Qubit Parity Measurement by Parametric Driving in Circuit QED

TL;DR

This paper introduces a hardware-efficient method for multi-qubit parity measurement in circuit QED using parametric driving, which simplifies quantum error correction by avoiding ancilla qubits and high-fidelity readout.

Contribution

It proposes a novel parity measurement technique based on bifurcation dynamics of a nonlinear oscillator, compatible with current circuit QED technology.

Findings

High-fidelity two- and four-qubit parity measurements demonstrated.

Method preserves parity eigenstates during measurement.

Potential for simplifying quantum error correction implementations.

Abstract

Multi-qubit parity measurements are essential to quantum error correction. Current realizations of these measurements often rely on ancilla qubits, a method that is sensitive to faulty two-qubit gates and which requires significant experimental overhead. We propose a hardware-efficient multi-qubit parity measurement exploiting the bifurcation dynamics of a parametrically driven nonlinear oscillator. This approach takes advantage of the resonator's parametric oscillation threshold which is a function of the joint parity of dispersively coupled qubits, leading to high-amplitude oscillations for one parity subspace and no oscillation for the other. We present analytical and numerical results for two- and four-qubit parity measurements with high-fidelity readout preserving the parity eigenpaces. Moreover, we discuss a possible realization which can be readily implemented with the current circuit QED experimental toolbox. These results could lead to significant simplifications in the experimental implementation of quantum error correction, and notably of the surface code.