25 research outputs found
Inelastic collisions in an exactly solvable two-mode Bose-Einstein Condensate
Inelastic collisions occur in Bose-Einstein condensates, in some cases,
producing particle loss in the system. Nevertheless, these processes have not
been studied in the case when particles do not escape the trap. We show that
such inelastic processes are relevant in quantum properties of the system such
as the evolution of the relative population, the self trapping effect and the
probability distribution of particles. Moreover, including inelastic terms in
the model of the two-mode condensate allows for an exact analytical solution.
Using this solution, we show that collisions favor the generation of
entanglement between the modes of the condensate as long as the collision rate
does not exceed the natural frequency of the system
Two-photon detuning and decoherence in cavity electromagnetically induced transparency for quantized fields
The interaction of a quantized field with three-level atoms in
configuration inside a two-mode cavity is analyzed in the small noise
approximation. The atoms are in a two-photon detuning with respect to the
carriers of the field. We calculate the stationary quadrature noise spectrum of
the field outside the cavity in the case where the input probe field is a
squeezed state and the input pump field is a coherent state. The mean value of
the field is unaltered in all the analysis: the atoms shows electromagnetically
induced transparency (EIT). The effect of the atoms' base level decoherence in
the cavity output field is also studied. It is found that the output field is
very sensitive to two-photon detuning.Comment: 8 page
Effects of environment correlations on the onset of collective decay in waveguide QED
We calculate the dynamics of one and two two-level atoms interacting with the
electromagnetic vacuum field in the vicinity of an optical nanofiber without
making either the Born or the Markov approximations. We use a constant
dielectric function and the Drude-Lorentz model, observing deviations from the
standard super- and sub-radiant decays. Despite the non-trivial environment
correlations, we discuss the validity of approximating the speed of atom-atom
communication to the group velocity of the guided field. Our work presents a
deeper understanding of the validity of commonly used approximations in recent
platforms for quantum optics applications in the context of waveguide QED.Comment: 10 pages, 17 figure
Opacity of electromagnetically induced transparency for quantum fluctuations
We analyze the propagation of a pair of quantized fields inside a medium of
three-level atoms in configuration. We calculate the stationary
quadrature noise spectrum of the field after propagating through the medium, in
the case where the probe field is in a squeezed state and the atoms show
electromagnetically induced transparency (EIT). We find an oscillatory transfer
of the initial quantum properties between the probe and pump fields which is
most strongly pronounced when both fields have comparable Rabi frequencies.
This implies that the quantum state measured after propagation can be
completely different from the initial state, even though the mean values of the
field are unaltered
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
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