London Underground hosts tests for 'quantum compass' that could replace GPS
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Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#2This 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.
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#3[deleted]
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#4Is 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?
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#5Is 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?
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?)
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#6Is 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?
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 )…
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.
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#7Highly accurate dead reckoning basically. I wonder how it compares to the other method of mapping subterranean patterns and matching to them.
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#8Is 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?
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 )…
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.
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#9I 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.
Re: London Underground hosts tests for 'quantum compass' that could replace GPS
#10Journalists 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.