Collective measurements can project a system into an entangled state withenhanced sensitivity for measuring a quantum phase, but measurement back-actionhas limited previous efforts to only modest improvements. Here we use acollective measurement to produce and directly observe, with no backgroundsubtraction, an entangled, spin-squeezed state with phase resolution improvedin variance by a factor of 10.5(1.5), or 10.2(6) dB, compared to the initiallyunentangled ensemble of N = 4.8 x 10^5 87Rb atoms. The measurement uses acavity-enhanced probe of an optical cycling transition to mitigate back-actionassociated with state-changing transitions induced by the probe. This workestablishes collective measurements as a powerful technique for generatingentanglement for precision measurement, with potential impacts in biologicalsensing, communication, navigation, and tests of fundamental physics.
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机译：集体测量可以将系统投射到纠缠态，并具有增强的灵敏度来测量量子相位，但是测量反向作用将先前的工作仅限于适度的改进。在这里，我们使用一个集体测量来产生并直接观察到一个纠缠的自旋压缩状态，该状态的相位分辨率与原始的N的无纠缠集合相比，方差提高了10.5（1.5）或10.2（6）dB，没有背景扣除。 = 4.8 x 10 ^ 5 87Rb原子。该测量使用了光循环跃迁的腔增强探针，以减轻与该探针引起的状态变化跃迁相关的反向作用。这项工作将集体测量确立为一种产生纠缠度以进行精确测量的有力技术，对生物传感，通信，导航和基础物理测试可能产生影响。
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