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

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.

8 pages, 5 figures. Replaced version includes one additional reference, and figures which are better suited to grayscale