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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

#81

Post by roywiggins »

Waterluvian wrote: post #80
greenavocado wrote: post #74

Earlier quoted context omitted.

[flagged]

The “nuke Moscow” case doesn’t require GPS. You’ll get plenty sufficient precision from inertial systems.

Precision is, counterintuitively, still a big deal in the logic of nuclear weapons strategy. Nuking Moscow is easy, nuking hardened targets can be a lot harder.

> Before the invention of this new fuzing mechanism, even the most accurate ballistic missile warheads might not detonate close enough to targets hardened against nuclear attack to destroy them. But the new super-fuze is designed to destroy fixed targets by detonating above and around a target in a much more effective way. Warheads that would otherwise overfly a target and land too far away will now, because of the new fuzing system, detonate above the target...

> As a consequence, the US submarine force today is much more capable than it was previously against hardened targets such as Russian ICBM silos. A decade ago, only about 20 percent of US submarine warheads had hard-target kill capability; today they all do.

https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...

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

#82

Post by Havoc »

Russian shenanigans was my first thought too, but the real game changer is probably:

>under ground and under water

Tunnels, fiber cables, pipelines, submarines, autonomous subs etc would all benefit from less location guessing. (Tunnels tbf you can do with lasers already)

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

#83

Post by PhasmaFelis »

Waterluvian wrote: post #80
greenavocado wrote: post #74

Earlier quoted context omitted.

[flagged]

The “nuke Moscow” case doesn’t require GPS. You’ll get plenty sufficient precision from inertial systems.

And if that's not enough, I'm sure you could get the rest of the way with cameras and AI. In 2024, it can't be too challenging to train a machine to recognize Moscow.

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

#85

Post by o11c »

4gotunameagain wrote: post #50
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…

Does it mean that using this mechanism you can only achieve cooling for a narrow temperature range ? As I assume you cannot shine laser light at a spread spectrum to capture all the possible ΔT

I imagine at higher temperatures, the lasers that hit at an angle would have the correct doppler shift.

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

#86

Post by jgeada »

refulgentis wrote: post #40
hi-v-rocknroll wrote: post #25

Earlier quoted context omitted.

There is no magic involved, so there will still be errors and limitations. https://physics.stackexchange.com/questions/679991/which-is-...

TL;DR-TL;DR: says the opposite of your implied claim, "atom-gyros are set to outperform light-based gyros" TL;DR: this is a StackExchange question with 1 answer, noting it is indeterminate if a quantum gyroscope would be more accurate than a laser-atom-based one. It looks like you rushed through and missed that in this context, TFA is describing an atom gyro. That leaves conversation at a point where either A) we ass…

Problem is always going to be sampling frequency.

All accelerometers tell you is the direction of the acceleration vector (ie how speed is changing and in which direction). You still have to add the individual vectors to derive where you actually are.

And if you don't sample fast enough and your acceleration has frequency components at frequency comparable to your sampling, the acceleration you measure may not reflect where you actually are (ref Nyquist sampling theorem)

Imagine sampling at 1hz, and you just happen to have a bump every 1 sec (eg your wheel happens to have a flat spot and is turning at 1Hz), followed almost instantly later by a bump in the opposite direction. Your sampling only sees (say) the +ve components, misses the -ve and accrues a bunch of error.

If you can sample fast enough, you can minimize this sort of error, but you can't really make it go away.

Oh, btw, if you make it work well enough you're considered munitions for export control purposes, so limits the number of countries you can sell to. Same reason civilian GPS units stop working somewhere around 1200mph

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

#87

Post by jiggawatts »

aeyes wrote: post #27
surfingdino wrote: post #20

Earlier quoted context omitted.

Russia launched a satellite capable of destroying GPS satellites and suddenly funding became available?

There has been constant development trying to improve accelerometer and gyros. There are even commercial products, for example: https://m2lasers.com/quantum-accelerometer.html

They claim 10E-7 m/s/s precision, which is is about 60cm of drift in an hour, and up to 375 meters after a day.

Obviously this won't work without re-calibrating to a known location at least a few times per day.

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

#88

Post by lbourdages »

nine_k wrote: post #60
lbourdages wrote: post #44

Earlier quoted context omitted.

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.

Reading the article, I was under the impression that this was to be used for stuff like submarines, or vehicles in the arctic... stuff where finding one's position might be tricky.

This is absolutely overkill for a train where you can just rely on a calibrated odometer to know your position.

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

#89

Post by GeorgeRichard »

matt123456789 wrote: post #12
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.

From the article: "This information, combined with the starting point of that object, allows its future positions to be calculated." It doesn’t go into the details of recalibration, I’ll give you that.

Surely it can only calculate its current position, calculating its future positions would seem to require a divination machine.

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

#90

Post by refulgentis »

jgeada wrote: post #86
refulgentis wrote: post #40

Earlier quoted context omitted.

TL;DR-TL;DR: says the opposite of your implied claim, "atom-gyros are set to outperform light-based gyros" TL;DR: this is a StackExchange question with 1 answer, noting it is indeterminate if a quantum gyroscope would be more accurate than a laser-atom-based one. It looks like you rushed through and missed that in this context, TFA is describing an atom gyro. That leaves conversation at a point where either A) we ass…

Problem is always going to be sampling frequency. All accelerometers tell you is the direction of the acceleration vector (ie how speed is changing and in which direction). You still have to add the individual vectors to derive where you actually are. And if you don't sample fast enough and your acceleration has frequency components at frequency comparable to your sampling, the acceleration you measure may not reflec…

These are all excellent elucidations of classic mechanical principles making it hard. I'm not sure they're enough to make me say the scientist/institution in the article a priori has it wrong, especially because it's not a one-off dude just messing around.
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