QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland.
School of Engineering and Information Technology, UNSW Canberra, Canberra, ACT 2600, Australia.
Science. 2021 May 7;372(6542):625-629. doi: 10.1126/science.abf5389.
Quantum mechanics sets a limit for the precision of continuous measurement of the position of an oscillator. We show how it is possible to measure an oscillator without quantum back-action of the measurement by constructing one effective oscillator from two physical oscillators. We realize such a quantum mechanics-free subsystem using two micromechanical oscillators, and show the measurements of two collective quadratures while evading the quantum back-action by 8 decibels on both of them, obtaining a total noise within a factor of 2 of the full quantum limit. This facilitates the detection of weak forces and the generation and measurement of nonclassical motional states of the oscillators. Moreover, we directly verify the quantum entanglement of the two oscillators by measuring the Duan quantity 1.4 decibels below the separability bound.
量子力学为振荡器位置的连续测量精度设定了一个限制。我们通过从两个物理振荡器构建一个有效振荡器，展示了如何在不进行量子反作用测量的情况下测量振荡器。我们使用两个微机械振荡器实现了这样一个无量子力学的子系统，并在两个振荡器上都规避了 8 分贝的量子反作用，同时对两个振荡器的两个集体正交分量进行了测量，从而获得了总噪声，比全量子极限低 2 倍。这便于检测弱力以及产生和测量振荡器的非经典运动状态。此外，我们通过测量 Duan 量，直接验证了两个振荡器的量子纠缠，该测量值比可分离性边界低 1.4 分贝。
