Systems and Methods for Generating Large Arrays of Optical Traps in Neutral Atom Array Quantum Processors

Abstract

Neutral-atom array quantum processors provide a scalable and controllable platform for quantum simulation, computation, sensing, and metrology. Strong Rydberg interactions enable entanglement and high-fidelity gates, while the ability to rearrange atoms allows for multi-qubit operations between spatially distant qubits and the implementation of quantum error-correcting codes with nonlocal stabilizers. These arrays also support electromagnetic field sensing and form the basis for next-generation atomic clocks with improved stability and precision. Recent progress has demonstrated platforms with thousands of qubits, the implementation of error-correction codes, and experimental realizations of quantum spin models, including studies of quantum phase transitions. Current efforts now focus on scaling to even larger arrays and reducing quantum gate errors, with the goal of achieving computations and simulations beyond the reach of classical devices.

However, increasing the scale and controllability of neutral-atom array platforms to address problems where quantum advantage can have practical impact remains challenging. Key difficulties include scaling to larger numbers of qubits, implementing fault-tolerant computation, and performing gates between spatially distant qubits. A critical experimental challenge is ensuring that qubits form an indistinguishable spatiotemporal ensemble, so that atoms across the array and over multiple experimental shots can be treated as identical. Achieving this uniformity becomes more difficult as the array size increases, due to the added complexity of ensuring that all atoms experience consistent control parameters, such as trap depth and magnetic fields. Without sufficient spatiotemporal uniformity, it is impossible to meaningfully average measurements across different qubits and experimental runs, undermining scalability and limiting the performance of quantum simulations, computations, and sensing applications.

In this thesis, I propose, design, and implement methods to scale up the number of qubits and improve the spatiotemporal uniformity of qubit properties in acousto-optically generated trap arrays for neutral-atom quantum processors. These methods enable magnetic-field imaging across an array of 1,305 optical traps containing 690 qubits, as well as high-fidelity fluorescence imaging of single atoms in optical tweezers.

First, I demonstrate a novel method for circularizing and de-astigmatizing the trapping beam using three cylindrical lenses. This approach is cost-effective, power-efficient, and broadly applicable. By improving the beam shape, we reduce the per-trap laser power, enabling the use of larger qubit arrays in neutral-atom quantum processors. Applied to a Ti:sapphire laser with an initial circularity of 0.69, this method achieves a circularity of 0.97 and a beam waist separation of 0.8 percent of the Rayleigh range, reducing the optical power required per trap by 5 percent.

After beam circularization, I develop a real-time closed-loop feedback system for an optical trap array generated by two orthogonal acousto-optical deflectors to enhance the spatiotemporal uniformity of qubit properties. The system stabilizes trap depths using power measurements from a fast CMOS camera and in-situ depth estimates from an EMCCD camera based on the atomic signal. Noise is decomposed into uncorrelated temporal modes, each regulated by an independent PID loop. Unlike approaches that regulate only total laser power, our method stabilizes the depth of individual traps, eliminating the need for frequent recalibration of cooling-beam parameters and enabling higher duty cycles. In a 45 by 29 array, the generated traps exhibit a standard deviation of 6 percent relative to the mean trap depth, limited by the number of independent control parameters actuating the acousto-optical deflectors.

Having established these capabilities, we demonstrate the controllability and practical utility of the platform by performing magnetic-field sensing using microwave horn spectroscopy on a 45 by 29 trap array, mapping field gradients across the array. This establishes the foundation for advanced quantum sensing protocols, such as quantum lock-in amplification, and paves the way toward entanglement-based quantum sensors capable of offering a quantum advantage in sensing.

Lastly, to improve readout fidelity, I describe the optimization of imaging beam parameters in neutral-atom array quantum processors. This optimization maximizes atom classification accuracy while minimizing the probability of ejecting atoms from the traps. Applied to a 45 by 29 trap array, the method achieves a classification fidelity of 99.98 percent and a loss probability of 0.12 percent with a 75 millisecond imaging time. These improvements reduce measurement errors, enhance quantum state readout, and increase the sensitivity of neutral-atom-based quantum sensors.