# Microwave quantum illumination using a digital receiver

## TL;DR

This paper demonstrates microwave quantum illumination using entangled photons and a digital receiver, showing potential advantages over classical radar in low-noise, low-power scenarios, with experimental and simulated results.

## Contribution

First experimental demonstration of microwave quantum illumination with a digital receiver, highlighting practical challenges and advantages over classical methods.

## Key findings

- Digital phase conjugate receiver outperforms classical noise radar.
- Simulated perfect idler detection yields quantum advantage.
- Experimental setup illuminates objects at 1 meter with entangled microwaves.

## Abstract

Quantum illumination is a powerful sensing technique that employs entangled signal-idler photon pairs to boost the detection efficiency of low-reflectivity objects in environments with bright thermal noise. The promised advantage over classical strategies is particularly evident at low signal powers, a feature which could make the protocol an ideal prototype for non-invasive biomedical scanning or low-power short-range radar. In this work we experimentally investigate the concept of quantum illumination at microwave frequencies. We generate entangled fields using a Josephson parametric converter to illuminate a room-temperature object at a distance of 1 meter in a free-space detection setup. We implement a digital phase conjugate receiver based on linear quadrature measurements that outperforms a symmetric classical noise radar in the same conditions despite the entanglement-breaking signal path. Starting from experimental data, we also simulate the case of perfect idler photon number detection, which results in a quantum advantage compared to the relative classical benchmark. Our results highlight the opportunities and challenges on the way towards a first room-temperature application of microwave quantum circuits.