What do/will "quantum gyroscopes using nitro­gen-vacancy centers in diamond" for space applications actually look like, and how do they work?

Question

The NASA page ELaNa 41 Mission has a section labeled QubeSat - University of California, Berkeley which says:

QubeSat is a technology demonstration mission. It will test and character­ize the effects of space conditions on quantum gyroscopes using nitro­gen-vacancy centers in diamond. Nitrogen-vacancy centers are ni­trogen defect points in diamond with quantum properties that allow scientists to form gyro­scopes that measure an­gular velocity. Nitrogen-vacancy center-based technologies are particu­larly well suited for space because of their high accuracy, small form factor, and radiation tolerance.

It also links to the UC Berkeley page QubeSat: An Investigation in Quantum Sensors for CubeSats which begins:

The Place for CubeSats in the Second Quantum Revolution

This project is well aligned to the Second Quantum Revolution, a recent scientific phenomenon whereby quantum effects are utilized in technology to achieve better sensitivity and lifetime.

and includes the drawing shown below which I don't understand.

Question: What do "quantum gyroscopes using nitro­gen-vacancy centers in diamond" look like, and how do they work?

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Figure 1: Quantum Gyroscrope (source)

Answer 1

(Disclaimer: I'm just a software engineer that happens to work in a quantum research center. This answer is based on my understanding of NV centers, which is limited to what I need to know for my software work plus things I pick up here and there, and takes a lot of shortcuts. I hope someone more knowledgable can correct the mistakes I'm bound to make).

Unfortunately, I think I need to explain a few concepts in order to answer this. I'm probably taking a lot of shortcuts and butchering a few concepts, in particular playing fast and loose with electron and nuclear spin. I hope it is more or less clear.

NV center

A diamond is a lattice of carbon atoms. A carbon atom has 4 valence electrons, meaning each carbon atom can bind to four other atoms. An NV center is a naturally occurring deficiency in the diamond lattice where a nitrogen (N) atom has replaced a carbon atom and in addition a neighboring carbon atom is missing (the vacancy V). This NV combination has 5 sort of "free" electrons: 3 due to the missing carbon atom, 2 from the nitrogen atom that has 5 valence electrons but only 3 are bound to nearby carbon atoms. The NV center may actually capture a 6th electron from its environment, which makes the NV center negatively charged. This negatively charged NV center has all kinds of funky properties (see e.g. Wikipedia or any of the numerous resources). For the purpose of this explanation it is sufficient to think of the negatively charged NV center as having a single "free" electron.

Electron spin resonance

For this story, three properties of electrons are relevant:

• electrons can be excited by absorbing a photon
• once excited, the electron will decay after some time and when doing so they release a photon
• electrons have a spin (-1, 0, +1)

Resonant excitation of an electron means that you bring it to the excited state by shooting a photon of a specific frequency at it (read: laser). If the frequency is wrong, the electron will not be excited. The crucial thing here is that the spin state of the electron determines what their resonant frequency is. Also, once excited, they don't necessarily decay to the same spin state. I won't go into details, but the result of this is that if you manage to bring the electron in e.g. the 0 spin state, and you shoot at it with a laser that is resonant with that state, you will initially see the electron emitting photons as it decays (read: shoot really short laser pulse and see if after some time you see a photon come out). But after a while (it's a stochastic process) the electron will decay to a different spin state that is not resonant with your laser and you won't see any photons come out any more.

Magnetic dipole

The negatively charged (because of the extra electron) NV center is a magnetic dipole. If you apply an external magnetic field to the NV center, it will start precessing (here comes your gyroscope). As it precesses, the spin state will change. Usually this is used to manipulate the spin state as a qubit: by applying radio frequency and microwave frequency EM fields to the NV center, you manipulate the spin state to do "computations". Then you shoot a laser at it to see in which state it ended up (think: photon = 1/no photon = 0, but that is a very rough analogy and breaks down in many ways I don't go into).

How the gyroscope works

I'm going by the paper @GrapefruitIsAwesome linked; I'm not sure if that is the same as the one they're launching, but I assume the concept is the same.

They (the paper) are allowing the magnetic dipole to precess freely in a stationary magnetic field. If you rotate the sample, the orientation between the NV dipole and the external field changes, which affects the spin state. They "read" the spin state by shooting laser pulses at it with a frequency that is only resonant with one of the states. The number of photons detected is a measure of the spin state and by proxy a measure of how much the sample precessed, from which they can then compute the gyration rate.

What it could look like

Educated guess, based on the building blocks as described in the paper:

1. Diamond sample. This looks less exciting than one might think: it roughly looks like a small PCB with a bunch of strip lines and contacts to apply the RF and MW EM fields. This page has a microscopic photo of one. The "bubble" is a lens etched in the diamond. (I don't think I'm allowed to post photo's from what I work on...).
2. RF and MW sources to generate EM fields to manipulate the qubit.
3. One or more lasers to initialize and "read" the qubit.
4. Control electronics.

I'm surprised they can manage to squeeze that in a Cubesat form factor...!