We give instructions for the construction and operation of a simple apparatus for performing optically detected magnetic resonance measurements on diamond samples containing high concentrations of nitrogen-vacancy (NV) centers. Each NV center has a spin degree of freedom that can be manipulated and monitored by a combination of visible and microwave radiation. We observe Zeeman shifts in the presence of small external magnetic fields and describe a simple method to optically measure magnetic field strengths with a spatial resolution of several microns. The activities described are suitable for use in an advanced undergraduate lab course, powerfully connecting core quantum concepts to cutting edge applications. An even simpler setup, appropriate for use in more introductory settings, is also presented.
References
Other examples of quantum materials include single atomic layer materials such as graphene (Ref. 29) which could enable ultrafast signal processing, and topological insulators (Ref. 30) which may lead to error-free channels for transporting spin information. Developing next generation electronic devices based on quantum materials is the mission of the National Science Foundation supported Center for Integrated Quantum Materials (CIQM), which is supporting the work described here. See <ciqm.harvard.edu> for more information.
A number of factors are responsible for the weakness of the interaction of the spin with its surroundings. For example, because the nucleus has a spin of zero, the “spin-spin” interactions are small. Also, the low mass and stiff interatomic bonds of the carbon lattice lead to a high Einstein temperature (), which makes the interaction of the NV center) with the vibrational modes of the surrounding lattice unusually weak at room temperature.
Equation (2) is only valid in the limit that the magnetic field strength is much smaller than the zero-field splitting between the ms = 0 state and the states; i.e., when . This condition is satisfied for all the experiments described here.
Element Six sells HPHT diamond with suitably high nitrogen concentrations. See Ref. 31 for more detailed guidance on creating high NV concentrations in such samples via electron irradiation and annealing.