报告时间：2021年5月12日 下午15:30

报告地点：物质楼A309会议室

报告题目: Measurements with prediction and retrodiction on the collective spin of 1011 atoms beat the standard quantum limit

报告人：山西大学 申恒教授

报告人简介：申恒, 山西大学量子光学与光量子器件国家重点实验室-光电研究所教授。2015年在丹麦哥本哈根大学尼尔斯玻尔研究所获得博士学位。之后在奥地利因斯布鲁克国家科学院量子信息与量子光学中心从事基于离子阵列的量子模拟与计算实验博士后研究，并于2017年获得英国皇家学会牛顿国际基金支持在牛津大学从事光力/原子混合系统的研究。以通信作者或第一作者在国际著名刊物发表多篇论文，包括Nature、Nature Physics、Nature Communications及Phys. Rev. Lett.等。研究方向包括量子模拟与计算、量子精密测量及新型量子材料等。

报告摘要：Quantum probes using N uncorrelated particles give a limit on the measurement sensitivity referred to as the standard quantum limit (SQL). The SQL, however, can be overcome by exploiting quantum entangled states, such as spin squeezed states. I will talk about the generation of a quantum state, that surpasses the SQL for probing of the collective spin of 1011 Rb atoms contained in a vapor cell. The state is prepared and verified by sequences of stroboscopic quantum non-demolition (QND) measurements, and we apply the theory of past quantum states to obtain the spin state information from the outcomes of both earlier and later QND measurements. In this way, we obtain a conditional noise reduction of 5.6 dB, and a metrologically-relevant squeezing of 4.5±0.40 dB. The past quantum state yields tighter information on the spin component than we can obtain by a conventional QND measurement. Our squeezing results are obtained with 1000 times more atoms than in any previous experiments with a corresponding record 4.6 × 10−13rad2 variance of the angular fluctuations of a squeezed collective spin. We have applied the protocol to experimentally demonstrate a quantum-enhanced atomic magnetometer.

Reference

1. Generation of a squeezed state of an oscillator by stroboscopic back-action-evading measurement, Georgios Vasilakis#, Heng Shen#, Kasper Jensen, Misha Balabas, Daniel Salart, Bing Chen, Eugene S. Polzik*, Nature Physics, 11, 389-492 (2015). 

2. Spin squeezing of 1011 atoms by prediction and retrodiction measurements, Han Bao, Junlei Duan, Shenchao Jin, Xingda Lu, Pengxiong Li, Weizhi Qu, Mingfeng Wang, Irina Novikova, Eugeniy E. Mikhailov, Kai-Feng Zhao, Klaus Mølmer*, Heng Shen*, and Yanhong Xiao*, Nature 581, 159-163 (2020).