Quantization of the superconducting energy gap in an intense microwave field

Abstract

We study photon assisted tunneling in Nb/AlOx/Nb Josephson junctions. A quantitative calibration of the microwave field in the junction allowed direct verification of the quantum efficiency of microwave photon detection by the junctions. 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 staircase-like. 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.

5 pages 2 figures

References in corpus (5)

• Non-Poissonian Quantum Jumps of a Fluxonium Qubit due to Quasiparticle Excitations
• Evidence of a nonequilibrium distribution of quasiparticles in the microwave response of a superconducting aluminium resonator
• Excitation of superconducting qubits from hot non-equilibrium quasiparticles
• Dynamic parity recovery in a strongly driven Cooper-pair box
• Non-equilibrium probing of two-level charge fluctuators using the step response of a single electron transistor

Cited by in corpus (3)

• Nonadiabatic Landau-Zener-Stückelberg-Majorana transitions, dynamics, and interference
• Quantifying quantum coherence of multiple-charge states in tunable Josephson junctions
• Dynamics of dissipative Landau-Zener transitions in an anisotropic three-level system