Photon-activated electron hopping in a single-electron trap enhanced by Josephson radiation

Using a Josephson junction interferometer (DC SQUID) as a microwave source for irradiating a single-electron trap, both devices fabricated on the same chip, we study the process of photon-assisted tunneling as an effective mechanism of single photon detection. High sensitivity down to a very small oscillation amplitude $v_{\mathrm{J}}\sim$ 10 nV$\ll E_{\rm act} \lesssim hf_{\rm J}$anddowntolowphotonabsorptionrates$\Gamma_{\rm ph} \sim$ (1–50)Hz, as well as a clear threshold type of operation with an activation energy $E_{\mathrm{a}\mathrm{c}\mathrm{t}}\sim$ 400 $\mu$eV, are demonstrated for the trap with respect to the microwave photons of frequency $f_{\mathrm{J}}\sim$ (100–200)GHz. Tunable generation is demonstrated with respect to the power and frequency of the microwave signal produced by the SQUID source biased within the subgap voltage range. A much weaker effect is observed at the higher junction voltages along the quasiparticle branch of the $I-V$ curve; this response mostly appears due to the recombination phonons.