Enhanced quantum sensing with a nitrogen-vacancy centre as gateway to the electron spin of phosphorus

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In order to investigate the key scientific question, "can the electron spins of phosphorus donors nearby NV centres in diamond be used as quantum sensors", at first a couple of phosphorus doped samples were measured. The doping concentrations were about 10^16 atoms/cm^3. However, as opposed to the initial measurements, there was no response from any defects/impurities nearby the measured NV centres. There are several potential explanations for this, which are researched currently. The first, a higher phosphorus concentration might be needed to have a fair chance to have a donor close enough to the NV centre. This will be tried by increasing the phosphorus concentration as much as possible. Secondly, the measurement method might be insufficient. To study this, we decided to look at a more "straightforward" (yet new) situation: coupling two NV centres. With the help of QST, we implanted molecules with multiple nitrogen atoms into phosphorus-doped diamond to have a high chance to have NV centres close together. The idea was to first try to use such couples for quantum sensing, as interaction with both NV centres is possible (if their orientation is different), hence it is easier compared to using dark spins. Although we were able to find couples of NV centers with different orientations fairly easily, they were either not stable (probably charge state), or their coherence times were very short (about a microsecond instead of close to a millisecond). Thirdly, we looked at a different measurement method that might be more suitable. The latter we will submit for publication soon.