title: A New Setup for Scaling Up Microlens-Based Individual-Atom Quantum Processors
Creators: name: Pause, Lars
Publisher: name: UNSPECIFIED
Year: 2023

description: In current efforts, many platforms based e.g. on ions, neutral atoms, or superconducting qubits are being pursued with the goal to establish large-scale quantum devices for quantum computation and quantum simulation. Neutral atoms trapped in arrays of optical tweezers offer a versatile implementation in which the quantum system is well decoupled from its environment and the internal and external degrees of freedom of each individual atom can be precisely manipulated. Utilizing excitations of the atoms into Rydberg states enables interactions of selectable strengths thus allowing to perform gate operations or to implement spin Hamiltonians. As for all quantum processors, scaling up the system size is key for future progress. In this work, a new experimental setup for trapping neutral Rb85 atoms in microlens-based tweezer arrays has been developed, addressing the challenge of scalability and demonstrating methods for enhancing the preparation of large-scale neutral atom quantum systems. A detailed introduction into the new setup and its essential elements is given. The design of a new vacuum chamber with versatile optical access allowing for different Rydberg excitation schemes used in state-of-the-art quantum experiments is presented. The experimental setup is controlled by a python-based experiment control-software which has been optimized to feature conditional control within an experimental cycle. Based on this new setup, large sets of individual atoms are prepared by loading the trap arrays from a laser-cooled cloud of neutral atoms which is the state-of-the-art procedure to provide a single-atom quantum processing platform. For future quantum processing applications this procedure limits the data rate since the quantum operations have to be alternated with phases of laser cooling and trapping to compensate for unavoidable atom loss. In order to overcome these limitations a large-focus dipole trap providing a reservoir of laser-cooled atoms is introduced from which atoms are transported to the tweezer array using a single, movable tweezer. Utilizing an array of buffer traps, deterministic loading of a target structure with individual atoms from the cold-atom reservoir is demonstrated for the first time. Using solely reservoir atoms to load an empty trap array a cumulative success rate of 91.5(6) % for a defect-free target array is achieved. For a pre-loaded tweezer array an enhancement of the cumulative success rate from 62.1(6) % to 98.6(2) % is demonstrated. With this new method, it is possible to split the process of deterministic single-atom preparation into several functional units allowing for spatial separation as well as parallelized operation. Implementing a new microscope objective with a higher numerical aperture of 0.385(5) in a modified optical setup allowed to reduce the volume of individual trapping sites and thereby reduce the necessary laser power for each individual trap. Utilizing this improvement together with the application of interleaved tweezer arrays based on multiple, individual laser beams, circumvented laser power limitations and for the first time enhanced the number of trapped individual atoms above 1000. With a single laser beam up to 600 individual atoms could be trapped in a quadratic trap array having a pitch of 5.17(2) µm. This number could be increased with the use of two interleaved arrays to an average of 1167(45) atoms. As this clearly demonstrates the scalability of microlens-based neutral atom platforms, approaches to deterministically arrange such large atom arrays and to further scale the system towards several thousand trapped atoms are outlined.