Multi-qubit gates and Schrödinger cat states in an optical clock

Alec Cao, William J. Eckner, Theodor Lukin Yelin, Aaron W. Young, Sven Jandura, Lingfeng Yan, Kyungtae Kim, Guido Pupillo, Jun Ye, Nelson Darkwah Oppong and Adam M. Kaufman ()
Additional contact information
Alec Cao: University of Colorado Boulder and National Institute of Standards and Technology
William J. Eckner: University of Colorado Boulder and National Institute of Standards and Technology
Theodor Lukin Yelin: University of Colorado Boulder and National Institute of Standards and Technology
Aaron W. Young: University of Colorado Boulder and National Institute of Standards and Technology
Sven Jandura: University of Strasbourg and CNRS, CESQ and ISIS (UMR 7006)
Lingfeng Yan: University of Colorado Boulder and National Institute of Standards and Technology
Kyungtae Kim: University of Colorado Boulder and National Institute of Standards and Technology
Guido Pupillo: University of Strasbourg and CNRS, CESQ and ISIS (UMR 7006)
Jun Ye: University of Colorado Boulder and National Institute of Standards and Technology
Nelson Darkwah Oppong: University of Colorado Boulder and National Institute of Standards and Technology
Adam M. Kaufman: University of Colorado Boulder and National Institute of Standards and Technology

Nature, 2024, vol. 634, issue 8033, 315-320

Abstract: Abstract Many-particle entanglement is a key resource for achieving the fundamental precision limits of a quantum sensor1. Optical atomic clocks2, the current state of the art in frequency precision, are a rapidly emerging area of focus for entanglement-enhanced metrology3–6. Augmenting tweezer-based clocks featuring microscopic control and detection7–10 with the high-fidelity entangling gates developed for atom-array information processing11,12 offers a promising route towards making use of highly entangled quantum states for improved optical clocks. Here we develop and use a family of multi-qubit Rydberg gates to generate Schrödinger cat states of the Greenberger–Horne–Zeilinger (GHZ) type with up to nine optical clock qubits in a programmable atom array. In an atom-laser comparison at sufficiently short dark times, we demonstrate a fractional frequency instability below the standard quantum limit (SQL) using GHZ states of up to four qubits. However, because of their reduced dynamic range, GHZ states of a single size fail to improve the achievable clock precision at the optimal dark time compared with unentangled atoms13. Towards overcoming this hurdle, we simultaneously prepare a cascade of varying-size GHZ states to perform unambiguous phase estimation over an extended interval14–17. These results demonstrate key building blocks for approaching Heisenberg-limited scaling of optical atomic clock precision.

Date: 2024
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DOI: 10.1038/s41586-024-07913-z

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