QCD Labs, QTF Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland.
IQM, Espoo, Finland.
Nature. 2020 Oct;586(7827):47-51. doi: 10.1038/s41586-020-2753-3. Epub 2020 Sep 30.
Radiation sensors based on the heating effect of absorbed radiation are typically simple to operate and flexible in terms of input frequency, so they are widely used in gas detection, security, terahertz imaging, astrophysical observations and medical applications. Several important applications are currently emerging from quantum technology and especially from electrical circuits that behave quantum mechanically, that is, circuit quantum electrodynamics. This field has given rise to single-photon microwave detectors and a quantum computer that is superior to classical supercomputers for certain tasks. Thermal sensors hold potential for enhancing such devices because they do not add quantum noise and they are smaller, simpler and consume about six orders of magnitude less power than the frequently used travelling-wave parametric amplifiers. However, despite great progress in the speed and noise levels of thermal sensors, no bolometer has previously met the threshold for circuit quantum electrodynamics, which lies at a time constant of a few hundred nanoseconds and a simultaneous energy resolution of the order of 10h gigahertz (where h is the Planck constant). Here we experimentally demonstrate a bolometer that operates at this threshold, with a noise-equivalent power of 30 zeptowatts per square-root hertz, comparable to the lowest value reported so far, at a thermal time constant two orders of magnitude shorter, at 500 nanoseconds. Both of these values are measured directly on the same device, giving an accurate estimation of 30h gigahertz for the calorimetric energy resolution. These improvements stem from the use of a graphene monolayer with extremely low specific heat as the active material. The minimum observed time constant of 200 nanoseconds is well below the dephasing times of roughly 100 microseconds reported for superconducting qubits and matches the timescales of currently used readout schemes, thus enabling circuit quantum electrodynamics applications for bolometers.
基于吸收辐射的热效应的辐射传感器通常操作简单，输入频率灵活，因此它们被广泛应用于气体检测、安全、太赫兹成像、天体物理观测和医疗应用。目前，从量子技术，特别是从表现出量子力学行为的电路中，出现了几个重要的应用，即电路量子电动力学。该领域催生了单光子微波探测器和量子计算机，在某些任务上，量子计算机优于经典超级计算机。热传感器具有增强此类设备的潜力，因为它们不会增加量子噪声，而且比常用的行波参量放大器更小、更简单，功耗约低六个数量级。然而，尽管热传感器在速度和噪声水平方面取得了巨大进展，但以前没有任何测辐射热计达到电路量子电动力学的阈值，该阈值的时间常数为几百纳秒，同时能量分辨率约为 10h 吉赫兹（其中 h 是普朗克常数）。在这里，我们通过实验证明了一种工作在该阈值下的测辐射热计，其噪声等效功率为 30 zeptowatts 每平方根赫兹，与迄今为止报道的最低值相当，热时间常数短两个数量级，为 500 纳秒。这两个值都是在同一个器件上直接测量的，这对热计量能量分辨率的准确估计为 30h 吉赫兹。这些改进源于使用单层石墨烯作为活性材料，其比热极低。观察到的最小时间常数为 200 纳秒，远低于超导量子比特报道的约 100 微秒的退相时间，与当前使用的读出方案的时间尺度相匹配，从而为测辐射热计的电路量子电动力学应用铺平了道路。
