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.
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.
Yeah, it is an extremely sensitive accelerometer which it calls out about halfway through the article.
"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 over time."
>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
Spooky.
It's like having a Maxwell's demon for photons sitting on top of every atom!
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.
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.
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.
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 :-).
It's pretty amazing what's slowly but surely becoming possible. This company, for example, has successfully made chip-scale "fiber" ring gyros with incredible performance that would have been very large heavy units 5-10 years ago: https://www.anellophotonics.com/products/x3
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-cost inertial systems with enough accuracy to remove GPS dependence. Exactly how good those systems are and which weapons systems now use them is not talked about much. Here's the project poster.[1] This is an improved form of MEMS accelerometers and gyros, not new physics. DARPA has a project for that, too, but the near term goal is small, cheap, and disposable for munitions.
There's much current interest in weapons which combine gun, bomb, and missile technology to boost range. Bombs with a small jet engine and wings for extra range exist. Both the US and Russia have them. Artillery rounds with a rocket upper stage are becoming available. The general idea is to have stuff you can shoot into heavily defended territory.[2]
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.
> 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, "collateral damage" can actually be a war crime, and even if not, it will provoke significant opposition.
This can at the moment be seen in Ukraine, where Ukraine regularly (and rightfully, IMHO) claims that Russia's strikes violate the rules of war by hitting civilian infrastructure en masse, and where Ukraine's strike capability against Russia is severely impeded by Russian GPS jamming (that also causes serious safety issues for civilian airlines [1]), but also in the current Israel/Palestine war, where Hamas regularly claims that Israeli strikes are too imprecise [2] or unguided [3], while Israel claims it hits hidden weapons caches that subsequently explode and cause a lot of secondary damage [4].
While the V2 made use of a key element of inertial navigation systems (the Pendulous Integrating Gyroscopic Accelerometer [1]), it was apparently only used to cut off the motor when the desired velocity was reached (the other elements of the control system guided it on a trajectory which curved from vertical to 74 degrees as a function of time, with the azimuth determined by the positioning of the rocket on its launch stand prior to firing.) Consequently, the performance of modern inertial navigation cannot be deduced from V2 accuracy (or, rather, the lack thereof.)
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.
If NATO ever has any intention of deterrence through detonating a nuke, it will be done in exactly the way it's been specifically planned and openly explained: France has a specific nuclear policy, one of the only ones, that allows them to use nukes before an adversary does. They have a specific nuclear missile fired by plane that will be used as essentially a giant warning shot.
Nobody would fire a warning shot using an ICBM, because if things are hot enough to require a warning shot, that leaves a whole lot of interpretation up to your adversary who is quite likely to respond with their own ICBMs, before finding out yours were loaded with conventional munitions to make a point.
There are however, shorter range ballistic missiles, Russia has a lot of them (the US mostly gave up mid range ballistic missiles in a nuclear treaty) and has even launched a few with concrete "nuclear warhead simulation masses" at Ukraine.
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.
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 ratified by the USA, so its not even that mystical international law thing - its domestic law.
The nuclear powers have spent the next 25 years trying to lobby and bully their way out of this inconvenient bit of international law. Expect to see some in the comments.
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.
> 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.
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.
The USA does belong to the ICJ and has since its inception (the USA not a member of the ICC - different court).
Its just that after the invasion of Nicaragua in 1984 it decided to abide by the court "on a case to case basis". Russia also decided to ignore the ICJ in 2022.
FWIW I agree that everyone should have nukes, there would be a lot fewer military adventures. But that's not the _current_ USA/UK/FR domestic* and international law.
I'm not sure there are much in the way of geolocation countermeasures against ICBMs anyway, they're inertially guided. Unless you can generate localized gravity anomalies at will, I guess.
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.
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 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.
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.
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).
>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).
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.
> 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.
Yes, satellites are tracked by ground stations, and receive an update every 24 hours with information about their project positions in the future.
GPS satellites transmit this data in the form of an almanac which includes all the high level parameters for estimating the location of every satellite, and ephemeris data which allows you to calculate the precise location of the satellite, when used in tandem with the almanac.
The almanac doesn’t change too often, but ephemeris data is only valid for a few hours. The satellites recalculate the ephemeris data themselves, and normally have a few months of needed data stored on board, just in case they can’t get updates. But the expectation is they’re updated every 24 hours.
This is also why, in a zombie apocalypse type scenario, GPS would become inaccurate past the point of usability within a few weeks, maybe a few months max.
Amongst other things, the clocks need to be corrected for relativistic effects.
Due to the net effect of both kinetic and gravitational time dilation, clocks onboard a satellite advance more quickly than they would on Earth (when observed from Earth).
They use atomic clocks, so it's accurate to something like 1 part in 10^16, or about 1 second in a billion years! A friend of mine is working on the next generation, which will be even more accurate.
In contrast, the force of gravity experienced by the satellite is known to much less accuracy. In fact, changes on a monthly basis due to rainfall/rivers and tides. The GRACE satellites measure the change, although I couldn't find any information on how accurate their measurements are, except that they can measure the distance between the two satellites to within a micrometer (10^-6), so substantially less precision than the clock!
Not quite that accurate. Apparently it’s more like 3 seconds per million years for a rubidium atomic clock, and 1 second per 3 million years for a hydrogen maser. (Caesium atomic clocks are somewhere in between)
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.
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.
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.
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.
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.
Generally trains do everything they can to avoid slipping. They have anti-lock breaks and traction control just like your car, and stuff your car doesn’t have, like “sanders” which pour sand onto the track just in front of the wheels.
Regardless of material, dynamic friction is always lower than static friction. So for maximum acceleration and breaking it’s important to ensure you wheels stay in “rolling” mode of interaction, and don’t slip.
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.
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.
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
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.
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.
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?
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.
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.
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.
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.
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?
Maybe, I don't know enough about magnetic fields to say much. In my head they're directional so you'd know how it's aligned and can measure how strong it is, and that might function similar to a gravity map, especially if you know where you're coming from: there may be two places on earth with the same amount of gravity, or in this case, the same magnetic field strength, but if those places aren't next to each other that may still be tolerable depending on the system requirements.
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.
The science is cool, but I wonder if a specialized popular science magazine of yester-year would do a better job at presenting it? "We made a high-precision accelerometer that uses lasers and quantum effects; let me tell you everything about it." Right now, it reads more like "Dr. C has this very peculiar quirk when he goes to the London underground. Admittedly, it is not as bizarre as his habit of drinking coffee instead of tea, but going to the underground carrying an aluminum tube instead of a newspaper is just a tad flummoxing..."
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.
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.
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 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.
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:
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.
> The point I was making is that you do not need to make operation of Russian airplanes more difficult
I'm saying that "make flights difficult" is kinda-besides-the-point. 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."
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!
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?
“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”
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?)
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.
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)
I realize no one would be allowed to tell me if I am correct, but this tech sounds like it is perfect for military use. I am guessing there is already a pretty polished version of this roaming the oceans now.
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.
* 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.