近日，美国哈佛大学的Norman Y. Yao及其研究团队取得一项新进展。经过不懈努力，他们实现有限温度易面磁性的可伸缩自旋压缩。相关研究成果已于2024年7月29日在国际知名学术期刊《自然—物理学》上发表。

该研究团队为以下猜想提供了数值和分析证据:任何具有有限温度易平面铁磁性的哈密顿量都可以用来产生可扩展的自旋压缩，从而实现量子增强传感。这一猜想是由纯态的量子费雪信息与连续对称的自发破缺之间的联系所指导的。研究人员证明了自旋压缩表现出一个在可伸缩压缩和非压缩之间急剧转变的相图。这种转变符合有限温度下XY阶的平衡相边界。

在可伸缩压缩阶段，研究人员预测了一个灵敏度尺度，该尺度位于标准量子极限和全对全耦合单轴扭转模型所达到的尺度之间。他们的一个推论是，短距离版本的两轴扭转无法实现可伸缩的计量增益。这一研究结果为理解哈密顿量景观提供了新的见解，有助于生成在计量学上有应用价值的量子态。

据悉，自旋压缩是一种纠缠形式，它可以重塑量子投影噪声以提高测量精度。

附：英文原文

Title: Scalable spin squeezing from finite-temperature easy-plane magnetism

Author: Block, Maxwell, Ye, Bingtian, Roberts, Brenden, Chern, Sabrina, Wu, Weijie, Wang, Zilin, Pollet, Lode, Davis, Emily J., Halperin, Bertrand I., Yao, Norman Y.

Issue&Volume: 2024-07-29

Abstract: Spin squeezing is a form of entanglement that reshapes the quantum projection noise to improve measurement precision. Here, we provide numerical and analytic evidence for the following conjecture: any Hamiltonian exhibiting finite-temperature easy-plane ferromagnetism can be used to generate scalable spin squeezing, thereby enabling quantum-enhanced sensing. Our conjecture is guided by a connection between the quantum Fisher information of pure states and the spontaneous breaking of a continuous symmetry. We demonstrate that spin squeezing exhibits a phase diagram with a sharp transition between scalable squeezing and non-squeezing. This transition coincides with the equilibrium phase boundary for XY order at a finite temperature. In the scalable squeezing phase, we predict a sensitivity scaling that lies between the standard quantum limit and the scaling achieved in all-to-all coupled one-axis twisting models. A corollary of our conjecture is that short-ranged versions of two-axis twisting cannot yield scalable metrological gain. Our results provide insights into the landscape of Hamiltonians that can be used to generate metrologically useful quantum states.

DOI: 10.1038/s41567-024-02562-5

Source: https://www.nature.com/articles/s41567-024-02562-5