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arXiv:2205.09457 · New Journal of Physics

Preparation of 87Rb and 133Cs in the motional ground state of a single optical tweezer

Stefan Spence, R V Brooks, Daniel K. Ruttley, Alexander Guttridge, Simon L. Cornish

Published Sep 28, 2022• 17 citations
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Abstract

Abstract We report simultaneous Raman sideband cooling of a single 87Rb atom and a single 133Cs atom held in separate optical tweezers at 814 nm and 938 nm, respectively. Starting from outside the Lamb-Dicke regime, after 45 ms of cooling we measure probabilities to occupy the three-dimensional motional ground state of 0.8 6 − 0.04 + 0.03 for Rb and 0.9 5 − 0.04 + 0.03 for Cs. Our setup overlaps the Raman laser beams used to cool Rb and Cs, reducing hardware requirements by sharing equipment along the same beam path. The cooling protocol is scalable, and we demonstrate cooling of single Rb atoms in an array of four tweezers. After motional ground-state cooling, a 938 nm tweezer is translated to overlap with a 814 nm tweezer so that a single Rb and a single Cs atom can be transferred into a common 1064 nm trap. By minimising the heating during the merging and transfer, we prepare the atoms in the relative motional ground state with an efficiency of 0.8 1 − 0.08 + 0.08 . This is a crucial step towards the formation of single RbCs molecules confined in optical tweezer arrays.

DOI
10.1088/1367-2630/ac95b9

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Abstract We report simultaneous Raman sideband cooling of a single 87Rb atom and a single 133Cs atom held in separate optical tweezers at 814 nm and 938 nm, respectively. Starting from outside the Lamb-Dicke regime, after 45 ms of cooling we measure probabilities to occupy the three-dimensional motional ground state of 0.8 6 − 0.04 + 0.03 for Rb and 0.9 5 − 0.04 + 0.03 for Cs. Our setup overlaps the Raman laser beams used to cool Rb and Cs, reducing hardware requirements by sharing equipment along the same beam path. The cooling protocol is scalable, and we demonstrate cooling of single Rb atoms in an array of four tweezers. After motional ground-state cooling, a 938 nm tweezer is translated to overlap with a 814 nm tweezer so that a single Rb and a single Cs atom can be transferred into a common 1064 nm trap. By minimising the heating during the merging and transfer, we prepare the atoms in the relative motional ground state with an efficiency of 0.8 1 − 0.08 + 0.08 . This is a crucial step towards the formation of single RbCs molecules confined in optical tweezer arrays.
Abstract We report the preparation of exactly one 87Rb atom and one 133Cs atom in the same optical tweezer as the essential first step towards the construction of a tweezer array of individually trapped 87Rb133Cs molecules. Through careful selection of the tweezer wavelengths, we show how to engineer species-selective trapping potentials suitable for high-fidelity preparation of Rb + Cs atom pairs. Using a wavelength of 814 nm to trap Rb and 938 nm to trap Cs, we achieve loading probabilities of 0.508(6) for Rb and 0.547(6) for Cs using standard red-detuned molasses cooling. Loading the traps sequentially yields exactly one Rb and one Cs atom in 28.4(6)% of experimental runs. Using a combination of an acousto-optic deflector and a piezo-controlled mirror to control the relative position of the tweezers, we merge the two tweezers, retaining the atom pair with a probability of 0.9 9 ( − 0.02 ) ( + 0.01 ) . We use this capability to study hyperfine-state-dependent collisions of Rb and Cs in the combined tweezer and compare the measured two-body loss rates with coupled-channel quantum scattering calculations.
We report Raman sideband cooling of a single sodium atom to its three-dimensional motional ground state in an optical tweezer. Despite a large Lamb-Dicke parameter, high initial temperature, and large differential light shifts between the excited state and the ground state, we achieve a ground-state population of 93.5(7)% after 53 ms of cooling. Our technique includes addressing high-order sidebands, where several motional quanta are removed by a single laser pulse, and fast modulation of the optical tweezer intensity. We demonstrate that Raman sideband cooling to the three-dimensional motional ground state is possible, even without tight confinement and low initial temperature.
We report cooling of a single neutral atom to its three-dimensional vibrational ground state in an optical tweezer.After employing Raman sideband cooling for tens of milliseconds, we measure via sideband spectroscopy a three-dimensional ground-state occupation of about 90%.We further observe coherent control of the spin and motional state of the trapped atom.Our demonstration shows that an optical tweezer, formed simply by a tightly focused beam of light, creates sufficient confinement for efficient sideband cooling.This source of ground-state neutral atoms will be instrumental in numerous quantum simulation and logic applications that require a versatile platform for storing and manipulating ultracold single neutral atoms.For example, these results will improve current optical-tweezer experiments studying atom-photon coupling and Rydberg quantum logic gates, and could provide new opportunities such as rapid production of single dipolar molecules or quantum simulation in tweezer arrays.
We demonstrate full quantum state control of two species of single atoms using optical tweezers and assemble the atoms into a molecule.Our demonstration includes 3D ground-state cooling of a single atom (Cs) in an optical tweezer, transport by several microns with minimal heating, and merging with a single Na atom.Subsequently, both atoms occupy the simultaneous motional ground state with 61(4)% probability.This realizes a sample of exactly two cotrapped atoms near the phase-space-density limit of one, and allows for efficient stimulated-Raman transfer of a pair of atoms into a molecular bound state of the triplet electronic ground potential a 3 Σ þ .The results are key steps toward coherent creation of single ultracold molecules for future exploration of quantum simulation and quantum information processing.
Ultracold polar molecules are promising for quantum information processing and searches for physics beyond the standard model. Laser cooling to ultracold temperatures is an established technique for trapped diatomic and triatomic molecules. Further cooling of the molecules to near the motional ground state is crucial for reducing various dephasings in quantum and precision applications. In this work, we demonstrate Raman sideband cooling (RSC) of CaF molecules in optical tweezers to near their motional ground state, with average motional occupation quantum numbers of n ¯ x = 0.16 ( 12 ) , n ¯ y = 0.17 ( 17 ) (radial directions), and n ¯ z = 0.22 ( 16 ) (axial direction), and a 3-D motional-ground-state probability of 54 ± 18 % of the molecules that survive the RSC. This process paves the way to increase molecular coherence times in optical tweezers for robust quantum computation and simulation applications. Published by the American Physical Society 2024
We demonstrate the formation of a single RbCs molecule during the merging of two optical tweezers, one containing a single Rb atom and the other a single Cs atom. Both atoms are initially predominantly in the motional ground states of their respective tweezers. We confirm molecule formation and establish the state of the molecule formed by measuring its binding energy. We find that the probability of molecule formation can be controlled by tuning the confinement of the traps during the merging process, in good agreement with coupled-channel calculations. We show that the conversion efficiency from atoms to molecules using this technique is comparable to magnetoassociation.