15 research outputs found
Study of light-assisted collisions between a few cold atoms in a microscopic dipole trap
We study light-assisted collisions in an ensemble containing a small number
(~3) of cold Rb87 atoms trapped in a microscopic dipole trap. Using our ability
to operate with one atom exactly in the trap, we measure the one-body heating
rate associated to a near-resonant laser excitation, and we use this
measurement to extract the two-body loss rate associated to light-assisted
collisions when a few atoms are present in the trap. Our measurements indicate
that the two-body loss rate can reach surprisingly large values beta>10^{-8}
cm^{3}.s^{-1} and varies rapidly with the trap depth and the parameters of the
excitation light.Comment: 6 pages, 7 figure
Measurement of the atom number distribution in an optical tweezer using single photon counting
We demonstrate in this paper a method to reconstruct the atom number
distribution of a cloud containing a few tens of cold atoms. The atoms are
first loaded from a magneto-optical trap into a microscopic optical dipole trap
and then released in a resonant light probe where they undergo a Brownian
motion and scatter photons. We count the number of photon events detected on an
image intensifier. Using the response of our detection system to a single atom
as a calibration, we extract the atom number distribution when the trap is
loaded with more than one atom. The atom number distribution is found to be
compatible with a Poisson distribution.Comment: 6 pages, 5 figure
Evaporative cooling of a small number of atoms in a single-beam microscopic dipole trap
We demonstrate experimentally the evaporative cooling of a few hundred
rubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800
atoms at a temperature of 125microKelvins, we produce an unpolarized sample of
40 atoms at 110nK, within 3s. The phase-space density at the end of the
evaporation reaches unity, close to quantum degeneracy. The gain in phase-space
density after evaporation is 10^3. We find that the scaling laws used for much
larger numbers of atoms are still valid despite the small number of atoms
involved in the evaporative cooling process. We also compare our results to a
simple kinetic model describing the evaporation process and find good agreement
with the data.Comment: 7 pages, 5 figure
Sub-Poissonian atom number fluctuations using light-assisted collisions
We investigate experimentally the number statistics of a mesoscopic ensemble
of cold atoms in a microscopic dipole trap loaded from a magneto-optical trap,
and find that the atom number fluctuations are reduced with respect to a
Poisson distribution due to light-assisted two-body collisions. For numbers of
atoms N>2, we measure a reduction factor (Fano factor) of 0.72+/-0.07, which
differs from 1 by more than 4 standard deviations. We analyze this fact by a
general stochastic model describing the competition between the loading of the
trap from a reservoir of cold atoms and multi-atom losses, which leads to a
master equation. Applied to our experimental regime, this model indicates an
asymptotic value of 3/4 for the Fano factor at large N and in steady state. We
thus show that we have reached the ultimate level of reduction in number
fluctuations in our system.Comment: 4 pages, 3 figure
Imaging a single atom in a time-of-flight experiment
We perform fluorescence imaging of a single 87Rb atom after its release from
an optical dipole trap. The time-of-flight expansion of the atomic spatial
density distribution is observed by accumulating many single atom images. The
position of the atom is revealed with a spatial resolution close to 1
micrometer by a single photon event, induced by a short resonant probe. The
expansion yields a measure of the temperature of a single atom, which is in
very good agreement with the value obtained by an independent measurement based
on a release-and-recapture method. The analysis presented in this paper
provides a way of calibrating an imaging system useful for experimental studies
involving a few atoms confined in a dipole trap.Comment: 14 pages, 8 figure
Spatial Light Modulators for the Manipulation of Individual Atoms
We propose a novel dipole trapping scheme using spatial light modulators
(SLM) for the manipulation of individual atoms. The scheme uses a high
numerical aperture microscope to map the intensity distribution of a SLM onto a
cloud of cold atoms. The regions of high intensity act as optical dipole force
traps. With a SLM fast enough to modify the trapping potential in real time,
this technique is well suited for the controlled addressing and manipulation of
arbitrarily selected atoms.Comment: 9 pages, 5 figure
Fast cavity-enhanced atom detection with low noise and high fidelity
Cavity quantum electrodynamics describes the fundamental interactions between
light and matter, and how they can be controlled by shaping the local
environment. For example, optical microcavities allow high-efficiency detection
and manipulation of single atoms. In this regime fluctuations of atom number
are on the order of the mean number, which can lead to signal fluctuations in
excess of the noise on the incident probe field. Conversely, we demonstrate
that nonlinearities and multi-atom statistics can together serve to suppress
the effects of atomic fluctuations when making local density measurements on
clouds of cold atoms. We measure atom densities below 1 per cavity mode volume
near the photon shot-noise limit. This is in direct contrast to previous
experiments where fluctuations in atom number contribute significantly to the
noise. Atom detection is shown to be fast and efficient, reaching fidelities in
excess of 97% after 10 us and 99.9% after 30 us.Comment: 7 pages, 4 figures, 1 table; extensive changes to format and
discussion according to referee comments; published in Nature Communications
with open acces
Free-Space Lossless State Detection of a Single Trapped Atom
4 pages, 4 figuresInternational audienceWe demonstrate the lossless state-selective detection of a single rubidium 87 atom trapped in an opticaltweezer. This detection is analogous to the one used on trapped ions. After preparation in either a dark or abright state, we probe the atom internal state by sending laser light that couples an excited state to thebright state only. The laser-induced fluorescence is collected by a high numerical aperture lens.The single-shot fidelity of the detection is 98.6 +/- 0.2% and is presently limited by the dark count noiseof the detector. The simplicity of this method opens new perspectives in view of applications to quantummanipulations of neutral atoms
Nonlinear spectroscopy of photons bound to one atom
Optical nonlinearities typically require macroscopic media, thereby making
their implementation at the quantum level an outstanding challenge. Here we
demonstrate a nonlinearity for one atom enclosed by two highly reflecting
mirrors. We send laser light through the input mirror and record the light from
the output mirror of the cavity. For weak laser intensity, we find the
vacuum-Rabi resonances. But for higher intensities, we find an additional
resonance. It originates from the fact that the cavity can accommodate only an
integer number of photons and that this photon number determines the
characteristic frequencies of the coupled atom-cavity system. We selectively
excite such a frequency by depositing at once two photons into the system and
find a transmission which increases with the laser intensity squared. The
nonlinearity differs from classical saturation nonlinearities and is direct
spectroscopic proof of the quantum nature of the atom-cavity system. It
provides a photon-photon interaction by means of one atom, and constitutes a
step towards a two-photon gateway or a single-photon transistor.Comment: 7 figures, Nature Physic