A Robust Strontium Tweezer Apparatus for Quantum Computing

TL;DR

This work presents a compact, versatile Sr-based tweezer platform capable of stochastically loading a $5×5$ array of optical tweezers with single $^{88}$Sr atoms while preserving ultra-high vacuum through a deflection-stage loading path. The system integrates eight CW lasers stabilized to a frequency comb, a custom oven, Zeeman slower, and a deflection chamber to deliver a high-quality atomic flux into a tightly controlled science chamber with flexible magnetic-field control. Achieving a final MOT temperature near $5 μK$ and an imaging fidelity of approximately $0.997$ with a per-site occupancy of roughly $46 ext{%}$, the setup demonstrates the viability of Sr tweezer arrays as a core platform for clock-state qubits and Rydberg-mediated entanglement in quantum chemistry simulations. The authors outline a clear path toward full-stack quantum processing, including reconfiguration of tweezers, clock-transition manipulation at 698 nm, and Rydberg access at 317 nm, integrated with open platforms like Quantum Inspire.

Abstract

Neutral atoms for quantum computing applications show promise in terms of scalability and connectivity. We demonstrate the realization of a versatile apparatus capable of stochastically loading a 5x5 array of optical tweezers with single $^{88}$Sr atoms featuring flexible magnetic field control and excellent optical access. A custom-designed oven, spin-flip Zeeman slower, and deflection stage produce a controlled flux of Sr directed to the science chamber. In the science chamber, featuring a vacuum pressure of $3 \times 10^{-11}$ mbar, the Sr is cooled using two laser cooling stages, resulting in $\sim 3 \times 10^5$ atoms at a temperature of 5(1) $μ$K. The optical tweezers feature a $1/e^2$ waist of 0.81(2) $μ$m, and loaded atoms can be imaged with a fidelity of $\sim 0.997$ and a survival probability of $0.99^{+0.01}_{-0.02}$. The atomic array presented here forms the core of a full-stack quantum computing processor targeted for quantum chemistry computational problems.

Figures (10)

• Figure 1: Laser system stabilization for the Sr-88 clock qubit. 8 continuous wave (CW) lasers are locked to a commercial frequency comb. The frequency comb is short-term stabilized to a high finesse cavity as optical reference and long-term steered using software-implemented feedback to an RF reference obtained from a fiber link to the Dutch Metrology Institute. The inset shows the energy level structure of Sr-88 and the atomic transitions addressed by the CW lasers. Not shown: triplet-P transitions used for repumping.
• Figure 2: CAD image of the Sr tweezer apparatus. From the oven, the atoms are slowed in the spin-flip Zeeman slower using the Zeeman laser (light blue array). In the deflection chamber, the slowed atoms (purple dashed line), are deflected towards the science chamber using the deflection lasers (light blue arrows). The fast atoms (red dashed line) hit the heated window at $200\,\text{\degree}$. The science chamber consists of a glass cell mounted between MOT coils and microscope objectives (see \ref{['fig:coils']}).
• Figure 3: CAD images of the oven. a) Cutout image of the inside of the oven, showing the heating bands, thermocouple access points and a zoomed image of the oven nozzle. b) Oven enclosed in isolation material to avoid heat transferring to the rest of the vacuum system.
• Figure 4: The science chamber (glass cell) with surrounding magnetic field coils and microscope objectives. The Sr atoms enter the cell along the $\textbf{x}$ direction. The central thick copper winding represents the main coil, constructed from hollow, water-cooled wire, and employed for generating MOT and Helmholtz magnetic fields. Three pairs of bias coils corresponding to the cartesian coordinates x, y and z, depicted in orange, produce offset fields. These coils are wound and mounted onto the coil holder (beige). Detailed parameters for all coils are summarized in \ref{['tab:coils']}. The layout of the x bias coils allow the diagonal MOT beams ($5\,\text{mm}$$1/e^2$ waist) to enter the glass cell at a $25\,\text{\degree}$ angle w.r.t the x-axis (see \ref{['fig:optics_setup']}) to make room for the microscope objectives.
• Figure 5: Blue MOT operation. a) In-situ absorption image for a deflector beam power $P_{\text{defl}}=25\,\text{mW}$. b) Number of atoms in the blue MOT $N$ as a function of $P_{\text{defl}}$. The loading time used is $t_{\text{load}}=1500\,\text{ms}$.