"Quantum computing with magnetic color center in diamond"
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Magnetic color centers in diamond have received a lot of interest in the
research community due to their potential use as qubits for solid-state quantum
computing or as single photon source for quantum key distribution in quantum
cryptography. Indeed, diamond's wide band gap and long spin lifetimes offers the
possibility to initialize, manipulate and readout the quantum state of the qubit
and allows the existence of more than 500 color centers with most of them yet to
be characterized. Transition metal (TM) impurities in diamond are known to
produce numerous color centers and we propose here to study TM-related defect.
After an introduction on solid-state quantum computing in diamond, we present
our results.
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The electronic and magnetic properties of a neutral substitutional nickel
impurity in diamond are studied using density functional theory in the
generalized gradient approximation (GGA). The spin-one ground state consists of
two electrons with parallel spins, one located on the nickel ion in the 3d9
configuration and the other distributed among the nearest-neighbor carbons. The
exchange interaction between these spins is due to p-d hybridization and is
controllable with compressive hydrostatic or uniaxial strain. For sufficient
strain the antiparallel spin configuration becomes the ground state. Hence, the
Ni impurity forms a controllable two-electron exchange-coupled system that
should be a robust qubit for solid-state quantum information processing. The
chemical trends of neutral substitutional TMs0 impurities is calculated within
GGA. Crs0 is shown to be another potential candidate for quantum computing
applications.
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We then provide an ab-initio characterization of the negatively charged
substitutional Nis- impurity in diamond using hybrid density functional calculation.
Nis- is shown to carry a spin S = 3/2. The calculated hyperfine couplings on this
defect support the identification of the W8 electron paramagnetic resonance
center with Nis- defect. We unambiguously determine the position of Nis- acceptor
level in the gap. This level is located at about 2.0 eV above the valence band
maximum and corresponds to a totally occupied triplet state responsible for the
magnetization. We calculated the excited state properties of the defect. Our
results indicate that Nis- is associated with the 3.1 eV center which has not yet
been assigned to any Ni-related defect.