The article links to a better article, https://news.sky.com/story/royal-navys-experimental-ship-car..., which calls the device an accelerometer. I think the article linked here got literally all its information from that other article. Apparently it's a small number of rubidium atoms, cooled to near-absolute zero, under which conditions they can apparently measure gravitational effects and make deductions from that ("measure extremely accurately the influence of gravity on their system, which in turn allows them to measure the speed and direction of its movement").

》measure gravitational effects and make deductions from that ("measure extremely accurately the influence of gravity on their system

Aha! So it might be able to detect other submarines, even if they use some stealth tech.

Submarines generally have neutral bouyancy while underway so there's not much density difference to discern.

That sounds absurd, but the $5 pressure sensor on my weather station could detect a volcanic explosion 5,000 miles away.

Is there even a difference between a submarine and the surrounding water's gravitational fields when the sub has neutral buoyancy?

I'd argue that the gravity field of a sub is not uniform despite having neutral buoyancy. No idea though how significant that is vs. how sensible the measurement is

You'd have better luck trying to measure a neutron with a bathroom scale.

There probaly would be, the displacement might be the same but the distribution of mass wouldn't. But I recon these instruments are only sensitive enough to measure the difference between the seafloor and the water above.

Not even close.

The article lacks detail, but sounds like it's talking about something like an atomic gyroscope[1].

There are a few types of passive quantum navigation systems, but the principle is similar to a using a stopwatch and an old-school gyroscope to measure changes in momentum and then calculating your position via dead reckoning. It just sounds like quantum methods have let them get a lot more precise.

This is actually pretty exciting from the perspective of deep sea exploration. Once you get below the surface there's no GPS and it becomes difficult to fix your position. With one of these, you'd have something like GPS no matter how deep you go.

[1]https://www.nist.gov/noac/technology/time-and-frequency/atom...

Submarines have had good inertial navigation systems since the 1960s. Early gyros occupied about a cubic meter.[1] With a really big, heavy flywheel, it's easier to keep drift down. Nuclear submarines usually had three installed, for redundancy.

[1] https://www.ion.org/museum/item_view.cfm?cid=2&scid=4&iid=4

This is pretty exciting from the perspective of any kind of navigation. If this gets into a phone, we will be able to navigate on a digital map with no signal at all.