Zav Shotan

Nuclear-spin-independent short-range three-body physics in ultracold atoms.

We investigate three-body recombination loss across a Feshbach resonance in a gas of ultracold 7Li atoms prepared in the absolute ground state and perform a comparison with previously reported results of a different nuclear-spin state [N. Gross, Phys. Rev. Lett. 103, 163202 (2009)]. We extend the previously reported universality in three-body recombination loss across a Feshbach resonance to the absolute ground state. We show that the positions and widths of recombination minima and Efimov resonances are identical for both states which indicates that the short-range physics is nuclear-spin independent.

Association of Efimov trimers from a three-atom continuum.

We develop an experimental technique for rf association of Efimov trimers from a three-atom continuum. We apply it to probe the lowest accessible Efimov energy level in bosonic lithium in the region where strong deviations from the universal behavior are expected, and provide a quantitative study of this effect. The position of the Efimov resonance at the atom-dimer threshold, measured using a different experimental technique, concurs with the rf association results.

Study of Efimov physics in two nuclear-spin sublevels of 7Li

Abstract Efimov physics in two nuclear-spin sublevels of bosonic lithium is studied and it is shown that the positions and widths of recombination minima and Efimov resonances are identical for both states within the experimental errors, which indicate that the short-range physics is nuclear-spin independent. We also find that the Efimov features are universally related across Feshbach resonances. These results crucially depend on careful mapping between the scattering length and the applied magnetic field which we achieve by characterization of the two broad Feshbach resonances in the different states by means of rf-spectroscopy of weakly bound molecules. By fitting the binding energies numerically with a coupled channels calculation we precisely determine the absolute positions of the Feshbach resonances and the values of the singlet and triplet scattering lengths.

Three-body recombination at vanishing scattering lengths in an ultracold bose gas.

We report on measurements of three-body recombination loss rates in an ultracold gas of ^{7}Li atoms in the extremely nonuniversal regime where the two-body scattering length vanishes. We show that the loss rate coefficient is well defined and can be described by two-body parameters only: the scattering length a and the effective range R_{e}. We find the rate to be energy independent, and, by connecting our results with previously reported measurements in the universal limit, we cover the behavior of the three-body recombination rate in the whole range from weak to strong two-body interactions. We identify a nontrivial magnetic field value in the nonuniversal regime where the rate should be suppressed.

Semiconductor laser subject to intense feedback with variably rotated polarization

A semiconductor laser subject to delayed optical feedback is investigated in the limit of intense feedback power. Back-injection of light with variably rotated polarization reveals a symmetry breaking in laser emission spectra and output power when the rotation angle is changed in the vicinity of the orthogonal orientation. To explain the observed asymmetry we propose a simple geometric model which includes the relative contributions of both TE and TM lasing modes into the feedback light. In a range of feedback polarization rotation angles the emission spectra of the laser reveal a gap with width of more than a terahertz. The position of the gap and its width are shown to be regulated by means of feedback polarization rotation angle. We demonstrate that a theoretical approach, based on carrier density grating induced potential, explains our experimental results.

Inelastic collisions near Feshbach resonances in ultra-cold 7Li

Recently we reported on a successful achievement of 7Li Bose-Einstein condensate (BEC) by all-optical means [1]. Forced evaporation was performed in a crossed-beam optical trap and BEC was observed on a spontaneously purified |F=1,mF=0≫ spin state. Feshabch resonances were used to tune elastic collision rate. However, inelastic processes such as dipole relaxation and three-body recombination show dramatic enhancement in the vicinity of Feshabch resonances and may limit atom densities and trap lifetime [2]. Indeed, working in between the resonances (866G) we obtained only a few hundreds of atoms in the BEC and its lifetime was extremely short [1].