[HN Gopher] London Underground hosts tests for 'quantum compass'...
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London Underground hosts tests for 'quantum compass' that could
replace GPS
Author : beejiu
Score : 54 points
Date : 2024-06-15 20:03 UTC (2 days ago)
(HTM) web link (www.theguardian.com)
(TXT) w3m dump (www.theguardian.com)
| mojomark wrote:
| This work proposes a more accurate means of dead reckoning using
| a quantum-level source for inertial measurement in an Inertial
| Navitagation System (INS). Useful for robotic navigation
| underground, inside RF-shielded structures, on other planetary
| bodies, or underwater. The issue of localization error drift
| reduction from INS's seems very much like a Moore's law
| challenge, though I haven't mapped out the advances in intertial
| measurement accuracy/precision by year to see if the projected
| rate is similar or not. In any event, pretty cool; we'll see if
| this one pans out.
| tomtom1337 wrote:
| Is the idea here to accurately track the acceleration that the
| sensor is undergoing? So, if you started at a known location with
| velocity=0 and integrate the acceleration data wrt time twice,
| you get the relative change in position and can thus know your
| new location?
| Someone wrote:
| Looks like it, given (FTA):
|
| _"The aim of the Imperial College project [...] is to create a
| device that [...] does not rely on receiving external
| signals."_
|
| and
|
| _"At the heart of the quantum compass - which could be ready
| for widespread use in a few years - is a device known as an
| accelerometer that can measure how an object's velocity
| changes"_
|
| So, it's advanced dead reckoning
| (https://en.wikipedia.org/wiki/Dead_reckoning).
|
| I wonder whether they really don't use external signals at all
| or occasionally use them to correct for accumulation of errors.
| For example, the ability to detect that velocity w.r.t. earth
| is zero would help with that.
|
| (Of course, for the London subway, the fact that trains tend to
| follow the tracks can help, if the system knows the track
| layout. That probably is the simplest way to prevent
| accumulation of errors, but then, do they really need such a
| complex accelerometer?)
| haiku2077 wrote:
| They're just using the subway as a convenient moving lab. The
| real-world application of this technology is for military
| submarines and marine drones.
| gus_massa wrote:
| My guess is that calculating the initial velocity is hard, so
| it will drift slowly. Perhapa keep the device on a table for
| a minute to ensure v=0, or sync it at every subway stop.
| vsskanth wrote:
| Highly accurate dead reckoning basically. I wonder how it
| compares to the other method of mapping subterranean patterns and
| matching to them.
| porphyra wrote:
| 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 it from all directions but at a wavelength
| slightly longer than the wavelength at which it will absorb. Now,
| if the rubidium atom is moving, the light hitting it head on will
| be Doppler shifted into the wavelength that it absorbs, slowing
| it down, whereas the other light wouldn't affect it. So, no
| matter how it is moving, it will slow down.
|
| Rubidium is a good material since it has an S shell on the
| outside as though it were a big hydrogen atom, but it is so
| massive that it is a lot nicer to work with for this application.
| tanseydavid wrote:
| >> It's really cool how it works
|
| Pun intended? Please say yes.
| contravariant wrote:
| 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.
| gridspy wrote:
| Most technology has a limit like this (for instance CPU
| transistor size in the past). However once this is a proven
| technology, money will be invested in solving these issues.
| porphyra wrote:
| Theoretically you might be able to do it with some VCSELs,
| not sure though...
| nine_k wrote:
| 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.
| horstbort wrote:
| You don't need any helium or nitrogen here, cooling happens
| only by laser cooling and evaporative cooling from magnetic
| or optical traps. The atoms are perfectly insulated in an
| ultra high vacuum. Electronics still take the bulk of the
| volume here, as does the laser system. While the lasers
| themselves are tiny indeed, the light needs to be
| manipulated before reaching the atoms. And yes, it involves
| quite a lot of fiber optics :-).
| greenavocado wrote:
| It just has to fit inside a nuclear warhead with a less than
| 30 minute flight time to Moscow. That is what this is about
| because Russian electronic warfare has utterly crippled
| exisiting missile navigation systems. Their hit rate can be
| in the single digit percentage depending on the system.
