Demonstration of Quantum Advantage in Microwave Quantum Radar*

The quantum radar promises to improve the speed of detection of a target placed in a noisy background by a factor of up to 4 in the low power regime compared to best possible classical radar. Observing this quantum advantage requires exploiting the quantum correlations through a joint measurement of the initially entangled probe and the idler which has never been performed in the previous microwave quantum radar attempts. Following a proposal by Guha and Erkmen [1], we demonstrate a quantum advantage of up to 1.2±0.1 in a proof-of-principle quantum radar operating at microwave frequencies.

Using a dual-purpose quantum emitter/receiver based on a Josephson ring modulator, we are able to generate two-mode squeezed states as well as perform the required joint measurement between the idler and the noisy reflected signal. After generation, the idler is stored in a memory mode while the signal half is emitted into a transmission line, goes through a tunable target after which it comes back to the quantum transceiver where it can be jointly measured with the idler using a two-mode squeezing operation followed by a photon-counting measurement via an auxiliary transmon qubit.

[1] Guha, S., Erkmen, B.I., Gaussian-state quantum-illumination receivers for target detection. Phys. Rev. A 80, 052310 (2009)