Dimers, Inelastic Collisions, and Interactions with Ultrashort Laser Pulses Juris Ulmanis,† Johannes Deiglmayr,‡ Marc Repp,† Roland Wester, and Matthias Weidemüller*,† †Physikalisches Institut, Ruprecht-Karls-Universitaẗ Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany ‡Laboratorium für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland Institut für Ionenphysik und Angewandte Physik, Universitaẗ Innsbruck, Technikerstrasse 25/3, 6020 Innsbruck, Austria

Ultracold Molecules Formed by Photoassociation: Heteronuclear Dimers, Inelastic Collisions, and Interactions with Ultrashort Laser Pulses

We demonstrate the direct formation of vibronic ground state RbCs molecules by photoassociation of ultracold atoms followed by radiative stabilization. The photoassociation proceeds through deeply bound levels of the (2)3?0+ state. From analysis of the relevant free-to-bound and bound-to-bound Franck?Condon factors, we have predicted and experimentally verified a set of photoassociation resonances that lead to efficient creation of molecules in the v?=?0 vibrational level of the X1?+ electronic ground state. We also compare the observed and calculated laser intensity required to saturate the photoassociation rate. We discuss the prospects for using short-range photoassociation to create and accumulate samples of ultracold polar molecules in their rovibronic ground state.

https://iopscience.iop.org/article/10.1088/1367-2630/16/2/023018/pdf

Continuous formation of vibronic ground state RbCs molecules via photoassociation

We demonstrate the direct formation of vibronic ground state RbCs molecules by photoassociation of ultracold atoms followed by radiative stabilization. The photoassociation proceeds through deeply-bound levels of the (2)^{3}\Pi_{0^{+}} state. From analysis of the relevant free-to-bound and bound-to-bound Franck-Condon factors, we have predicted and experimentally verified a set of photoassociation resonances that lead to efficient creation of molecules in the v=0 vibrational level of the X^{1}\Sigma^{+} electronic ground state. We also compare the observed and calculated laser intensity required to saturate the photoassociation rate. We discuss the prospects for using short-range photoassociation to create and accumulate samples of ultracold polar molecules in their rovibronic ground state.

Continuous Formation of Vibronic Ground State RbCs Molecules via Photoassociation

We report continuous direct photoassociative formation of ultracold KRb molecules in the lowest vibrational levels $({v}^{\ensuremath{'}\ensuremath{'}}=0\ensuremath{-}10)$ of the electronic ground state $(X{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Sigma}}^{+})$, starting from ${}^{39}$K and ${}^{85}$Rb atoms in a magneto-optical trap. The process exploits a new-found resonant coupling between the $2(1),\phantom{\rule{0.16em}{0ex}}{v}^{\ensuremath{'}}=165$ and $4(1),\phantom{\rule{0.16em}{0ex}}{v}^{\ensuremath{'}}=61$ levels, which exhibit an almost equal admixture of the uncoupled eigenstates. The production rate of the ${X}^{1}{\ensuremath{\Sigma}}^{+}$ $({v}^{\ensuremath{'}\ensuremath{'}}=0)$ level is estimated to be $5\ifmmode\times\else\texttimes\fi{}{10}^{3}$ molecules/s.

Direct photoassociative formation of ultracold KRb molecules in the lowest vibrational levels of the electronic ground state

A comprehensive study of the $X {}^{1}\ensuremath{\Sigma}{}^{+}$ and $a {}^{3}\ensuremath{\Sigma}{}^{+}$ electronic states of the Rb and Cs atom pair in RbCs is presented. Abundant spectroscopic data for the $^{85}\mathrm{Rb}$$^{133}\mathrm{Cs}$ and $^{87}\mathrm{Rb}$$^{133}\mathrm{Cs}$ isotopologues were obtained from Fourier-transform spectra of laser-induced fluorescence (LIF) from the $B {}^{1}\ensuremath{\Pi}$ and $(4){}^{1}\ensuremath{\Sigma}{}^{+}$ states to the $a {}^{3}\ensuremath{\Sigma}{}^{+}$ (4549 transitions) and $X {}^{1}\ensuremath{\Sigma}{}^{+}$ (15 709 transitions) states. The $X {}^{1}\ensuremath{\Sigma}{}^{+}$ state data were complemented by about 15 500 transitions obtained by Fellows et al. [J. Mol. Spectrosc. 197, 19 (1999)]. LIF progressions to the $a {}^{3}\ensuremath{\Sigma}{}^{+}$ state range from ${v}_{a}=0$ to 37, reaching an outer turning point at 15.97 \AA{}. For the $X {}^{1}\ensuremath{\Sigma}{}^{+}$ state, by analyzing LIF from the shelflike $(4){}^{1}\ensuremath{\Sigma}{}^{+}$, the data are extended from ${v}_{x}=119$ as observed in the above-cited paper to ${v}_{x}=129$, extending the outer turning point from 10.7 to 17.55 \AA{}. From these data, potential energy curves were constructed simultaneously for both hyperfine coupled states $X {}^{1}\ensuremath{\Sigma}{}^{+}$ and $a {}^{3}\ensuremath{\Sigma}{}^{+}$ in a coupled-channels fitting routine. This allowed us to accurately model the potential close to the Rb(5$s$) $+$ Cs(6$s$) atom-pair asymptote, which is required to simulate cold collision processes and to analyze the Feshbach resonances observed for $^{87}\mathrm{Rb}$$^{133}\mathrm{Cs}$ by Pilch et al. [Phys. Rev. A 79, 042718 (2009)]. Dissociation energies were determined for the $X {}^{1}\ensuremath{\Sigma}{}^{+}$ state as ${D}_{e}=3836.373(40)$ cm${}^{\ensuremath{-}1}$ and for the $a {}^{3}\ensuremath{\Sigma}{}^{+}$ state as ${D}_{e}=259.341(30)$ cm${}^{\ensuremath{-}1}$.

Singlet and triplet potentials of the ground-state atom pair Rb + Cs studied by Fourier-transform spectroscopy

Promising pathways for photoassociative formation of ultracold heteronuclear alkali metal dimers in their lowest rovibronic levels (denoted X(0,0)) are examined using high quality ab initio calculations of potential energy curves currently available. A promising pathway for KRb, involving the resonant coupling of the $2 ^1\Pi$ and $1 ^1\Pi $ states just below the lowest excited asymptote (K($4s$)+Rb($5p_{1/2}$)), is found to occur also for RbCs and less promisingly for KCs as well. The resonant coupling of the $3 ^1 \Sigma ^+ $ and $1 ^1\Pi $ states, also just below the lowest excited asymptote, is found to be promising for LiNa, LiK, LiRb, and less promising for LiCs and KCs. Direct photoassociation to the $1 ^1\Pi $ state near dissociation appears promising in the final dimers, NaK, NaRb, and NaCs, although detuning more than 100 cm$^{-1}$ below the lowest excited asymptote may be required.

J. RayMajumder

Papers

Resonant Coupling in the Heteronuclear Alkali Dimers for Direct Photoassociative Formation of X(0,0) Ultracold Molecules