| ziddoap wrote:
| You don't need to copy/paste the exact same comment three
| times in one topic. We read it the first time.
| greenavocado wrote:
| Fixed
| dekhn wrote:
| There's a whole bunch of laser cooling science/applications:
| https://en.wikipedia.org/wiki/Laser_cooling
| 4gotunameagain wrote:
| 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 DT
| shadowgovt wrote:
| Thank you for this explanation. I've often wondered how laser
| cooling works and never found a clean explanation.
| bl0rg wrote:
| Great explanation :)
| hi-v-rocknroll wrote:
| 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.
| matt123456789 wrote:
| 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.
| hi-v-rocknroll wrote:
| 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.
| ForHackernews wrote:
| > There are always cumulative errors in INS.
|
| Is that necessarily true of this quantum thing? I know
| nothing about it except this article, theoretically if it
| kept track of exact Plank lengths or something, then there
| would be no errors to accumulate, right? Lots of the things
| that seem intuitively true break down in weird ways when
| dealing with quantum effects.
| hi-v-rocknroll wrote:
| There is no magic involved, so there will still be errors
| and limitations.
|
| https://physics.stackexchange.com/questions/679991/which-
| is-...
| refulgentis wrote:
| 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
| assume the scientist interviewed knows what they're
| doing, or B) following your unstated lead, assume they're
| a crackpot and the whole article is irrelevant because
| they're untrustworthy, and thus in an ideal world,
| there's 0 comments on the article.
| akira2501 wrote:
| > theoretically if it kept track of exact Plank lengths
| or something,
|
| Sure, just show me a way to measure something in terms of
| "exact Planck lengths" and we're money.
| refulgentis wrote:
| _stares at TFA_
|
| Not really sure what to say, here.
| contingencies wrote:
| 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 feature could live within an environmental
| enclosure protected from dust and grime); (C) you are
| constantly doing exactly the same trip-segments over and
| over again.
|
| So for a train with an offline positioning requirement, I'd
| suggest that an odometer based solution is _close to
| ideal_.
| playingalong wrote:
| 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.
| contingencies wrote:
| If you are averaging axels across multiple carriages
| slippage is unlikely to amount to much. Moreover, because
| you are traveling known segments, you can reset your
| position at each station or known intersection/detectable
| segment terminus, so you're going to have zero accrued
| drift at that point. It's a perfect deployment scenario
| for an odometer based solution. If you want to be higher
| confidence, sensor-fusion with an IMU, laser TOF/LIDAR,
| camera, ambient light sensor, radio signals, or MEMS
| microphone can verify position. _Et voila!_ - no need for
| GNSS.
| closewith wrote:
| Not only do they slide, the "known size" changes not only
| due to wear but also due to variations in the gauge from
| metre to metre along the track.
| horstbort wrote:
| There is no liquid nitrogen involved here. The instrument
| from the article is actually rather big, current
| generations of quantum IMUs are roughly half this size with
| lots of room for miniaturization.
|
| One big advantage of these atom interferometers is that
| they actually don't need to be recalibrated because the
| reference is the wavelength of the lasers which can be
| controlled with extreme precision.
|
| A big disadvantage is however the limited repetition rate,
| which is on the order of only 1 Hz at the moment.
| Currently, combinations with "classical" IMUs seem most
| promising, and there is lots of interest in these devices
| for applications in planes, cars and spacecraft.
| sandworm101 wrote:
| >>> 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 replacement of GNSS might happen. An extremely
| sensitive gyroscope could probably determine latitude based on
| the earth's rotation (Foucault Pendulum). Then layer on a
| detailed map of variations in the earth's gravity and/or
| magnetic fields and one might be able to pinpoint a location
| absent external signals.
|
| https://en.wikipedia.org/wiki/Advanced_Inertial_Reference_Sp...
| hi-v-rocknroll wrote:
| 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.)
