Quantum Sciences Seminar - Greg Fuchs, Cornell University - Quantum control and coherence of single electronic and nuclear spins in diamond

Fri, Apr 6, 2012, 3:00 pm to 4:00 pm
Location: 
PCTS Seminar Room

The spin of individual nitrogen vacancy (NV) centers in diamond is a promising solid-state platform for quantum information processing and precision metrology at room temperature. Understanding and using the built-in resources of these point defects is critical to achieving these goals. I’ll describe two experiments with that aim. In the first, we harness the nuclear spin of the intrinsic nitrogen atom as a quantum memory. The nitrogen nuclear spin is an attractive candidate for a quantum memory because nuclear spins have long coherence times and because a single nitrogen nucleus is deterministically present with each NV center. We demonstrate coherent state transfer using Landau-Zener transitions across a hyperfine mediated avoided-level crossing [1]. We find that by working in the Landau-Zener finite-time regime, we can coherently transfer the electronic spin state to the nuclear spin in as little as 120 ns with a fidelity of 88±6% for 10 μs storage. In the second experiment, we study the spin coherence of an NV center electronic spin as it undergoes non-resonant optical excitation at room temperature. Although fluorescence-based measurement of NV centers relies on preservation of the longitudinal projection of spin, the lack of orbital coherence might suggest that the quantum phase would be destroyed. We address this question using Ramsey experiments and quantum process tomography where the spin state is initialized in the ground state and measured in the excited state. We find that within experimental uncertainty, the full spin state is preserved over this transition despite the incoherent orbital dynamics [2]. These results provide a new understanding of NV centers’ spin coherence during optical excitation and may lead to rapid spin control using the excited state. * In collaboration with G. Burkard, A. L. Falk, V. V. Dobrobitski, P. V. Klimov, and D. D. Awschalom [1] G. D. Fuchs, G. Burkard, P. V. Klimov, and D. D. Awschalom, Nature Physics 7, 789 (2011). [2] G. D. Fuchs, A. L. Falk, V. V. Dobrovitski, and D. D. Awschalom, Phys. Rev. Lett. (in press) (2012); arXiv:1111.3687.