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We use multipulse dynamical decoupling to increase the coherence lifetime (T2) of large numbers of nitrogen-vacancy (NV) electronic spins in room temperature diamond, thus enabling scalable applications of multispin quantum information processing and metrology. We realize an order-of-magnitude extension of the NV multispin T2 in three diamond samples with widely differing spin impurity environments. In particular, for samples with nitrogen impurity concentration ≲1 ppm, we extend T2 to >2 ms, comparable to the longest coherence time reported for single NV centers, and demonstrate a tenfold enhancement in NV multispin sensing of ac magnetic fields., Physics

A common limitation of experiments using color centers in diamond is the poor photon collection efficiency of microscope objectives due to refraction at the diamond interface. We present a simple and effective technique to detect a large fraction of photons emitted by color centers within a planar diamond sample by detecting light that is guided to the edges of the diamond via total internal reflection. We describe a prototype device using this “side-collection” technique, which provides a photon collection efficiency ≈47% and a photon detection efficiency ≈39%. We apply the enhanced signal-to-noise ratio gained from side collection to ac magnetometry using ensembles of nitrogen-vacancy (NV) color centers, and demonstrate an ac magnetic field sensitivity ≈100pT/Hz‾‾‾√, limited by added noise in the prototype side-collection device. Technical optimization should allow significant further improvements in photon collection and detection efficiency as well as subpicotesla NV-diamond magnetic field sensitivity using the side-collection technique., Physics

We demonstrate preferential orientation of nitrogen-vacancy (NV) color centers along two of four possible crystallographic axes in diamonds grown by chemical vapor deposition on the {100} face. We identify the relevant growth regime and present a possible explanation of this effect. We show that preferential orientation provides increased optical readout contrast for NV multispin measurements, including enhanced ac magnetic-field sensitivity, thus providing an important step towards high-fidelity multispin-qubit quantum information processing, sensing, and metrology., Physics