4 ms·

It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and s

by Traster 9mo ago

It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and so even small errors accumulate. The article doesn't really address what makes this different - and in fact I don't think it is different. You're still just measuring acceleration using a sensor and that sensor will have errors that accumulate. So the question is how much better is it? I would wager that actually this is probably just a way of funnelling money into research around quantum rather than genuinely trying to solve this specific problem. This specific problem sounds like it could be solved for a lot less money using conventional accelerometers in combination with some other local location data (optical sensors for example, you're in a very controlled environment).

otikik 9mo ago
It’s quantum so it’s better
vasco 9mo ago
At every station at least it should be very cheap to install optical markers that could allow for many opportunities for recalibration.
- BiteCode_dev 9mo ago
  Agreed, but then said optical markers regularly positioned in tunnels and a map of the tube is enough to position yourself already. That's likely how it works right now, and it's fine.
  - bluGill 9mo ago
    The article says they just use wheel sensors. Most of them time they don't need to be very accurate so that is more than good enough, but in stations much higher accuracy should be needed and so they need an additional correction there. (note that I said should: I'm a strong believer in automated edge of platform doors which require stopping so the train doors align. Few systems in the world have this though)
    - avianlyric 9mo ago
      A number of parts of the underground already have platform edge doors, and train stopping locations are tightly controlled regardless of the presence of platform edge doors.
smuenkel 9mo ago
[dead]
dariosalvi78 9mo ago
the accumulation is due to integration when converting acceleration to distance, not the accelerometer itself
- dukoid 9mo ago
  I wonder if it theoretically could (or already does) benefit from something like this: https://www.youtube.com/watch?v=nCg3aXn5F3M https://www.youtube.com/watch?v=nCg3aXn5F3M
- avianlyric 9mo ago
  The accumulation might be from the integration, but the error is clearly from the accelerometers. Smaller error means smaller accumulated error, which means your magic box is usefully accurate for longer.
avianlyric 9mo ago
> I would wager that actually this is probably just a way of funnelling money into research around quantum rather than genuinely trying to solve this specific problem. You’re absolutely correct, from the government’s perspective the interest in the technology is for high accuracy inertial navigation systems for defence purposes, not for the London Tube. If you look at the other companies involved in this project, there’s a number of defence contractors involved. This project isn’t really new, and historically the pitch has always been: We want to develop GPS grade navigation that doesn’t depend on satellites, and is smaller and better existing inertial navigation units. Oh look the London Underground is the perfect test bed for our technology! It’s underground, so no GPS or many external signals. It’s already well mapped so we have something to compare against. Tube trains are loud, hot and vibrant a lot, which makes it a challenging environment for inertial systems. Plus it’s cheap and very easy to roll a box on an existing train, drive a few km under the city, and then compare your results to GPS from when you go underground, to when you surface again. https://www.theguardian.com/science/article/2024/jun/15/london-underground-quantum-compass-gps-subatomic-instrument-locations https://www.theguardian.com/science/article/2024/jun/15/lond... The idea of using it map the underground I think is a bit of a red herring. Makes a good story, and TfL will probably be grateful for the data. But it’s not the kinda thing anyone thinks is worth developing quantum accelerometers for.
- bluGill 9mo ago
  Given all the GPS jamming in Russia/Ukraine the defense world needs something not GPS based that works. The civilian world also needs this since they are often hit with the same jamming (both as collateral damage and intentional harm to the enemy)

by Traster 9mo ago

otikik 9mo ago

It’s quantum so it’s better

vasco 9mo ago

At every station at least it should be very cheap to install optical markers that could allow for many opportunities for recalibration.

BiteCode_dev 9mo ago
Agreed, but then said optical markers regularly positioned in tunnels and a map of the tube is enough to position yourself already. That's likely how it works right now, and it's fine.
- bluGill 9mo ago
  The article says they just use wheel sensors. Most of them time they don't need to be very accurate so that is more than good enough, but in stations much higher accuracy should be needed and so they need an additional correction there. (note that I said should: I'm a strong believer in automated edge of platform doors which require stopping so the train doors align. Few systems in the world have this though)
  - avianlyric 9mo ago
    A number of parts of the underground already have platform edge doors, and train stopping locations are tightly controlled regardless of the presence of platform edge doors.

smuenkel 9mo ago

[dead]

dariosalvi78 9mo ago

the accumulation is due to integration when converting acceleration to distance, not the accelerometer itself

dukoid 9mo ago
I wonder if it theoretically could (or already does) benefit from something like this: https://www.youtube.com/watch?v=nCg3aXn5F3M https://www.youtube.com/watch?v=nCg3aXn5F3M
avianlyric 9mo ago
The accumulation might be from the integration, but the error is clearly from the accelerometers. Smaller error means smaller accumulated error, which means your magic box is usefully accurate for longer.

avianlyric 9mo ago

> I would wager that actually this is probably just a way of funnelling money into research around quantum rather than genuinely trying to solve this specific problem. You’re absolutely correct, from the government’s perspective the interest in the technology is for high accuracy inertial navigation systems for defence purposes, not for the London Tube. If you look at the other companies involved in this project, there’s a number of defence contractors involved. This project isn’t really new, and historically the pitch has always been: We want to develop GPS grade navigation that doesn’t depend on satellites, and is smaller and better existing inertial navigation units. Oh look the London Underground is the perfect test bed for our technology! It’s underground, so no GPS or many external signals. It’s already well mapped so we have something to compare against. Tube trains are loud, hot and vibrant a lot, which makes it a challenging environment for inertial systems. Plus it’s cheap and very easy to roll a box on an existing train, drive a few km under the city, and then compare your results to GPS from when you go underground, to when you surface again. https://www.theguardian.com/science/article/2024/jun/15/london-underground-quantum-compass-gps-subatomic-instrument-locations https://www.theguardian.com/science/article/2024/jun/15/lond... The idea of using it map the underground I think is a bit of a red herring. Makes a good story, and TfL will probably be grateful for the data. But it’s not the kinda thing anyone thinks is worth developing quantum accelerometers for.

bluGill 9mo ago
Given all the GPS jamming in Russia/Ukraine the defense world needs something not GPS based that works. The civilian world also needs this since they are often hit with the same jamming (both as collateral damage and intentional harm to the enemy)