4,073 research outputs found
Effect of atomic beam alignment on photon correlation measurements in cavity QED
Quantum trajectory simulations of a cavity QED system comprising an atomic
beam traversing a standing-wave cavity are carried out. The delayed photon
coincident rate for forwards scattering is computed and compared with the
measurements of Rempe et al. [Phys. Rev. Lett. 67, 1727 (1991)] and Foster et
al. [Phys. Rev. A 61, 053821 (2000)]. It is shown that a moderate atomic beam
misalignment can account for the degradation of the predicted correlation. Fits
to the experimental data are made in the weak-field limit with a single
adjustable parameter--the atomic beam tilt from perpendicular to the cavity
axis. Departures of the measurement conditions from the weak-field limit are
discussed.Comment: 15 pages and 13 figure
Nonlinear photon transport in a semiconductor waveguide-cavity system containing a single quantum dot: Anharmonic cavity-QED regime
We present a semiconductor master equation technique to study the
input/output characteristics of coherent photon transport in a semiconductor
waveguide-cavity system containing a single quantum dot. We use this approach
to investigate the effects of photon propagation and anharmonic cavity-QED for
various dot-cavity interaction strengths, including weakly-coupled,
intermediately-coupled, and strongly-coupled regimes. We demonstrate that for
mean photon numbers much less than 0.1, the commonly adopted weak excitation
(single quantum) approximation breaks down, even in the weak coupling regime.
As a measure of the anharmonic multiphoton-correlations, we compute the Fano
factor and the correlation error associated with making a semiclassical
approximation. We also explore the role of electron--acoustic-phonon scattering
and find that phonon-mediated scattering plays a qualitatively important role
on the light propagation characteristics. As an application of the theory, we
simulate a conditional phase gate at a phonon bath temperature of K in the
strong coupling regime.Comment: To appear in PR
Phonon-dressed Mollow triplet in the regime of cavity-QED
We study the resonance fluorescence spectra of a driven quantum dot placed
inside a high semiconductor cavity and interacting with an acoustic phonon
bath. The dynamics is calculated using a time-convolutionless master equation
obtained in the polaron frame. We demonstrate pronounced spectral broadening of
the Mollow sidebands through cavity-emission which, for small cavity-coupling
rates, increases quadratically with the Rabi frequency. However, for larger
cavity coupling rates, this broadening dependence is found to be more complex.
This field-dependent Mollow triplet broadening is primarily a consequence of
the triplet peaks sampling different parts of the asymmetric phonon bath, and
agrees directly with recent experiments with semiconductor micropillars. The
influence from the detuned cavity photon bath and multi-photon effects is shown
to play a qualitatively important role on the fluorescence spectra.Comment: 4 pages, 4 figure
Entanglement signature in the mode structure of a single photon
It is shown that entanglement, which is a quantum correlation property of at
least two subsystems, is imprinted in the mode structure of a single photon.
The photon, which is emitted by two coupled cavities, carries the information
on the concurrence of the two intracavity fields. This can be useful for
recording the entanglement dynamics of two cavity fields and for entanglement
transfer.Comment: 4 pages, 3 figure
A theoretical investigation into the microwave spectroscopy of a phosphorus-donor charge-qubit in silicon: Coherent control in the Si:P quantum computer architecture
We present a theoretical analysis of a microwave spectroscopy experiment on a
charge qubit defined by a P donor pair in silicon, for which we calculate
Hamiltonian parameters using the effective-mass theory of shallow donors. We
solve the master equation of the driven system in a dissipative environment to
predict experimental outcomes. We describe how to calculate physical parameters
of the system from such experimental results, including the dephasing time,
, and the ratio of the resonant Rabi frequency to the relaxation rate.
Finally we calculate probability distributions for experimentally relevant
system parameters for a particular fabrication regime
Effect of frequency mismatched photons in quantum information processing
Many promising schemes for quantum information processing (QIP) rely on
few-photon interference effects. In these proposals, the photons are treated as
being indistinguishable particles. However, single photon sources are typically
subject to variation from device to device. Thus the photons emitted from
different sources will not be perfectly identical, and there will be some
variation in their frequencies. Here, we analyse the effect of this frequency
mismatch on QIP schemes. As examples, we consider the distributed QIP protocol
proposed by Barrett and Kok, and Hong-Ou-Mandel interference which lies at the
heart of many linear optical schemes for quantum computing. In the distributed
QIP protocol, we find that the fidelity of entangled qubit states depends
crucially on the time resolution of single photon detectors. In particular,
there is no reduction in the fidelity when an ideal detector model is assumed,
while reduced fidelities may be encountered when using realistic detectors with
a finite response time. We obtain similar results in the case of Hong-Ou-Mandel
interference -- with perfect detectors, a modified version of quantum
interference is seen, and the visibility of the interference pattern is reduced
as the detector time resolution is reduced. Our findings indicate that problems
due to frequency mismatch can be overcome, provided sufficiently fast detectors
are available.Comment: 14 pages, 8 figures. Comments welcome. v2: Minor changes. v3: Cleaned
up 3 formatting error
Quantum estimation of a damping constant
We discuss an interferometric approach to the estimation of quantum
mechanical damping. We study specific classes of entangled and separable probe
states consisting of superpositions of coherent states. Based on the assumption
of limited quantum resources we show that entanglement improves the estimation
of an unknown damping constant.Comment: 7 pages, 5 figure
Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath
The interrelationship between the non-Markovian stochastic Schr\"odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.Comment: 19 pages, typos corrected, references adde
Collective spin systems in dispersive optical cavity QED: Quantum phase transitions and entanglement
We propose a cavity QED setup which implements a dissipative
Lipkin-Meshkov-Glick model -- an interacting collective spin system. By varying
the external model parameters the system can be made to undergo both first-and
second-order quantum phase transitions, which are signified by dramatic changes
in cavity output field properties, such as the probe laser transmission
spectrum. The steady-state entanglement between pairs of atoms is shown to peak
at the critical points and can be experimentally determined by suitable
measurements on the cavity output field. The entanglement dynamics also
exhibits pronounced variations in the vicinities of the phase transitions.Comment: 19 pages, 18 figures, shortened versio
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