Quantum radar that neutralises stealth technology demonstrated for first time, again

One of the advantages of the quantum revolution is its ability to sense the world in new ways using the properties of the quantum realm to create quantum sensors and sensing systems that are millions of times more sensitive than anything we have today – one example of which is a quantum compass that replaces the need for GPS that the UK Royal Navy developed recently.

For most researchers though the general idea behind using quantum mechanics is to use its special properties to make measurements or produce images that are otherwise impossible, with one example being quantum radar – something that I first discussed  a little while ago after Chinese researchers claimed to have created the world’s first quantum radar – a new type of radar system that would render all stealth technology obsolete over night – and then quickly followed that up with new so called "ghost imaging" satellite technology. And both these developments then kick started a new arms race as other countries piled in to develop their own systems.

Much of the work in the quantum realm is done with photons, but as far as the electromagnetic spectrum is concerned, the quantum revolution has been a little one-sided. Almost all the advances in quantum computing, cryptography, teleportation, and so on have involved visible or near-visible light.

Now though another team, led by Shabir Barzanjeh at the Institute of Science and Technology in Austria, who also demonstrated the world’s first unhackable quantum internet video call, have announced they’ve used entangled microwaves to create the world’s first quantum radar. Again… but this time it’s real.

Their device, which can detect objects at a distance using only a few photons, raises the prospect of stealthy radar systems that emit little detectable electromagnetic radiation.

The device is simple in essence. The researchers create pairs of entangled microwave photons using a superconducting device called a Josephson parametric converter. They beam the first photon, called the signal photon, toward the object of interest and listen for the reflection. In the meantime, they store the second photon, called the idler photon. When the reflection arrives, it interferes with this idler photon, creating a signature that reveals how far the signal photon has travelled, and that’s it – a  quantum radar system.

This technique also has some hugely important advantages over conventional radar. Ordinary radar works in a similar way but fails at low power levels that involve small numbers of microwave photons. That’s because hot objects in the environment emit microwaves of their own.

In a room temperature environment, this amounts to a background of around 1,000 microwave photons at any instant, and these overwhelm the returning echo. This is why radar systems use powerful transmitters. Entangled photons overcome this problem. The signal and idler photons are so similar that it is easy to filter out the effects of other photons. So it becomes straightforward to detect the signal photon when it returns.

Of course, entanglement is a fragile property of the quantum world, and the process of reflection destroys it.  Nevertheless, the correlation between the signal and idler photons is still strong enough to distinguish them from background noise.

This allows Barzanjeh and co to detect a room temperature object in a room temperature environment with just a handful of photons, in a way that is impossible to do with ordinary photons.

“We generate entangled fields using a Josephson parametric converter at millikelvin temperatures to illuminate a room-temperature object at a distance of 1 meter in a proof of principle radar setup,” they say.

The researchers go on to compare their quantum radar with conventional systems operating with similarly low numbers of photons and say it significantly outperforms them, albeit only over relatively short distances. That’s interesting work revealing the significant potential of quantum radar and a first application of microwave-based entanglement. But it also shows the potential application of quantum illumination more generally, whose big advantage is the low levels of electromagnetic radiation required.

“Our experiment shows the potential as a non-invasive scanning method for biomedical applications, e.g., for imaging of human tissues or non-destructive rotational spectroscopy of proteins,” say Barzanjeh.

Then there’s the obvious application as a stealthy radar that is difficult for adversaries to detect over background noise. The researchers say it could be useful for short-range low-power radar for security applications in closed and populated environments.

Ref: arxiv.org/abs/1908.03058 : Experimental Microwave Quantum Illumination