Microwave photon detection by an Al Josephson junction

Abstract

An aluminium Josephson junction (JJ), with a critical current suppressed by a factor of three compared with the maximal value calculated from the gap, is experimentally investigated for application as a threshold detector for microwave photons. We present the preliminary results of measurements of the lifetime of the superconducting state and the probability of switching by a 9 GHz external signal. We found an anomalously large lifetime, not described by the Kramers’ theory for the escape time over a barrier under the influence of fluctuations. We explain it by the phase diffusion regime, which is evident from the temperature dependence of the switching current histograms. Therefore, phase diffusion allows for a significant improvement of the noise immunity of a device, radically decreasing the dark count rate, but it will also decrease the single-photon sensitivity of the considered threshold detector. Quantization of the switching probability tilt as a function of the signal attenuation for various bias currents through the JJ is observed, which resembles the differentiation between N and N + 1 photon absorption.

Josephson Junctions as Single Microwave Photon Counters: Simulation and Characterization

“…The best performances of currently running axion experiments were achieved with quantum-limited devices, such as superconducting quantum interference devices (SQUIDs) and Josephson parametric amplifiers (JPAs) [17][18][19]26,47], but efforts have been put toward counting single photons from axion interactions [42,46,48,49]. The reason is clear from [50]: working at higher frequencies while having a good scan rate at the same time requires single photon counters, which have better noise performances with respect to linear amplifiers above about 10 GHz.…”

“…Devices based on qubits have dark-counts rates ν dc ∼ p err /t qubit where p err ∼ 10% is a typical qubit readout error and t qubit ∼ 10 µs is a typical qubit decoherence time, corresponding to ν dc ∼ 10 kHz. On the contrary, switching devices, such as those based on current-biased Josephson junctions (CBJJ) [41,42,48], have the potential to reach dark counts at mHz rates. However, previous realization of a photon counter based on CBJJ [41] was operated in a regime with far higher dark counts, and no clear evidence exists that dark counts can be lowered without affecting the device efficiency.…”

Approaching microwave photon sensitivity with Al Josephson junctions

“…Superconductor-insulator-superconductor (SIS) junctions have not been seriously considered previously for the role of detectors of single photons in the microwave range, despite sporadic works showing such a possibility [1][2][3][4][5][6][7]. Recently, the interest in microwave SPCs has been increased [8,9] due to new experi- ments of dark matter search [10][11][12] and the corresponding program initiated by INFN in Italy [13][14][15][16][17][18][19][20][21][22].…”

Nonmonotonous temperature dependence of Shapiro steps in YBCO grain boundary junctions

“…High-temperature superconducting (HTSC) Josephson junctions (JJs) are of great interest since many physical properties can be observed in dynamics during the changing the temperature within a wide range from nitrogen temperatures down to sub-kelvin, such as the phase diffusion regime [1][2][3], evidence for a minigap [4], and low-noise nano-junctions [5]. Such abilities raise not only fundamental interest in HTSC JJs but also an active search for ways to practically use such JJs.…”