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1. Precise high-fidelity electron–nuclear spin entangling gates in NV centers via hybrid dynamical decoupling sequences

   https://doi.org/10.1088/1367-2630/ab9bc0  

   Dong, Wenzheng ; Calderon-Vargas, F. A. ; Economou, Sophia E. ( July 2020 , New Journal of Physics)

   Color centers in solids, such as the nitrogen-vacancy center in diamond, offer well-protected and well-controlled localized electron spins that can be employed in various quantum technologies. Moreover, the long coherence time of the surrounding spinful nuclei can enable a robust quantum register controlled through the color center. We design pulse sequence protocols that drive the electron spin to generate robust entangling gates with these nuclear memory qubits. We find that compared to using Carr-Purcell-Meiboom-Gill (CPMG) alone, Uhrig decoupling sequence and hybrid protocols composed of CPMG and Uhrig sequences improve these entangling gates in terms of fidelity, spin control range, and spin selectivity. We provide analytical expressions for the sequence protocols and also show numerically the efficacy of our method on nitrogen-vacancy centers in diamond. Our results are broadly applicable to color centers weakly coupled to a small number of nuclear spin qubits.

    

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2. Photonic crystal cavities with germanium vacancy color centers in diamond (Conference Presentation)

   https://doi.org/10.1117/12.2507722  

   Akimov, Alexey Alajlan ( March 2019 , Proc. SPIE)

   Development of quantum information processing requires realization of solid state structures able to manipulate light or matter quantum bits. One of the promising candidates for been active elements of such solid-state platform are color centers in diamond. The most famous nitrogen-vacancy color center has number of attractive features and found a lot of applications in sensing and imaging. Still, it has number of considerable disadvantages, among which it sensitivity to the surface damages and thus its incompatibility with nanostructures. On another side implementation of nano- and micro- structures enabled considerable progress in manipulation of light quanta. In particular photonic crystal cavities allowed to realize strong coupling of cavity and spin system. This led to demonstration of efficient light collection and realization of simple quantum gates with artificial or real atoms. Novel color centers such as silicon-vacancy or germanium-vacancy color center due to inversion symmetry of the electron structure are not sensitive to the surface damages and presence of surface nearby. Thus, those are perfect candidates for been combined with photonic crystal structures. Novel technologies enabled growing of the nanodiamonds of ultra-small size having well-defined color center inside. Along with techniques to position those precisely on the nano- and micro structures these achievements opened opportunity to integrate high-fines photonic-crystal cavities with the germanium-vacancy containing nanocrystals thus forming fully solid-state platform for quantum manipulation of light. In my talk I will describe our progress towards realization of this ambitious goal 

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3. Carbon-13 dynamic nuclear polarization in diamond via a microwave-free integrated cross effect

   https://doi.org/10.1073/pnas.1908780116  

   Henshaw, Jacob ; Pagliero, Daniela ; Zangara, Pablo R. ; Franzoni, María B. ; Ajoy, Ashok ; Acosta, Rodolfo H. ; Reimer, Jeffrey A. ; Pines, Alexander ; Meriles, Carlos A. ( September 2019 , Proceedings of the National Academy of Sciences)

   Color-center–hosting semiconductors are emerging as promising source materials for low-field dynamic nuclear polarization (DNP) at or near room temperature, but hyperfine broadening, susceptibility to magnetic field heterogeneity, and nuclear spin relaxation induced by other paramagnetic defects set practical constraints difficult to circumvent. Here, we explore an alternate route to color-center–assisted DNP using nitrogen-vacancy (NV) centers in diamond coupled to substitutional nitrogen impurities, the so-called P1 centers. Working near the level anticrossing condition—where the P1 Zeeman splitting matches one of the NV spin transitions—we demonstrate efficient microwave-free 13 C DNP through the use of consecutive magnetic field sweeps and continuous optical excitation. The amplitude and sign of the polarization can be controlled by adjusting the low-to-high and high-to-low magnetic field sweep rates in each cycle so that one is much faster than the other. By comparing the 13 C DNP response for different crystal orientations, we show that the process is robust to magnetic field/NV misalignment, a feature that makes the present technique suitable to diamond powders and settings where the field is heterogeneous. Applications to shallow NVs could capitalize on the greater physical proximity between surface paramagnetic defects and outer nuclei to efficiently polarize target samples in contact with the diamond crystal. 

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4. Spin coherent quantum transport of electrons between defects in diamond

   https://doi.org/10.1515/nanoph-2019-0144  

   Oberg, Lachlan M. ; Huang, Eric ; Reddy, Prithvi M. ; Alkauskas, Audrius ; Greentree, Andrew D. ; Cole, Jared H. ; Manson, Neil B. ; Meriles, Carlos A. ; Doherty, Marcus W. ( August 2019 , Nanophotonics)

   Abstract The nitrogen-vacancy (NV) color center in diamond has rapidly emerged as an important solid-state system for quantum information processing. Whereas individual spin registers have been used to implement small-scale diamond quantum computing, the realization of a large-scale device requires the development of an on-chip quantum bus for transporting information between distant qubits. Here, we propose a method for coherent quantum transport of an electron and its spin state between distant NV centers. Transport is achieved by the implementation of spatial stimulated adiabatic Raman passage through the optical control of the NV center charge states and the confined conduction states of a diamond nanostructure. Our models show that, for two NV centers in a diamond nanowire, high-fidelity transport can be achieved over distances of order hundreds of nanometers in timescales of order hundreds of nanoseconds. Spatial adiabatic passage is therefore a promising option for realizing an on-chip spin quantum bus. 

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5. Demonstration of diamond nuclear spin gyroscope

   https://doi.org/10.1126/sciadv.abl3840  

   Jarmola, Andrey ; Lourette, Sean ; Acosta, Victor M. ; Birdwell, A. Glen ; Blümler, Peter ; Budker, Dmitry ; Ivanov, Tony ; Malinovsky, Vladimir S. ( October 2021 , Science Advances)

   We demonstrate the operation of a rotation sensor based on the nitrogen-14 ( 14 N) nuclear spins intrinsic to nitrogen-vacancy (NV) color centers in diamond. The sensor uses optical polarization and readout of the nuclei and a radio-frequency double-quantum pulse protocol that monitors 14 N nuclear spin precession. This measurement protocol suppresses the sensitivity to temperature variations in the 14 N quadrupole splitting, and it does not require microwave pulses resonant with the NV electron spin transitions. The device was tested on a rotation platform and demonstrated a sensitivity of 4.7°/ s (13 mHz/ Hz ), with a bias stability of 0.4 °/s (1.1 mHz). 

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