| ForHackernews wrote:
| ...yeah? I don't think anyone has claimed they're
| developing this for consumer use.
| hi-v-rocknroll wrote:
| _... that could replace GPS_
|
| That's the implied application, which is wrong.
| rob74 wrote:
| ... and GPS was initially developed for - right, the
| military.
| hi-v-rocknroll wrote:
| GPS can and was miniaturized. LRGs and QGs aren't for
| retail use because they're very expensive, bulky, and
| largely unnecessary.
| refulgentis wrote:
| F(T) != F(T+1)
|
| I, for one, am glad to see people working to innovate
| along well-trodden paths.
| hi-v-rocknroll wrote:
| Yes, for their relevant applications. If you were a
| commercial spelunker or were the Ukrainian army needing
| to lob missiles into Russia that were impervious to
| encrypted GPS jamming, then you would gladly welcome your
| quantum overlords. Neither LRG or QG are ever going to be
| made into MEMS devices shoved into an iPhone. Its
| application is dead reckoning. For the use-case of
| navigation underground useable by everyday people,
| Skyhook-like services that rely on 5G UWB microcells are
| the most likely evolution beyond relying on Wi-Fi SSIDs
| and conventional cell towers for tower-assisted GNSS.
| TooKool4This wrote:
| Why does it matter if it's not for consumer applications?
| GNSS is used for many more applications (and arguably more
| critical) than consumer applications (agriculture, mapping
| & surveying, aeronautics, shipping, etc.)
|
| Also just want to mention that, yes, integration errors
| accumulate when using intero-receptive sensors but if
| errors are small enough (white noise, various biases,
| sample rates, quantization, etc.) from the inertial sensors
| an odometry solution might be adequate until an extero-
| receptive sensor can localize the sensor within an external
| frame.
|
| This can shift the discussion from solving a problem that
| has no solution (i.e. how do I integrate a signal with
| white noise without any error) to an engineering problem
| (i.e. what error parameters allow the odometry to be
| accurate within x% over some timeframe).
|
| There was interesting work DARPA was sponsoring around the
| above idea that you can read more about here:
| https://www.darpa.mil/program/micro-technology-for-
| positioni...
|
| >The end goals of the TIMU program are the demonstration of
| a single-chip IMU which maintains an accumulated position
| error of less than 1 nmi/hour with device volume of less
| than 10 mm3 and power consumption of less than 200 mW.
|
| (My job is related to estimating location of things).
| gridspy wrote:
| nmi - Nautical mile (1 nmi/hour mentioned above)
|
| Today the international nautical mile is defined as 1,852
| metres (about 6,076 ft; 1.151 mi).
|
| https://en.wikipedia.org/wiki/Nautical_mile
| gnatman wrote:
| When one of the potential customers in this "extremely
| niche" space has an $800 billion annual budget, you don't
| lose sleep over it.
| forgetfreeman wrote:
| Underground surveying or jam-proof guidance for long range
| ordinance?
| lawlessone wrote:
| Fair point, this would fit quite snugly on a ship or a sub.
|
| the real ones will probably smaller.
|
| I wonder will having more than one improve accuracy.
| soulofmischief wrote:
| Never go to sea with two chronometers, take one or three.
| actinium226 wrote:
| You could combine it with another IMU using a Kalman filter
| and improve accuracy that way.
| lbourdages wrote:
| 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.
| nine_k wrote:
| Every time a train arrives in a station, its exact position
| becomes known.
| BiteCode_dev wrote:
| Not to mention wireless networks like the ones for the
| airtag or the wifi endpoints mapping google has could be
| adapted to share positions of "right here, right now"
| anonymously.
|
| Which means that if only one device knows where it is, you
| can calibrate, and if several know, you can even correct
| for mistakes.
|
| If the system is precise enough, you only need to calibrate
| once in a while. Being at home/office, on the local wifi,
| once, could be enough.
|
| Besides, nobody wants the GPS to go, but it's a nice
| alternative that can't be jammed by enemy forces and can be
| used for hiking, diving, etc.
| nine_k wrote:
| Yes, but these are approximate.
