140 research outputs found
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 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
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 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 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
Proposal for laser-cooling of rare-earth ions
The efficiency of laser-cooling relies on the existence of an almost closed
optical-transition cycle in the energy spectrum of the considered species. In
this respect rare-earth elements exhibit many transitions which are likely to
induce noticeable leaks from the cooling cycle. In this work, to determine
whether laser-cooling of singly-ionized erbium Er is feasible, we have
performed accurate electronic-structure calculations of energies and
spontaneous-emission Einstein coefficients of Er, using a combination of
\textit{ab initio} and least-square-fitting techniques. We identify five weak
closed transitions suitable for laser-cooling, the broadest of which is in the
kilohertz range. For the strongest transitions, by simulating the cascade
dynamics of spontaneous emission, we show that repumping is necessary, and we
discuss possible repumping schemes. We expect our detailed study on Er to
give a good insight into laser-cooling of neighboring ions like Dy.Comment: 5 pages, 2 figure
Ultracold atom-dimer long-range interactions beyond the expansion
We investigate theoretically the combination of first-order
quadrupole-quadrupole and second-order dipole-dipole effects on the long-range
electrostatic interactions between a ground-state homonuclear alkali-metal
dimer and an excited alkali-metal atom. As the electrostatic energy is
comparable to the dimer rotational structure, we develop a general description
of the long-range interactions which allows for couplings between the dimer
rotational levels. The resulting adiabatic potential energy curves, which
exhibit avoided crossings, cannot be expanded on the usual series. We
study in details the breakdown of this approximation in the particular case
CsCs. Our results are found promising in the prospect of accomplishing
the photoassociation of ultracold trimers.Comment: Submitted to EPJD, special issue "Cold Quantum Matter - Achievements
and Prospects
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 and
an oxygen molecule O, both in their electronic ground state.
We have calculated the interaction energy induced by the permanent electric
quadrupoles of O and O and the van der Waals energy. On one hand we
determined the 27 electronic potential energy surfaces including spin-orbit
connected to the O + O dissociation limit of the
O--O complex. On the other hand we computed the potential energy curves
characterizing the interaction between O and a O
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 thus complementing the knowledge
relevant for the ozone formation mechanism.Comment: Submitted to J. Chem. Phys. after revisio
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