Graphene-based Josephson junction microwave bolometer

TL;DR

This paper introduces a graphene-based Josephson junction microwave bolometer with high sensitivity and near fundamental thermal fluctuation limits, suitable for advanced radioastronomy and quantum applications.

Contribution

It develops a monolayer graphene superconductor-graphene-superconductor Josephson junction embedded in a microwave resonator, achieving high coupling efficiency and ultra-low noise equivalent power.

Findings

Achieved NEP of 7×10^{-19} W/Hz^{1/2}

Energy resolution capable of detecting single 32 GHz photons

Reaches thermal fluctuation limit at 0.19 K

Abstract

Sensitive microwave detectors are critical instruments in radioastronomy, dark matter axion searches, and superconducting quantum information science. The conventional strategy towards higher-sensitivity bolometry is to nanofabricate an ever-smaller device to augment the thermal response. However, this direction is increasingly more difficult to obtain efficient photon coupling and maintain the material properties in a device with a large surface-to-volume ratio. Here we advance this concept to an ultimately thin bolometric sensor based on monolayer graphene. To utilize its minute electronic specific heat and thermal conductivity, we develop a superconductor-graphene-superconductor (SGS) Josephson junction bolometer embedded in a microwave resonator of resonant frequency 7.9 GHz with over 99\% coupling efficiency. From the dependence of the Josephson switching current on the operating temperature, charge density, input power, and frequency, we demonstrate a noise equivalent power (NEP) of 7 $\times 10^{-19}$ W/Hz$^{1/2}$, corresponding to an energy resolution of one single photon at 32 GHz and reaching the fundamental limit imposed by intrinsic thermal fluctuation at 0.19 K.