近日，美国科罗拉多大学博尔德分校和美国国家标准与技术研究所的Adam M. Kaufman及其研究团队取得一项新进展。经过不懈努力，他们实现一个光学时钟中的多量子比特门和薛定谔猫态。相关研究成果已于2024年10月9日在国际权威学术期刊《自然》上发表。

该研究团队开发并使用了一系列多量子比特里德伯（Rydberg）门，在可编程原子阵列中生成了最多包含九个光学钟量子比特的格林伯格-霍恩-蔡林格（Greenberger–Horne–Zeilinger, GHZ）型薛定谔猫态。在足够短的暗时间下的原子-激光比较中，研究人员使用最多四个量子比特的GHZ态展示了低于标准量子极限（SQL）的分数频率不稳定性。

然而，由于动态范围减小，与未纠缠原子相比，单一大小的GHZ态在最佳暗时间下无法提高可实现的时钟精度。为了克服这一障碍，研究人员同时制备了一系列不同大小的GHZ态，以在扩展区间内进行明确的相位估计。这些结果展示了接近光学原子钟精度海森堡极限缩放的关键构建模块。

据悉，多粒子纠缠是实现量子传感器基本精度极限的关键资源。光学原子钟作为当前频率精度领域的顶尖技术，正迅速成为纠缠增强测量技术的研究焦点。将用于原子阵列信息处理的高保真度纠缠门与具有微观控制和检测功能的光镊钟相结合，为利用高度纠缠的量子态来改进光学钟提供了一条有希望的途径。

附：英文原文

Title: Multi-qubit gates and Schrdinger cat states in an optical clock

Author: Cao, Alec, Eckner, William J., Lukin Yelin, Theodor, Young, Aaron W., Jandura, Sven, Yan, Lingfeng, Kim, Kyungtae, Pupillo, Guido, Ye, Jun, Darkwah Oppong, Nelson, Kaufman, Adam M.

Issue&Volume: 2024-10-09

Abstract: Many-particle entanglement is a key resource for achieving the fundamental precision limits of a quantum sensor. Optical atomic clocks, the current state of the art in frequency precision, are a rapidly emerging area of focus for entanglement-enhanced metrology. Augmenting tweezer-based clocks featuring microscopic control and detection with the high-fidelity entangling gates developed for atom-array information processing 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 Schrdinger 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 atoms. Towards overcoming this hurdle, we simultaneously prepare a cascade of varying-size GHZ states to perform unambiguous phase estimation over an extended interval. These results demonstrate key building blocks for approaching Heisenberg-limited scaling of optical atomic clock precision.

DOI: 10.1038/s41586-024-07913-z

Source: https://www.nature.com/articles/s41586-024-07913-z