Variable electrostatic transformer: controllable coupling of two charge qubits

TL;DR

This paper introduces a variable electrostatic transformer that enables controllable coupling between two charge qubits, allowing dynamic adjustment of interaction strength for quantum computing applications.

Contribution

It presents a novel method to control qubit coupling via a discretized curvature of a Josephson junction's energy band, enabling positive, negative, or zero coupling.

Findings

Calculated the charging diagram showing coupling transition from positive to negative.

Demonstrated potential for constructing a phase gate using the controllable coupling.

Showed the feasibility of dynamic coupling control in charge qubits.

Abstract

We propose and investigate a novel method for the controlled coupling of two Josephson charge qubits by means of a variable electrostatic transformer. The value of the coupling capacitance is given by the discretized curvature of the lowest energy band of a Josephson junction, which can be positive, negative, or zero. We calculate the charging diagram of the two-qubit system that reflects the transition from positive to negative through vanishing coupling. We also discuss how to construct a phase gate making use of the controllable coupling.