Dynamics of ultracold dipolar particles in a confined geometry and tilted fields

We develop a collisional formalism adapted for the dynamics of ultracold dipolar particles in a confined geometry and in fields tilted relative to the confinement axis. Using tesseral harmonics instead of the usual spherical harmonics to expand the scattering wavefunction, we recover a good quantum number $\xi = \pm 1$ which is conserved during the collision. We derive the general expression of the dipole-dipole interaction in this convenient basis set as a function of the polar and azimuthal angles of the fields. We apply the formalism to the collision of fermionic and bosonic polar KRb molecules in a tilted electric field and in a one-dimensional optical lattice. The presence of a tilted field drastically changes the magnitude of the reactive and inelastic rates as well as the inelastic threshold properties at vanishing collision energies. Setting an appropriate strength of the confinement for the fermionic system, we show that the ultracold particles can even further reduce their kinetic energy by inelastic excitation to higher states of the confinement trap.Comment: 13 page

Collective modes of trapped Fermi gases with in-medium interaction

Due to Pauli blocking of intermediate states, the scattering matrix (or $T$ matrix) of two fermionic atoms in a Fermi gas becomes different from that of two atoms in free space. This effect becomes particularly important near a Feshbach resonance, where the interaction in free space is very strong but becomes effectively suppressed in the medium. We calculate the in-medium $T$ matrix in ladder approximation and study its effects on the properties of collective modes of a trapped gas in the normal-fluid phase. We introduce the in-medium interaction on both sides of the Boltzmann equation, namely in the calculation of the mean field and in the calculation of the collision rate. This allows us to explain the observed upward shift of the frequency of the quadrupole mode in the collisionless regime. By including the mean field, we also improve considerably the agreement with the measured temperature dependence of frequency and damping rate of the scissors mode, whereas the use of the in-medium cross section deteriorates the description, in agreement with previous work.Comment: 17 page

Role of fourth-order phase-space moments in collective modes of trapped Fermi gases

We study the transition from hydrodynamic to collisionless behavior in collective modes of ultracold trapped Fermi gases. To that end, we solve the Boltzmann equation for the trapped Fermi gas via the moments method. We showed previously that it is necessary to go beyond second-order moments if one wants to reproduce the results of a numerical solution of the Boltzmann equation. Here, we will give the detailed description of the method including fourth-order moments. We apply this method to the case of realistic parameters, and compare the results for the radial quadrupole and scissors modes at unitarity to experimental data obtained by the Innsbruck group. It turns out that the inclusion of fourth-order moments clearly improves the agreement with the experimental data. In particular, the fourth-order moments reduce the effect of collisions and therefore partially compensate the effect of the enhanced in-medium cross section at low temperatures.Comment: 10 pages, 2 figures; published versio

Long-range interactions in the ozone molecule: spectroscopic and dynamical points of view

Using the multipolar expansion of the electrostatic energy, we have characterized the asymptotic interactions between an oxygen atom O$(^3P)$ and an oxygen molecule O$_2(^3\Sigma_g^-)$, both in their electronic ground state. We have calculated the interaction energy induced by the permanent electric quadrupoles of O and O$_2$ and the van der Waals energy. On one hand we determined the 27 electronic potential energy surfaces including spin-orbit connected to the O$(^3P)$ + O$_2(^3\Sigma_g^-)$ dissociation limit of the O--O$_2$ complex. On the other hand we computed the potential energy curves characterizing the interaction between O$(^3P)$ and a O$_2(^3\Sigma_g^-)$ molecule in its lowest vibrational level and in a low rotational level. Such curves are found adiabatic to a good approximation, namely they are only weakly coupled to each other. These results represent a first step for modeling the spectroscopy of ozone bound levels close to the dissociation limit, as well as the low energy collisions between O and O$_2$ thus complementing the knowledge relevant for the ozone formation mechanism.Comment: Submitted to J. Chem. Phys. after revisio

Suppression of decoherence effects in the quantum kicked rotor

We describe a method allowing transient suppression of decoherence effects on the atom-optics realization of the kicked rotor. The system is prepared in an initial state with a momentum distribution concentrated in an interval much sharper than the Brillouin zone; the measure of the momentum distribution is restricted to this interval of quasimomenta: As most of the atoms undergoing decoherence processes fall outside this detection range and thus are not detected, the measured signal is effectively decoherence-free.Comment: 5 pages, 4 figures, revtex 4, submitted to PR

Kicked-rotor quantum resonances in position space: Application to situations of experimental interest

In this work we apply the formalism developed in [M. Lepers \emph{et al}., Phys. Rev. A \textbf{77}, 043628 (2008)] to different initial conditions corresponding to systems usually met in real-life experiments, and calculate the observable quantities that can be used to characterize the dynamics of the system. The position space point of view allows highly intuitive pictures of the physics at play.Comment: accepted in Eur. Phys. J.

Theory of long-range ultracold atom-molecule photoassociation

The creation of ultracold molecules is currently limited to diatomic species. In this letter we present a theoretical description of the photoassociation of ultracold atoms and molecules to create ultracold excited triatomic molecules, thus being a novel example of light-assisted ultracold chemical reaction. The calculation of the photoassociation rate of ultracold Cs atoms with ultracold Cs$_2$ molecules in their rovibrational ground state is reported, based on the solution of the quantum dynamics involving the atom-molecule long-range interactions, and assuming a model potential for the short-range physics. The rate for the formation of excited Cs$_3$ molecules is predicted to be comparable with currently observed atom-atom photoassociation rates. We formulate an experimental proposal to observe this process relying on the available techniques of optical lattices and standard photoassociation spectroscopy.Comment: 5 pages, 3 figure