Generating and verifying entangled itinerant microwave fields with efficient and independent measurements

TL;DR

This paper demonstrates the generation and verification of entangled propagating microwave fields using efficient, independent measurements, advancing quantum network capabilities with superconducting microwave systems.

Contribution

It introduces a method to generate and verify entangled microwave fields with high measurement efficiency and independence, enabling better quantum communication.

Findings

Successfully generated entangled microwave modes.

Measured entanglement witness and negativity confirming entanglement.

Achieved measurement efficiencies of over 25% for both channels.

Abstract

By combining a squeezed propagating microwave field and an unsqueezed vacuum field on a hybrid (microwave beam-splitter), we generate entanglement between the two output modes. We verify that we have generated entangled states by making independent and efficient single-quadrature measurements of the two output modes. We observe the entanglement witness $E_\mathrm{W}=-0.263^{+0.001}_{-0.036}$ and the negativity $N=0.0824^{+0.01}_{-0.0004}$ with measurement efficiencies at least $26\pm{0.1}\%$ and $41\pm{0.2}\%$ for channel~1 and 2 respectively. These measurements show that the output two-mode state violates the separability criterion and therefore demonstrate entanglement. This shared entanglement between propagating microwaves provides an important resource for building quantum networks with superconducting microwave systems.