157 research outputs found
Cavity-assisted spontaneous emission as a single-photon source: Pulse shape and efficiency of one-photon Fock state preparation
Within the framework of exact quantum electrodynamics in dispersing and
absorbing media, we have studied the quantum state of the radiation emitted
from an initially in the upper state prepared two-level atom in a high-
cavity, including the regime where the emitted photon belongs to a wave packet
that simultaneously covers the areas inside and outside the cavity. For both
continuing atom--field interaction and short-term atom--field interaction, we
have determined the spatio-temporal shape of the excited outgoing wave packet
and calculated the efficiency of the wave packet to carry a one-photon Fock
state. Furthermore, we have made contact with quantum noise theories where the
intracavity field and the field outside the cavity are regarded as
approximately representing independent degrees of freedom such that two
separate Hilbert spaces can be introduced.Comment: 16 pages, 7 eps figures; improved version as submitted to Phys. Rev.
Numerical time propagation of quantum systems in radiation fields
Atoms, molecules or excitonic quasiparticles, for which excitations are
induced by external radiation fields and energy is dissipated through radiative
decay, are examples of driven open quantum systems. We explain the use of
commutator-free exponential time-propagators for the numerical solution of the
associated Schr\"odinger or master equations with a time-dependent Hamilton
operator. These time-propagators are based on the Magnus series but avoid the
computation of commutators, which makes them suitable for the efficient
propagation of systems with a large number of degrees of freedom. We present an
optimized fourth order propagator and demonstrate its efficiency in comparison
to the direct Runge-Kutta computation. As an illustrative example we consider
the parametrically driven dissipative Dicke model, for which we calculate the
periodic steady state and the optical emission spectrum.Comment: 23 pages, 11 figure
Calculation of the micromaser spectrum. I. Green's-function approach and approximate analytical techniques
We first calculate the "exact" micromaser spectrum by solving numerically for the Green's function of the approximate master equation for the one-atom (micro-) maser. We then proceed to calculate approximate analytical expressions for the maser linewidth using (i) a phase-operator approach, (ii) an ansatz similar to the standard quantum theory of the laser, and (iii) a linear expansion of the correlation function. Novel features, quite distinct from the familiar Schawlow-Townes linewidth, are found, e.g., the linewidth decreases as the number of thermal photons increases
Nonlinear Jaynes-Cummings model of atom-field interaction
Interaction of a two-level atom with a single mode of electromagnetic field
including Kerr nonlinearity for the field and intensity-dependent atom-field
coupling is discussed. The Hamiltonian for the atom-field system is written in
terms of the elements of a closed algebra, which has
SU(1,1) and Heisenberg-Weyl algebras as limiting cases. Eigenstates and
eigenvalues of the Hamiltonian are constructed.
With the field being in a coherent state initially, the dynamical behaviour
of atomic-inversion, field-statistics and uncertainties in the field
quadratures are studied. The appearance of nonclassical features during the
evolution of the field is shown. Further, we explore the overlap of initial and
time-evolved field states.Comment: 14 pages, 6 figures is PS forma
Five Lectures On Dissipative Master Equations
1 First Lecture: Basics
1.1 Physical Derivation of the Master Equation
1.2 Some Simple Implications
1.3 Steady State
1.4 Action to the Left
2 Second Lecture: Eigenvalues and Eigenvectors of L
2.1 A Simple Case First
2.2 The General Case
3 Third Lecture: Completeness of the Damping Bases
3.1 Phase Space Functions
3.2 Completeness of the Eigenvectors of L
3.3 Positivity Conservation
3.4 Lindblad Form of Liouville Operators
4 Fourth Lecture: Quantum-Optical Applications
4.1 Periodically Driven Damped Oscillator
4.2 Conditional and Unconditional Evolution
4.3 Physical Signicance of Statistical Operators
5 Fifth Lecture: Statistics of Detected Atoms
5.1 Correlation Functions
5.2 Waiting Time Statistics
5.3 Counting StatisticsComment: 58 pages, 10 figures; book chapter to appear in ``Coherent Evolution
