Physics

"Quantum radar" uses entangled photons to detect objects

"Quantum radar" uses entangled...
An illustration of the "Quantum radar" prototype
An illustration of the team's new "Quantum radar" prototype
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An illustration of the "Quantum radar" prototype
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An illustration of the team's new "Quantum radar" prototype

The weird world of quantum physics is being harnessed for some fascinating use cases. In the latest example, physicists have developed and demonstrated a “quantum radar” prototype that uses the quantum entanglement phenomenon to detect objects, a system which could eventually outperform conventional radar in some circumstances.

Quantum entanglement describes the bizarre state where two particles can become linked so tightly that they seem to communicate instantly, no matter how far apart they are. Measuring the state of one particle will instantly change the state of the other, hypothetically even if it’s on the other side of the universe. That implies that the information is moving faster than the speed of light, which is thought to be impossible – and yet, it’s clearly and measurably happening. The phenomenon even unnerved Einstein himself, who famously described it as “spooky action at a distance.”

While we still don’t entirely understand why or how it works, that’s not stopping scientists figuring out ways to use it to our advantage. Strides are being made towards creating quantum computers and a quantum internet, both of which would be super fast and nigh-unhackable. And now, in a new study by physicists at the Institute of Science and Technology Austria (IST Austria), MIT and the University of York, the phenomenon been applied to radar.

Radar works by sending out radio waves or microwaves, and then listening for how they bounce back to the receiver, which paints a clear picture of what objects are in the area. The new prototype system works on the same basic principle, but it’s sending out quantum-entangled photons.

One of each entangled pair is a “signal” photon, while the other is called an “idler.” The signal photons are the ones that are sent out towards the object of interest. The idlers, meanwhile, are kept in isolation, away from any interference. When the signal photon reflects back, it changes, which instantly affects the idler photon. And the device can then check the idler and determine whether a target object is present or absent in the area.

True quantum entanglement is lost between the two types of photons when the signal is reflected, but enough information is retained to create a signature that can determine a reading of an object.

While the process is fragile and very much experimental, the team says that the quantum radar is better than classical radar in some circumstances. For one, the new technique is more effective at picking a target object out of the background noise than low-power radar.

“What we have demonstrated is a proof of concept for Microwave Quantum Radar,” says Shabir Barzanjeh, lead author of the study. “Using entanglement generated at a few thousandths of a degree above absolute zero (-273.14 °C), we have been able to detect low reflectivity objects at room-temperature.”

Besides improving radar systems, the team says the new technology could also eventually be applied to security scanners and medical imaging of human tissue.

The research was published in the journal Science Advances.

Source: IST Austria

8 comments
notarichman
could it be used for space exploration? tracking asteroids? could more than a pair of photons be paired?
chuito
It would seem that this could be applied to astronomical telescopes for better viewing of distant worlds in other solar systems for spectroscopic analysis of atmospheres and potentially dangerous asteroids, meteors and other space debris etc.?
Username
Since it uses photons and not radio waves should it not be named a quantum lidar?
Kpar
You do realize that this tech rings the death knell for SETI? If we could use this tech for communications at our level of scientific knowledge, would any slightly more developed race use EM waves? Unlikely.
CraigAllenCorson
Note that the technique uses photons, and so is limited by the speed of light. If, say, you wanted to detect an object ten light-days away, it would take ten days for the photons to impinge on the object, thus altering their entangled pairs and providing a signal. That's twice as fast as ordinary radar, because the photons do not need to return to the source for detection, but it is still very limited in effective range - unless you're in no particular hurry to see what's out there. The inverse square law introduces another limitation.
HimarAli
@CraigAllenCorson -- Actually you can immediately detect the object, and don't have to wait 10 days. Just send out a continuous stream of photons well in advance, like a month beforehand. When the object appears, you will be instantly notified. With ordinary radar, you will have to wait 10 days. But we were told that according to relativity information cannot fly faster than light. So how is it that this quantum radar can alert us of the presence of the object instantaneously? Isn't that 'information'?
HimarAli
This device seems to violate the laws of relativity, as it is described in this article. We are told information cannot travel faster than light. So imagine someone on Alpha Centauri 4 light years away wants to send an instant message to Earth. We can shoot a continuous stream of entangled photons there well in advance. We have to wait 4 years for the first entangled photon to reach there. But once they start arriving, the person in Alpha Centauri can block the photons, which is immediately detected on earth, or let them pass through. This way, the person can send a Morse code back to Earth instantaneously. What is wrong with this picture?
clay
This seems like a REALLY BIG DEAL that is not getting the attention is deserves. I mean: Observing the sequestered photo means you [A] effectively cut the RRM in HALF (look up Radar Range Mile) and because of this you get to [B] reduce the size of the transmitter for a given db or use the same size (as without entanglement) and get more effective range due to the complete lack of signal attenuation! So blasting through clutter is easier, reaching out farther becomes very doable. I am sure I could scrounge up more things too.. like STEALTH? Think about how this completely kills stealth: With conventional radar, the signal bounces back to the receiver, but with stealth the signal either bounces in some OTHER direction or is attenuated (absorbed) via stealth material/coating. With this entangled signal, the photo (e.g.: signal) does not NEED to return to the receiver... All it needs to do is change its orientation, so if that photon bounces off a stealth plane in a non-returning direction, you will still get a response with the entangled counterpart photon. This could make all current stealth craft completely obsolete. VERY interesting.