60 research outputs found
Accurate Hyperfine Tensors for Solid State Quantum Applications: Case of the NV Center in Diamond
The decoherence of point defect qubits is often governed by the electron
spin-nuclear spin hyperfine interaction that can be parameterized by using ab
inito calculations in principle. So far most of the theoretical works have
focused on the hyperfine interaction of the closest nuclear spins, while the
accuracy of the predictions for distinct nuclear spins is barely discussed. We
demonstrate for the case of the NV center in diamond that the absolute relative
error of the computed hyperfine parameters can exceed 100\% in VASP for weakly
coupled nuclear spins. To overcome this issue, we implement an alternative
method and report on significantly improved hyperfine values with (1\%)
relative mean error at all distances. The provided accurate hyperfine data for
the NV center enables high-precision simulation of NV quantum nodes for quantum
information processing and positioning of nuclear spins by comparing
experimental and theoretical hyperfine data
Hybrid-DFT+V method for accurate band structure of correlated transition metal compounds: the case of cerium dioxide
Hybrid functionals' non-local exchange-correlation potential contains a
derivative discontinuity that improves on standard semi-local density
functional theory (DFT) band gaps. Moreover, by careful parameterization,
hybrid functionals can provide self-interaction reduced description of selected
states. On the other hand, the uniform description of all the electronic states
of a given system is a know drawback of these functionals that causes varying
accuracy in the description of states with different degrees of localization.
This limitation can be remedied by the orbital dependent exact exchange
extension of hybrid functionals; the hybrid-DFT+V method [V. Iv{\'a}dy, et
al., Phys. Rev. B 90, 035146 (2014)]. Based on the analogy of quasi-particle
equations and hybrid-DFT single particle equations, here we demonstrate that
parameters of hybrid-DFT+V functional can be determined from approximate
quasi-particle spectra. The proposed technique leads to a reduction of
self-interaction and provides improved description for both / and /
-electrons of the simulated system. The performance of our charge
self-consistent method is illustrated on the electronic structure calculation
of cerium dioxide where good agreement with both quasi-particle and
experimental spectra is achieved
Identification of Si-vacancy related room temperature qubits in 4H silicon carbide
Identification of microscopic configuration of point defects acting as
quantum bits is a key step in the advance of quantum information processing and
sensing. Among the numerous candidates, silicon vacancy related centers in
silicon carbide (SiC) have shown remarkable properties owing to their
particular spin-3/2 ground and excited states. Although, these centers were
observed decades ago, still two competing models, the isolated negatively
charged silicon vacancy and the complex of negatively charged silicon vacancy
and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] are
argued as an origin. By means of high precision first principles calculations
and high resolution electron spin resonance measurements, we here unambiguously
identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively
charged silicon vacancies. Moreover, we identify the Si-vacancy qubit
configurations that provide room temperature optical readout.Comment: 3 figure
ADAQ: Automatic workflows for magneto-optical properties of point defects in semiconductors
Automatic Defect Analysis and Qualification (ADAQ) is a collection of
automatic workflows developed for high-throughput simulations of
magneto-optical properties of point defect in semiconductors. These workflows
handle the vast number of defects by automating the processes to relax the unit
cell of the host material, construct supercells, create point defect clusters,
and execute calculations in both the electronic ground and excited states. The
main outputs are the magneto-optical properties which include zero-phonon
lines, zero-field splitting, and hyperfine coupling parameters. In addition,
the formation energies are calculated. We demonstrate the capability of ADAQ by
performing a complete characterization of the silicon vacancy in silicon
carbide in the polytype 4H (4H-SiC).Comment: Typo corrected in eq. 3, references adde
All-optical hyperpolarization of electron and nuclear spins in diamond
Low thermal polarization of nuclear spins is a primary sensitivity limitation
for nuclear magnetic resonance. Here we demonstrate optically pumped
(microwave-free) nuclear spin polarization of and
in -doped diamond.
polarization enhancements up to above thermal equilibrium are observed
in the paramagnetic system . Nuclear spin polarization is
shown to diffuse to bulk with NMR enhancements of at
room temperature and at , enabling a route to
microwave-free high-sensitivity NMR study of biological samples in ambient
conditions.Comment: 5 pages, 5 figure
Theoretical model of the dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point
defects in semiconductors is a key resource for both initializing nuclear
quantum memories and producing nuclear hyperpolarization. DNP is therefore an
important process in the field of quantum-information processing,
sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based
spintronics. DNP based on optical pumping of point defects has been
demonstrated by using the electron spin of nitrogen-vacancy (NV) center in
diamond, and more recently, by using divacancy and related defect spins in
hexagonal silicon carbide (SiC). Here, we describe a general model for these
optical DNP processes that allows the effects of many microscopic processes to
be integrated. Applying this theory, we gain a deeper insight into dynamic
nuclear spin polarization and the physics of diamond and SiC defects. Our
results are in good agreement with experimental observations and provide a
detailed and unified understanding. In particular, our findings show that the
defects' electron spin coherence times and excited state lifetimes are crucial
factors in the entire DNP process
The Principles of Social Order. Selected Essays of Lon L. Fuller, edited With an introduction by Kenneth I. Winston
The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance with ab initio simulations, we show that spin-spin interactions in 4H-SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10(-6) strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%-36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields
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