Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark.
Center for Hybrid Quantum Networks, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark.
Phys Rev Lett. 2019 Oct 18;123(16):163601. doi: 10.1103/PhysRevLett.123.163601.
Continuous weak measurement allows localizing open quantum systems in state space and tracing out their quantum trajectory as they evolve in time. Efficient quantum measurement schemes have previously enabled recording quantum trajectories of microwave photon and qubit states. We apply these concepts to a macroscopic mechanical resonator, and we follow the quantum trajectory of its motional state conditioned on a continuous optical measurement record. Starting with a thermal mixture, we eventually obtain coherent states of 78% purity-comparable to a displaced thermal state of occupation 0.14. We introduce a retrodictive measurement protocol to directly verify state purity along the trajectory, and we furthermore observe state collapse and decoherence. This opens the door to measurement-based creation of advanced quantum states, as well as potential tests of gravitational decoherence models.
连续弱测量允许在状态空间中对开放量子系统进行定位，并在它们随时间演化时追踪它们的量子轨迹。以前，有效的量子测量方案已经能够记录微波光子和量子位状态的量子轨迹。我们将这些概念应用于宏观机械谐振器，并跟踪其运动状态的量子轨迹，条件是连续的光学测量记录。从热混合物开始，我们最终获得了 78%纯度的相干态——可与占据 0.14 的位移热态相媲美。我们引入了一种回溯测量协议，直接沿轨迹验证状态纯度，并且我们还观察到状态塌缩和退相干。这为基于测量的先进量子态的创建以及引力退相干模型的潜在测试开辟了道路。
