World's first GPS-free quantum navigation trial succeeds at sea

“Quantum sensors can sense the tiniest of changes in the gravity or magnetic field and use a previously prepared map of these properties to determine their location. Since a quantum sensor does not need to receive or send a signal to an external device, it cannot be hacked or be spoofed by a fake incoming signal either. “ Very cool!

Don’t these fields fluctuate in some currently not understood way?

Yes, constantly. The prepared map becomes less accurate over time.

So you constantly need updated maps. Reminds me of celestial navigation where you always need an up-to-date almanac.