报告题目: Measurements with prediction and retrodiction on the collective spin of 10^11 atoms beat the standard quantum limit
基于过去量子态的千亿原子自旋压缩

报告人：申恒教授 山西大学

报告地点：理六栋302

邀请人:张善超

报告内容：
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. We report 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 veri?ed 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 ?uctuations of a squeezed collective spin. We have applied the protocol to experimentally demonstrate a quantum-enhanced atomic magnetometer.

个人简介：

申恒本科毕业于南开大学天津大学合办光电子技术科学专业。 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。现为山西大学量子光学与光量子器件国家重点实验室教授。以通信作者或第一作者在国际著名刊物发表多篇论文，包括自然主刊，自然物理及物理评论快报等。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。