Entanglement-based sensors

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phavoc
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Entanglement-based sensors

Postby phavoc » Tue Aug 27, 2019 5:28 pm

Using the idea of quantum entanglement, there is a new radar technology that promises to be able to be 'active' while not being detectable - at least based on current tech. The radar operates using the quantum entanglement principle - two photons are linked and then one is sent out like the standard radar would emit a signal. But instead of getting the bounced-back signal, the quantum entangled radar monitors the entangled photon at the emitter. I won't say I fully understand the physics behind all this, but essentially what it means is you get real-time data on what the other photon is doing without giving away your position.

So while the debate about stealth in spacecraft is possible/impossible, now there is a potential to have active targeting radars online instead of relying upon only passive radar for a target fix. This is a huge plus for an attacking ship trying not to be seen during a sneak attack.

https://www.yahoo.com/news/quantum-rada ... 00966.html
Moppy
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Re: Entanglement-based sensors

Postby Moppy » Tue Aug 27, 2019 7:40 pm

I can't see how stealth is impossible in space. Stealth just means doing enough to sneak past at an expectedly close range, or the abiliy to shoot first. It doesn't require full undetectability. Given this, a military radar whose emissions resemble "harmless" civilian navigation signals can be considered stealthy when active.

Like anything else stealth/sensors go through an arms race of new system, counter system and counter-counter system.

I consider the crossover between stealth and regular countermeasures to be whether or not they know you're doing it. Blanket radar jamming reveals someone is there even if they can't be seen. But a jammer that jams without revealing the presence of jamming is a stealth system (for example it beams back a signal that your radar interprets as no target).
AnotherDilbert
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Re: Entanglement-based sensors

Postby AnotherDilbert » Wed Aug 28, 2019 7:47 am

Lots of unwarranted hype in the Yahoo article. If you read the MITNews item:

"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."

"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."

"The researchers say it could be useful for short-range low-power radar for security applications in closed and populated environments."


It seems to basically be a way of lowering the noise floor in the detector.

You still have to bounce photons off the target back to the sensor, so would presumably require high power at longer ranges, hence still be very noticeable on the vehicle and spacecraft scale.
locarno24
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Re: Entanglement-based sensors

Postby locarno24 » Wed Aug 28, 2019 10:10 am

AnotherDilbert wrote:
Wed Aug 28, 2019 7:47 am
It seems to basically be a way of lowering the noise floor in the detector.
Exactly so. Any radar/lidar receiver is continuously getting bombarded with countless photons, many of which are on the same frequency as your transmitted 'pulses'.
Figuring out which of them may actually have been one of your transmitted pulses which has bounced off a bad guy is an art form that radar operators and designers lavish endless effort on. It does kind of contribute to stealthiness, but as noted you do still need to actively transmit.

If you could use entanglement to 'fingerprint' the photons you transmitted and identify them out of the mass of noise swamping your returns, theoretically:
1) You can ignore any amount of background noise - including hostile jamming - because any received photon gets disregarded if it fails a yes/no entanglement check
2) You can afford to transmit much lower powered pulses, meaning your active sensor is much 'quieter' and easier for an enemy's passive sensor to miss.
Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.
Moppy
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Re: Entanglement-based sensors

Postby Moppy » Wed Aug 28, 2019 12:45 pm

I believe locarno24 has a correct explanation of how this thing works.

Note that for radars the unit doing the detection doing the detection work doesn't need to be the one actively transmitting.

You might for example have a large radar emitter located well away from the enemy and heavily protected (AWACS plane?) and have the fighter jets on the front line equipped with receivers. They would then gain the benefit of active sensors without emitting themselves. Sensor fusion on modern jets like the F-35 might allow a squadron to do this organically without needing a specialised radar plane.

I thought it was quite a good piece of journalism for the popular press. Usually, anything that contains the word "quantum" or "AI" quickly goes off the crazy end.
Condottiere
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Re: Entanglement-based sensors

Postby Condottiere » Fri Sep 13, 2019 4:58 pm

Stealth would be not getting detected; one variant of invisibility would be bending radiation around an object so that what's directly behind the object can be sensed, creating not a black hole, more of a pocket universe.
Sigtrygg
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Re: Entanglement-based sensors

Postby Sigtrygg » Sat Sep 14, 2019 7:45 am

If you are bending the radiation around you how do you observe the universe?
Condottiere
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Re: Entanglement-based sensors

Postby Condottiere » Sun Sep 15, 2019 3:14 am

Image
Moppy
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Re: Entanglement-based sensors

Postby Moppy » Sun Sep 15, 2019 3:58 am

That won't work. What they mean is "if light bends around you, instead of hitting you, it can't get into your eye, therefore an invisible person is blind". Bending light through a fiber optic cable isn't going to help.

edit: Basically your camera has to be visible, which means you aren't invisible. Then again, stealth doesn't mean invisbility. Just hard enough to see that you can get the job done.
Condottiere
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Re: Entanglement-based sensors

Postby Condottiere » Sun Sep 22, 2019 8:56 am

Poking a pin prick through the fabric of reality.

Or just the cloaking fabric.

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