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

• 成果类型: Article
• 署名作者: Cao, Alec; Eckner, William J.; Yelin, Theodor Lukin; Young, Aaron W.; Jandura, Sven; Yan, Lingfeng; Kim, Kyungtae; Pupillo, Guido; Ye, Jun; Oppong, Nelson Darkwah; Kaufman, Adam M.
• 署名单位: University of Colorado System; University of Colorado Boulder; National Institute of Standards & Technology (NIST) - USA; University of Colorado System; University of Colorado Boulder; Universites de Strasbourg Etablissements Associes; Universite de Strasbourg; Centre National de la Recherche Scientifique (CNRS); Centre National de la Recherche Scientifique (CNRS); CNRS - Institute of Chemistry (INC)
• 刊物名称: Nature
• ISSN/ISSBN: 0028-5543
• DOI: 10.1038/s41586-024-07913-z
• 发表日期: 2024-10-10
• 关键词: standard quantum limit; erasure conversion; rydberg atom; entanglement; STABILITY; DYNAMICS; sensors

摘要

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 Schr & ouml;dinger 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. A family of multi-qubit Rydberg quantum gates is developed and used to generate Schr & ouml;dinger cat states in an optical clock, allowing improvement in frequency measurement precision by taking advantage of entanglement.