Spectroscopy of capacitively coupled Josephson-junction qubits

TL;DR

This paper investigates a coupled Josephson-junction qubit system, demonstrating how its energy levels can be tuned and measured spectroscopically to facilitate the creation and detection of entangled multiqubit states.

Contribution

It introduces a method to control and analyze coupled Josephson-junction qubits using spectroscopic techniques, advancing quantum circuit design.

Findings

Energy levels are tunable via junction bias currents.

Spectroscopy can detect entangled multiqubit states.

Numerical analysis confirms controllable coupling in the system.

Abstract

We show that two capacitively-coupled Josephson junctions, in the quantum limit, form a simple coupled qubit system with effective coupling controlled by the junction bias currents. We compute numerically the energy levels and wave functions for the system, and show how these may be tuned to make optimal qubits. The dependence of the energy levels on the parameters can be measured spectroscopically, providing an important experimental test for the presence of entangled multiqubit states in Josephson-junction based circuits.