Fig. 1: Dirac-fermion single-photon bolometer.
From: Thermal detection of single photons using Dirac fermions
A Illustration of the experiment. A photon is absorbed on one end of the graphene heating the electrons. The hot electrons then diffuse throughout the graphene while dissipating into the lattice via electron-phonon coupling. This diffusion and dissipation is determined by the geometry of the device, the base temperature and the electron density (which is contolled by an electrostatic backgate voltage, Vg. Inset: Junction voltage VJJ as a function of time. When the photon is absorbed, the junction switches from superconducting (SC) to resistive causing a voltage drop across the junction corresponding to the product of the switching current, Is and normal state resistance Rn. The device is then reset to the superconducting state. B Optical image of one of the Dirac-fermion single photon bolometers (SPBs). Scale bar is 5 μm. C The 2D reflectometry measurement of the device at low temperature. D Switching rate Γmeas vs. current bias Ib for laser on (red) and off (blue). The mean value of quantum efficiency, η, in the plateau from 2.7 μA < Ib < 3 μA with 1 fW of laser power is 0.77 ± 0.08. Error bars correspond to the standard deviation in Γmeas over multiple runs. Inset: Current-biased Josephson junction (JJ) can be described as a macroscopic quantum phase particle (of phase φ) subjected to a tilted-washboard potential in the Resistively Capacitance Shunted Junction model. When dark, the junction is nominally in the macroscopic quantum tunneling (MQT) regime, however the photon raises the temperature of the junction causing a thermally activated (TA) switching event over the barrier potential ΔU. E Junction switching probability vs. laser power at Vg = 2 V and Ib/〈Is〉 ≃ 0.87. The junction switching probability is linearly proportional to the laser power (see orange dashed line highlighting the linear trend), confirming a single photon can switch the Josephson junction from superconducting to resistive. Deviation from the linear trend at lower powers is due to dark counts. Inset: Histogram of switching events with 60 aW (blue) and 500 aW (red) of laser powers adhere to Poissonian statistics. Error bars correspond to the standard deviation in switching probability over multiple runs.
