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Production, detection and trapping of ultracold molecular rubidium

Yiyan Huang

Published Jan 1, 2006• 4 citations
OpenAlex

Abstract

Production and state-selective detection of ultracold molecular rubidium (85Rb2) in the singlet ground state and the metastable triplet state are described. Ultracold 85Rb2 molecules are produced via photoassociation followed by radiative decay. State-selective detection of high-ν ground-state and metastable-state molecules is carried out by resonant Two-photon ionization (R2PI) with a pulsed laser. The spectra of both the ground singlet and metastable triplet states are investigated. Spectroscopy of several intermediate excited states, some of which are observed for the first time, is also studied. Mixing between excited singlet and triplet states is observed in both the singlet and triplet spectra. A proposal for producing ν = 0 ground-state molecules by utilizing this singlet-triplet mixing is given. Magnetic trapping and filtering of metastable triplet-state molecules is also described, and a scheme for optical trapping of molecules is proposed.^

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Photoassociative Production and Detection of Ultracold Polar RbCs Molecules

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We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85 Rb and 133 Cs atoms in a dual-species, forced dark magneto-optical trap. The formed electronically excited RbCs* molecules correlated to the Rb(5S 1/2 ) + Cs(6P 1/2 ) dissociation limit are observed by trap loss spectroscopy. Following the decay of these excited RbCs* molecules, the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser, which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.

Chinese Physics Letters•Aug 1, 2011•8 citations
Production and state-selective detection of ultracold molecular rubidium (85Rb2) in the singlet ground state and the metastable triplet state are described. Ultracold 85Rb2 molecules are produced via photoassociation followed by radiative decay. State-selective detection of high-ν ground-state and metastable-state molecules is carried out by resonant Two-photon ionization (R2PI) with a pulsed laser. The spectra of both the ground singlet and metastable triplet states are investigated. Spectroscopy of several intermediate excited states, some of which are observed for the first time, is also studied. Mixing between excited singlet and triplet states is observed in both the singlet and triplet spectra. A proposal for producing ν = 0 ground-state molecules by utilizing this singlet-triplet mixing is given. Magnetic trapping and filtering of metastable triplet-state molecules is also described, and a scheme for optical trapping of molecules is proposed.^
Using resonance-enhanced two-photon ionization, we detect ultracold, metastable RbCs molecules formed in their lowest triplet state $a\text{ }^{3}\ensuremath{\Sigma}^{+}$ via photoassociation in a laser-cooled mixture of 85Rb^{85}\mathrm{Rb}85Rb and 133Cs^{133}\mathrm{Cs}133Cs atoms. We obtain extensive bound-bound excitation spectra of these molecules, which provide detailed information about their vibrational distribution, as well as spectroscopic data on several RbCs molecular states including $a\text{ }^{3}\ensuremath{\Sigma}^{+}$, $(2)\text{ }^{3}\ensuremath{\Sigma}^{+}$, and $(1)\text{ }^{1}\ensuremath{\Pi}$. Analysis of this data allows us to predict strong transitions from observed levels to the absolute vibronic ground state of RbCs, potentially allowing the production of stable, ultracold polar molecules at rates in excess of ${10}^{6}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$.
We have produced ultracold heteronuclear KRb molecules by the process of photoassociation in a two-species magneto-optical trap. Following decay of the photoassociated KRb*, the molecules are detected using two-photon ionization and time-of-flight mass spectroscopy of KRb+{\mathrm{K}\mathrm{R}\mathrm{b}}^{+}KRb+. A portion of the metastable triplet molecules thus formed are magnetically trapped. Photoassociative spectra down to $91\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}1}$ below the K(4s)+Rb(5p1/2)\mathrm{K}(4s)+\mathrm{R}\mathrm{b}(5{p}_{1/2})K(4s)+Rb(5p1/2​) asymptote have been obtained. We have made assignments to all eight of the attractive Hund's case (c) KRb* potential curves in this spectral region.
We form ultracold ground-state Rb 2 molecules by photoassociating pairs of atoms in a magneto-optical trap into the 0 u + state, which decays radiatively into high vibrational levels of the X 1 Σ g + state. Sensitive and vibrationally state-selective detection is achieved by means of resonantly-enhanced two-photon ionization with a pulsed laser. Frequency scans of the detection laser reveal a long vibrational progression to a previously unobserved electronic excited state, which we identify as the 2 1 Σ u + state. Most of its vibrational spectrum is in excellent agreement with predictions based on ab initio potentials, although the lowest vibrational levels exhibit strong perturbative mixing with the triplet 2 3 Π u state. The detection method reported here, with minor variations, should be effective for the entire potential well of the X state. In this work no transitions are observed from vibrational levels above v = 118, but this turns out to be a limitation not of the detection method but rather of the photoassociative formation scheme, due to re-excitation of the highest- v levels by the same photoassociation laser that produces them.
Ultracold polar RbCs molecules are produced via photoassociation in a dual dark-SPOT magneto-optical trap, in which ultracold rubidium and cesium atoms with high densities are formed by laser cooling and trapping. The a3∑+ triplet metastable state ultracold RbCs molecules with 104/s production rate are detected using resonance-enhanced two-photon ionization. The ultra-high resolution rovibrational spectra of (2)0+, (3)0- and (2)0- rovibrational states are observed by scanning the photoassociation laser frequency. The rotational constants of (2)0+, (3)0- and (2)0- vibrational states are 0.00349 cm-1, 0.00649 cm-1 and 0.00372 cm-1 by fitting respectively.
In the first part of this dissertation we develop and successfully demonstrate two methods, based on photoassociation of ultracold potassium atoms, for producing ultracold K2 molecules, with sub mK temperatures, in deeply bound vibrational levels of the ground XS+g 1 state. The principal objective has been to develop an “ultracold molecule factory” that can be used to support experiments on spectroscopy, collisions, and chemistry of ultracold molecules. ^ In the first experiment the ground-state molecules are produced by the radiative decay of excited, n≅191 AS+u 1 state molecules, photoassociated from ultracold potassium atoms in a vapor-cell MOT. The decay is primarily into the vibrational continuum, but a small fraction decays into bound levels of the X state near n = 36. The experimentally observed molecule production rate is about 103 per second. ^ In our second experiment, we use two-step laser excitation to effect an “R-transfer” from long-range to intermediate internuclear separations, greatly increasing the efficiency for radiative production of low- n molecules in the X state. Molecules are formed in the Pg1 state by photoassociation, then excited by a second laser to the 51Pu or 61Pu Rydberg states, in selected vibrational levels from n = 13–18. Finally, radiative decay produces very large numbers of X state molecules with n≅25 and significant numbers of molecules in very low vibrational levels, including n = 0. We have observed production rates up to about 105 molecules/second per vibrational level. ^ In both experiments the ground-state molecules are detected with a sensitive and selective resonant two-color photoionization with nanosecond pulses. ^ In the second part of this dissertation we demonstrate a novel method for high sensitivity absorption measurements, that combines a phase modulated, high-resolution pulsed laser with an actively stabilized optical cavity to achieve a sensitivity of ∼10−9 per cm. This is comparable to the best existing methods for pulsed absorption measurements, but unlike most other methods, it can also be readily extended to the UV region and to Doppler-free spectroscopy. ^
We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85 Rb and 133 Cs atoms in a dual-species, forced dark magneto-optical trap. The formed electronically excited RbCs* molecules correlated to the Rb(5S 1/2 ) + Cs(6P 1/2 ) dissociation limit are observed by trap loss spectroscopy. Following the decay of these excited RbCs* molecules, the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser, which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.