MoD’s ‘quantum compass’ offers potential to replace GPS – FT.com

The Ministry of Defence is investing millions of pounds to look for the holy grail of navigation: a tamper and interference-proof device capable of pinpointing a location anywhere on the globe.

Scientists at Porton Down and the National Physical Laboratory believe they are three to five years away from developing a “quantum compass” that would be able to locate itself based on the subatomic effects of the earth’s magnetic field.

The technology, which would have no need for satellites or fixed points of reference such as radio masts, is of military interest around the world, because of the limitations of space-based navigation systems.

In February, the US pioneer of GPS, the most widely used satellite navigational array, warned that the system was under strain and was extremely vulnerable to deliberate disruption or attack.

via MoD’s ‘quantum compass’ offers potential to replace GPS – FT.com.

The incredible leap that GPS technology provided will be hard to duplicate (for instance, GPS is as much a timing system as it is a navigation system). But a totally passive system would be immune to enemy attack.

9 thoughts on “MoD’s ‘quantum compass’ offers potential to replace GPS – FT.com”

  1. I would like to know more about how this works. I understand quantum entanglement but I am wondering just how that translates into determining position. Also how they avoid decoherence and similar issues.

    Anyone have any links to deeper stuff than the news blurbs?

    1. It can not be quantum entanglement. That’s decades in the future for soldier/sailor-proof tech, especially for more than one measurement.

      They are using a Bose–Einstein condensate. Not very portable.

      My guess is it’s correlating the measured magnetic field in the Bose–Einstein condensate with a regularly updated database, or a “robust” model.

    2. I am sure they are using a laser super-cooled condensate to produce correlated electron pairs and measuring the magnetically induced variations to determine direction relative to the earth’s magnetic poles, Some birds are believed to do something like this albeit at normal temperatures. But all that seems to give is a compass. And unless one already knows one’s location to some degree, one does not know the declination to apply to determine true north vs. magnetic north.

      In any case, compasses of any kind are problematic on a ship containing potentially magnetic substances such as a chrome vanadium hull. A moving, maneuvering sub will interact with the earth’s magnetic field and distort it somewhat, not to mention everything else happening on a sub.. Shielding the device from magnetic fields would of course defeat the whole idea. In determining direction, how does this end up better than a laser ring gyro?

      But again as far as I can see this is still only a compass. Where is the GPS replacement? GPS gives location in three dimensions relative to a frame of reference aligned to the rotating earth. How does this do that?

      In addition there is still the issue of a device ruggedized to mil spec able to reliably maintain entanglement correlation sufficient to be useful. Interaction with the environment de-coheres entanglement pretty quickly, Doing that in a lab is hard enough.

      So how does this really work? The various articles obviously do not have the whole story.

    1. Interesting, thanks. I knew about the drift but was unaware there was finally a decent theory to account for it.

      Still trying to figure how the magnetic field ties into entanglement correlation and how they can stay correlated after a measurement.

  2. ” GPS is as much a timing system as it is a navigation system.” This is not a true statement.

    In celestial navigation, you determine longitude by measuring the time difference between the prime meridian (“zero longitude”) and your location. You do this by star sightings. GPS works in a similar fashion, except it does it by measuring the time differential between the signal leaving the satellite and its reception at the receiver. When you know the position of the satellite, then the time differential between broadcast and reception yields one line of position. A minimum of three satellites are needed to produce a two dimensional fix.

    The reality is that all navigation, other than dead reckoning, is completely dependent on time.

    1. Well, DR and inertial aren’t completely dependent on time (though both require some timing).

      And from what little I can grasp of the technology behind this quantum system, it would be reliant upon variations in the earth’s magnetic field, rather than relying on timing signals from a master station.

      My point is, there are quite a few applications that use GPS that don’t care where they are, but only what time it is, to a very precise degree. For instance, automated trading programs rely on precision timing. There telephony switching systems also reliant on timing, which, again, don’t really care where they are.

      Should the quantum system be completely independent of outside signal, it would only provide positional data, not timing data.

    2. GPS receivers use signals from four satellites. The position and timing signal from one satellite puts the receiver on the surface of an imaginary sphere. The radius of that sphere is deduced from the time lag of the signal. A second signal creates a second sphere that overlaps the first in a circle. (Think two soap bubbles.) A third sphere intersects that circle at two points. A fourth sphere intersects one of those points.

      This all depends on the receiver having an accurate clock to determine the distances of the satellites. Since atomic clocks are a bit large to carry in one’s pocket (and a mite expensive as well), a different method is needed. The receiver first assumes that the latest time signal is the current time, that is, that it is right next to the satellite. The candidate time is then advanced until the several signals converge on a single point.

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