Strontium Tweezer Array Achieves 0.81m Waist for Quantum Computing Advances

Neutral atoms represent a compelling platform for scalable and connected quantum computing. Researchers Marijn Venderbosch, Rik van Herk, and Zhichao Guo, alongside colleagues from Eindhoven University of Technology and the University of Amsterdam, have developed a robust strontium tweezer apparatus designed to address key challenges in this burgeoning field. Their newly realised system stochastically loads a 5×5 array of individual strontium atoms, offering flexible magnetic field control and excellent optical access , crucial for manipulating and observing quantum states. This innovative setup, detailed in their recent work, incorporates a custom-designed oven and cooling stages to achieve atomic temperatures of just 5 Kelvin, paving the way for high-fidelity atom trapping and imaging with impressive survival probabilities , ultimately forming the foundation for a full-stack quantum processor aimed at tackling complex chemistry computational problems.

The optical tweezers themselves possess a 1/e2 waist of 0.81(2) μm, enabling precise manipulation of the individual atoms. This atomic array forms the foundational core of a quantum computing processor specifically targeted for tackling complex problems in quantum chemistry. The researchers opted for a deflection stage, rather than a traditional 2-D magneto-optical trap, to maintain a low vacuum pressure, a critical factor for extending Qubit coherence times, while simultaneously sustaining a sufficient loading rate for tweezer experiments.

The laser system comprises eight continuous wave lasers, ranging from 317nm to 813nm, each playing a specific role in cooling, imaging, tweezer creation, qubit control, and repumping. These lasers are meticulously stabilized, achieving a frequency stability of approximately 10Hz after 104 seconds of averaging, ensuring the precision required for quantum operations. This innovative strontium tweezer apparatus represents a significant advancement in neutral atom quantum computing. The work opens possibilities for single-qubit gate operations and Rydberg-mediated entanglement, crucial components for building scalable quantum processors. In the near future, this apparatus will serve as a neutral atom-based backend for the openly accessible Quantum Inspire platform, and the team is actively implementing a full-stack approach with a digital twin, RySP, to further enhance its capabilities and accessibility.

Strontium Atom Loading and Laser Cooling Setup

Within this chamber, a two-stage laser cooling process reduced atomic velocities, ultimately achieving temperatures of 5(1) K for subsequent manipulation. Experiments employed a blue MOT, followed by a broadband (bMOT) and single-frequency (sMOT) red MOT to further cool the atoms. Initially, the blue MOT operated for 1500ms, delivering approximately 3 × 10^5 atoms, before transitioning to the red MOT sequence. The bMOT utilized 1.7MHz frequency modulation with a 45kHz modulation frequency, alongside a rapidly changing quadrupole field gradient of 1.3 G/cm, compressing the atomic cloud and enhancing density.

Subsequently, the gradient field increased to 5.6 G/cm, and smooth magnetic field trajectories, generated by bias coils, spatially overlapped the bMOT with the tweezer array’s focal point. Cooling continued in the sMOT stage, disabling frequency modulation and exponentially reducing laser intensities to final values of s ∼6 and a detuning of −150kHz. Time-of-flight (ToF) fluorescence imaging on the blue transition then measured final temperatures of Tx = Ty = 5(1) μK, fitting 2-D Gaussian functions to images acquired at ToF = 0ms and ToF = 10ms to extract temperature parameters. The team harnessed a spatial light modulator (SLM) and a high-resolution microscope objective to create the tweezer array.

5×5 strontium array via optical tweezers enables precise

Experiments revealed that the Sr atoms, after undergoing two stages of laser cooling, reach a remarkably low temperature of 5(1) K. The optical tweezers themselves possess a waist of 0.81(2) m, enabling precise atom positioning and manipulation. Tests prove the deflection stage, utilizing a single retro-reflected laser beam, is remarkably forgiving with respect to beam alignment, simplifying setup and maintenance. Measurements confirm the frequency comb, short-term stabilized to a high-finesse cavity, and long-term steered using a 10MHz RF reference, delivers exceptional frequency stability. For the clock and Rydberg lasers, locking to a comb index of approximately 1.4 × 10⁶, the achieved frequency stability is ∆f = mfRσ(τ) = O(10) Hz, utilizing a modified Allan deviation σ(τ) ∼4 × 10⁻¹³ after 10⁴ seconds of averaging.

Researchers achieved a vapor pressure of approximately 3 × 10⁻⁴ mbar within the oven by heating a strontium sample to 420°C. The oven design, inspired by previous work, focuses on generating a collimated atomic beam while maintaining thermal isolation. The apparatus will soon serve as a neutral atom-based backend for the openly accessible Quantum Inspire platform, and the team is currently operating the Rydberg emulator RySP as a digital twin of their experimental setup, further accelerating development and accessibility.

High-fidelity strontium atom arrays demonstrated scalable quantum computation

This achievement establishes a robust platform for exploring neutral atom quantum computing. Characterisation measurements reveal a tweezer waist of 0.81 micrometres, slightly above the diffraction limit, and trap frequencies suitable for qubit manipulation. Future work will focus on implementing movable tweezers for atomic rearrangement, coherent manipulation using a 698nm laser, and Rydberg state targeting with a 317nm laser, alongside integration with the Quantum Inspire platform and the RySP Rydberg emulator.