|
| I mean the exact position, down to a millimeter, when
| e.g. a photo sensor on a train passes past a LED mounted
| below the station platform. The LED's light is modulated
| so there can be no mistake, and its location is precisely
| known.
| BiteCode_dev wrote:
| A meter precision is fine for what most people use GPS
| for. If the device is as precise as they say, you won't
| add much imprecision to the original calibration, so you
| will be in the right tunnel at the right time.
| pugworthy wrote:
| I've been looking for some data on estimated drift from this,
| but no specifics. That said, since it's looking at wave
| properties of cooled atoms, I'm assuming we're talking
| "wavelength" accuracy as opposed to more conventional inertial
| nav systems.
|
| My point perhaps is that though this is "nothing new", it's
| (probably) way more accurate than anything before it. So the
| "pain points" of recalibration and drift are extremely
| minimized.
| ben_w wrote:
| So far as I can tell, it's this accelerometer:
| https://www.imperial.ac.uk/news/188973/quantum-compass-could...
|
| (2018, I'm unclear what's changed since then?)
| surfingdino wrote:
| Russia launched a satellite capable of destroying GPS
| satellites and suddenly funding became available?
| aeyes wrote:
| There has been constant development trying to improve
| accelerometer and gyros.
|
| There are even commercial products, for example:
| https://m2lasers.com/quantum-accelerometer.html
| Terr_ wrote:
| Also changes in the status-quo of international politics:
| Russia has been chronically sabotaging non-Russian navigation
| systems in neighboring countries, beaming jamming and
| spoofing signals across the borders.
|
| Russian airplanes aren't affected because nobody has chosen
| to retaliate in kind... Yet.
| surfingdino wrote:
| 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.
| Terr_ wrote:
| 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
| time around an imminent violent confrontation, chronic
| disruption in a peaceful country is now A Thing That
| Happens.
|
| That, in turn, changes the engineering considerations for
| how robust a product needs to be.
| mopsi wrote:
| 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
| surfingdino wrote:
| 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.
| Terr_ wrote:
| > The point I was making is that you do not need to make
| operation of Russian airplanes more difficult
|
| My point is that "make flights difficult" isn't the real
| goal, the real goal is to impose _some_ kind of return-
| pain to make the offender stop. Poetic symmetry is merely
| an ideal bonus.
|
| In other words, it may be true that "the ideal
| retaliation is not very effective because of other
| circumstances", however that is not the same as "there is
| no need to retaliate at all."
| akira2501 wrote:
| Planes have inertial measurement units which are the
| primary source. GPS or GNSS are just backups. You can
| switch these off with zero consequence during the flight.
| It may cause your satellite TV and internet to stop working
| but no critical systems will be impacted.
|
| Russian airplanes are commercially purchased from the same
| sources as the rest of the world and are generally
| outfitted with identical equipment.
|
| The impacts to flights has to do with certain types of GPS
| coordinated instrument approaches for landings. Most of
| these runways have alternative approach strategies that can
| be used during jamming or other unavailability.
| Terr_ wrote:
| > Russian airplanes are
|
| The simpler answer is that Russia is not directing the
| sabotaging signals into their domestic flight paths.
| dejj wrote:
| Related: South-pointing chariot, 5th century BC
|
| https://en.wikipedia.org/wiki/South-pointing_chariot
| lxgr wrote:
| 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.
| mizzao wrote:
| So, basically an extremely accurate dead reckoning system?
| rjeli wrote:
| With high enough accelerometer accuracy, you need to start
| adjusting your subtracted gravity vector with maps, right?
| greesil wrote:
| If this was developed in the US this would immediately be ITAR
| restricted
| gravescale wrote:
| It's a shame all the cool stuff is all hidden in a white box, but
| I suppose it does look a bit like a Hollywood depiction of a
| homemade nuclear bomb so the British Transport Police would be
| getting a few panicked calls if it were in a perspex box.
|
| There's also no step-free access at South Kensington or
| Gloucester Road, so that must be a fun struggle for a grad
| student!
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