量子信息交叉中心学术报告035
Title: Measurements with prediction and retrodiction on the collective spin of 1011 atoms beat the standard quantum limit
Speaker:申恒，牛津大学
Place: RM 101，Bulg. 2，Xixi Campus（西溪校区西二教学楼101室）
Date and time:10:00，Dec. 23th，2019 (12月23日上午10:00)
Abstract：
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 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.
Biography:
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，2011年在山西大学光电研究所获得硕士学位。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2018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。
Dr. Heng Shen obtained his PhD degree in 2015 in Niles Bohr Institute at Copenhagen University, under the supervision of Prof. Eugene Polzik. His PhD work is focused on spin squeezing and entanglement with room temperature atoms, main results including high performance quantum magnetometer, Deterministic quantum teleportation between distant atomic objects. Afterwards, he moved to Rainer Blatt’s group as a postdoctoral research associate Institute for Quantum Optics and Quantum Information Austrian Academy of Sciences. The new field is quantum simulation based on trapped ions, main completed projects including quantum chemistry simulation and dynamical phase transitions. In 2018, he received the Newton International Fellowship to move to Oxford University as a researcher assistant, mainly focus on Quantum state engineering of hybrid spin-mechanical quantum systems.