Department of Physics, Harvard University, Cambridge, MA, USA.
Department of Physics, Pohang University of Science and Technology, Pohang, Republic of Korea.
Nature. 2020 Oct;586(7827):42-46. doi: 10.1038/s41586-020-2752-4. Epub 2020 Sep 30.
Sensitive microwave detectors are essential in radioastronomy, dark-matter axion searches and superconducting quantum information science. The conventional strategy to obtain higher-sensitivity bolometry is the nanofabrication of ever smaller devices to augment the thermal response. However, it is difficult to obtain efficient photon coupling and to maintain the material properties in a device with a large surface-to-volume ratio owing to surface contamination. Here we present an ultimately thin bolometric sensor based on monolayer graphene. To utilize the minute electronic specific heat and thermal conductivity of graphene, we develop a superconductor-graphene-superconductor Josephson junction bolometer embedded in a microwave resonator with a resonance frequency of 7.9 gigahertz and over 99 per cent coupling efficiency. The dependence of the Josephson switching current on the operating temperature, charge density, input power and frequency shows a noise-equivalent power of 7 × 10 watts per square-root hertz, which corresponds to an energy resolution of a single 32-gigahertz photon, reaching the fundamental limit imposed by intrinsic thermal fluctuations at 0.19 kelvin. Our results establish that two-dimensional materials could enable the development of bolometers with the highest sensitivity allowed by the laws of thermodynamics.
敏感的微波探测器在射电天文学、暗物质轴子搜索和超导量子信息科学中是必不可少的。为了获得更高灵敏度的量热计，传统的策略是通过纳米制造来制作更小的器件来增强热响应。然而，由于表面污染，在具有大表面积与体积比的器件中，很难获得有效的光子耦合并保持材料性能。在这里，我们提出了一种基于单层石墨烯的终极超薄量热传感器。为了利用石墨烯微小的电子比热和热导率，我们开发了一种超导-石墨烯-超导约瑟夫森结量热计，嵌入到一个共振频率为 79 千兆赫、耦合效率超过 99%的微波谐振器中。约瑟夫森开关电流对工作温度、电荷密度、输入功率和频率的依赖关系表明，噪声等效功率为 7×10 瓦/根号赫兹，这对应于单个 32 千兆赫光子的能量分辨率，达到了 0.19 开尔文下由固有热波动施加的基本极限。我们的结果表明，二维材料可以实现由热力学定律允许的最高灵敏度的量热计的发展。
