37 research outputs found
The effective mass of atom-radiation field system and the cavity-field Wigner distribution in the presence of a homogeneous gravitational field in the Jaynes-Cummings model
The effective mass that approximately describes the effect of a classical
homogeneous gravitational field on an interacting atom-radiation field system
is determined within the framework of the Jaynes-Cummings model.
By taking into account both the atomic motion and gravitational field, a full
quantum treatment of the internal and external dynamics of the atom is
presented. By solving exactly the Schrodinger equation in the interaction
picture, the evolving state of the system is found. Influence of a classical
homogeneous gravitational field on the energy eigenvalues, the effective mass
of atom-radiation field system and the Wigner distribution of the radiation
field are studied, when initially the radiation field is prepared in a coherent
state and the two-level atom is in a coherent superposition of the excited and
ground states.Comment: 12 pages, 9 figure
Two-Pulse Propagation in a Partially Phase-Coherent Medium
We analyze the effects of partial coherence of ground state preparation on
two-pulse propagation in a three-level medium, in contrast to
previous treastments that have considered the cases of media whose ground
states are characterized by probabilities (level populations) or by probability
amplitudes (coherent pure states). We present analytic solutions of the
Maxwell-Bloch equations, and we extend our analysis with numerical solutions to
the same equations. We interpret these solutions in the bright/dark dressed
state basis, and show that they describe a population transfer between the
bright and dark state. For mixed-state media with partial ground
state phase coherence the dark state can never be fully populated. This has
implications for phase-coherent effects such as pulse matching, coherent
population trapping, and electromagnetically induced transparency (EIT). We
show that for partially phase-coherent three-level media, self induced
transparency (SIT) dominates EIT and our results suggest a corresponding
three-level area theorem.Comment: 29 pages, 12 figures. Submitted to Phys. Rev.
Tavis-Cummings model beyond the rotating wave approximation: Quasi-degenerate qubits
The Tavis-Cummings model for more than one qubit interacting with a common
oscillator mode is extended beyond the rotating wave approximation (RWA). We
explore the parameter regime in which the frequencies of the qubits are much
smaller than the oscillator frequency and the coupling strength is allowed to
be ultra-strong. The application of the adiabatic approximation, introduced by
Irish, et al. (Phys. Rev. B \textbf{72}, 195410 (2005)), for a single qubit
system is extended to the multi-qubit case. For a two-qubit system, we identify
three-state manifolds of close-lying dressed energy levels and obtain results
for the dynamics of intra-manifold transitions that are incompatible with
results from the familiar regime of the RWA. We exhibit features of two-qubit
dynamics that are different from the single qubit case, including calculations
of qubit-qubit entanglement. Both number state and coherent state preparations
are considered, and we derive analytical formulas that simplify the
interpretation of numerical calculations. Expressions for individual collapse
and revival signals of both population and entanglement are derived.Comment: 12 Pages, 8 Figures. Comparison to the rotating wave approximation
adde
Two-Pulse Propagation in Media with Quantum-Mixed Ground States
We examine fully coherent two-pulse propagation in a lambda-type medium,
under two-photon resonance conditions and including inhomogeneous broadening.
