Generation of discord through a remote joint continuous variable measurement

TL;DR

This paper demonstrates how weak joint measurements on two remote qubits can generate quantum discord, using a circuit-QED setup with a Josephson Parametric Converter to erase single-qubit information and produce quantum correlations.

Contribution

It introduces a method to generate quantum discord through remote joint measurements with a JPC, erasing single-qubit info and aligning with theoretical models.

Findings

Quantum discord can be generated via weak joint measurements.

The JPC effectively erases single-qubit information.

Experimental results match theoretical predictions.

Abstract

In quantum mechanics, continuously measuring an observable steers the system into one eigenstate of that observable. This property has interesting and useful consequences when the observable is a joint property of two remotely separated qubits. In particular, if the measurement of the two-qubit joint observable is performed in a way that is blind to single-qubit information, quantum back-action generates correlation of the discord type even if the measurement is weak and inefficient. We demonstrate the ability to generate these quantum correlations in a circuit-QED setup by performing a weak joint readout of two remote, non-interacting, superconducting transmon qubits using the two non-degenerate modes of a Josephson Parametric Converter (JPC). Single-qubit information is erased from the output in the limit of large gain and with properly tailored cavity drive pulses. Our results of the measurement of discord are in quantitative agreement with theoretical predictions, and demonstrate the utility of the JPC as a which-qubit information eraser.