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Klaus Mølmer

Spin squeezing of 1011 atoms by prediction and retrodiction measurements

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  • Han Bao, Fudan University
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  • Junlei Duan, Fudan University
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  • Shenchao Jin, Fudan University
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  • Xingda Lu, Fudan University
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  • Pengxiong Li, Fudan University
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  • Weizhi Qu, Fudan University
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  • Mingfeng Wang, Fudan University, Wenzhou University
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  • Irina Novikova, College of William and Mary
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  • Eugeniy E. Mikhailov, College of William and Mary
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  • Kai-Feng Zhao, Fudan University
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  • Klaus Mølmer
  • Heng Shen, Shanxi University, University of Oxford
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  • Yanhong Xiao, Fudan University, Shanxi University
Nature | Vol 581 | 14 May 2020 | 159ArticleSpin squeezing of 1011 atoms by prediction and retrodiction measurementsHan Bao1, Junlei Duan1, Shenchao Jin1, Xingda Lu1, Pengxiong Li1, Weizhi Qu1, Mingfeng Wang1,2, Irina Novikova3, Eugeniy E. Mikhailov3, Kai-Feng Zhao4, Klaus Mølmer5 ✉, Heng Shen6,7 ✉ & Yanhong Xiao1,6 ✉The measurement sensitivity of quantum probes using N uncorrelated particles is restricted by the standard quantum limit1, which is proportional to N1/. This limit, however, can be overcome by exploiting quantum entangled states, such as spin-squeezed states2. Here we report the measurement-based generation of a quantum state that exceeds the standard quantum limit for probing the collective spin of 1011 rubidium atoms contained in a macroscopic vapour cell. The state is prepared and verified by sequences of stroboscopic quantum non-demolition (QND) measurements. We then apply the theory of past quantum states3,4 to obtain spin state information from the outcomes of both earlier and later QND measurements. Rather than establishing a physically squeezed state in the laboratory, the past quantum state represents the combined system information from these prediction and retrodiction measurements. This information is equivalent to a noise reduction of 5.6 decibels and a metrologically relevant squeezing of 4.5 decibels relative to the coherent spin state. The past quantum state yields tighter constraints on the spin component than those obtained by conventional QND measurements. Our measurement uses 1,000 times more atoms than previous squeezing experiments5–10, with a corresponding angular variance of the squeezed collective spin of 4.6 × 10−13 radians squared. Although this work is rooted in the foundational theory of quantum measurements, it may find practical use in quantum metrology and quantum parameter estimation, as we demonstrate by applying our protocol to quantum enhanced atomic magnetometry.
Sider (fra-til)159-163
Antal sider5
StatusUdgivet - 2020

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