Quantum Radar Could Make Stealth Technology Obsolete

a reply to: C0bzz

this would increase the usefulness of stealth shaping ...

Kinda

increases the SNR of a radar, which increases detection and tracking ranges, ...

So in that respect, it makes stealth less effective than not.

I think you get it already, but here's the primer...

Think of it this way. Normal radar sends out photons, too, right? It sends out radio or microwave photons then it looks for them in return. The thing is, there are a lot of photons out there just zipping along. So how do we know which photons are ours?
Let's use visible light (Lidar) as an analogue just to demonstrate the idea. Let's say we send out "green light" from a powerful searchlight and look for green light coming back. Well, if you look in the sky using a filter that only allows green light, there's still a lot of green light hitting the filter/eyes. A lot of it came from the sun, moon, or other lights shining around. Some of it is from our search light. It bounced all over-- the ground, water, clouds, refraction has sent a bunch of dull green light everywhere. We call all that green light "background noise" or just "noise." So we need to filter out some of the green light, too, and just look for the bright spots lit up by our powerful green light. Aha, there's a bright spot right over there!
If something isn't reflecting a lot of light back or is absorbing some of it ("stealthy") then there's a good chance it gets filtered out unless it gets real close so that our green searchlight is reflecting enough green light back (signal) to get through the background light (noise) filter.

So the quantum radar works the same way -- sends out green light, too. Only it finger prints the green photons as it spits each out (by keeping an entagled photon). Both photons stay entangled (for awhile anyway). So instead of filtering out the dull green light everywhere ( "noise"), it looks only for photons with the fingerprints it has on file. It filters everything else out. The odds of getting a random photon with that fingerprint are astronomical. So when something not reflecting alot or is absorbing a lot of our green light (stealthy), it still is reflectingng some of the green light back. Instead of being filtered out as not very strong, it gets matched up against the fingerprints sent out-- aha, we got fingerprinted photons back! Only a few, but we know exactly when they left and when it came back! And that's really the information we need. We also don't need to send out as many photons, because we aren't worried about overcoming noise. We just need a few fingerprinted photons back to get a solid return and useable data.

Now there are some problems measuring the fingerprints and uncertainty which increases with time (decoherence). That's why there are range constraints. After a certain amount of measuring the fingerprinted photon, the measurements themselves increasingly cause the fingerprint photon on file to deviate from the other photon. And obviously the quantum radar is not using green light. But that's the really basic gist.