We examine both the effects of short pulse preparation and the effects of
medium preparation. We contrast cases in which the two pulses have matched
envelopes or not, and contrast cases in which ground state coherence is present
or not. We find that an extended interpretation of the Area Theorem for
single-pulse self-induced transparency (SIT) is able to unify two-pulse
propagation scenarios, including some aspects of electromagnetically-induced
transparency (EIT) and stimulated Raman scattering (SRS). We present numerical
solutions of both three-level and adiabatically reduced two-level density
matrix equations and Maxwell's equations, and show that many features of the
solutions are quickly interpreted with the aid of analytic solutions that we
also provide for restricted cases of pulse shapes and preparation of the
medium. In the limit of large one-photon detuning, we show that the two-level
equations commonly used are not reliable for pulse Areas in the 2 range,
which allows puzzling features of previous numerical work to be understood.Comment: 28 pages, 7 figures. Replaced with version accepted in PR
Spatial evolution of short pulses under coherent population trapping
Spatial and temporal evolution is studied of two powerful short laser pulses
having different wavelengths and interacting with a dense three-level
Lambda-type optical medium under coherent population trapping. A general case
of unequal oscillator strengths of the transitions is considered. Durations of
the probe pulse and the coupling pulse () are assumed to be
shorter than any of the relevant atomic relaxation times. We propose analytical
and numerical solutions of a self-consistent set of coupled Schr\"{o}dinger
equations and reduced wave equations in the adiabatic limit with the account of
the first non-adiabatic correction. The adiabaticity criterion is also
discussed with the account of the pulse propagation. The dynamics of
propagation is found to be strongly dependent on the ratio of the transition
oscillator strengths. It is shown that envelopes of the pulses slightly change
throughout the medium length at the initial stage of propagation. This distance
can be large compared to the one-photon resonant absorption length. Eventually,
the probe pulse is completely reemitted into the coupling pulse during
propagation. The effect of localization of the atomic coherence has been
observed similar to the one predicted by Fleischhauer and Lukin (PRL, {\bf 84},
5094 (2000).Comment: 16 pages revtex style, 7 EPS figures, accepted to Physical Review
Delay-dependent amplification of a probe pulse via stimulated Rayleigh scattering
Stimulated Rayleigh scattering of pump and probe light pulses of close
carrier frequencies is considered. A nonzero time delay between the two pulses
is shown to give rise to amplification of the delayed (probe) pulse accompanied
by attenuation of the pump, both on resonance and off resonance. In either
case, phase-matching effects are shown to provide a sufficiently large gain,
which can exceed significantly direct one-photon-absorption losses
Number-phase-squeezed few-photon state generated from squeezed atoms
This paper develops a method of manipulating the squeezed atom state to
generate a few-photon state whose phase or photon-number fluctuations are
prescribed at our disposal. The squeezed atom state is a collective atomic
state whose quantum fluctuations in population difference or collective dipole
are smaller than those of the coherent atom state. It is shown that the
squeezed atom state can be generated by the interaction of atoms with a
coherent state of the electromagnetic field, and that it can be used as a
tunable source of squeezed radiation. A variety of squeezed states, including
the photon-number squeezed state and the phase squeezed state, can be produced
by manipulating the atomic state. This is owing to the fact that
quantum-statistical information of the atomic state is faithfully transferred
to that of the photon state. Possible experimental situations to implement our
theory are discussed.Comment: 17 pages, RevTex, 14 figures, using epsf.sty, title is changed,
discussion about dissipation is added, accepted for publication in Physical
Review
Propagation dynamics in an autoionization medium
Published versio
Quantum entanglement and disentanglement of multi-atom systems
We present a review of recent research on quantum entanglement, with special
emphasis on entanglement between single atoms, processing of an encoded
entanglement and its temporary evolution. Analysis based on the density matrix
formalism are described. We give a simple description of the entangling
procedure and explore the role of the environment in creation of entanglement
and in disentanglement of atomic systems. A particular process we will focus on
is spontaneous emission, usually recognized as an irreversible loss of
information and entanglement encoded in the internal states of the system. We
illustrate some certain circumstances where this irreversible process can in
fact induce entanglement between separated systems. We also show how
spontaneous emission reveals a competition between the Bell states of a two
qubit system that leads to the recently discovered "sudden" features in the
temporal evolution of entanglement. An another problem illustrated in details
is a deterministic preparation of atoms and atomic ensembles in long-lived
stationary squeezed states and entangled cluster states. We then determine how
to trigger the evolution of the stable entanglement and also address the issue
of a steered evolution of entanglement between desired pairs of qubits that can
be achieved simply by varying the parameters of a given system.Comment: Review articl