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Enhanced coherence properties and solid-state spin ensemble magnetometry using optimized dynamical decoupling


  Demitry Farfurnik [1,2]  ,  Andrey Jarmola [3]  ,  My Linh Pham [4]  ,  Zhihui Wang [5]  ,  Viatcheslav V. Dobrovitski [6]  ,  Ronald L. Walsworth [4,7]  ,  Dmitry Budker [3,8]  ,  Nir Bar-Gill [1,2,9]  
 [1] The Racah Institute of Physics, The Hebrew University of Jerusalem
[2] The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem
[3] Department of Physics, University of California, Berkeley
[4] Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts
[5] Department of Chemistry, University of Southern California, Los Angeles
[6] Ames Laboratory, Iowa State University
[7] Department of Physics, Harvard University, Cambridge, Massachusetts
[8] Helmholtz Institute, Johannes Gutenberg-University, Mainz
[9] Department of Applied Physics, Rachel and Selim School of Engineering, The Hebrew University of Jerusalem

The unique spin and optical properties of nitrogen vacancy (NV) color centers in diamond position them as leading candidates for creating nanoscale quantum information building blocks (qubits) and magnetic nano-sensors.

For most applications in quantum information and sensing, long coherence times (T2) must be achieved for any arbitrary NV spin states, overcoming decoherence sources such as internal fluctuating magnetic fields ("spin-bath"), caused by 13C nuclear spins, nitrogen (P1) electronic spins and other defects in the diamond.

In this work, we extend previously achieved results of single-axis (Curr-Purcell-Meiboom-Gill) spin preservation, and optimize a dynamical decoupling (DD) protocol for preserving arbitrary spin state of a dense ensemble of NV centers in diamond. By characterizing the effects of pulse and detuning errors, minimizing experimental imperfections, and comparing the performance of various DD protocols, we identify that the optimal control scheme for preserving an arbitrary spin state is a symmetric and recursive protocol, the concatenated version of the XY8 pulse sequence. We achieve an order-of-magnitude improvement in the coherence of an arbitrary quantum state, reaching a T2 coherence time of 30 ms, while maintaining a high signal contrast. Using the obtained DD protocol, we demonstrate immediate improvements in the sensitivity of AC magnetometry, reaching sensitivities in the order of nT/sqrt(Hz).

Another future direction is to use the optimized DD protocol on diamond samples with higher conversion (N to NV) efficiencies in order to reach NV-NV interaction dominated regime. Such an achievement may pave the way toward the creation of interesting non-classical spin states. For example, squeezed states are commonly created and used in optical systems, improving optical measurement sensitivities beyond the shot-noise limit, but have not yet been created in the solid-state. Demonstration of such control could, beyond improved magnetometry, pave the way to novel research directions in quantum simulation and quantum computing.