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 vJ∼10 nV≪Eact≲hfJ and down to low photon absorption rates Γph ∼ (1–50) Hz, as well as a clear threshold type of operation with an activation energy Eact ∼ 400 μeV, is demonstrated for the trap with respect to the microwave photons of frequency fJ ∼ (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.