in Noisy Environments'', Lecture Notes in Physics, (Springer Verlag,
Berlin-Heidelberg-New York). Notes of lectures given in Dresden,23-27 April
200
Quantum-state control in optical lattices
We study the means to prepare and coherently manipulate atomic wave packets
in optical lattices, with particular emphasis on alkali atoms in the
far-detuned limit. We derive a general, basis independent expression for the
lattice operator, and show that its off-diagonal elements can be tailored to
couple the vibrational manifolds of separate magnetic sublevels. Using these
couplings one can evolve the state of a trapped atom in a quantum coherent
fashion, and prepare pure quantum states by resolved-sideband Raman cooling. We
explore the use of atoms bound in optical lattices to study quantum tunneling
and the generation of macroscopic superposition states in a double-well
potential. Far-off-resonance optical potentials lend themselves particularly
well to reservoir engineering via well controlled fluctuations in the
potential, making the atom/lattice system attractive for the study of
decoherence and the connection between classical and quantum physics.Comment: 35 pages including 8 figures. To appear in Phys. Rev. A. March 199
Influence of a classical homogeneous gravitational field on dissipative dynamics of the Jaynes-Cummings model with phase damping
In this paper, we study the dissipative dynamics of the Jaynes-Cummings model
with phase damping in the presence of a classical homogeneous gravitational
field. The model consists of a moving two-level atom simultaneously exposed to
the gravitational field and a single-mode traveling radiation field in the
presence of the phase damping. We present a quantum treatment of the internal
and external dynamics of the atom based on an alternative su(2) dynamical
algebraic structure. By making use of the super-operator technique, we obtain
the solution of the master equation for the density operator of the quantum
system, under the Markovian approximation. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, we investigate the influence of gravity on the
temporal evolution of collapses and revivals of the atomic population
inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting
statistics and quadrature squeezing of the radiation field in the presence of
phase damping.Comment: 25 pages, 15 figure
Diclofenac Hypersensitivity: Antibody Responses to the Parent Drug and Relevant Metabolites
Background: Hypersensitivity reactions against nonsteroidal antiinflammatory drugs (NSAIDs) like diclofenac (DF) can manifest as Type I-like allergic reactions including systemic anaphylaxis. However, except for isolated case studies experimental evidence for an IgE-mediated pathomechanism of DF hypersensitivity is lacking. In this study we aimed to investigate the possible involvement of drug-and/or metabolite-specific antibodies in selective DF hypersensitivity.
Methodology/Principal Findings: DF, an organochemically synthesized linkage variant, and five major Phase I metabolites were covalently coupled to carrier proteins. Drug conjugates were analyzed for coupling degree and capacity to crosslink receptor-bound IgE antibodies from drug-sensitized mice. With these conjugates, the presence of hapten-specific IgE antibodies was investigated in patients' samples by ELISA, mediator release assay, and basophil activation test. Production of sulfidoleukotrienes by drug conjugates was determined in PBMCs from DF-hypersensitive patients. All conjugates were shown to carry more than two haptens per carrier molecule. Immunization of mice with drug conjugates induced drug-specific IgE antibodies capable of triggering mediator release. Therefore, the conjugates are suitable tools for detection of drug-specific antibodies and for determination of their anaphylactic activity. Fifty-nine patients were enrolled and categorized as hypersensitive either selectively to DF or to multiple NSAIDs. In none of the patients' samples evidence for drug/metabolite-specific IgE in serum or bound to allergic effector cells was found. In contrast, a small group of patients (8/59, 14%) displayed drug/metabolite-specific IgG.
Conclusions/Significance: We found no evidence for an IgE-mediated effector mechanism based on haptenation of protein carriers in DF-hypersensitive patients. Furthermore, a potential involvement of the most relevant metabolites in DF hypersensitivity reactions could be excluded
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