919 research outputs found
Controlled light storage in a double lambda system
It is shown theoretically that after light storing in a medium of four-level
atoms it is possible to release a new pulse of a different frequency, the
process being steered by another driving beam. It is also possible to store one
pulse and to release two different ones, with their time separation and heights
being controlled.Comment: 7 pages,3 figure
Formation of solitons in atomic Bose-Einstein condensates by dark-state adiabatic passage
We propose a new method of creating solitons in elongated Bose-Einstein
Condensates (BECs) by sweeping three laser beams through the BEC. If one of the
beams is in the first order (TEM10) Hermite-Gaussian mode, its amplitude has a
transversal phase slip which can be transferred to the atoms creating a
soliton. Using this method it is possible to circumvent the restriction set by
the diffraction limit inherent to conventional methods such as phase
imprinting. The method allows one to create multicomponent (vector) solitons of
the dark-bright form as well as the dark-dark combination. In addition it is
possible to create in a controllable way two or more dark solitons with very
small velocity and close to each other for studying their collisional
properties.Comment: 10 figure
Non-Abelian gauge potentials for ultra-cold atoms with degenerate dark states
We show that the adiabatic motion of ultracold, multilevel atoms in spatially varying laser fields can give rise to effective non-Abelian gauge fields if degenerate adiabatic eigenstates of the atom-laser interaction exist. A pair of such degenerate dark states emerges, e.g., if laser fields couple three internal states of an atom to a fourth common one under pairwise two-photon-resonance conditions. For this so-called tripod scheme we derive general conditions for truly non-Abelian gauge potentials and discuss special examples. In particular we show that using orthogonal laser beams with orbital angular momentum an effective magnetic field can be generated that has a monopole component
Coherent processing of a light pulse stored in a medium of four-level atoms
It is demonstrated that the properties of light stored in a four-level atomic
system can be modified by an additional control interaction present during the
storage stage. By choosing the pulse area of this interaction one can in
particular continuously switch between two channels into which light is
released.Comment: text+4 figure
Light slowdown in the vicinity of cross-over resonances
Pulse propagation is considered in an inhomogeneously broadened medium of
three-level atoms in a V-configuration, dressed by a counter-propagating pump
pulse. A significant signal slowdown is demonstrated in this of the three
frequency windows of a reduced absorption and a steep normal dispersion, which
is due to a cross-over resonance. Particular properties of the group index in
the vicinity of such a resonance are demonstrated in the case of closely spaced
upper levels.Comment: 4 figure
Quantum-field-theoretical techniques for stochastic representation of quantum problems
We describe quantum-field-theoretical (QFT) techniques for mapping quantum
problems onto c-number stochastic problems. This approach yields results which
are identical to phase-space techniques [C.W. Gardiner, {\em Quantum Noise}
(1991)] when the latter result in a Fokker-Planck equation for a corresponding
pseudo-probability distribution. If phase-space techniques do not result in a
Fokker-Planck equation and hence fail to produce a stochastic representation,
the QFT techniques nevertheless yield stochastic difference equations in
discretised time
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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