[论文解读] Tomography of Entangled Macroscopic Mechanical Objects

Shlomi Kotler, G. A. Peterson+10 more|arXiv (Cornell University)|Apr 12, 2020

Mechanical and Optical Resonators参考文献 44被引用 9

一句话总结

该论文通过超导机电电路和脉冲微波协议，实现了两个宏观机械鼓膜（每个70 pg）的确定性基态冷却、纠缠以及量子态层析成像。关键成果是通过近乎量子极限的联合位置与动量测量，实现了无需噪声扣除的纠缠验证，从而实现了对大质量纠缠量子系统的高保真度表征。

ABSTRACT

Observing quantum mechanics at the macroscopic scale has captured the attention of scientists and the imagination of the public for more than a century. While quantum mechanics was conceived in the context of electrons and atoms, the ability to observe its properties on ever more macroscopic systems holds great promise for fundamental research and technological applications. Therefore, researchers have been preparing larger material systems in interesting quantum states and, in particular, entangled states of separate mechanical oscillators[1-3]. As these quantum devices move from demonstrations to applications, their full potential can only be realized by combining entanglement generation with an efficient measurement of the joint mechanical state. Unfortunately, such a high level of control and measurement can expose the system to undesired interactions with its environment, a problem that becomes more pronounced at the macroscopic scale. Here, using a superconducting electromechanical circuit and a pulsed microwave protocol, we ground-state cool, entangle and perform state tomography of two mechanical drumheads with masses of 70 pg. Entanglement is generated deterministically and is followed by a nearly quantum-limited measurement of the positions and momentums of both mechanical oscillators. From these efficient measurements, the resulting tomography demonstrates entanglement without noise subtraction. Highly entangled, massive quantum systems, as demonstrated here, are uniquely poised to address fundamental tests of quantum mechanics[4,5], enable force sensing beyond the standard quantum limit[6], and possibly serve as long-lived nodes of a future quantum network[7,8].

研究动机与目标

• 在纳克量级的两个宏观机械振子之间实现确定性纠缠。
• 对两个振子实现高保真度、近乎量子极限的联合位置与动量测量。
• 在无需噪声扣除的情况下执行纠缠机械系统的量子态层析成像，确保纠缠的直接观测。
• 为宏观系统中的量子力学基础检验，以及在量子传感和量子网络中的应用提供支持。
• 通过精确的控制与测量协议，应对宏观量子系统中环境退相干的挑战。

提出的方法

• 利用超导机电电路，将两个机械鼓膜（每个70 pg）耦合至微波腔。
• 采用脉冲微波协议，确定性地将鼓膜冷却至其量子基态。
• 通过微波脉冲施加受控相互作用，生成两个机械振子之间的纠缠。
• 利用量子极限的本振检测对微波输出进行位置与动量的联合测量。
• 基于测量的正交分量数据，通过量子态层析成像重构完整量子态。
• 采用一种避免噪声扣除的协议，确保测量保真度仅受量子噪声限制，而非经典噪声。

实验结果

研究问题

• RQ1 是否可以在质量为70 pg的两个宏观机械振子之间确定性地生成纠缠？
• RQ2 是否可能在不依赖噪声扣除的情况下，对如此大质量的系统执行量子态层析成像？
• RQ3 在宏观机械系统中，联合位置与动量测量是否可实现近乎量子极限的精度？
• RQ4 在真实环境相互作用下，大质量机械振子中的纠缠具有多强的鲁棒性？
• RQ5 此类系统是否可作为未来量子网络中的长寿命节点，或实现超越标准量子极限的力传感？

主要发现

• 作者成功使用脉冲微波协议，将两个70 pg的机械鼓膜冷却至其量子基态。
• 通过量子态层析成像，确定性地生成并验证了两个鼓膜之间的纠缠。
• 层析成像重构结果表明，无需噪声扣除即可确认纠缠，证实了测量过程的保真度。
• 位置与动量的联合测量实现了近乎量子极限的灵敏度，表明经典噪声污染极低。
• 该系统在宏观系统中进行量子力学基础检验方面展现出高度潜力。
• 结果支持使用大质量机械振子作为未来量子网络节点以及实现量子增强传感的可行性。