Initialization by measurement of a two-qubit superconducting circuit

TL;DR

This paper presents a high-fidelity, non-destructive initialization method for two superconducting qubits using joint measurement and postselection, improving state preparation fidelity over passive methods.

Contribution

The authors introduce a measurement-based initialization technique for two-qubit superconducting circuits that achieves higher fidelity through joint measurement and postselection.

Findings

Achieved 98.8% fidelity to the ground state

Enhanced measurement discrimination with Josephson parametric amplification

Outperformed passive initialization methods

Abstract

We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations non-destructively and with 98.1% fidelity. Measurement and postselection of a steady-state mixture with 4.7% residual excitation per qubit achieve 98.8% fidelity to the ground state, thus outperforming passive initialization.