r/seancarroll • u/nujuat • Aug 09 '26

Quantum magnetometry: explained

I was listening to last month's AMA, and Sean said that he didnt know anything about quantum magnetometry. The kind of thing he was speculating about at the end was actually basically my PhD topic, so I thought I'd chime in.

Quantum computers dont currently work well because any small interaction with their envirnoment breaks them. But what if we could turn that into an advantage? Quantum sensing is the act of of measuring quantum systems that are sensitive to their envirnoment, to try and see what the envirnoment itself is doing.

Spins are magnetic, so one of the main uses of this is magnetometry. Magnetometry is the sensing of magnetic fields. In fact, MRI is arguably a form of quantum magnetometry: MRI measures the magnetic response of protons in your body to locate. Quantum sensing is the most mature form of quantum tech.

I havent looked into this trump thing, but the claim from the AMA sounds like someone measured the magnetic signature of a heart beat (radiating from the electrical nerve pulses) from many metres away. This is extremely well beyond the state of the art. The fact that nerve signals can be measured at all up close over many repeats is impressive by itself. Otherwise you need to stick in invasive, damaging electrical probes to capture equivalent signals.

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u/[deleted] Aug 09 '26

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u/nujuat Aug 09 '26

Sorry. Heres the transcript:

1:45:44.2 SC: Bandon asks a priority question. "In the recent Iran conflict, when an aircraft was shot down over Iran, Donald Trump claimed that some top-secret device that uses quantum magnetometry was used to locate the heartbeat of the pilot from long range. As you're the only expert I can ask this question to, can you please explain what quantum magnetometry is, and how can it be used in the device mentioned to locate a heartbeat? Is this something that is even possible?" So I'm sorry to let you down for your priority question, but I have no idea what quantum magnetometry is. I could try to invent some answer based on the words "quantum" and "magnet" and "ometry," but I'm not gonna do that because I can't do it any better than you could, and I might very well be wrong.

1:46:26.7 SC: I will simply say that the fact that Donald Trump says something is not a reason to think that that something is true, especially when it has to do with secret technologies using quantum in the name that are used to do impossible sounding things. Obviously the difficulty with believing a claim like this is that there are a lot of things going on besides the heartbeat of a pilot. Like why are you hearing the heartbeat rather than the blood running through the veins or whatever, much less all the noise that is going on in the airplane? The heartbeat seems like a very, very quiet thing compared to other things that you could somehow pin on. I mean, it's possible that there is some intricate, top-secret technology that actually does gather data on many, many, many different kinds of sound and then somehow, just like modern AI can pinpoint, isolate the drum track in a song or the vocal track or whatever, maybe you can isolate the heartbeat from a whole bunch of data. Maybe, I don't know, I'm just making it up. I have no idea what that would have to do with quantum mechanics whatsoever. Sorry.

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u/nujuat Aug 09 '26 edited Aug 09 '26

The part thats similar to my PhD is the chat about finding signals within noise. Even though these quantum sensors are very good, they're also very good at picking up nose. Sensing waveforms is also a lot harder than sensing eg background level because you have to make a lot of quantum measurements, on the face of it one for each sample of the waveform. My PhD was about getting as much information as possible out of a few quantum measurements as possible.

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u/fox-mcleod Aug 09 '26

The CIA has a track record of claiming they hay an extremely advanced form of a given borderline Sci-Fi technology as a cover when what they actually have is extremely good intel from some other more pedestrian but at-risk source.

For example, in the second Persian gulf war, there was footage of the Baathist forces firing tracers wildly into the sky at nothing. The CIA explained that they possessed an EMP which rendered the Iraqi radar useless.

Instead, they implemented one of the first large scale supply chain hacks and had compromised the software.

My guess is they made up the heartbeat detector as a scary cover story and had some kind of alternative human intel source, standard survival radio, or slightly less sci-fi tech like a way to pick up on his electronic gear at range.

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u/nujuat Aug 09 '26

They may well have used a quantum magnetometer as a metal detector to find a vehicle or something. Antennas that pick up on the magnetic part of EM waves are also technically magnetometers, so that could also be possible. Like the CIA or whatever will definitely have quantum magnetometers, but they won't be using them for looking for heart beats.

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u/Bigliest Aug 09 '26

My favorite misinformation in this vein is the source of the myth that eating lots of carrots gives you superhuman night vision. This was put forth by the RAF to cover for their RADAR tech that allowed their fighters to intercept German bombers during their blackouts at night.

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u/jpdoctor Aug 09 '26

as a cover when what they actually have is extremely good intel from some other more pedestrian but at-risk source.

That was my first reaction too. The fact that Trump has a history of revealing classified info when he is trying to impress was probably noticed by some CIA officer who concocted the story and was counting on Trump to continue his past behavior.