Discussion: the first quantum orienteering

Off-topic, but interesting that somebody thought this effect was "orienteering".

In quantum orienteering, Alice wants to use quantum resources to communicate a random space direction of military importance to Bob.

The first quantum orienteering by quantum entangling measurements enhancement

My head hurts trying to read the article!

Did they mean to use 'orientation'? And what is a quantum, anyway? Or is it there used as an adjective?

Probably from SCIgen (or should be.)

Is this a case of using the word quantum to make the article appear smart? I'm sure if you did a count of uses of the word in that article, it'd break the counter (I counted five uses in just one sentence).

I did see the word parallel mentioned and that's orienteering related (parallel error) so I guess the article's relevant to us though I'm not really sure what a parallel spin is, perhaps something to do with compasses sitting side-by-side causing magnetic shifts?

I'd also assume a quantum walk is when you can see a control as well as a fellow competitor who has not yet seen it so are trying to sneak up on it without giving away its location.

Could someone start by explaining "entanglement"

"One simple scheme is for Alice to polarize a spin along the direction and send it to Bob."
How do you polarize a spin?
How do you send it?
How does Bob read it?

If I remember correctly...
It's possible to create two particles that have this mysterious magical connection, so that something that happens to one also happens to the other, instantaneously, no waiting for the speed of light. These particles are "entangled". Alice takes one, Bob takes the other, and they go different places, and one does a thing tio the particle and the other observes it. I think they've done this in the lab to prove the theory, but nobody's created a way to do it for practical communications. You probably need a pair of billion-dollar labs to transfer a single bit.

Could someone start by explaining "entanglement"

That's usually the result of an unsuccessful fence crossing.

J-J’s “mysterious magical connection,” the idea of which Einstein hated and referred to as “spooky action at a distance,” has indeed been empirically demonstrated. That is, instantaneous influences between entangled particles, even though the particles are at a considerable distance apart, has been confirmed. The confirmations are robust, from lab results starting in the early 1980s and continuing today.

However, it does not appear possible to use these instantaneous influences to send information/communications faster than light.

In short, we can set up situations where we can instantaneously influence what happens at a distant location. But we can’t use that setup to send information instantaneously.

My MSEE from NTH in 1981 used a singe-modus laser fed into a single-modus fiber.

If you add the capability to send single photons which are polarized either vertically or horizontally, then you have a setup which can send bits of information which in theory cannot be eavesdropped upon. I.e. you would use this to transmit a session key and if anyone is tapping the fiber, then that will be evident.

I wasn't expecting these questions.

For barb,
How do you polarize a spin?
The Stern-Gerlach experiment was an early demonstration of electron spin. In the diagram, two beams of particles emerge from the apparatus, one containing electrons with spin polarized "up" and one with electrons having spin polarized "down". The axis of the spin is set by the magnetic field lines across the input particle beam.
How do you send it?
AFAIK, the particles carrying the spin are going fast through a vacuum. (It seems Alice is also entangling multiple electrons with their spins oriented antiparallel, i.e. opposite)
How does Bob read it?
Not that I understand this, but Bob uses "quantum metrology" which is the advance reported by the researchers. It uses "quantum walks" to obtain a more accurate direction in space than could be had by conventional methods. This depends on the spins being entangled.

I have received the random space direction of military importance. Nothing more to see here.

Bob

Entanglement: its when you can affect the behaviour of two objects, but not one of them independently. So if you "measure" one of them, you automatically change the other one, no matter where it is.

I think, sadly, what they're doing is more like quantum orientation than orienteering.

Proper quantum orienteering might be to use the uncertainty principle (you can't know exactly where you are) to argue that (with some probability) you did actually visit every controi.