L. V. Il’ichev

Polarization effects in recoil-induced resonances

A model of the formation of recoil-induced resonances accompanying the interaction of an ensemble of slow atoms with a pair of plane light waves with different polarizations is constructed in the framework of the semiclassical approach to the description of the angular momentum of atoms. The approach used reduces the problem to the description of the resonances in the effective model of atoms with nondegenerate levels. The resonance amplitudes exhibit a strong dependence on the type of model used (with or without the inclusion of the degeneration of levels) and on the polarization of light waves. At the same time, the shape of the resonances that is normalized to unit amplitude from which the velocity distribution of atoms can be reconstructed is much less sensitive to the model type.

Photoemission statistics in resonance fluorescence of an atom with degenerate levels

The problem of the statistics of photoemission events in a specified direction and with a given polarization is solved for a resonantly fluorescing atom with degenerate levels. The degeneracy of the levels is taken into account within the semiclassical approach to the description of the atomic angular momentum. Relationships for the probability distribution of photoemission events in a specified solid angle and with a given helicity are derived for all components of the resonance fluorescence triplet. The results obtained make it possible to elucidate the influence of the polarization of a pump field on the statistics and correlations of photoemission events of different types.

Statistics of resonance fluorescence of a pair of atoms in a feedback loop

The statistics of photoemission events of a pair of closely spaced two-level atoms is calculated in a classical light field whose phase is changed by π after the detection of each spontaneous photon. This statistics is compared with the statistics in the case when the feedback is missing. In both cases, one can observe noticeable antibunching of photons in the range of parameters where no antibunching is observed in a single-atom system. The feedback substantially increases the antibunching. This effect manifests itself more strongly in relatively weak fields and for considerable frequency detunings.

The quantum state of a pair of isotopes coupled by simultaneous spontaneous emission in a magnetic field

The steady state of a pair of isotopes resulting from the incoherent process of excitation-de-excitation and spontaneous decay is found. When the applied magnetic field corresponds to resonance between Zeeman sublevels in the pair, simultaneous spontaneous decay induces interatomic correlations. The resulting state belongs to the class of states with positive partial transpose. One consequence of the correlations is a redistribution of the probabilities for the directions of spontaneous emission at the resonant transition frequency.

Anomalous drift of resonant particles in a buffer medium under pressure of light

We study theoretically the drift of resonant particles in a buffer medium when a traveling light wave impinges on the medium, with allowance for the velocity dependence of the transport collision rate. When the pressure of light dominates over the light-induced drift (low pressure of the buffer gas or the drift of conduction electrons in semiconductors), we discover a new sudden transformation of the spectral dependence of the drift velocity of the resonant particles: Instead of the ordinary bell-shaped function representing the velocity spectrum we have a double-humped curve with deep dip at the center of the absorption line. We show that the largest transformation of the drift velocity spectrum occurs in the atmosphere of a heavy buffer gas in the case of Coulomb interaction between the resonant and buffer particles. The transformation effect is caused by the variation of the transport rate of the collisions of the resonant and buffer particles due to the recoil effect in the absorption of radiation.

Decoherence of an atomic condensate in a double-well trap at optical probing

A model of an atomic condensate in a double-well potential with the possibility of tunneling between wells has been considered. The process of tunneling is modified by the optical probing of one of the wells by a beam of nonresonance radiation. The phase of the passing beam is correlated with the number of atoms in the probed well; as a result, coherence between states with different numbers of atoms is partially destroyed. The solution of the initial quantum kinetic equation for the states of the condensate has been obtained under the assumption of the dominant role of such a decoherence. An expression has been obtained for the correlation function of the amplitude of radiation passing through the probed well. The opposite situation of a slow destruction of coherence as compared to the rate of tunneling has also been considered. The stationary distribution in the numbers of atoms in wells for a given number of atoms in the condensate is uniform in both cases.

Interactions of condensate atoms in the process of velocity-selective coherent population trapping

The properties of a one-dimensional atomic Bose condensate are studied under the assumption that the condensation leads to a state of velocity-selective coherent population trapping. This state is characterized by the quantum correlation (entanglement) between the intrinsic angular momentum of an atom and its translational motion underlying nontrivial features of the condensate. The effects of weak interatomic interaction are taken into account. The steady state of above-condensate atoms corresponding to the slow decay of the state with coherent population trapping is found. The dynamic problem concerning the evolution of the system of above-condensate atoms after switching off the optical field forming the state with coherent population trapping is solved. The solution is found by the diagonalization of the Hamiltonian based on introducing the Bogoliubov quasiparticles with the unusual dispersion law.

Light-induced conversion of nuclear spin modifications of molecules

We report on a new phenomenon of molecular nuclear spin isomers conversion in the field of resonant laser radiation. It is based on the isomer-selective optical excitation and the difference of conversion rates for excited and unexcited molecules. We expect the considerable magnitude of the effect for all molecules which absorb the radiation of existing lasers.We report a new effect in which one nuclear spin modification of molecules is converted into another in a resonance laser radiation field. The effect is based on selective (with respect to modifications) optical excitation and the difference of the conversion rates of spin modifications for excited and unexcited molecules. The effect is expected to be very substantial and should occur for all molecules capable of absorbing the radiation of existing lasers.

Nuclear spin conversion in diatomic molecules

A mechanism of the internal interaction in dimers that mixes different nuclear spin modifications has been proposed. It has been shown that the intramolecular current associated with transitions between electronic terms of different parities can generate different magnetic fields on nuclei, leading to transitions between spin modifications and to the corresponding changes in rotational states. In the framework of the known quantum relaxation process, this interaction initiates irreversible conversion of nuclear spin modifications. The estimated conversion rate for nitrogen at atmospheric pressure is quite high (10−3–10−5 s−1).

Dynamic effect of collision phase lockout in a gas of cold dark atoms

In a gas of slow atoms exhibiting the effect of coherent population trapping (CPT) on the sublevels of the ground state in a spatially nonuniform light field, rare collisions destroying the CPT state initiate the irreversible exchange of momentum between radiation and atoms. This exchange is manifested as an additional force that acts on the particles and is of geometric origin; i.e., it is determined only by the structure of the field of local CPT states. When this force is not masked by the standard collision change in atomic momentum, the observation of the kinetics of the particles may provide information on the physics of the collisions.