Optically coherent NV centers in um-thick etched diamond membranes for quantum applications

Future quantum networks depend on efficient entanglement generation between nodes. Recently, we have generated entanglement between nitrogen-vacancy (NV) center nodes with a success rate of up to 40 Hz. This rate is now limited by the zero-phonon-line emission probability as well as the photon collection efficiency. Embedding a diamond slab containing individually resolvable NV centers between two highly reflective mirrors can address both challenges, benefitting from large Purcell enhancement due to a low optical mode volume.

Until now, cavity-enhanced entanglement generation between NV centers has not been achieved, predominantly due to poor optical properties of NV centers close to the diamond surface. Via a combination of electron irradiation and an optimized etch sequence, we have fabricated a 3.5 um thick membrane that combines low surface roughness (< 0.4 nm) and narrow optical NV transitions (<100 MHz). We incorporate such devices in an open, tunable micro-cavity setup, with the potential for a two orders-of-magnitude increase in remote entangling rates.