72 research outputs found
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
Light-induced effective magnetic fields for ultracold atoms in planar geometries
We propose a scheme to create an effective magnetic field for ultracold atoms in a planar geometry. The setup allows the experimental study of classical and quantum Hall effects in close analogy to solid-state systems including the possibility of finite currents. The present scheme is an extention of the proposal in Phys. Rev. Lett. 93, 033602 (2004), where the effective magnetic field is now induced for three-level Lambda-type atoms by two counterpropagating laser beams with shifted spatial profiles. Under conditions of electromagnetically induced transparency the atom-light interaction has a space-dependent dark state, and the adiabatic center-of-mass motion of atoms in this state experiences effective vector and scalar potentials. The associated magnetic field is oriented perpendicular to the propagation direction of the laser beams. The field strength achievable is one flux quantum over an area given by the transverse beam separation and the laser wavelength. For a sufficiently dilute gas the field is strong enough to reach the lowest Landau level regime
Stability of linear and non-linear lambda and tripod systems in the presence of amplitude damping
We present the stability analysis of the dark states in the adiabatic passage
for the linear and non-linear lambda and tripod systems in the presence of
amplitude damping (losses). We perform an analytic evaluation of the real parts
of eigenvalues of the corresponding Jacobians, the non-zero eigenvalues of
which are found from the quadratic characteristic equations, as well as by the
corresponding numerical simulations. For non-linear systems, we evaluate the
Jacobians at the dark states. Similarly to the linear systems, here we also
find the non-zero eigenvalues from the characteristic quadratic equations. We
reveal a common property of all the considered systems showing that the
evolution of the real parts of eigenvalues can be split into three stages. In
each of them the evolution of the stimulated Raman adiabatic passage (STIRAP)
is characterized by different effective dimension. This results in a possible
adiabatic reduction of one or two degrees of freedom.Comment: 30 pages, 12 figure
Polarisation rotation of slow light with orbital angular momentum in ultracold atomic gases
We consider the propagation of slow light with an orbital angular momentum
(OAM) in a moving atomic medium. We have derived a general equation of motion
and applied it in analysing propagation of slow light with an OAM in a rotating
medium, such as a vortex lattice. We have shown that the OAM of slow light
manifests itself in a rotation of the polarisation plane of linearly polarised
light. To extract a pure rotational phase shift, we suggest to measure a
difference in the angle of the polarisation plane rotation by two consecutive
light beams with opposite OAM. The differential angle is
proportional to the rotation frequency of the medium
and the winding number of light, and is inversely proportional to the
group velocity of light. For slow light the angle should
be large enough to be detectable. The effect can be used as a tool for
measuring the rotation frequency of the medium.Comment: 5 pages, 1 figur
Eliminating ground-state dipole moments in quantum optics via canonical transformation
By means of a canonical transformation it is shown how it is possible to
recast the equations for molecular nonlinear optics to completely eliminate
ground-state static dipole coupling terms. Such dipoles can certainly play a
highly important role in nonlinear optical response - but equations derived by
standard methods, in which these dipoles emerge only as special cases of
transition moments, prove unnecessarily complex. It has been shown that the
elimination of ground-state static dipoles in favor of dipole shifts results in
a considerable simplification in form of the nonlinear optical
susceptibilities. In a fully quantum theoretical treatment the validity of such
a procedure has previously been verified using an expedient algorithm, whose
defense was afforded only by a highly intricate proof. In this paper it is
shown how a canonical transformation method entirely circumvents such an
approach; it also affords new insights into the formulation of quantum field
interactions.Comment: 18 pages including 1 figur
Effective magnetic fields in degenerate atomic gases induced by light beams with orbital angular momenta
We investigate the influence of two resonant laser beams on the mechanical
properties of degenerate atomic gases. The control and probe beams of light are
considered to have Orbital Angular Momenta (OAM) and act on the three-level
atoms in the Electromagnetically Induced Transparency (EIT) configuration. The
theory is based on the explicit analysis of the quantum dynamics of cold atoms
coupled with two laser beams. Using the adiabatic approximation, we obtain an
effective equation of motion for the atoms driven to the dark state. The
equation contains a vector potential type interaction as well as an effective
trapping potential. The effective magnetic field is shown to be oriented along
the propagation direction of the control and probe beams containing OAM. Its
spatial profile can be controlled by choosing proper laser beams. We
demonstrate how to generate a constant effective magnetic field, as well as a
field exhibiting a radial distance dependence. The resulting effective magnetic
field can be concentrated within a region where the effective trapping
potential holds the atoms. The estimated magnetic length can be considerably
smaller than the size of the atomic cloud.Comment: 11 pages, 5 figures Corrected some mistakes in equation
Slow light in degenerate Fermi gases
We investigate the effect of slow light propagating in a degenerate atomic
Fermi gas. In particular we use slow light with an orbital angular momentum. We
present a microscopic theory for the interplay between light and matter and
show how the slow light can provide an effective magnetic field acting on the
electrically neutral fermions, a direct analogy of the free electron gas in an
uniform magnetic field. As an example we illustrate how the corresponding de
Haas-van Alphen effect can be seen in a neutral gas of fermions.Comment: Slightly updated. Phys. Rev. Lett. 93, 033602 (2004
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