What they are saying is that they produced a low noise sensor array and managed to increase the SNR through computation. They also stated that it was an ideal environment with no other electrical/magnetic interference.
Not anymore. That is exactly the purpose of Darpa Ambient program: https://www.darpa.mil/research/programs/atomic-magnetometer-...
Demo from 2022: https://www.youtube.com/watch?v=VTnIXWCBYTw
As with all DARPA projects, there is a civilian use-case and a military use-case.
That demo was at a conference, in a city, surrounded by electronics and RF noise. The fact that it worked at all in that environment is surprising. As the subject got closer to the apparatus, the signal became larger than the background noise. So, I think the distance is limited mostly by background noise. The press release did state that it was an optimal environment for locating their target, i.e., an isolated person with only geomagnetic noise and known signatures of the aircraft.
Oh, but you say that you simply cool the sensor to 0K. Cooling helps, but you're still many orders of magnitude short even at near 0K, and you're doing this in Iranian mountains, not a dilution refrigerator.
> A magnetic dipole doesn't radiate energy outward the way a radio antenna does.
See Section 15-5 of https://www.feynmanlectures.caltech.edu/II_15.html#Ch15-S5
Veritasium has a video on the weirdness of MVP: https://m.youtube.com/watch?v=XKSjCOKDtpk
See https://pubs.aip.org/aip/adv/article/13/2/025127/2877320/Dif... for an experiment measuring MVP with an optical-atomic magnetometer.
> Oh, but you say that you simply cool the sensor to 0K.
These sensors do not require cryogenics and have been developed with sensitivities of 10s of fT/√Hz, so approaching the quantum noise limit.
Essentially, you can think of it as measuring the energy of a magnetic dipole in space instead of measuring a magnetic field.