Quantum technology crash course 6: Quantum sensing
An important but slept upon set of technologies.
This one was difficult to do. I’d like to thank QED-C and the Quantum Security and Defense Working Group for providing the vast majority of resources on the subject that I used to create this.
A quick summary of why quantum sensing has less attention paid to it.
The main reason this post was hard and took so long to write was that there are not too many great resources, it is very clear that quantum computing and the quantum internet are the two most popular subjects in quantum technology. I suspect it has something to do with the cryptography portions of both, where quantum computing will endanger what we hold most dear (or at least our banking) quantum key distribution can be a (partial) fix. Quantum sensing does not have either headline-grabbing attribute.
In many ways it’s already in use too, the technology isn’t as “new”. While quantum computing has claims of “quantum supremacy” or breaking “military grade encryption” every other week. Meanwhile standards organizations (NIST in the U.S) have timekeeping groups that are quietly building and using atomic clocks, a type of quantum sensor. We just don’t hear about it.
Types of quantum sensors
There’s definitely other types of quantum sensors that I won’t cover, but I am trying to cover a lot of ground and technologies. I’ve chosen three that seem to be representative of the range of solutions implemented.
There’s also multiple types of technologies for each sensor type, and a common theme is that researchers are looking for solid state, typically photonic, alternatives.
Clocks
The NIST-F2 clock is an example of a cesium fountain clock. Basically we make cesium atoms really cold, launch them through microwaves that are close to the frequency that will make the most electrons jump to a higher energy state, and tune that to maximize the energy jumps.
So in this technology we use the properties of atoms to find a certain frequency.
Accurate timekeeping like this is needed for communication, satellites and especially GPS. Without it we’d need to revert to letters and paper maps…. Or use “quantum GPS”.
Position
What if we had accelerometers so sensitive that given a starting position, they could pinpoint your location in 3d space given your starting position. All they need is to move along with you. They don’t need satellites, cell towers or other external devices. They can work in mines, under water and in areas where satellites can’t be trusted. In fact, they can probably be used in deep space.
I like to hike, and even in my local parks, getting a good GPS fix is sometimes impossible. I can’t imagine knowing I’m doing something where my location actually matters, but GPS is impossible to get.
There’s a good handful of technologies that can be applied to location, but the main way I’m currently seeing is to trap a quantum dot of some sort in a low energy point using standing waves. We then use the disturbances of those waves to determine the acceleration vectors.
Chemistry
This is actually the first quantum sensor type I encountered and knew were quantum sensors. I had known about the atomic clocks, but never realized they were built on quantum sensing. Some of these are absolutely ridiculous in how they work. Like, we have a mini soccer ball made out of carbon atoms, but one is missing so when we dump a bunch of these into polluted water it glows.
To highlight the ridiculousness of this, imagine having a black powder that glows to tell you what specific pollutant is in your cup of water. It feels like alchemy. “Your majesty I have created this powder that will make your wine light up if it’s poisoned.” And yet it works by some of the most technologically advanced processes available to us.
In summary
Quantum sensing is a wide field, I suspect that for every classical sensor there’s a similar Quantum one. I’m excited to continue to watch this field, despite its popular sleepiness there’s a lot of work going on. I just saw research on how some Quantum sensors can be used to improve prosthesis fit.
Most technologies right now seem to be built around manipulation of nanoparticles, but there’s a massive push to move to photonic technology as well.