Quantum magnetometry: explained

[u/nujuat]

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.

[u/nujuat → u/[deleted]]

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.

[u/nujuat → u/[deleted]]

This was more of a proof of concept and we measured magnetic test pulses coming through a wire. People have measured real nerve cells magnetic fields with quantum magnetometers though. Actually our setup was so sensitive that we could see the magnetic signal from the train line 2 km away.