Non-demolition Adiabatic Measurement of the Phase Qubit State

TL;DR

This paper proposes a non-demolition, adiabatic measurement method for phase qubits using a coupled resonator to detect phase shifts, achieving high fidelity and rapid measurement times.

Contribution

It introduces a novel adiabatic measurement technique for phase qubits that enhances fidelity and speed, with detailed analysis of parameter requirements.

Findings

Measurement fidelity of 0.9989 achieved

Measurement time approximately 100 ns

Phase difference increases at 0.0044 rad/ns

Abstract

An adiabatic method for a single-shot non-demolition measurement of the phase qubit is suggested. The qubit is inductively coupled to a low-frequency resonator, which in turn is connected with a classical measurement device (phase meter). The resonator drives adiabatic oscillations of the supercurrent in the qubit loop. The back reaction of the qubit loop on the resonator depends on the qubit state. Measuring the phase shift of the resonator's oscillations one can determine the state of the qubit. Numerical computations with available experimental parameters show that the phase difference between the two qubit states increases at a rate of 0.0044 rad/ns with the fidelity of about 0.9989 and the measurement time of about 100 ns. The fidelity of the measurement is estimated taking into consideration possible quantum transitions inside and outside the qubit manifold. An increase of the phase difference is possible but it is linked to a reduction of the fidelity. The requirements for the reproducibility of the qubit and resonator parameters are formulated.