Gediminas Juzeliunas

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 gas of neutral atomic fermions.

Generalized Rashba-Dresselhaus spin-orbit coupling for cold atoms

We study the possibility for generating a new type of spin-orbit coupling for the center-of-mass motion of cold atoms, using laser beams that resonantly couple N atomic internal ground states to an extra state. After a general analysis of the scheme, we concentrate on the tetrapod setup (N = 4) where the atomic state can be described by a three-component spinor, evolving under the action of a Rashba-Dresselhaus-type spin-orbit coupling for a spin 1 particle. We illustrate a consequence of this coupling by studying the negative refraction of atoms at a potential step and show that the amplitude of the refracted beam is significantly increased in comparison to the known case of spin 1/2 Rashba-Dresselhaus coupling. Finally, we explore a possible implementation of this tetrapod setup, using stimulated Raman couplings between Zeeman sublevels of the ground state of alkali-metal atoms.

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.

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 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.

A QED theory of intermolecular energy transfer in dielectric media

Abstract A microscopic QED theory is presented featuring dipole-dipole energy transfer between molecules at arbitrary distances in a dielectric medium. The medium is shown to produce modifications of the transfer rates due to screening contributions, (1/ɛ) 2 , local field effects, [(ɛ + 2)/3] 4 , and energy losses in the medium, exp(- 2 Imɛ 1/2 KR ), ℏcK being the transfer energy.

Storing and releasing light in a gas of moving atoms

We propose a scheme of storing and releasing pulses or cw beams of light in a moving atomic medium illuminated by two stationary and spatially separated control lasers. The method is based on electromagnetically induced transparency but in contrast to previous schemes, storage and retrieval of the probe pulse can be achieved at different locations and without switching off the control laser.

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 responsei?½but 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 insights into the formulation of quantum field interactions.

Effective magnetic fields induced by EIT in ultra-cold atomic gases

We study the influence of two resonant laser beams (to be referred to as the control and probe beams) on the centre-of-mass motion of ultra-cold atoms characterized by three energy levels of the Λ-type. The laser beams being in the electromagnetically induced transparency (EIT) configuration drive the atoms to their dark states. We impose the adiabatic approximation and obtain an effective equation of motion for the dark state atoms. The equation contains a vector potential type interaction as well as an effective trapping potential. We concentrate on the situation where the control and probe beams are co-propagating and have orbital angular momenta (OAM). The effective magnetic field is then oriented along the propagation direction of the control and probe beams. Its spatial profile can be shaped by choosing proper laser beams. We analyse several situations where the effective magnetic field exhibits a radial dependence. In particular, we study effective magnetic fields induced by Bessel beams, and demonstrate how to generate a constant effective magnetic field for a ring geometry of the atomic trap. We also discuss a possibility of creating an effective field of a magnetic monopole.

Formation of optical flux lattices for ultra cold atoms

We explore the optical flux lattices produced for ultra-cold atoms in the radiation field when both the atom-light coupling and the detuning exhibit an oscillatory behavior. We analyze not only the magnetic flux but also the geometric vector potential generating the flux, as well as the accompanying geometric scalar potential. We show how to deal with the gauge-dependent singularities of the Aharonov-Bohm (AB) type appearing in the vector potentials for the optical flux lattices. We present a way to calculate the continuous magnetic flux through the elementary cell via the singularities of the vector potential inside the cell. The analysis is illustrated with a square optical flux lattice. We present a way of creating such a lattice using the Raman transitions induced by a set of properly chosen polarization-dependent standing waves propagating at a right angle and containing a time-phase difference.