How to Think about Diamonds

Most of us think about diamonds as a precious gem, hard, with high refractive index and perhaps a good investment (EU thinks so as well, hence our research grants). Today, diamonds find variety of usage, in cutting industry, bijouterie, and also as radiation and heat shields in modern space probes. A rather unrelated use can be found in modern quantum optics labs-this is how we think of diamonds-as the host material for one of the most precise and responsive quantum sensor.

Diamond has impurities (Carbon atom replaced with a non-carbon atom) and vacancy (missing Carbon atom). These vacancies often act as a trap for electrons, and these electrons in the vacancy have extraordinary sensitivity towards external changes in magnetic/electric fields and temperature. To put this in practice we need to address individual vacancies in diamond, or sometimes a bunch of them. There are sophisticated techniques to artificially grow these diamonds with suitable properties and sizes (preferably small), but the very first nanodiamonds were obtained with brute force. Natural diamonds are in abundance in Russia, so what do they do with it? Well, they put them with explosives in a closed chamber and press the button, this produces very fine diamond particles and this is how the very first nanodiamonds were produced, and are known as detonation nanodiamonds.

Now back in the lab again, lasers and microwaves are used to manipulate and control the electrons in the vacancies in order to quantify the external perturbation by its effect on the state of the electron. Rather complicated NMR techniques are used for more accurate measurement.

To enhance the efficiency of the tiny sensors further, ‘’optimized’’ microwave pulses are used. This is where quantum optimal control comes into picture. Ample of optimization algorithms come handy in this particular case. It’s a fad to have unusual names for these algorithms. There is GRAPE, CRAB, and GOAT (and it’s not Lionel Messi for a change). Technically these algorithms aim to converge to an extremum, either by performing a gradient based search or a simple search. Implementing optimized microwave pulses to control the sensors results in enhances sensitivity and improved robustness towards experimental imperfections. Although, this may not be the most aesthetic use of diamonds, prospects of it being the next generation quantum sensors makes diamonds even more precious.