The 2nd Solid-State Physics Seminar
NV centers in diamond – solid state spins applied in quantum registers and as multipurpose nanoscale probes
Lecturer: Dr. Philipp Neumann
(3. Physikalisches Institut, Stuttgart University, Germany)
Time: 14:40-16:10, 15th (Thu) May, 2014
Place: B300 (3F of Buld. B, Graduate School of Engineering Science)
Single nitrogen-vacancy (NV) defect centers in diamond are extraordinary color centers with a remarkable set of properties. First, they are optically addressable at the single level. The latter gives access to the ground state electronic spin triplet, which can be optically initialized and read out. Furthermore, at room temperature coherence times (a few milliseconds) are long compared to manipulation times (down to nanoseconds) mainly due to recent advances synthetic diamond quality.
In recent years, NV center spins were used to detect tiny magnetic fields and proximal electron and nuclear spins. While the first application opens up many possibilities for quantum metrology especially at the nanometer scale, the second application has led to small, functional quantum registers. Particularly, 13C nuclear spins in the diamond lattice and near NV centers were used to create non-local quantum states. [1, 2]
Here, we are going to present novel knowledge about the NV center’s electronic and spin properties which allows improving sensing capabilities. As an example, the NV electron spin can be made sensitive to further quantities like temperature, electric fields and lattice strain. Very recently, we achieved the detection of a single elementary charge at room temperature. 
Furthermore, we presenting recent achievements in scaling our solid state spin registers. On the one hand, we couple and entangle proximal NV electron spins via their mutual magnetic dipole interaction. On the other hand, individual NV centers are equipped with several nuclear spins to demonstrate essential quantum algorithms. As a prominent example, we protect stored quantum coherences against dephasing via quantum error correction.  The latter is essential for any scalable architecture of quantum computation or long-range quantum communication via quantum repeaters.
As the high fidelity spin control becomes challenging in continuously growing registers we started applying optimal control techniques. We will show recent applications and discuss the scalability of this approach.
 P. Neumann, N. Mizuochi, et al.,Science 320, 1326 (2008).
 P. Neumann et al., Science 329, 5991 (2010).
 F. Dolde,P. Neumann et al., Phys. Rev. Lett. 112, 097603 (2014).
 G. Waldherr, P. Neumann et al., Nature, 506, 7487 (2014).
Contact information : Norikazu MIZUOCHI