212 research outputs found
Optical pumping in dense atomic media: Limitations due to reabsorption of spontaneously emitted photons
Resonant optical pumping in dense atomic media is discussed, where the
absorption length is less than the smallest characteristic dimension of the
sample. It is shown that reabsorption and multiple scattering of spontaneous
photons (radiation trapping) can substantially slow down the rate of optical
pumping. A very slow relaxation out of the target state of the pump process is
then sufficient to make optical pumping impossible. As model systems an
inhomogeneously and a radiatively broadened 3-level system resonantly driven
with a strong broad-band pump field are considered.Comment: 6 pages, 5 figure
Dynamics of pair correlations in the attractive Lieb-Liniger gas
We investigate the dynamics of a 1D Bose gas after a quench from the
Tonks-Girardeau regime to the regime of strong attractive interactions applying
analytical techniques and exact numerical simulations. After the quench the
system is found to be predominantly in an excited gas-like state, the so-called
super-Tonks gas, however with a small coherent admixture of two-particle bound
states. Despite its small amplitude, the latter component leads to a rather
pronounced oscillation of the local density-density correlation with a
frequency corresponding to the binding energy of the pair, making two-particle
bound states observable in an experiment. Contributions from bound states with
larger particle numbers are found to be negligible.Comment: 4 pages, 4 figure
Long-time dynamics of spontaneous parametric down-conversion and quantum limitations of conversion efficiency
We analyze the long-time quantum dynamics of degenerate parametric
down-conversion from an initial sub-harmonic vacuum (spontaenous
down-conversion). Standard linearization of the Heisenberg equations of motions
fails in this case, since it is based on an expansion around an unstable
classical solution and neglects pump depletion. Introducing a mean-field
approximation we find a periodic exchange of energy between the pump and
subharmonic mode goverened by an anharmonic pendulum equation. From this
equation the optimum interaction time or crystal length for maximum conversion
can be determined. A numerical integration of the 2-mode Schr"odinger equation
using a dynamically optimized basis of displaced and squeezed number states
verifies the characteristic times predicted by the mean-field approximation. In
contrast to semiclassical and mean-field predictions it is found that quantum
fluctuations of the pump mode lead to a substantial limitation of the
efficiency of parametric down-conversion.Comment: 5 pages, 4 figure
Photon-number selective group delay in cavity induced transparency
We show that the group velocity of a probe pulse in an ensemble of
-type atoms driven by a quantized cavity mode depends on the quantum
state of the input probe pulse. In the strong-coupling regime of the
atom-cavity system the probe group delay is photon number selective. This can
be used to spatially separate the single photon from higher photon-number
components of a few-photon probe pulse and thus to create a deterministic
single-photon source.Comment: 5 pages, 2 figures. revised versio
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