Tunable joint measurements in the dispersive regime of cavity QED

TL;DR

This paper introduces a tunable homodyne detection method for joint qubit measurements in cavity QED, enabling flexible extraction of single- or multi-qubit information with high fidelity.

Contribution

It presents a novel approach to tune the measurement from single-qubit to multi-qubit properties in cavity QED using homodyne detection, along with a reduced stochastic master equation.

Findings

Achieved near-unit probability of generating entanglement from unentangled states.

Demonstrated parity measurement capability for two qubits.

Provided a theoretical framework for tunable joint measurements.

Abstract

Joint measurements of multiple qubits have been shown to open new possibilities for quantum information processing. Here, we present an approach based on homodyne detection to realize such measurements in the dispersive regime of cavity/circuit QED. By changing details of the measurement, the readout can be tuned from extracting only single-qubit to only multi-qubit properties. We obtain a reduced stochastic master equation describing this measurement and its effect on the qubits. As an example, we present results showing parity measurements of two qubits. In this situation, measurement of an initially unentangled state can yield with near unit probability a state of significant concurrence.