Characterization of an entangled system of two superconducting qubits using a multiplexed capacitance readout

TL;DR

This paper demonstrates a scalable multiplexed quantum capacitance measurement technique to characterize entanglement in a two-qubit superconducting system, providing detailed spectroscopic and capacitance data.

Contribution

It introduces a scalable multiplexed measurement method for superconducting qubits and applies it to characterize entanglement in a two-qubit system.

Findings

Successfully measured ground-state quantum capacitance of two qubits

Estimated entanglement degree (concurrence) from capacitance data

Demonstrated scalability potential of the measurement technique

Abstract

We characterize a pair of Cooper-pair boxes coupled with a fixed capacitor using spectroscopy and measurements of the ground-state quantum capacitance. We use the extracted parameters to estimate the concurrence, or degree of entanglement between the two qubits. We also present a thorough demonstration of a multiplexed quantum capacitance measurement technique, which is in principle scalable to a large array of superconducting qubits.