Quantum Sensing for Gravity Cartography | Hacker News Reader

Quantum Sensing for Gravity Cartography

nature.com

19 pointsbookofjoe10 comments

Wonder if we’ll be able to make something equivalent to a gravitational camera at some point.

That's what LIGO is, in essence.

The French navy is going to equip 4 ships with ONERA's GIRAFE quantum interference gravimeters, starting in 2023, based on a prototype developed in 2012:

https://www.capital.fr/economie-politique/la-marine-francais...

One of the goals is to be resistant to GPS jammers.

Maybe it's explained in the article but my french isn't great

But how would that work to replace (?) GPS?

Not french speaking but I will guess that by using extremely precise inertial navigation. Accelerometers measure acceleration + gravity. You need to subtract the gravity.

Submarines have been using gravity gradiometers for navigation for decades. Tom Clancy revealed what was then classified information about these in The Hunt for Red October. They can serve as passive collision avoidance systems or let the navigators use geological features to correct drift in inertial navigation. The later application requires gravity gradient maps. They are useful for submarines because they are completely passive, unlike active sonar that produces a signal others can detect.

I did some simulations of doing this (in Qbasic). The issues that I ran into was that effectively the matrices were singular. I think this might not be mathematically possible for static gravity measurements.

Interesting! Perhaps that could’ve been a numerical accuracy issue? Do you have code somewhere you’d be willing to share?

I dont have my qbasic code from 1998. I wish I did.

The setup was like a sensing array vs a much smaller array of test gravity sources (all in 2d).

Apologies for the paywall, but this paper describes imaging cargo containers with gravity gradient sensors (to look for, e.g., plutonium):

https://ieeexplore.ieee.org/document/4215058

Basically you can image anything if there is a density contrast, it's "just" a matter of how good your sensor and inversion algorithm is.

I spend my day-to-day working on measuring gravitational changes to determine groundwater storage change. There's a huge difference between demonstrating something in the lab vs. building an actual field instrument you can use in the real world.

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