Nitrogen-vacancy center, a molecular structure formed by a substitutional Nitrogen impurity and a nearby vacancy in diamond, have promising properties for quantum information and communication applications. First, optical spin initialization and measurement is possible simply by using green pulsed laser. Second, the spin triplet qubit exhibits coherence time exceeding 100 micro seconds even at room temperature. Third, this electron spin qubit has intrinsic quantum memory : nuclear spin qubit formed by Nitrogen atom. 

Figure 1. (Left) Home-built laser scanning confocal microscope - excitation, single NV tracking mechanism, and photon collection part. (Right) 2D vector electromagnet in the sample area with high frequency coplanar waveguide. 

We are exploring quantum coherent properties and its application to quantum magnetometry, quantum simulation, and simple quantum algorithms. Below are some examples of quantum coherent measurements of a single NV center routinely done in our lab. 

Figure 2. Bright NV centers on a surface of bulk diamond. Photoluminescence of NV centers in a typeIb diamond

Figure 3. Time-correlated single photon counting of a single NV center in diamond. Clear antibunching showing g2 < 0.5 near Delay = 0 indicates single quantum emitter.

Figure 4. Electron spin resonance (ESR) of a single NV center. Zero field splitting of 2,87 GHz and Zeeman splitting can be clearly seen.

Figure 5. Coherent Rabi oscillations and microwave power dependence.