
Quantum radar has been demonstrated for the first time - wjSgoWPm5bWAhXB
https://www.technologyreview.com/s/614160/quantum-radar-has-been-demonstrated-for-the-first-time/
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xt00
Here’s some background on the concept:
[https://physics.aps.org/articles/v8/18](https://physics.aps.org/articles/v8/18)

Basic idea is that you send out a microwave signal and at the same time send
entangled microwaves/photons (in the microwave band) into a trap where they
basically spin around “idling”/waiting for the potential weak signal to come
back. You then feed both the returned signal which is super weak and the idled
signal into a josephsen parametric converter. Basically an amplifier based
upon a Josephsen junction. The result is that using that type of amplifier it
amplifies signals that are quantum entangled more than it amplifies non
entangled signals. And you get increased SNR on your signal you get back. So
the microwave still has to hit the target and bounce back to you / receiver
station you just can use a much weaker signal to transmit the microwave and as
a result it acts similarly to passive radar that uses ambient RF to detects
objects in the air.

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mrfusion
Makes me wonder if this could be applied to cameras? With visible light
instead of microwaves.

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ganzuul
Don't understand it, but one guy interviewed on the subject said resolution is
a function of all the entangled photons. That seems to mean you circumvent the
diffraction limit.

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fspeech
First published result? There were reports of military work before:
[https://www.scmp.com/news/china/diplomacy-
defence/article/21...](https://www.scmp.com/news/china/diplomacy-
defence/article/2151086/chinas-latest-quantum-radar-wont-just-track-stealth)
This publication gave some credibility to the earlier reports of presumably
classified work.

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magicsmoke
>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.

No rendering stealth aircraft obsolete just yet

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krzat
Only over short distances? Is this because entangled photons decohere as they
go longer?

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lisper
Yes, exactly.

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ganzuul
Some more recent discussion: [https://hackaday.com/2019/08/26/quantum-radar-
hides-in-plain...](https://hackaday.com/2019/08/26/quantum-radar-hides-in-
plain-sight/)

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bookofjoe
[https://news.ycombinator.com/item?id=20820196](https://news.ycombinator.com/item?id=20820196)

