Xu C, Wang S G, Feng Y Y, Zhao L, Wang L J
Joint Institute for Measurement Science (JMI), Tsinghua University, Beijing 100084, China.
Department of Physics, Tsinghua University, Beijing 100084, China.
Sci Rep. 2016 Jun 30;6:28169. doi: 10.1038/srep28169.
Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ(-1/2). Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ(-1) rule. A mean sensitivity of 240 from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks.
利用原子内禀态的相干叠加进行量子测量具有绝对测量的优势，并且能够形成计量标准。一个例子是通过监测原子自旋的拉莫尔进动来进行磁场的绝对测量，另一个例子是拉姆齐型原子钟。然而，在几乎所有的相干量子测量中，精度都受到相干时间的限制，超过这个时间，不确定性仅按τ^(-1/2)减小。在这里我们表明，通过无损测量拉莫尔进动的相位并通过光泵浦再生相干性，自持的拉莫尔进动信号可以无限持续。因此，磁力计的精度按照快得多的τ^(-1)规则随时间增加。实现了从1赫兹到10赫兹平均灵敏度为240，接近散粒噪声水平。这种相干性再生方法在提高原子钟性能方面也可能会有重要应用。
