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arXiv:2302.03940 · Physical Review Research

Motional ground-state cooling of single atoms in state-dependent optical tweezers

Christian Hölzl, Aaron Götzelmann, M. Wirth, Marianna S. Safronova, Sebastian Weber, Florian Meinert

Published Aug 9, 2023• 24 citations
arXivHTMLPDF

Abstract

Laser cooling of single atoms in optical tweezers is a prerequisite for neutral atom quantum computing and simulation. Resolved sideband cooling comprises a well-established method for efficient motional ground-state preparation, but typically requires careful cancellation of light shifts in so-called magic traps. Here, we study a novel laser cooling scheme which overcomes such constraints, and applies when the ground state of a narrow cooling transition is trapped stronger than the excited state. We demonstrate our scheme, which exploits sequential addressing of red sideband transitions via frequency chirping of the cooling light, at the example of $^{88}\mathrm{Sr}$ atoms and report ground-state populations compatible with recent experiments in magic tweezers. The scheme also induces light-assisted collisions, which are key to the assembly of large atom arrays. Our work enriches the toolbox for tweezer-based quantum technology, also enabling applications for tweezer-trapped molecules and ions that are incompatible with resolved sideband cooling conditions.

DOI
10.1103/physrevresearch.5.033093

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We propose a cooling scheme for realizing single-photon sideband cooling on particles trapped in a statedependent optical potential.We develop a master rate equation from an ab initio model and find that in experimentally feasible conditions it is possible to reduce the average occupation number of the vibrational levels in one dimension by more than 90% by applying a frequency sweep on the cooling laser that sequentially cools all the motional states.Notably, this cooling scheme works also when a particle experiences a deeper trap in its internal ground state than in its excited state, a condition for which conventional single-photon sideband cooling does not work.In our analysis, we consider two cases: a two-level particle confined in an optical tweezer, and Li atoms confined in an optical lattice, and we find conditions for efficient cooling in both cases.The results from the model are confirmed by a full quantum Monte Carlo simulation of the system Hamiltonian.Our findings provide an alternative cooling scheme that can be applied in principle to any particle, e.g., atoms, molecules, or ions, confined in a state-dependent optical potential.
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.
Single neutral atoms trapped in optical tweezers and laser-coupled to Rydberg states provide a fast and flexible platform to generate configurable atomic arrays for quantum simulation. The platform is especially suited to study quantum spin systems in various geometries. However, for experiments requiring continuous trapping, inhomogeneous light shifts induced by the trapping potential and temperature broadening impose severe limitations. Here we show how Raman sideband cooling allows one to overcome those limitations, thus, preparing the stage for Rydberg dressing in tweezer arrays.
We perform narrowline cooling of single dysprosium atoms trapped in a 1D optical tweezers array, employing the narrow single-photon transition at 741 nm. At the trapping wavelength of 532 nm, the excited state is less trapped than the ground state. To obtain efficient cooling performances, we chirp the frequency of the cooling beam to subsequently address the red sidebands of different motional states. We demonstrate the effectiveness of the cooling protocol through Raman thermometry, which we characterize for our experimental conditions. We obtain an array of 75 atoms close to the motional ground state in the radial direction of the tweezers. Our results demonstrate the possibility to manipulate the motional degree of freedom of dysprosium in optical tweezers arrays, a key ingredient to exploit the potential of lanthanide-based tweezers platforms for quantum science.
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.
Cooling atoms to the ground-state of optical tweezers is becoming increasingly important for high-fidelity imaging, cooling, and molecular assembly. While extensive theoretical work has been conducted on cooling in free space, fewer studies have focused on cooling in bound states. In this work, we present a unified formalism for optical cooling mechanisms in neutral atom tweezers, including resolved and unresolved sideband cooling with different trapping potentials, polarization gradient cooling, gray molasses cooling, ΛΛΛ-enhanced gray molasses cooling, and Raman sideband cooling. We perform simulations and demonstrate good agreement with a simplified spin model. We derive and discuss the fundamental limits of each cooling mechanism and propose new strategies for achieving ground-state cooling in optical tweezers. Our findings provide valuable insights into optimizing cooling schemes for neutral atoms in optical tweezers, paving the way for minimizing thermal decoherence in Rydberg and molecular gates and improving efficiencies of molecular assembly.