Recent Paper Claims Quantum Radar Performs 20% Better Than Classical Radar

In the ever-evolving world of quantum technology, researchers are relentless in their pursuit of the coveted “quantum advantage” over classical computing methods. Harnessing the extraordinary principles of quantum mechanics, a variety of quantum technologies have emerged, displaying the potential to outperform classical devices in a wide variety of tasks. Among these recent innovations, groundbreaking discoveries have been made in the field of radar technology.

Unrivaled Performance

A research team from Lyon Normal School, CNRS, recently introduced a pioneering quantum radar that exhibits unparalleled performance, outperforming all existing radars based on classical principles. Their breakthrough is featured in a paper published in Natural Physicsfeatures a radar that simultaneously measures entangled probe and idle microwave photon states, cleverly blending with thermal noise.

The paper, published on June 29, begins with an abstract:

The main goal of any quantum technology consists in demonstrating superiority in its performance compared to the best classical implementations. Quantum radar improves the detection of targets placed in noisy environments by exploiting the quantum correlation between the two modes, probe and idler. The predicted quantum enhancement is not only less sensitive to loss than most applications of quantum metrology, but is also supposed to increase with additional noise. Here we demonstrate a superconducting circuit implementing a quantum microwave radar that can provide more than 20% better performance than any classical radar. This scheme involves co-measurement of the entangled probe and the state of the idle microwave photon after the probe is reflected from the target and mixed with thermal noise. By storing idler states in the resonator, we mitigate the detrimental impact of idler loss on quantum gain. Measuring the quantum advantage over various parameters, we find that the purity of the initial probe-idler entangled state is a major limiting factor and needs to be considered in any practical application.

Three Years On…

“Our journey started in 2020 when we designed a superconducting circuit capable of generating entanglement, manipulating the microwave quantum state and measuring the photons of the microwave field,” said Benjamin Huard, one of the leading researchers behind the study, in an interview with Phys.org. “Little did we know that this circuit holds the key to overcoming one of the most significant challenges in microwave quantum metrology — achieving quantum excellence in radar sensing.”

Previous efforts have explored the realm of quantum radar aiming to go beyond conventional radar. While some success has been achieved using optical systems, the realm of microwave radiation has yet to witness such feats.

Huard and his colleagues became pioneers, achieving the first quantum microwave-based radar that outperformed any classical radar known to date. Their radar operates by exploiting the correlation beyond classical physics, which is imprinted between two microwave radiations.

“Our radar generates quantum entanglement between the microwave resonator and the target-directed signal that is obscured by excessive microwave noise, such as atmospheric interference,” explained Huard. “When the target is present, it reflects a small fraction of the signal amidst the tremendous noise. Our device cleverly combines this interesting fraction of the signal with the stored field of the resonator in a way that generates a varying number of photons depending on the presence of the target. The built-in microwave photon counter then checks for these photons.”

In initial evaluations, quantum microwave radar demonstrated a remarkable 20% increase in radar detection speed over its classical counterpart. However, reaching this milestone is no easy feat.

What a difficult task

“It was a difficult task to make this demonstration successful, even though the operating conditions appeared to be easy,” said Huard. “We dealt with one unknown — presence or absence of a target — and conducted the entire experiment at a very cold 10 mK, away from open air. One significant challenge for direct application in quantum radar lies in the significantly lower signal requirements than for microwave photons to observe quantum superiority. Moreover, we found pure entanglement of the initial signal with the resonator to be an important factor for usability.”

Undeterred, Huard and his team began a series of tests, carefully measuring their radar’s quantum advantage across various parameters. These assessments reveal that the purity of the initial entanglement between the probe and the idler can introduce limitations, requiring careful consideration when using the radar in real-world scenarios.

Huard found certain aspects interesting:

“What I find most exciting is the fact that we can achieve quantum superiority even though operating in such a noisy environment that entanglement cannot persist. It stands as a rare example where correlations beyond the classical can be harnessed to advantage, even with no lingering attachment,” he said.

This recent achievement by a team of enterprising researchers has significantly contributed to the ongoing efforts to improve the performance of quantum radar technology. In the future, their pioneering approach could inspire the development of a similar quantum microwave radar, potentially achieving even greater quantum advantages.

“I firmly believe that many unexplored applications await us, in which these non-classical correlations, without entanglement, play an important role,” said Huard. “We now aim to delve deeper into microwave sensing using quantum resources, particularly in the context of electron spin resonance or axion research.”

Featured image: Optical image of a superconducting circuit at the core of a quantum radar experiment. By inflating the tunnel junction ring (purple zoom), the resonator (blue) is entangled with the signal (orange) that is outgoing towards a possible target. By pumping it again at a time when a possible signal is reflected back, the resonator and incoming signal are measured together via a quantum bit (green) which counts how many photons are in the resonator. Credit: Quantum Circuits Group (ENS de Lyon)