656 research outputs found
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.
Cascade atom in high-Q cavity: The spectrum for non-Markovian decay
The spontaneous emission spectrum for a three level cascade configuration
atom in a single mode high-Q cavity coupled to a zero temperature reservoir of
continuum external modes is determined from the atom-cavity mode master
equation using the quantum regression theorem. Initially the atom is in its
upper state and the cavity mode empty of photons. Following Glauber, the
spectrum is defined via the response of a detector atom. Spectra are calculated
for the detector located inside the cavity (case A), outside the cavity end
mirror (Case B-end emission), or placed for emission out the side of the cavity
(Case C). The spectra for case A and case B are found to be essentially the
same. In all the cases the predicted lineshapes are free of instrumental
effects and only due to cavity decay. Spectra are presented for intermediate
and strong coupling regime situations (where both atomic transitions are
resonant with the cavity frequency), for cases of non-zero cavity detuning, and
for cases where the two atomic transition frequencies differ. The spectral
features for Cases B(A) and C are qualitatively similar, with six spectral
peaks for resonance cases and eight for detuned cases. These general features
of the spectra can be understood via the dressed atom model. However, Case B
and C spectra differ in detail, with the latter exhibiting a deep spectral hole
at the cavity frequency due to quantum interference effects.Comment: 29 pages, 14 figures; v2: very minor correction to two equations,
thicker lines in some figure
The Geometry of Entanglement Sudden Death
In open quantum systems, entanglement can vanish faster than coherence. This
phenomenon is usually called sudden death of entanglement. In this paper sudden
death of entanglement is discussed from a geometrical point of view, in the
context of two qubits. A classification of possible scenarios is presented,
with important known examples classified. Theoretical and experimental
construction of other examples is suggested as well as large dimensional and
multipartite versions of the effect.Comment: 6 pages, 2 figures, references added, initial paragraph corrected,
sectioning adopted, some parts rewritten; accepted by New J. Phy
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
-Pb deep inelastic scattering
Nuclear-medium effects in the weak structure functions and
in the charged current neutrino and antineutrino induced deep
inelastic reactions in Pb have been studied. The calculations have been
performed in a theoretical model using relativistic nuclear spectral functions
which incorporate Fermi motion, binding and nucleon correlations.
We also consider the pion and rho meson cloud contributions calculated from a
microscopic model for meson-nucleus self-energies. Using these structure
functions, the results for the differential cross section have been obtained
and compared with the CERN Hybrid Oscillation Research apparatUS (CHORUS) data.
The results for the ratios ,
, ,
, and (i=2,3)
have also been obtained and a few have been compared with some of the
phenomenological fits.Comment: 19Pages, 12 Fig
Cooperating or Fighting with Decoherence in the Optimal Control of Quantum Dynamics
This paper explores the use of laboratory closed-loop learning control to
either fight or cooperate with decoherence in the optimal manipulation of
quantum dynamics. Simulations of the processes are performed in a Lindblad
formulation on multilevel quantum systems strongly interacting with the
environment without spontaneous emission. When seeking a high control yield it
is possible to find fields that successfully fight with decoherence while
attaining a good quality yield. When seeking modest control yields, fields can
be found which are optimally shaped to cooperate with decoherence and thereby
drive the dynamics more efficiently. In the latter regime when the control
field and the decoherence strength are both weak, a theoretical foundation is
established to describe how they cooperate with each other. In general, the
results indicate that the population transfer objectives can be effectively met
by appropriately either fighting or cooperating with decoherence
Non-Markovian dynamics in atom-laser outcoupling from a double-well Bose-Einstein condensate
We investigate the dynamics of a continuous atom laser based on the merging
of independently formed atomic condensates. In a first attempt to understand
the dynamics of the system, we consider two independent elongated Bose-Einstein
condensates which approach each other and focus on intermediate inter-trap
distances so that a two-mode model is well justified. In the framework of a
mean-field theory, we discuss the quasi steady-state population of the traps as
well as the energy distribution of the outcoupled atoms.Comment: 21 pages, 9 figure, to appear in J. Phys.
Atom-photon entanglement generation and distribution
We extend an earlier model by Law {\it et al.} \cite{law} for a cavity QED
based single-photon-gun to atom-photon entanglement generation and
distribution. We illuminate the importance of a small critical atom number on
the fidelity of the proposed operation in the strong coupling limit. Our result
points to a promisingly high purity and efficiency using currently available
cavity QED parameters, and sheds new light on constructing quantum computing
and communication devices with trapped atoms and high Q optical cavities.Comment: 7 fig
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
Double Ionization by Strong Elliptically Polarized Laser Pulses
We join the tribute to Professor N.B. Delone in this memorial issue by
presenting the results of new calculations on the effects of ellipticity on
double ionization by short and strong near-optical laser pulses.Comment: 3 pages, 4 figures, accepted in Professor N.B. Delone's memorial
issu
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