Reading-out the state inductively and microwave spectroscopy of an interferometer-type charge qubit

TL;DR

This paper demonstrates an experimental setup for reading out an interferometer-type charge qubit using microwave spectroscopy, revealing energy level dynamics through inductance measurements.

Contribution

The work introduces a novel interferometer-type charge qubit with inductive readout via a tank circuit, enabling detailed spectroscopy of energy levels.

Findings

Measured energy gap varies with quasicharge

Observed inductance changes due to energy level redistribution

Extracted Josephson phase dependence on quasicharge

Abstract

We implemented experimentally an interferometer-type charge qubit consisting of a single-Cooper-pair transistor closed by a superconducting loop that is in flip-chip configuration inductively coupled to a radio frequency tank circuit. The tank permits to readout the qubit state, acting as inductance measuring apparatus. By applying continuous microwave power to the quantum device, we observed inductance alterations caused by redistributions of the energy level populations. From the measured data, we extracted the energy gap between ground and upper levels as a function of the transistor quasicharge as well as the Josephson phase across both junctions.