2015/10/20 by A. A. Boris, V. M. Krasnov
Physics and Astronomy · #Computer science #Condensed matter physics #Engineering physics #Microwave #Physics #Physics of Superconductivity and Magnetism #Quantization (signal processing) #Quantum mechanics #Superconducting and THz Device Technology #Superconductivity #Superconductivity in MgB2 and Alloys #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.92.174506
published as Phys. Rev. B 92, 174506 (2015) · 5 pages 2 figures
arxiv created 2015/10/20 · openalex publication_date 2015/11/04 · arxiv updated 2018/02/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We study experimentally photon-assisted tunneling in Nb/AlOx/Nb Josephson junctions. We perform a quantitative calibration of the microwave field inside the junction. This allows direct verification of the quantum efficiency of microwave photon detection, which corresponds to tunneling of one electron per one absorbed microwave photon. We observe that voltages of photon-assisted tunneling steps vary both with the microwave power and the tunneling current. However, this variation is not monotonous but staircaselike. The phenomenon is caused by mutual locking of positive and negative step series. A similar locking is observed with Shapiro steps. As a result, the superconducting gap assumes quantized values equal to multiples of the quarter of the photon energy. The quantization is a manifestation of nonequilibrium tuning (suppression or enhancement) of superconductivity by the microwave field.