AC Josephson effect and resonant Cooper pair tunneling emission of a Cooper Pair Transistor

TL;DR

This paper reports on high-frequency emission measurements of a single Cooper pair transistor, demonstrating the AC Josephson effect and resonant tunneling phenomena through photon-assisted tunneling detection.

Contribution

It introduces a novel on-chip measurement technique for directly detecting the AC Josephson effect in a Cooper pair transistor.

Findings

Direct detection of the AC Josephson effect in a SCPT

Observation of Landau-Zener transitions with gate voltage

Analysis of resonant Cooper pair tunneling emission

Abstract

We measure the high-frequency emission of a single Cooper pair transistor(SCPT) in the regime where transport is only due to tunneling of Cooper pairs. This is achieved by coupling on-chip the SCPT to a superconductor-insulator-superconductor junction and by measuring the photon assisted tunneling current of quasiparticles across the junction. This technique allows a direct detection of the AC Josephson effect of the SCPT and provides evidence of Landau-Zener transitions for proper gate voltage. The emission in the regime of resonant Cooper pair tunneling is also investigated. It is interpreted in terms of transitions between charge states coupled by the Josephson effect.