4,653 research outputs found
Theory of collective Raman scattering from a Bose-Einstein condensate
Recent experiments have demonstrated superradiant Raman scattering from a
Bose-Einstein condensate driven by a single off-resonant laser beam. We present
a quantum theory describing this phenomenon, showing Raman amplification of
matter wave due to collective atomic recoil from 3-level atoms in a
-configuration. When atoms are initially in a single lower internal
state, a closed two-level system is realized between atoms with different
internal states, and entangled atom-photon pairs can be generated. When atoms
are initially prepared in both the lower internal states, a fraction of atoms
recoiling in the backward direction can be generated.Comment: 5 pages, 2 figure
Non-classical Photon Statistics For Two-mode Optical Fields
The non-classical property of subpoissonian photon statistics is extended
from one to two-mode electromagnetic fields, incorporating the physically
motivated property of invariance under passive unitary transformations.
Applications to squeezed coherent states, squeezed thermal states, and
superposition of coherent states are given. Dependences of extent of
non-classical behaviour on the independent squeezing parameters are graphically
displayed.Comment: 15 pages, RevTex, 5 figures, available by sending email to
[email protected]
Number-Phase Wigner Representation for Efficient Stochastic Simulations
Phase-space representations based on coherent states (P, Q, Wigner) have been
successful in the creation of stochastic differential equations (SDEs) for the
efficient stochastic simulation of high dimensional quantum systems. However
many problems using these techniques remain intractable over long integrations
times. We present a number-phase Wigner representation that can be unraveled
into SDEs. We demonstrate convergence to the correct solution for an anharmonic
oscillator with small dampening for significantly longer than other phase space
representations. This process requires an effective sampling of a non-classical
probability distribution. We describe and demonstrate a method of achieving
this sampling using stochastic weights.Comment: 7 pages, 1 figur
Alice falls into a black hole: Entanglement in non-inertial frames
Two observers determine the entanglement between two free bosonic modes by
each detecting one of the modes and observing the correlations between their
measurements. We show that a state which is maximally entangled in an inertial
frame becomes less entangled if the observers are relatively accelerated. This
phenomenon, which is a consequence of the Unruh effect, shows that entanglement
is an observer-dependent quantity in non-inertial frames. In the high
acceleration limit, our results can be applied to a non-accelerated observer
falling into a black hole while the accelerated one barely escapes. If the
observer escapes with infinite acceleration, the state's distillable
entanglement vanishes.Comment: I.F-S published before with maiden name Fuentes-Guridi Replaced with
published version. Phys. Rev. Lett. in pres
The role of quantum fluctuations in the optomechanical properties of a Bose-Einstein condensate in a ring cavity
We analyze a detailed model of a Bose-Einstein condensate trapped in a ring
optical resonator and contrast its classical and quantum properties to those of
a Fabry-P{\'e}rot geometry. The inclusion of two counter-propagating light
fields and three matter field modes leads to important differences between the
two situations. Specifically, we identify an experimentally realizable region
where the system's behavior differs strongly from that of a BEC in a
Fabry-P\'{e}rot cavity, and also where quantum corrections become significant.
The classical dynamics are rich, and near bifurcation points in the mean-field
classical system, the quantum fluctuations have a major impact on the system's
dynamics.Comment: 11 pages, 11 figures, submitted to PR
Intensity fluctuations in steady state superradiance
Alkaline-earth like atoms with ultra-narrow optical transitions enable
superradiance in steady state. The emitted light promises to have an
unprecedented stability with a linewidth as narrow as a few millihertz. In
order to evaluate the potential usefulness of this light source as an
ultrastable oscillator in clock and precision metrology applications it is
crucial to understand the noise properties of this device. In this paper we
present a detailed analysis of the intensity fluctuations by means of
Monte-Carlo simulations and semi-classical approximations. We find that the
light exhibits bunching below threshold, is to a good approximation coherent in
the superradiant regime, and is chaotic above the second threshold.Comment: 8 pages, 5 figure
Photon production from the vacuum close to the super-radiant transition: When Casimir meets Kibble-Zurek
The dynamical Casimir effect (DCE) predicts the generation of photons from
the vacuum due to the parametric amplification of the quantum fluctuation of an
electromagnetic field\cite{casimir1,casimir2}. The verification of such effect
is still elusive in optical systems due to the very demanding requirements of
its experimental implementation. This typically requires very fast changes of
the boundary conditions of the problem, such as the high-frequency driving of
the positions of the mirrors of a cavity accommodating the field. Here, we show
that an ensemble of two-level atoms collectively coupled to the electromagnetic
field of a cavity (thus embodying the quantum Dicke model\cite{dicke}), driven
at low frequencies and close to a quantum phase transition, stimulates the
production of photons from the vacuum. This paves the way to an effective
simulation of the DCE through a mechanism that has recently found an
outstanding experimental demonstration\cite{esslinger}. The spectral properties
of the emitted radiation reflect the critical nature of the system and allow us
to link the detection of DCE to the Kibble-Zurek mechanism for the production
of defects when crossing a continuous phase transition\cite{KZ1,KZ2}. We
illustrate the features of our proposal by addressing a simple cavity
quantum-electrodynamics (cQED) setting of immediate experimental realisation.Comment: 4+1 pages, major changes in the second part of the paper. To appear
in Physical Review Letter
Spatial fluctuations in an optical parametric oscillator below threshold with an intracavity photonic crystal
We show how to control spatial quantum correlations in a multimode degenerate
optical parametric oscillator type I below threshold by introducing a spatially
inhomogeneous medium, such as a photonic crystal, in the plane perpendicular to
light propagation. We obtain the analytical expressions for all the
correlations in terms of the relevant parameters of the problem and study the
number of photons, entanglement, squeezing, and twin beams. Considering
different regimes and configurations we show the possibility to tune the
instability thresholds as well as the quantumness of correlations by breaking
the translational invariance of the system through a photonic crystal
modulation.Comment: 12 pages, 7 figure
High-Fidelity Readout in Circuit Quantum Electrodynamics Using the Jaynes-Cummings Nonlinearity
We demonstrate a qubit readout scheme that exploits the Jaynes-Cummings
nonlinearity of a superconducting cavity coupled to transmon qubits. We find
that in the strongly-driven dispersive regime of this system, there is the
unexpected onset of a high-transmission "bright" state at a critical power
which depends sensitively on the initial qubit state. A simple and robust
measurement protocol exploiting this effect achieves a single-shot fidelity of
87% using a conventional sample design and experimental setup, and at least 61%
fidelity to joint correlations of three qubits.Comment: 5 pages, 4 figure
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