3,948 research outputs found
Proposed realization of the Dicke-model quantum phase transition in an optical cavity QED system
The Dicke model describing an ensemble of two-state atoms interacting with a single quantized mode of the electromagnetic field (with omission of the Â^2 term) exhibits a zero-temperature phase transition at a critical value of the dipole coupling strength. We propose a scheme based on multilevel atoms and cavity-mediated Raman transitions to realize an effective Dicke model operating in the phase transition regime. Optical light from the cavity carries signatures of the critical behavior, which is analyzed for the thermodynamic limit where the number of atoms is very large
Feedback in a cavity QED system for control of quantum beats
Conditional measurements on the undriven mode of a two-mode cavity QED system
prepare a coherent superposition of ground states which generate quantum beats.
The continuous system drive induces decoherence through the phase interruptions
from Rayleigh scattering, which manifests as a decrease of the beat amplitude
and an increase of the frequency of oscillation. We report recent experiments
that implement a simple feedback mechanism to protect the quantum beat. We
continuously drive the system until a photon is detected, heralding the
presence of a coherent superposition. We then turn off the drive and let the
superposition evolve in the dark, protecting it against decoherence. At a later
time we reinstate the drive to measure the amplitude, phase, and frequency of
the beats. The amplitude can increase by more than fifty percent, while the
frequency is unchanged by the feedback.Comment: 13 pages, 5 figures, ICAP 2012 23rd International Conference on
Atomic Physic
Spontaneous dressed-state polarization in the strong driving regime of cavity QED
We utilize high-bandwidth phase quadrature homodyne measurement of the light
transmitted through a Fabry-Perot cavity, driven strongly and on resonance, to
detect excess phase noise induced by a single intracavity atom. We analyze the
correlation properties and driving-strength dependence of the atom-induced
phase noise to establish that it corresponds to the long-predicted phenomenon
of spontaneous dressed-state polarization. Our experiment thus provides a
demonstration of cavity quantum electrodynamics in the strong driving regime,
in which one atom interacts strongly with a many-photon cavity field to produce
novel quantum stochastic behavior.Comment: 4 pages, 4 color figure
Observation of ground-state quantum beats in atomic spontaneous emission
We report ground-state quantum beats in spontaneous emission from a
continuously driven atomic ensemble. Beats are visible only in an intensity
autocorrelation and evidence spontaneously generated coherence in radiative
decay. Our measurement realizes a quantum eraser where a first photon detection
prepares a superposition and a second erases the "which-path" information in
the intermediate state.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Letter
Quantum coherence of discrete kink solitons in ion traps
We propose to realize quantized discrete kinks with cold trapped ions. We
show that long-lived solitonlike configurations are manifested as deformations
of the zigzag structure in the linear Paul trap, and are topologically
protected in a circular trap with an odd number of ions. We study the
quantum-mechanical time evolution of a high-frequency, gap separated internal
mode of a static kink and find long coherence times when the system is cooled
to the Doppler limit. The spectral properties of the internal modes make them
ideally suited for manipulation using current technology. This suggests that
ion traps can be used to test quantum-mechanical effects with solitons and
explore ideas for the utilization of the solitonic internal-modes as carriers
of quantum information.Comment: 5 pages, 4 figures ; minor correction
Vacuum fluctuations and the conditional homodyne detection of squeezed light
Conditional homodyne detection of quadrature squeezing is compared with
standard nonconditional detection. Whereas the latter identifies
nonclassicality in a quantitative way, as a reduction of the noise power below
the shot noise level, conditional detection makes a qualitative distinction
between vacuum state squeezing and squeezed classical noise. Implications of
this comparison for the realistic interpretation of vacuum fluctuations
(stochastic electrodynamics) are discussed.Comment: 14 pages, 7 figures, to appear in J. Opt. B: Quantum Semiclass. Op
Indistinguishability of independent single photons
The indistinguishability of independent single photons is presented by
decomposing the single photon pulse into the mixed state of different transform
limited pulses. The entanglement between single photons and outer environment
or other photons induces the distribution of the center frequencies of those
transform limited pulses and makes photons distinguishable. Only the single
photons with the same transform limited form are indistinguishable. In details,
the indistinguishability of single photons from the solid-state quantum emitter
and spontaneous parametric down conversion is examined with two-photon
Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the
indistinguishability are discussed, where the usage of spectral filter is
highlighted.Comment: 6 pages, 3 figure
Review of world experience and properties of materials for encapsulation of terrestrial photovoltaic arrays
Published and unpublished information relating to encapsulation systems and materials properties was collected by searching the literature and appropriate data bases (over 1,300 documents were selected and reviewed) and by personal contacts including site and company visits. A data tabulation summarizing world experience with terrestrial photovoltaic arrays (50 installations) is presented in the report. Based on criteria of properties, processability, availability, and cost, candidate materials were identified which have potential for use in encapsulation systems for arrays with a lifetime of over 20 years high reliability, an efficiency greater than 10 percent, a total price less than $500/kW, and a production capacity of 500,000 kW/yr. The recommended materials (all commercially available) include, depending upon the device design, various borosilicate and soda-lime glasses and numerous polymerics suitable for specific encapsulation system functions
Qubit-induced phonon blockade as a signature of quantum behavior in nanomechanical resonators
The observation of quantized nanomechanical oscillations by detecting
femtometer-scale displacements is a significant challenge for experimentalists.
We propose that phonon blockade can serve as a signature of quantum behavior in
nanomechanical resonators. In analogy to photon blockade and Coulomb blockade
for electrons, the main idea for phonon blockade is that the second phonon
cannot be excited when there is one phonon in the nonlinear oscillator. To
realize phonon blockade, a superconducting quantum two-level system is coupled
to the nanomechanical resonator and is used to induce the phonon
self-interaction. Using Monte Carlo simulations, the dynamics of the induced
nonlinear oscillator is studied via the Cahill-Glauber -parametrized
quasiprobability distributions. We show how the oscillation of the resonator
can occur in the quantum regime and demonstrate how the phonon blockade can be
observed with currently accessible experimental parameters
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