Three-qubit direct dispersive parity measurement with Tunable Coupling Qubits

TL;DR

This paper proposes a method for direct three-qubit parity measurement using circuit QED, demonstrating how Tunable Coupling Qubits can overcome limitations faced with transmon qubits, enabling more effective quantum measurements.

Contribution

It introduces a novel approach employing Tunable Coupling Qubits to enable direct three-qubit parity measurement, overcoming issues with transmon-like qubits.

Findings

Tunable Coupling Qubits effectively cancel harmful coupling terms.

The analysis shows potential for optimal measurement performance.

The method improves the feasibility of multi-qubit parity measurements.

Abstract

We consider the direct three-qubit parity measurement scheme with two measurement resonators, using circuit quantum electrodynamics to analyze its functioning for several different types of superconducting qubits. We find that for the most common, transmon-like qubit, the presence of additional qubit-state dependent coupling terms of the two resonators hinders the possibility of performing the direct parity measurement. We show how this problem can be solved by employing the Tunable Coupling Qubit (TCQ) in a particular designed configuration. In this case, we effectively engineer the original model Hamiltonian by cancelling the harmful terms. We further develop an analysis of the measurement in terms of information gains and provide some estimates of the typical parameters for optimal operation with TCQs.