&Bullet; physics 14, 73
A small device performs rotational measurements with nuclear spins in a diamond wafer and paves the way for microchip-sized gyroscopes.
Future technologies for unmanned and autonomous vehicles require precise gyroscopes for reliable flight and reliable navigation. However, these devices are usually too large to be suitable for light microscopic electronics. Now researchers have demonstrated a tiny gyroscope that takes advantage of the behavior of atomic nuclei in diamonds  . Compared to previous diamond-based sensors, the device can measure slower speeds – in a range (several tens of degrees per second) that is relevant for aerospace applications. The researchers expect that further development could lead to a new generation of commercially viable and ultra-sensitive microchip gyroscopes.
A gyroscope detects changes in the orientation of an object such as an airplane. Today’s most accurate gyroscopes use laser light that moves in a closed path around a ring. However, the accuracy of such devices depends on the area enclosed by the ring. So if you shrink the gyroscopes they will be less reliable. The realization of small but still sensitive gyroscopes requires a different approach, and researchers have developed alternatives based on the exploitation of the behavior of elementary particles that have spin.
The spin state of a particle remains – like the spin axis of a toy gyroscope – as long as it is not influenced by an external force. A conceptually simple design for a gyroscope is therefore to put the spin of a particle in a certain state, leave it alone, and then measure the spin again. Any change would reveal a rotation of the object comprising the particle, such as a flying vehicle.
However, getting such a gyroscope to work in practice is challenging. Some researchers have tried working with atomic gases in small traps, but collisions with walls tend to disrupt atomic spins. The use of diamond avoids this problem. Diamond is made up almost entirely of carbon atoms, but also contains places where a nitrogen atom replaces a carbon, while a nearby atomic gap remains in the lattice. These nitrogen vacancy (NV) centers have both electronic and nuclear spins that researchers use to detect rotation (see Focus: Detecting the Rotation of a Quantum Spin), but not yet the level of sensitivity required for a gyroscope.
Alexey Akimov from the Lebedev Physical Institute in Russia and colleagues have now demonstrated a gyroscope based on NV centers in a thin diamond wafer. In contrast to previous work that focused on the spins of electrons or carbon nuclei associated with NV centers, the researchers chose the spins of nitrogen nuclei as their rotation detectors. The nitrogen spins are less prone to interference than the other spins. However, the electron spins still proved useful in initializing and reading out the nuclear spins.
To demonstrate how the gyroscope works, the researchers placed their diamond wafer on a rotating platform that was embedded in a magnetic field. In such a field, the electron and nitrogen spins in an NV center are coupled by a light-mediated interaction. Taking advantage of this property, the team used a series of light pulses to spin the nitrogen spins in an ensemble of NV centers. Then they let the spins develop for 2 milliseconds before reading out the new spin state with a second series of pulses.
This readout step made use of another convenient property of NV centers: the state of the electron spins – and thus the nuclear spins – can be derived from the amount of light emitted by the NV centers. The researchers slowly turned the platform at a speed of less than one revolution per second, measured the intensity of the emitted light and calculated the speed of the platform based on this signal.
In addition to setting up and reading out, the electron spins also played a subordinate role in significantly improving the accuracy of the measurements, says Akimov. By monitoring the electron spins, the team was able to correct a magnetic field effect that caused additional rotation of the nuclear spins. The team checked their gyroscope with a commercial microelectromechanical systems (MEMS) gyroscope and found a good match. According to Akimov, the NV gyroscope could have the advantage over other gyros that it does not require constant recalibration.
Another advantage is that diamond crystals can be more easily integrated into existing microchip technology than gas-based devices. “The solid-state property of the sensor is a great advantage,” says physicist Dmitry Budker from Johannes Gutenberg University in Germany, whose research group first proposed this approach in 2012. Akimov and colleagues are now miniaturizing their gyroscope so that it might eventually fit on a microchip. “A lot of things can be improved to make the device smaller,” says Akimov.
Mark Buchanan is a freelance science writer who splits his time between Abergavenny (UK) and Notre Dame de Courson (France).
- VV Soshenko et al., “Nuclear spin gyroscope based on the nitrogen vacancy center in diamond” Phys. Rev. Lett.126197702 (2021).