104 research outputs found
Flux lattices reformulated
We theoretically explore the optical flux lattices produced for ultra-cold
atoms subject to laser fields where both the atom-light coupling and the
effective detuning are spatially periodic. We analyze the geometric vector
potential and the magnetic flux it generates, as well as the accompanying
geometric scalar potential. We show how to understand the gauge-dependent
Aharonov-Bohm singularities in the vector potential, and calculate the
continuous magnetic flux through the elementary cell in terms of these
singularities. The analysis is illustrated with a square optical flux lattice.
We conclude with an explicit laser configuration yielding such a lattice using
a set of five properly chosen beams with two counterpropagating pairs (one
along the x axes and the other y axes), together with a single beam along the z
axis. We show that this lattice is not phase-stable, and identify the one
phase-difference that affects the magnetic flux. Thus armed with realistic
laser setup, we directly compute the Chern number of the lowest Bloch band to
identify the region where the non- zero magnetic flux produces a topologically
non-trivial band structure.Comment: 22 pages, 7 figure
Slow polaritons with orbital angular momentum in atomic gases
Polariton formalism is applied for studying the propagation of a probe field
of light in a cloud of cold atoms influenced by two control laser beams of
larger intensity. The laser beams couple resonantly three hyperfine atomic
ground states to a common excited state thus forming a tripod configuration of
the atomic energy levels involved. The first control beam can have an optical
vortex with the intensity of the beam going to zero at the vortex core. The
second control beam without a vortex ensures the loseless (adiabatic)
propagation of the probe beam at a vortex core of the first control laser. We
investigate the storage of the probe pulse into atomic coherences by switching
off the control beams, as well as its subsequent retrieval by switching the
control beams on. The optical vortex is transferred from the control to the
probe fields during the storage or retrieval of the probe field. We analyze
conditions for the vortex to be transferred efficiently to the regenerated
probe beam and discuss possibilities of experimental implementation of the
proposed scheme using atoms like rubidium or sodium.Comment: 4 figure
Optical vortices of slow light using tripod scheme
We consider propagation, storing and retrieval of slow light (probe beam) in
a resonant atomic medium illuminated by two control laser beams of larger
intensity. The probe and two control beams act on atoms in a tripod
configuration of the light-matter coupling. The first control beam is allowed
to have an orbital angular momentum (OAM). Application of the second
vortex-free control laser ensures the adiabatic (lossles) propagation of the
probe beam at the vortex core where the intensity of the first control laser
goes to zero. Storing and release of the probe beam is accomplished by
switching off and on the control laser beams leading to the transfer of the
optical vortex from the first control beam to the regenerated probe field. A
part of the stored probe beam remains frozen in the medium in the form of
atomic spin excitations, the number of which increases with increasing the
intensity of the second control laser. We analyse such losses in the
regenerated probe beam and provide conditions for the optical vortex of the
control beam to be transferred efficiently to the restored probe beam.Comment: 2 figure
Spinor Slow-Light and Dirac particles with variable mass
We consider the interaction of two weak probe fields of light with an atomic
ensemble coherently driven by two pairs of standing wave laser fields in a
tripod-type linkage scheme. The system is shown to exhibit a Dirac-like
spectrum for light-matter quasi-particles with multiple dark-states, termed
spinor slow-light polaritons (SSP). They posses an "effective speed of light"
given by the group-velocity of slow-light, and can be made massive by inducing
a small two-photon detuning. Control of the two-photon detuning can be used to
locally vary the mass including a sign flip. This allows e.g. the
implementation of the random-mass Dirac model for which localized zero-energy
(mid-gap) states exist with unsual long-range correlations.Comment: 5 pages, 4 figure
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