arXiv subjects

Françoise Masnou-Seeuws

Publications and source records attributed to Françoise Masnou-Seeuws.

5 recordsLinked to original sources

arXiv2007

The dynamical hole in ultrafast photoassociation: analysis of the compression effect

Photoassociation of a pair of cooled atoms by excitation with a short chirped laser pulse creates a dynamical hole in the initial continuum wavefunction. This hole is manifested by a void in the pair wavefunction and a momentum kick. Photoassociation into loosely bound levels of the external well in Cs_2 0$_g^-$(6S + 6P$_{3/2}$ is considered as a case study. After the pulse, the free evolution of the ground triplet state wavepacket is analyzed. Due to a negative momentum kick, motion to small distances is manifested and a compression effect is pointed out, markedly increasing the density of atom pairs at short distance. A consequence of the hole is the redistribution of the vibrational population in the ground triplet state, with population of the last bound level and creation of pairs of hot atoms. The physical interpretation makes use of the time dependence of the probability current and population on each channel to understand the role of the parameters of the photoassociation pulse. By varying such parameters, optimization of the compression effect in the ground state wavepacket is demonstrated. Due to an increase of the short range density probability by more than two orders of magnitude, we predict important photoassociation rates into deeply bound levels of the excited state by a second pulse, red-detuned relative to the first one and conveniently delayed.

quant-ph↗

arXiv2007

Dynamical interferences to probe short-pulse photoassociation of Rb atoms and stabilization of Rb_2 dimers

We analyze the formation of Rb_2 molecules with short photoassociation pulses applied to a cold Rb-85 sample. A pump laser pulse couples a continuum level of the ground electronic state X ^1Σ_{g}^+ with bound levels in the 0_{u}^+ (5S+5P_{1/2}) and 0_{u}^+ (5S+5P_{3/2}) vibrational series. The nonadiabatic coupling between the two excited channels induces time-dependent beatings in the populations. We propose to take advantage of these oscillations to design further laser pulses that probe the photoassociation process via photoionization or that optimize the stabilization in deep levels of the ground state.

physics.atom-ph↗

arXiv2006

Short-pulse photoassociation in rubidium below the D$_1$ line

Photoassociation of two ultracold rubidium atoms and the subsequent formation of stable molecules in the singlet ground and lowest triplet states is investigated theoretically. The method employs laser pulses inducing transitions via excited states correlated to the $5S+5P_{1/2}$ asymptote. Weakly bound molecules in the singlet ground or lowest triplet state can be created by a single pulse while the formation of more deeply bound molecules requires a two-color pump-dump scenario. More deeply bound molecules in the singlet ground or lowest triplet state can be produced only if efficient mechanisms for both pump and dump steps exist. While long-range $1/R^3$-potentials allow for efficient photoassociation, stabilization is facilitated by the resonant spin-orbit coupling of the $0_u^+$ states. Molecules in the singlet ground state bound by a few wavenumbers can thus be formed. This provides a promising first step toward ground state molecules which are ultracold in both translational and vibrational degrees of freedom.

physics.atom-ph↗

arXiv2005

Making ultracold molecules in a two color pump-dump photoassociation scheme using chirped pulses

This theoretical paper investigates the formation of ground state molecules from ultracold cesium atoms in a two-color scheme. Following previous work on photoassociation with chirped picosecond pulses [Luc-Koenig et al., Phys. Rev. A {\bf 70}, 033414 (2004)], we investigate stabilization by a second (dump) pulse. By appropriately choosing the dump pulse parameters and time delay with respect to the photoassociation pulse, we show that a large number of deeply bound molecules are created in the ground triplet state. We discuss (i) broad-bandwidth dump pulses which maximize the probability to form molecules while creating a broad vibrational distribution as well as (ii) narrow-bandwidth pulses populating a single vibrational ground state level, bound by 113 cm$^{-1}$. The use of chirped pulses makes the two-color scheme robust, simple and efficient.

physics.atom-ph↗

arXiv2004

Stabilization of Ultracold Molecules Using Optimal Control Theory

In recent experiments on ultracold matter, molecules have been produced from ultracold atoms by photoassociation, Feshbach resonances, and three-body recombination. The created molecules are translationally cold, but vibrationally highly excited. This will eventually lead them to be lost from the trap due to collisions. We propose shaped laser pulses to transfer these highly excited molecules to their ground vibrational level. Optimal control theory is employed to find the light field that will carry out this task with minimum intensity. We present results for the sodium dimer. The final target can be reached to within 99% if the initial guess field is physically motivated. We find that the optimal fields contain the transition frequencies required by a good Franck-Condon pumping scheme. The analysis is able to identify the ranges of intensity and pulse duration which are able to achieve this task before other competing process take place. Such a scheme could produce stable ultracold molecular samples or even stable molecular Bose-Einstein condensates.

quant-ph↗