991 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
Optical diode based on the chirality of guided photons
Photons are nonchiral particles: their handedness can be both left and right.
However, when light is transversely confined, it can locally exhibit a
transverse spin whose orientation is fixed by the propagation direction of the
photons. Confined photons thus have chiral character. Here, we employ this to
demonstrate nonreciprocal transmission of light at the single-photon level
through a silica nanofibre in two experimental schemes. We either use an
ensemble of spin-polarised atoms that is weakly coupled to the nanofibre-guided
mode or a single spin-polarised atom strongly coupled to the nanofibre via a
whispering-gallery-mode resonator. We simultaneously achieve high optical
isolation and high forward transmission. Both are controlled by the internal
atomic state. The resulting optical diode is the first example of a new class
of nonreciprocal nanophotonic devices which exploit the chirality of confined
photons and which are, in principle, suitable for quantum information
processing and future quantum optical networks
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