[论文解读] Optically heralded microwave photons

Wentao Jiang, Felix M. Mayor+6 more|arXiv (Cornell University)|Oct 19, 2022

Mechanical and Optical Resonators被引用 4

一句话总结

该论文展示了一种量子转导器，通过检测与微波光子纠缠的光学光子来后示微波光子，利用GHz频段的纳米机械谐振器，通过光机械和压电相互作用将光学场与微波场耦合。该系统实现了5%的频率转换效率和15 Hz的后示速率，热噪声低于两个微波光子，为未来超导量子节点之间的远距离量子纠缠提供了可能。

ABSTRACT

A quantum network that distributes and processes entanglement would enable powerful new computers and sensors. Optical photons with a frequency of a few hundred terahertz are perhaps the only way to distribute quantum information over long distances. Superconducting qubits on the other hand, which are one of the most promising approaches for realizing large-scale quantum machines, operate naturally on microwave photons that have roughly $40,000$ times less energy. To network these quantum machines across appreciable distances, we must bridge this frequency gap and learn how to generate entanglement across widely disparate parts of the electromagnetic spectrum. Here we implement and demonstrate a transducer device that can generate entanglement between optical and microwave photons, and use it to show that by detecting an optical photon we add a single photon to the microwave field. We achieve this by using a gigahertz nanomechanical resonance as an intermediary, and efficiently coupling it to optical and microwave channels through strong optomechanical and piezoelectric interactions. We show continuous operation of the transducer with $5\%$ frequency conversion efficiency, and pulsed microwave photon generation at a heralding rate of $15$ hertz. Optical absorption in the device generates thermal noise of less than two microwave photons. Joint measurements on optical photons from a pair of transducers would realize entanglement generation between distant microwave-frequency quantum nodes. Improvements of the system efficiency and device performance, necessary to realize a high rate of entanglement generation in such networks are within reach.

研究动机与目标

• 通过弥合用于通信的光学光子与用于超导量子比特的微波光子之间的频率差距，实现远距离量子网络通信。
• 开发一种低噪声、高效率的量子转导器，通过机械中介将光学光子转换为微波光子。
• 通过光学探测实现后示微波光子的生成，从而在混合量子网络中实现可扩展的量子纠缠分发。
• 通过在混合Si-LN/NbTiN平台中集成压电和光机械转换，最小化热噪声并优化耦合效率。

提出的方法

• 一种混合转导器将硅光子Fabry-Pérot腔与铌酸锂（Si-LN）纳米机械谐振器以及氮化铌钛（NbTiN）微波谐振器集成。
• 通过光机械谐振腔中的辐射压力实现自发布四波混频，生成纠缠的光学与微波频率声子对。
• 通过与高阻抗微波波导的强压电耦合，将机械振动转换为微波信号。
• 通过单光子探测器在探测到其光学伙伴时后示微波光子的存在。
• 通过芯片间打线键合将转导器芯片与微波芯片连接，并采用集总元件电路模型以优化耦合效率。
• 采用线性检测层析成像技术表征微波场，并验证单个光子的加入。

Figure 1: Transducer schematics and implementation. a , Definition of modes in the transducer and the coupling rates between the modes and channels. b , Physical implementation of the coupling mechanism and the possible conversion processes. The silicon optical mode is represented by the blue Fabry-

实验结果

研究问题

• RQ1 能否在混合光机械系统中通过光学探测以高保真度后示单个微波光子？
• RQ2 在具有低热噪声的纳米机械转导器中，可实现的最大频率转换效率是多少？
• RQ3 打线键合的几何结构如何影响机械模与微波通道之间的耦合效率？
• RQ4 该转导器能否以足够稳定性连续运行，适用于量子网络应用？
• RQ5 微波输出中的热噪声水平是多少，它如何影响后示单光子态的保真度？

主要发现

• 转导器实现了5%的连续频率转换效率，证明了其在量子网络中的实际可行性。
• 实现了15 Hz的后示速率，证实了在光学探测时单个微波光子的生成。
• 光学吸收引起的热噪声低于两个微波光子，表明热串扰极低。
• 系统以约0.5的相干声子数运行，表明对机械模具有强控制能力。
• 在垂直堆叠芯片结构中采用短单根打线（0.75 mm）可最大化耦合效率并最小化寄生电容。
• 对两个此类转导器的光学光子进行联合测量，可实现远距离微波频率量子节点间的量子纠缠分发。

Figure 2: Transducer characterization. a , Electromagnetically induced transparency (EIT). Top: schematic of the measurement allowing us to extract the optical reflection $S_{\text{oo}}$ with a red detuned pump. Bottom: measurement of the phase of the reflected optical sideband (blue) with the EIT v