurement apparatus. We give two
examples for the interaction of a monochromatic electromagnetic field in a
cavity (the system) with 2-level atoms and with a harmonic oscillator
(representing two different kinds of detectors). We show that derived quantum
jump super-operators have `nonlinear' form which depends on assumptions made
about the interaction between the system and the detector. A continuous
transition to the standard Srinivas--Davies form of the quantum jump
super-operatoris shown
The effective electrical conductivity of a two-phase liquid-metal flow
Electrical conductivity of two phase liquid metal flow in magnetohydrodynamic generato
Vibrating Cavities - A numerical approach
We present a general formalism allowing for efficient numerical calculation
of the production of massless scalar particles from vacuum in a one-dimensional
dynamical cavity, i.e. the dynamical Casimir effect. By introducing a
particular parametrization for the time evolution of the field modes inside the
cavity we derive a coupled system of first-order linear differential equations.
The solutions to this system determine the number of created particles and can
be found by means of numerical methods for arbitrary motions of the walls of
the cavity. To demonstrate the method which accounts for the intermode coupling
we investigate the creation of massless scalar particles in a one-dimensional
vibrating cavity by means of three particular cavity motions. We compare the
numerical results with analytical predictions as well as a different numerical
approach.Comment: 28 pages, 19 figures, accepted for publication in J. Opt. B: Quantum
Semiclass. Op
Resonant photon creation in a three dimensional oscillating cavity
We analyze the problem of photon creation inside a perfectly conducting,
rectangular, three dimensional cavity with one oscillating wall. For some
particular values of the frequency of the oscillations the system is resonant.
We solve the field equation using multiple scale analysis and show that the
total number of photons inside the cavity grows exponentially in time. This is
also the case for slightly off-resonance situations. Although the spectrum of a
cavity is in general non equidistant, we show that the modes of the
electromagnetic field can be coupled, and that the rate of photon creation
strongly depends on this coupling. We also analyze the thermal enhancement of
the photon creation.Comment: 13 pages. New section on off-resonance motion is included. To appear
in Physical Review
Truncated states obtained by iteration
Quantum states of the electromagnetic field are of considerable importance,
finding potential application in various areas of physics, as diverse as solid
state physics, quantum communication and cosmology. In this paper we introduce
the concept of truncated states obtained via iterative processes (TSI) and
study its statistical features, making an analogy with dynamical systems theory
(DST). As a specific example, we have studied TSI for the doubling and the
logistic functions, which are standard functions in studying chaos. TSI for
both the doubling and logistic functions exhibit certain similar patterns when
their statistical features are compared from the point of view of DST. A
general method to engineer TSI in the running-wave domain is employed, which
includes the errors due to the nonidealities of detectors and photocounts.Comment: 10 pages, 22 figure
Quantum singular oscillator as a model of two-ion trap: an amplification of transition probabilities due to small time variations of the binding potential
Following the paper by M. Combescure [Ann. Phys. (NY) 204, 113 (1990)], we
apply the quantum singular time dependent oscillator model to describe the
relative one dimensional motion of two ions in a trap. We argue that the model
can be justified for low energy excited states with the quantum numbers , provided that the dimensionless constant characterizing the
strength of the repulsive potential is large enough, . Time
dependent Gaussian-like wave packets generalizing odd coherent states of the
harmonic oscillator, and excitation number eigenstates are constructed. We show
that the relative motion of the ions, in contradistinction to its center of
mass counterpart, is extremely sensitive to the time dependence of the binding
harmonic potential, since the large value of results in a significant
amplification of the transition probabilities between energy eigenstate even
for slow time variations of the frequency.Comment: 19 pages, LaTeX, 5 eps-figures, to appear on Phys. Rev. A, one
reference correcte
Properties of Squeezed-State Excitations
The photon distribution function of a discrete series of excitations of
squeezed coherent states is given explicitly in terms of Hermite polynomials of
two variables. The Wigner and the coherent-state quasiprobabilities are also
presented in closed form through the Hermite polynomials and their limiting
cases. Expectation values of photon numbers and their dispersion are
calculated. Some three-dimensional plots of photon distributions for different
squeezing parameters demonstrating oscillatory behaviour are given.Comment: Latex,35 pages,submitted to Quant.Semiclassical Op
Noether's Theorem and time-dependent quantum invariants
The time dependent-integrals of motion, linear in position and momentum
operators, of a quantum system are extracted from Noether's theorem
prescription by means of special time-dependent variations of coordinates. For
the stationary case of the generalized two-dimensional harmonic oscillator, the
time-independent integrals of motion are shown to correspond to special
Bragg-type symmetry properties. A detailed study for the non-stationary case of
this quantum system is presented. The linear integrals of motion are
constructed explicitly for the case of varying mass and coupling strength. They
are obtained also from Noether's theorem. The general treatment for a
multi-dimensional quadratic system is indicated, and it is shown that the
time-dependent variations that give rise to the linear invariants, as conserved
quantities, satisfy the corresponding classical homogeneous equations of motion
for the coordinates.Comment: Plain TeX, 23 pages, preprint of Instituto de Ciencias Nucleares,
UNAM Departamento de F\ii sica and Matem\'aticas Aplicadas, No. 01 (1994
On the measure of nonclassicality of field states
The degree of nonclassicality of states of a field mode is analysed
considering both phase-space and distance-type measures of nonclassicality. By
working out some general examples, it is shown explicitly that the phase-space
measure is rather sensitive to superposition of states, with finite
superpositions possessing maximum nonclassical depth (the highest degree of
nonclassicality) irrespective to the nature of the component states. Mixed
states are also discussed and examples with nonclassical depth varying between
the minimum and the maximum allowed values are exhibited. For pure Gaussian
states, it is demonstrated that distance-type measures based on the
Hilbert-Schmidt metric are equivalent to the phase-space measure. Analyzing
some examples, it is shown that distance-type measures are efficient to
quantify the degree of nonclassicality of non-Gaussian pure states.Comment: Latex, 21 pages, 1 figur
Continuous photodetection model: quantum jump engineering and hints for experimental verification
We examine some aspects of the continuous photodetection model for
photocounting processes in cavities. First, we work out a microscopic model
that describes the field-detector interaction and deduce a general expression
for the Quantum Jump Superoperator (QJS), that shapes the detector's
post-action on the field upon a detection. We show that in particular cases our
model recovers the QJSs previously proposed ad hoc in the literature and point
out that by adjusting the detector parameters one can engineer QJSs. Then we
set up schemes for experimental verification of the model. By taking into
account the ubiquitous non-idealities, we show that by measuring the lower
photocounts moments and the mean waiting time one can check which QJS better
describes the photocounting phenomenon.Comment: 12 pages, 7 figures. Contribution to the conference Quantum Optics
III, Pucon - Chile, November 27-30, 200
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