121 research outputs found
Photon-Mediated Interaction between Two Distant Atoms
We study the photonic interactions between two distant atoms which are
coupled by an optical element (a lens or an optical fiber) focussing part of
their emitted radiation onto each other. Two regimes are distinguished
depending on the ratio between the radiative lifetime of the atomic excited
state and the propagation time of a photon between the two atoms. In the two
regimes, well below saturation the dynamics exhibit either typical features of
a bad resonator, where the atoms act as the mirrors, or typical characteristics
of dipole-dipole interaction. We study the coherence properties of the emitted
light and show that it carries signatures of the multiple scattering processes
between the atoms. The model predictions are compared with the experimental
results in J. Eschner {\it et al.}, Nature {\bf 413}, 495 (2001).Comment: 18 pages, 15 figure
Conditions for spin squeezing in a cold 87Rb ensemble
We study the conditions for generating spin squeezing via a quantum
non-demolition measurement in an ensemble of cold 87Rb atoms. By considering
the interaction of atoms in the 5S_{1/2}(F=1) ground state with probe light
tuned near the D2 transition, we show that, for large detunings, this system is
equivalent to a spin-1/2 system when suitable Zeeman substates and quantum
operators are used to define a pseudo-spin. The degree of squeezing is derived
for the rubidium system in the presence of scattering causing decoherence and
loss. We describe how the system can decohere and lose atoms, and predict as
much as 75% spin squeezing for atomic densities typical of optical dipole
traps.Comment: 9 pages, 3 figures, submitted to J. Opt. B: Quantum Semiclass. Opt.
Proceedings of ICSSUR'0
Polarization-based Light-Atom Quantum Interface with an All-optical Trap
We describe the implementation of a system for studying light-matter
interactions using an ensemble of cold rubidium 87 atoms, trapped in a
single-beam optical dipole trap. In this configuration the elongated shape of
the atomic cloud increases the strength of the collective light-atom coupling.
Trapping all-optically allows for long storage times in a low decoherence
environment. We are able to perform several thousands of measurements on one
atomic ensemble with little destruction. We report results on paramagnetic
Faraday rotations from a macroscopically polarized atomic ensemble. Our results
confirm that strong light-atom coupling is achievable in this system which
makes it attractive for single-pass quantum information protocols.Comment: 8 pages, 4 figure
Vacuum-field level shifts in a single trapped ion mediated by a single distant mirror
A distant mirror leads to a vacuum-induced level shift in a laser-excited
atom. This effect has been measured with a single mirror 25 cm away from a
single, trapped barium ion. This dispersive action is the counterpart to the
mirror's dissipative effect, which has been shown earlier to effect a change in
the ion's spontaneous decay [J. Eschner et al., Nature 413, 495-498 (2001)].
The experimental data are well described by 8-level optical Bloch equations
which are amended to take into account the presence of the mirror according to
the model in [U. Dorner and P. Zoller, Phys. Rev. A 66, 023816 (2002)].
Observed deviations from simple dispersive behavior are attributed to
multi-level effects.Comment: version accepted by PR
A tunable narrowband entangled photon pair source for resonant single-photon single-atom interaction
We present a tunable, frequency-stabilized, narrow-bandwidth source of
frequency-degenerate, entangled photon pairs. The source is based on
spontaneous parametric downconversion (SPDC) in periodically-poled KTiOPO4
(PPKTP). Its wavelength can be stabilized to 850 or 854 nm, thus allowing to
address two D-P transitions in 40Ca+ ions. Its output bandwidth of 22 MHz
coincides with the absorption bandwidth of the calcium ions. Its spectral power
density is 1.0 generated pairs/(s MHz mW).Comment: 3 pages, 3 figure
Quantum interference from remotely trapped ions
We observe quantum interference of photons emitted by two continuously
laser-excited single ions, independently trapped in distinct vacuum vessels.
High contrast two-photon interference is observed in two experiments with
different ion species, calcium and barium. Our experimental findings are
quantitatively reproduced by Bloch equation calculations. In particular, we
show that the coherence of the individual resonance fluorescence light field is
determined from the observed interference
Forces between a single atom and its distant mirror image
An excited-state atom whose emitted light is back-reflected by a distant
mirror can experience trapping forces, because the presence of the mirror
modifies both the electromagnetic vacuum field and the atom's own radiation
reaction field. We demonstrate this mechanical action using a single trapped
barium ion. We observe the trapping conditions to be notably altered when the
distant mirror is shifted by an optical wavelength. The well-localised barium
ion enables the spatial dependence of the forces to be measured explicitly. The
experiment has implications for quantum information processing and may be
regarded as the most elementary optical tweezers.Comment: 4 pages, 5 figures, published versio
Feedback cooling of a single trapped ion
Based on a real-time measurement of the motion of a single ion in a Paul
trap, we demonstrate its electro-mechanical cooling below the Doppler limit by
homodyne feedback control (cold damping). The feedback cooling results are well
described by a model based on a quantum mechanical Master Equation.Comment: 4 pages, 3 figure
Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits
We analyze two configurations for laser cooling of neutral atoms whose
internal states store qubits. The atoms are trapped in an optical lattice which
is placed inside a cavity. We show that the coupling of the atoms to the damped
cavity mode can provide a mechanism which leads to cooling of the motion
without destroying the quantum information.Comment: 12 page
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