Reducing inhomogeneous broadening of spin and optical transitions of nitrogen-vacancy centers in high-pressure, high-temperature diamond

With their optical addressability of individual spins and long coherence time, nitrogen-vacancy (NV) centers in diamond are often called “atom-like solid spin-defects”. As observed with trapped atomic ions, quantum interference mediated by indistinguishable photons was demonstrated between remote NV centers. In high sensitivity DC magnetometry at room temperature, NV ensembles are potentially rivaling with alkali-atom vapor cells. However, local strain induces center-to-center variation of both optical and spin transitions of NV centers. Therefore, advanced engineering of diamond growth toward crystalline perfection is demanded. Here, we report on the synthesis of high-quality HPHT (high-pressure, high-temperature) crystals, demonstrating a small inhomogeneous broadening of the spin transitions, of T2* = 1.28 μs, approaching the limit for crystals with natural 13C abundance, that we determine as T2* = 1.48 μs. The contribution from strain and local charges to the inhomogeneous broadening is lowered to ~17 kHz full width at half maximum for NV ensemble within a > 10 mm3 volume. Looking at optical transitions in low nitrogen crystals, we examine the variation of zero-phonon-line optical transition frequencies at low temperatures, showing a strain contribution below 2 GHz for a large fraction of single NV centers. Nitrogen-vacancy centers in diamond offer a promising platform for quantum applications but their optical and spin properties can be hampered by imperfections of the host crystal. Here, nitrogen-vacancy centers are created in high-pressure high-temperature diamond of high crystalline quality, demonstrating a small inhomogeneous broadening of the spin and optical transitions.