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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

#61

Post by horstbort »

hi-v-rocknroll wrote: post #14
matt123456789 wrote: post #12

Earlier quoted context omitted.

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.

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.

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

#62

Post by BiteCode_dev »

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.

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.

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

#63

Post by [deleted] »

Terr_ wrote: post #41
akira2501 wrote: post #34

Earlier quoted context omitted.

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 imp…

> Russian airplanes are The simpler answer is that Russia is not directing the sabotaging signals into their domestic flight paths.

[deleted]

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

#64

Post by [deleted] »

nine_k wrote: post #59
contravariant wrote: post #38

Earlier quoted context omitted.

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.

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.

[deleted]

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

#66

Post by horstbort »

nine_k wrote: post #59
contravariant wrote: post #38

Earlier quoted context omitted.

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.

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 :-).

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

#67

Post by pugworthy »

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.

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.

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

#68

Post by nine_k »

BiteCode_dev wrote: post #62
nine_k wrote: post #60

Earlier quoted context omitted.

Every time a train arrives in a station, its exact position becomes known.

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…

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.

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

#69

Post by Terr_ »

surfingdino wrote: post #57
Terr_ wrote: post #39

Earlier quoted context omitted.

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…

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."

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

#70

Post by contingencies »

playingalong wrote: post #56
contingencies wrote: post #36

Earlier quoted context omitted.

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 fea…

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.

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.
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