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London Underground hosts tests for 'quantum compass' that could replace GPS

theguardian.com

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Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#51

Post by porphyra »

contravariant wrote: post #38
porphyra wrote: post #9

I remember doing laser cooling of rubidium atoms in physics class. It's really cool how it works: * Rubidium will absorb photons of a certain wavelength and re-emit it in a random direction. Since photons have momentum, it will get some net momentum change from absorbing photons all coming from a particular direction, but the re-emissions are in random directions so they have net zero momentum. * Shine laser light at…

Maybe I'm missing something but hitting a gas just above absolute zero with lasers from every direction doesn't sound as something that could be miniaturised.

Theoretically you might be able to do it with some VCSELs, not sure though...

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#52

Post by shadowgovt »

porphyra wrote: post #9

I remember doing laser cooling of rubidium atoms in physics class. It's really cool how it works: * Rubidium will absorb photons of a certain wavelength and re-emit it in a random direction. Since photons have momentum, it will get some net momentum change from absorbing photons all coming from a particular direction, but the re-emissions are in random directions so they have net zero momentum. * Shine laser light at…

Thank you for this explanation. I've often wondered how laser cooling works and never found a clean explanation.

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#53

Post by mopsi »

Terr_ wrote: post #39
surfingdino wrote: post #30

Earlier quoted context omitted.

There is no need to jam GLONASS. Russian planes are affected using other means--sanctions have cut them off from access to parts and maintenance. It's more impactful because all planes are affected by this, not just those that fly near the border of NATO countries.

I feel like that is mixing separate issues. The sanctions aren't because of the jamming and spoofing. If some other country started foisting the same pollution/sabotage onto its neighbors, those neighbors would still have a problem deciding on how to respond. The main point is that the bar for someone breaking your navigation system has been lowered. It's not just something you'd expect in a small area or for a short…

The bar has been crossed. Finland and other airlines flying in Northern Europe are suffering from GPS disruptions that make landing at smaller less-equipped airports impossible:

https://www.reuters.com/world/europe/finnair-pauses-flights-...

https://thebarentsobserver.com/en/2024/06/gps-interference-p...

Disruptions happen over a large area from Finland down to Poland and southern Sweden:

https://x.com/auonsson/status/1772005350134210751

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#54

Post by forgetfreeman »

hi-v-rocknroll wrote: post #16
sandworm101 wrote: post #15

Earlier quoted context omitted.

>>> It will never replace GNSS. It will have to. That is the point. This isn't about better in-car navigation. The big money behind quantum gyroscopes is the potential to guide submarines/aircraft/missiles in times of war when the GNSS systems are down or otherwise unreliable, just like the best of traditional gyroscopes. Dead reckoning is a legitimate means of navigation, but there are also some aspects where actual…

That's an extremely niche application unlikely to be scaled down to anything smaller than a backpack like laser ring gyros. As such, this type of positioning gear isn't for consumer use and is targeted mostly for underground surveying. (I worked for Trimble.)

Underground surveying or jam-proof guidance for long range ordinance?

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#55

Post by bl0rg »

porphyra wrote: post #9

I remember doing laser cooling of rubidium atoms in physics class. It's really cool how it works: * Rubidium will absorb photons of a certain wavelength and re-emit it in a random direction. Since photons have momentum, it will get some net momentum change from absorbing photons all coming from a particular direction, but the re-emissions are in random directions so they have net zero momentum. * Shine laser light at…

Great explanation :)

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#56

Post by playingalong »

contingencies wrote: post #36
hi-v-rocknroll wrote: post #14

Earlier quoted context omitted.

Because it can't. There are always cumulative errors in INS. There is no way around this without external references, but then it's no longer inertial navigation and it's inertial-assisted navigation. An underground navigation system based on triangulation of UWB cells would be a better solution than some nonstarter project the size of a refrigerator that requires liquid nitrogen.

Actually, in a train context, inertial is pretty damn high accuracy because you already have the world's best odometer showing (A) how many times your known size wheel has turned on your known track; and (B) you can test many axels simultaneously to ensure no slippage (I guess you wouldn't test the wheels as they move faster creating a higher frequency sampling requirement for ~no benefit whereas a dedicated axel fea…

Re odometer - don't the wheels of a train slide a little bit? I know the train is big pile of heavy iron, but still. My naive thinking is that when braking or during a rush start some extra distance can be covered.

Don't know, just thinking out loud.

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#57

Post by surfingdino »

Terr_ wrote: post #39
surfingdino wrote: post #30

Earlier quoted context omitted.

There is no need to jam GLONASS. Russian planes are affected using other means--sanctions have cut them off from access to parts and maintenance. It's more impactful because all planes are affected by this, not just those that fly near the border of NATO countries.

I feel like that is mixing separate issues. The sanctions aren't because of the jamming and spoofing. If some other country started foisting the same pollution/sabotage onto its neighbors, those neighbors would still have a problem deciding on how to respond. The main point is that the bar for someone breaking your navigation system has been lowered. It's not just something you'd expect in a small area or for a short…

Russians definitely increased their jamming activity after sanctions were imposed. The point I was making is that you do not need to make operation of Russian airplanes more difficult by jamming GPS/GLONASS signals, it is sufficient to deny access to maintenance and parts.

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#59

Post by nine_k »

contravariant wrote: post #38
porphyra wrote: post #9

I remember doing laser cooling of rubidium atoms in physics class. It's really cool how it works: * Rubidium will absorb photons of a certain wavelength and re-emit it in a random direction. Since photons have momentum, it will get some net momentum change from absorbing photons all coming from a particular direction, but the re-emissions are in random directions so they have net zero momentum. * Shine laser light at…

Maybe I'm missing something but hitting a gas just above absolute zero with lasers from every direction doesn't sound as something that could be miniaturised.

Maybe not down to a pea size, but possibly down to an orange size. Lasers are tiny, and "every direction" does not involve many of them, it involves some fiber optics, I suppose. The bulk of the device would be thermal insulation, and a volume for liquid helium + some piping to let it evaporate, and to replenish it.

Re: London Underground hosts tests for 'quantum compass' that could replace GPS

#60

Post by nine_k »

lbourdages wrote: post #44
hi-v-rocknroll wrote: post #10

Journalists get it wrong, again. Sigh. It will never replace GNSS. It's quantum inertial navigation (QIN) that double-integrates acceleration like another method, requiring external position, heading, and velocity (re)calibration and drifts without them. It has absolutely no idea where it is from only itself.

So it doesn't solve the issue inherent will all inertial navigation approaches (error accumulates very quickly because of the double integration), it just has less error? Seems like an incremental improvement at best.

Every time a train arrives in a station, its exact position becomes known.
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