Very high frequency spectroscopy and tuning of a single-Cooper-pair-transistor with an on-chip generator

TL;DR

This paper demonstrates high-frequency spectroscopy of a single-Cooper-pair transistor (SCPT) using an on-chip generator, revealing control over energy levels, quasiparticle poisoning, and supercurrent through high-energy photon interactions.

Contribution

It introduces a method to probe and control SCPT energy levels and quasiparticle poisoning using high-frequency irradiation from an on-chip Josephson junction generator.

Findings

High-energy photons induce transitions beyond the first energy levels.

Photon irradiation can both increase and decrease the SCPT's supercurrent.

Control of quasiparticle poisoning via high-frequency excitation.

Abstract

We consider a single Cooper pair transistor (SCPT) coupled capacitively to a voltage biased Josephson junction, used as a high frequency generator. Thanks to the high energy of photons generated by the Josephson junction, transitions between energy levels, not limited to the first two levels, were induced and the effect of this irradiation on the DC Josephson current of the SCPT was measured. This allows to probe the phase and gate bias dependence of energy levels of the SCPT at high energy. Because the energies of photons can be higher than the superconducting gap we can induce not only transfer of Cooper pairs but also transfer of quasi-particles through the island of the SCPT, thus controlling the poisoning of the SCPT. We show that this can both decrease and increase the average Josephson energy of the SCPT : its supercurrent is then controlled by high-frequency