19 research outputs found
Near-ground-state cooling of atoms optically trapped 300nm away from a hot surface
Laser-cooled atoms coupled to nanophotonic structures constitute a powerful
research platform for the exploration of new regimes of light-matter
interaction. While the initialization of the atomic internal degrees of freedom
in these systems has been achieved, a full preparation of the atomic quantum
state also requires controlling the center of mass motion of the atoms at the
quantum level. Obtaining such control is not straightforward, due to the close
vicinity of the atoms to the photonic system that is at ambient temperature.
Here, we demonstrate cooling of individual neutral Cesium atoms, that are
optically interfaced with light in an optical nanofiber, preparing them close
to their three-dimensional motional ground state. The atoms are localized less
than 300nm away from the hot fiber surface. Ground-state preparation is
achieved by performing degenerate Raman cooling, and the atomic temperature is
inferred from the analysis of heterodyne fluorescence spectroscopy signals. Our
cooling method can be implemented either with externally applied or guided
light fields. Moreover, it relies on polarization gradients which naturally
occur for strongly confined guided optical fields. Thus, this method can be
implemented in any trap based on nanophotonic structures. Our results provide
an ideal starting point for the study of novel effects such as light-induced
self-organization, the measurement of novel optical forces, and the
investigation of heat transfer at the nanoscale using quantum probes
Thermal counting statistics in an atomic two-mode squeezed vacuum state
We measure the population distribution in one of the atomic twin beams
generated by four-wave mixing in an optical lattice.
Although the produced two-mode squeezed vacuum state is pure, each individual
mode is described as a statistical mixture.
We confirm the prediction that the particle number follows an exponential
distribution when only one spatio-temporal mode is selected.
We also show that this distribution accounts well for the contrast of an
atomic Hong--Ou--Mandel experiment.
These experiments constitute an important validation of our twin beam source
in view of a future test of a Bell inequalities.Comment: SciPost submissio
Clock spectroscopy of interacting bosons in deep optical lattices
We report on high-resolution optical spectroscopy of interacting bosonic
Yb atoms in deep optical lattices with negligible tunneling. We prepare
Mott insulator phases with singly- and doubly-occupied isolated sites and probe
the atoms using an ultra-narrow "clock" transition. Atoms in singly-occupied
sites undergo long-lived Rabi oscillations. Atoms in doubly-occupied sites are
strongly affected by interatomic interactions, and we measure their inelastic
decay rates and energy shifts. We deduce from these measurements all relevant
collisional parameters involving both clock states, in particular the intra-
and inter-state scattering lengths
Non-linear Relaxation of Interacting Bosons Coherently Driven on a Narrow Optical Transition
We study the dynamics of a two-component Bose-Einstein condensate (BEC) of
Yb atoms coherently driven on a narrow optical transition. The
excitation transfers the BEC to a superposition of states with different
internal and momentum quantum numbers. We observe a crossover with decreasing
driving strength between a regime of damped oscillations, where coherent
driving prevails, and an incoherent regime, where relaxation takes over.
Several relaxation mechanisms are involved: inelastic losses involving two
excited atoms, leading to a non-exponential decay of populations; Doppler
broadening due to the finite momentum width of the BEC and inhomogeneous
elastic interactions, both leading to dephasing and to damping of the
oscillations. We compare our observations to a two-component Gross-Pitaevskii
(GP) model that fully includes these effects. For small or moderate densities,
the damping of the oscillations is mostly due to Doppler broadening. In this
regime, we find excellent agreement between the model and the experimental
results. For higher densities, the role of interactions increases and so does
the damping rate of the oscillations. The damping in the GP model is less
pronounced than in the experiment, possibly a hint for many-body effects not
captured by the mean-field description.Comment: 7 pages, 4 figures; supplementary material available as ancillary
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