Karoly Holczer1 and Jason Cleveland2

1UCLA, Department of Physics & Astronomy
475 Portola Plaza
Los Angeles, CA 90095-1547, USA

2SomaLogic Inc.
2945 Wilderness Place
Boulder, CO 80301, USA

Among the various isolated impurity sites in diamond, Nitrogen – Vacancy (NV) centers have been extensively studied over the past 25 years or so. The exceptionally intense, non-bleaching fluorescence, which is sensitive to the spin state of the ground state allows for both “ensemble average” and single center ODMR (Optically Detected Magnetic Resonance) spectroscopy. Embedded in a large band gap material, the ground state magnetic sublevels of isolated NV center display remarkably long coherence times at room temperature, enabling precise single center spectroscopy, i.e. sensitive detection of local electromagnetic fields influencing the sublevel structure. An individual, negatively charged NV site is able to measure changes in its local environment, for example to detect a nanometer scale displacement of an elementary charge or a paramagnetic center induced by conformation changes of nearby biological molecules. These exceptional properties make NV centers in diamond the most exciting atomic scale quantum metrology tool available at present.

Almost all practical use of the demonstrated potentials relay on the use of a large number of NV centers at the same time. Interrogation of a large number of NV centers at the same time requires all of the NV centers to experience nearly identical local environment. Controlled positioning of the NV centers relative the objects being measured, typically situated on the surface of the diamond, is a challenge on two fronts. Positioning and orienting the NV centers identically relative to the surface remains an unsolved problem in spite of the tremendous recent developments made ion-implantation and refined MW-CVD diamond growth. Equally difficult is controlling the surface chemistry of the diamond and the target molecules to ensure, that the changes to be monitored dominate other unwanted fluctuations in the environment of the NV centers. Potentials for developments and compromises are discussed.