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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

#101

Post by kitd »

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 wearing smaller, cheaper accelerometers that connect to it regularly to reset their starting positions.

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

#102

Post by echoangle »

lucb1e wrote: post #93
lxgr wrote: post #33

Even as somebody relatively familiar with inertial navigation, it took me almost the entire article to figure out that that's what this is doing. I really wish the words "inertial navigation" or "dead reckoning" would have occurred at least once in the article, but obviously "quantum navigation" sounds much cooler and as an added bonus makes it sound more like magic than technology.

Especially with the word "compass" in the title, I figured they made an accurate map of the earth's magnetic field and would use that to avoid needing any satellites. Then I opened the comment thread... Come to think of it, the earth's magnetic pole shifts so I guess this isn't possible? Either way, "London Underground tests new dead reckoning system" would have been more accurate it sounds like

Regarding pole shift: you maybe could have multiple static measurement stations spread around which measure the current values at known positions and synchronize the data once per day to the trains. I’m not sure how you could even determine position just from magnetic field alone, surely there are multiple positions with the same magnetic conditions?

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

#103

Post by ptsneves »

ta20240528 wrote: post #98
Dylan16807 wrote: post #95

Earlier quoted context omitted.

But importantly, making sure a nuke can still hit Moscow despite geolocation countermeasures has lots of worrying consequences for normal people that are in normal cities. If nukes are hitting random countryside then a lot less people die. But when it's the difference between hitting a hardened target or being off by 200 meters, that doesn't really affect normal people.

> has lots of worrying consequences for normal people that are in normal cities. Which is precisely why even the mere ownership of nuclear weapons was ruled by the ICJ to be illegal: a violation of inter alia the Hague [1907], UN Charter and Geneva Conventions. Specifically the Geneva Convention Protocol I (1977) states that ‘the civilian population shall not be the object of attack’. The 1977 Geneva Protocol was rat…

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 nothing else.

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

#104

Post by amanaplanacanal »

ta20240528 wrote: post #98
Dylan16807 wrote: post #95

Earlier quoted context omitted.

But importantly, making sure a nuke can still hit Moscow despite geolocation countermeasures has lots of worrying consequences for normal people that are in normal cities. If nukes are hitting random countryside then a lot less people die. But when it's the difference between hitting a hardened target or being off by 200 meters, that doesn't really affect normal people.

> has lots of worrying consequences for normal people that are in normal cities. Which is precisely why even the mere ownership of nuclear weapons was ruled by the ICJ to be illegal: a violation of inter alia the Hague [1907], UN Charter and Geneva Conventions. Specifically the Geneva Convention Protocol I (1977) states that ‘the civilian population shall not be the object of attack’. The 1977 Geneva Protocol was rat…

Wouldn’t that only apply to strategic nukes, not tactical nukes? City busters, rather than low yield weapons intended for military targets.

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

#105

Post by mFixman »

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?

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

#106

Post by I_ »

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…

Thank you for this comment, it brought me back to signal processing lectures from many years ago.

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

#107

Post by krisoft »

ptsneves wrote: post #103
ta20240528 wrote: post #98

Earlier quoted context omitted.

> has lots of worrying consequences for normal people that are in normal cities. Which is precisely why even the mere ownership of nuclear weapons was ruled by the ICJ to be illegal: a violation of inter alia the Hague [1907], UN Charter and Geneva Conventions. Specifically the Geneva Convention Protocol I (1977) states that ‘the civilian population shall not be the object of attack’. The 1977 Geneva Protocol was rat…

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 are really potent deterrent. Ukraine's case is not the right one to show this.

If you are looking for an example where nuclear deterrent works Russia's case is much better. They are badly bogged down in Ukraine. The reason why nobody dares to escalate and turn Moscow to rubble is because they have the nukes as a credible deterrent. All the tiptoeing around the range of missiles given to Ukraine and the constraints they have on not targeting Russia directly with them is due to that.

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

#108

Post by dwighttk »

mschuster91 wrote: post #99
Animats wrote: post #97

Earlier quoted context omitted.

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…

> US ICBMs been inertially guided for decades. They predate GPS. Once launched, they have no radio inputs. That's how the original Third Reich V-rockets worked as well, and they were shockingly inaccurate. It didn't matter for the Nazis, as their intention was to spread terror among the British population instead of actually hitting specific military targets, but in a modern war waged under the rules of war, "collate…

ICBMs are gonna have collateral damage

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

#109

Post by dazzlefruit »

dwighttk wrote: post #108
mschuster91 wrote: post #99

Earlier quoted context omitted.

> US ICBMs been inertially guided for decades. They predate GPS. Once launched, they have no radio inputs. That's how the original Third Reich V-rockets worked as well, and they were shockingly inaccurate. It didn't matter for the Nazis, as their intention was to spread terror among the British population instead of actually hitting specific military targets, but in a modern war waged under the rules of war, "collate…

ICBMs are gonna have collateral damage

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.

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

#110

Post by beeboobaa3 »

ptsneves wrote: post #103
ta20240528 wrote: post #98

Earlier quoted context omitted.

> has lots of worrying consequences for normal people that are in normal cities. Which is precisely why even the mere ownership of nuclear weapons was ruled by the ICJ to be illegal: a violation of inter alia the Hague [1907], UN Charter and Geneva Conventions. Specifically the Geneva Convention Protocol I (1977) states that ‘the civilian population shall not be the object of attack’. The 1977 Geneva Protocol was rat…

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…

> I hope they continue to be a deterrent but never ever launched in war.

This is just naive. They'll become more and more common, and their usage is inevitable. In fact, the US has already used them in war: https://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_a...

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