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Posted by: algorimancer Mar 25 2008, 01:36 PM

This may be a bit of a far-out notion, but perhaps not. I've been seeing a lot of work on quantum entanglement showing up in various journals lately, commonly with the intent of secure communications or computation. Quantum mechanics is not my realm of expertise, but I wonder whether this might be employed as a remote sensing mechanism. Entanglement can be established between subatomic particles and/or photons, so I might envision entangling a photon with a particle (actually swarms of such pairs), then projecting the entangled photon towards some astronomical object of interest - perhaps towards an asteroid or comet or satellite or planet in our solar system, but conceivably towards another star. When the projected photon interacts with the distant target this interaction would be detected by observing the change in the paired particle retained in the transmitter, and interpretation would be something like performing spectroscopy (assuming multiple entangled states) or radar (single state) on the target object. By tracking time and direction of the transmitted photons this would even provide a remote imaging modality for targets which are otherwise too faint to detect telescopically. The same system if used to entangle particles with neutrinos would allow probing the interiors of the Earth and Sun - perhaps even other planets.

One obvious limitation with this notion is the length of time the entanglement can be maintained, which I think so far has been limited to a few seconds or minutes, so that near-term this technique would be of most use on the Moon and near-earth asteroids, but perhaps Mars & Venus as well. Progress seems to be continuing, so perhaps in a few years entanglements which last hours or even years may be feasible. Another limitation may be that interaction of the transmitted photons with the atmosphere may restrict this to a space-based activity, otherwise existing telescopes might be used as transmitters.

Posted by: Mongo Mar 25 2008, 04:40 PM

This is not directly applicable to what you propose, but there was an article many years ago in Scientific American about using quantum entanglement to create a scanned silhouette of an object that would explode if even a single photon were to strike it. The basic idea was to send a single photon at a given X-Y coordinate in an area containing the unviewable object, and using a series of wave splitters, have the probability function that reaches the object (as opposed to being diverted in another direction) be very very small, but still positive (such as 10^-15 or even smaller). The various entangled probability functions are then recombined, in a way that returns one value if a photon aimed at that X-Y coordinate would have impacted the object, and the other value if it would not have impacted. The procedure is repeated for every other X-Y coordinate being probed, resulting in a silhouette of the object, with arbitrarily small probability of a photon actually impacting the object and making it explode.

Posted by: algorimancer Mar 25 2008, 05:33 PM

Interesting. Gotta wonder what sort of things the government has been quietly up to in this realm.

Posted by: algorimancer Mar 29 2008, 02:32 PM

Possibly related:

http://www.eurekalert.org/pub_releases/2008-03/iop-fpm032808.php

"For the first time, physicists have been able to identify individual returning photons after firing and reflecting them off of a space satellite in orbit almost 1,500 kilometres above the earth. The experiment has proven the possibility of constructing a quantum channel between Space and Earth.

Research published on Friday, 28 March, in the New Journal of Physics, discusses the feasibility of building a completely secure channel for global communication, via satellites in space, all thanks to advances in quantum mechanics. "

Posted by: JRehling Mar 29 2008, 08:57 PM

One day, hackers will not only be able to take funds from your bank account, they will also be able to use quantum mechanics to take images of you in your shower. That's technology in action!

Posted by: nprev Mar 30 2008, 01:00 AM

Oh, no; we're gonna build a http://www.amazon.com/Macroscope-Piers-Anthony/dp/097236708X pretty soon at this rate (and if I was Piers Anthony I'd be seriously considering some way to establish intellectual property rights on the concept)!

Posted by: algorimancer Jul 13 2018, 06:22 PM

I see China is using quantum entanglement in a radar system:

https://www.popsci.com/china-quantum-radar-detects-stealth-planes-missiles

"The microwave beam's entangled photons bounce off of the target object and back to the quantum radar. The system compares them with the entangled photons of the optical idler beam. As a result, it can identify the position, radar cross section, speed, direction and other properties of detected objects."

"Additionally, the quantum radar could 'observe' on the composition of the target."

The system seems to need to operate in near vacuum (orbit or high altitude) conditions.

Makes me wonder if someone over there read my initial post

I wonder how a system like this would perform at mapping minerals from orbit (presumably over an airless body), as compared to optical or infrared remote sensing. Might be a nifty thing to send to Europa or Enceladus.