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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

#121

Post by ngcc_hk »

Animats wrote: post #97
greenavocado wrote: post #74

Earlier quoted context omitted.

[flagged]

US ICBMs been inertially guided for decades. They predate GPS. Once launched, they have no radio inputs. Some weapons do use GPS. The Joint Direct Attack Munition, the US's most common "smart bomb", is GPS-dependent. There's an inertial backup, but it's not that good. With GPS, it can hit a bunker or an artillery emplacement or a parked vehicle. Without GPS, small targets are out. DARPA has been working on small, low…

Is this the one technology used by Russia to bomb Ukraine. As it is so cheap the missile defend system is useless as it is just too expensive to fight it. The f16 is starting to prevent the airplane that throw the bomb with some gps guidance system.

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

#122

Post by robertlagrant »

kitd wrote: post #101
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.

> It has absolutely no idea where it is from only itself. Neither do GNSS satellites. You can't solve this problem with any method without giving each device a starting reference, and then either continually updating it or enabling some mechanism for multiple devices to vote/agree on reference(T+1). This new tech might allow other improvements, such as the QIN device being a relatively-static "hub", and the user wear…

> Neither do GNSS satellites

Is it a similar problem? I hadn't thought about how GPS satellites know where they are. Do they need regular correction?

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

#123

Post by BurningFrog »

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.

For many purposes, "every direction" is only three directions in our 3D space.

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

#124

Post by pas »

robertlagrant wrote: post #122
kitd wrote: post #101

Earlier quoted context omitted.

> It has absolutely no idea where it is from only itself. Neither do GNSS satellites. You can't solve this problem with any method without giving each device a starting reference, and then either continually updating it or enabling some mechanism for multiple devices to vote/agree on reference(T+1). This new tech might allow other improvements, such as the QIN device being a relatively-static "hub", and the user wear…

> Neither do GNSS satellites Is it a similar problem? I hadn't thought about how GPS satellites know where they are. Do they need regular correction?

There's some natural drift, and about yearly boost to keep them in their desired orbits

https://space.stackexchange.com/questions/30752/do-operating...

As far as I know - while their onboard clock is pretty good - they continuously get corrections from ground stations. (Once per day.)

https://gpsbeam.com/ground-stations/

the "navigation message" broadcast by the sats is described here https://gssc.esa.int/navipedia/index.php/GPS_Navigation_Mess...

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

#125

Post by [deleted] »

mFixman wrote: post #105
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…

If I understood this correctly, would this allow you to make an extremely good estimation of direction of velocity? If you want to use dead reckoning to estimate position, how would you know the abs of the velocity?

[deleted]

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

#126

Post by anovikov »

justusthane wrote: post #119
anovikov wrote: post #118

That smells like bs to me.

Why? It's just an extremely accurate accelerometer. It still needs to be giving a known starting position. It doesn't replace GPS so much as augments it. Granted, the article isn't very clear on that.

Yeah i understand the concept. But i am under an impression that those guys are just milking an easy source of dumb money this way.

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

#127

Post by roywiggins »

krisoft wrote: post #107
ptsneves wrote: post #103

Earlier quoted context omitted.

The US does not belong to the ICJ, so that judgement would only be valid if the US Supreme court would say so. I dislike a lot nuclear weapons but they are an escalation deterrent like the humanity never had[1]. I hope they continue to be a deterrent but never ever launched in war. [1] If Ukraine kept the nuclear weapons post USSR collapse we probably would not have the war on Ukraine, lots of dangerous threats but n…

> If Ukraine kept the nuclear weapons post USSR collapse we probably would not have the war on Ukraine, lots of dangerous threats but nothing else. If Ukraine tried to keep the nuclear weapons they would have been invaded within half an hour of that becoming apparent in or around 1994. They had no meaningful operational control over them, thus it would not have acted as a deterrent against that invasion. Yes, nukes a…

And even if they'd held onto them, keeping them operational for three decades without a nuclear weapons program of their own would have been impossible. They would have had to spend a huge amount of money they didn't have to build the infrastructure to do it.

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

#128

Post by GoldenRacer »

mFixman wrote: post #105
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…

If I understood this correctly, would this allow you to make an extremely good estimation of direction of velocity? If you want to use dead reckoning to estimate position, how would you know the abs of the velocity?

I'm way out of my depth here but I believe this would function as a very sensitive accelerometer. The rubidium would be still relative to the lasers so when you accelerated, it would have inertia and take some time to catch up with the rest of the device. You'd then integrate the acceleration to find the velocity and integrate that to find position.

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

#129

Post by dazzlefruit »

perryizgr8 wrote: post #112
dazzlefruit wrote: post #109

Earlier quoted context omitted.

President: ok, hit this military base with 100 soldiers to let them know we’re serious Million-inhabitants city nearby: burns to the ground due to garbage guidance President: …dig out the plan for world war 3, I guess.

ICBM is likely to deliver a nuke. Which will probably take out a 20 km radius circular area. It is not going to be used to target a base with 100 soldiers.

It is if the goal is to deter without launching a city roast fest. That’s one possible step to e.g. answer a first limited strike without starting a disastrous exchange. And US nukes can be set to low yield.
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