274 research outputs found
Theory of neutral nitrogen-vacancy center in diamond and its qubit application
The negatively charged nitrogen-vacancy defect (NV) in diamond has
attracted much attention in recent years in qubit and biological applications.
The negative charge is donated from nearby nitrogen donors that could limit or
stem the successful application of (NV). In this Letter, we unambiguously
identify the \emph{neutral} nitrogen-vacancy defect (NV) by \emph{ab
initio} supercell calculations. Our analysis shows that i) the spin state can
be \emph{selectively} occupied optically, ii) the electron spin state can be
manipulated by time-varying magnetic field, and iii) the spin state may be read
out optically. Based on this NV is a new hope for realizing qubit in
diamond \emph{without} the need of nitrogen donors.Comment: 4 pages, 1 figur
\emph{Ab initio} calculation of spin-orbit coupling for NV center in diamond exhibiting dynamic Jahn-Teller effect
Point defects in solids may realize solid state quantum bits. The spin-orbit
coupling in these point defects plays a key role in the magneto-optical
properties that determine the conditions of quantum bit operation. However,
experimental data and methods do not directly yield this highly important data,
particularly, for such complex systems where dynamic Jahn-Teller (DJT) effect
damps the spin-orbit interaction. Here, we show for an exemplary quantum bit,
nitrogen-vacancy (NV) center in diamond, that \emph{ab initio} supercell
density functional theory provide quantitative prediction for the spin-orbit
coupling damped by DJT. We show that DJT is responsible for the multiple
intersystem crossing rates of NV center at cryogenic temperatures. Our results
pave the way toward optimizing solid state quantum bits for quantum information
processing and metrology applications.Comment: 5 pages, 3 figures, 1 tabl
Theory of the optical spinpolarization loop of the nitrogen-vacancy center in diamond
The nitrogen-vacancy (NV) center in diamond is of high importance in quantum
information processing applications which relies on the efficient optical
polarization of its electron spin. However, the full optical spinpolarization
process, in particular, the intersystem crossing between the shelving singlet
state and the ground state triplet, is not understood. Here we develop a
detailed theory on this process which involves strong electron-phonon couplings
and correlation of electronic states that can be described as a combination of
pseudo and dynamic Jahn-Teller interactions together with spin-orbit
interaction. Our theory provides an explanation for the asymmetry between the
observed emission and absorption spectra of the singlet states. We apply
density functional theory to calculate the intersystem crossing rates and the
optical spectra of the singlets and we obtain good agreement with the
experimental data. As NV center serves as a template for other
solid-state-defect quantum bit systems, our theory provides a toolkit to study
them that might help optimize their quantum bit operation.Comment: 13 pages, 6 figures, 1 tabl
Characterization of oxygen defects in diamond by means of density functional theory calculations
Point defects in diamond are of high interest as candidates for realizing
solid state quantum bits, bioimaging agents, or ultrasensitive electric or
magnetic field sensors. Various artificial diamond synthesis methods should
introduce oxygen contamination in diamond, however, the incorporation of oxygen
into diamond crystal and the nature of oxygen-related point defects are largely
unknown. Oxygen may be potentially interesting as a source of quantum bits or
it may interact with other point defects which are well established solid state
qubits. Here we employ plane-wave supercell calculations within density
functional theory, in order to characterize the electronic and magneto-optical
properties of various oxygen-related defects. Beside the trivial single
interstitial and substitutional oxygen defects we also consider their complexes
with vacancies and hydrogen atoms. We find that oxygen defects are mostly
electrically active and introduce highly correlated orbitals that pose a
challenge for density functional theory modeling. Nevertheless, we are able to
identify the fingerprints of substitutional oxygen defect, the oxygen-vacancy
and oxygen-vacancy-hydrogen complexes in the electron paramagnetic resonance
spectrum. We demonstrate that first principles calculations can predict the
motional averaging of the electron paramagnetic resonance spectrum of defects
that are subject to Jahn-Teller distortion. We show that the high-spin neutral
oxygen-vacancy defect exhibits very fast non-radiative decay from its optical
excited state that might hinder to apply it as a qubit
The product Jahn-Teller effect in the neutral group-IV--vacancy quantum bits in diamond
The product Jahn-Teller (pJT) effect may occur for such coupled
electron-phonon systems in solids where single electrons occupy double
degenerate orbitals. We propose that the excited state of the neutral V
split-vacancy complex in diamond, where and V labels a group-IV impurity
atom of =Si, Ge, Sn, Pb and the vacancy, respectively, is such a system with
and double degenerate orbitals and quasi-localized phonons.
We develop and apply \emph{ab initio} theory to quantify the strength of
electron-phonon coupling for neutral V complexes in diamond, and find a
significant impact on the corresponding optical properties of these centers.
Our results show good agreement with recent experimental data on the
prospective SiV() quantum bit, and reveals the complex nature of the excited
states of neutral V color centers in diamond.Comment: 2 figures, 1 tabl
An \emph{ab initio} study on split silicon-vacancy defect in diamond: electronic structure and related properties
The split silicon-vacancy defect (SiV) in diamond is an electrically and
optically active color center. Recently, it has been shown that this color
center is bright and can be detected at the single defect level. In addition,
the SiV defect shows a non-zero electronic spin ground state that potentially
makes this defect an alternative candidate for quantum optics and metrology
applications beside the well-known nitrogen-vacancy color center in diamond.
However, the electronic structure of the defect, the nature of optical
excitations and other related properties are not well-understood. Here we
present advanced \emph{ab initio} study on SiV defect in diamond. We determine
the formation energies, charge transition levels and the nature of excitations
of the defect. Our study unravel the origin of the dark or shelving state for
the negatively charged SiV defect associated with the 1.68-eV photoluminescence
center.Comment: 8 pages, 5 figures, 1 tabl
Ab initio supercell calculations on nitrogen-vacancy center in diamond: its electronic structure and hyperfine tensors
The nitrogen-vacancy center in diamond is a promising candidate for realizing
the spin qubits concept in quantum information. Even though this defect is
known for a long time, its electronic structure and other properties have not
yet been explored in detail. We study the properties of the nitrogen-vacancy
center in diamond through density functional theory within the local spin
density approximation, using supercell calculations. While this theory is
strictly applicable for ground state properties, we are able to give an
estimate for the energy sequence of the excited states of this defect. We also
calculate the hyperfine tensors in the ground state. The results clearly show
that: (i) the spin density and the appropriate hyperfine constants are spread
along a plane and unevenly distributed around the core of the defect; (ii) the
measurable hyperfine constants can be found within about 7 A from the vacancy
site. These results have important implications on the decoherence of the
electron spin which is crucial in realizing the spin qubits in diamond.Comment: 28 pages, 7 figures, 2 table
Hyperfine tensors of nitrogen-vacancy center in diamond from \emph{ab initio} calculations
We determine and analyze the charge and spin density distributions of
nitrogen-vacancy (N-V) center in diamond for both the ground and excited states
by \emph{ab initio} supercell calculations. We show that the hyperfine tensor
of N nuclear spin is negative and strongly anisotropic in the excited
state, in contrast to previous models used extensively to explain electron spin
resonance measurements. In addition, we detect a significant redistribution of
the spin density due to excitation that has serious implications for the
quantum register applications of N-V center.Comment: 4 pages, 2 figures, 1 tabl
\emph{Ab initio} theory of nitrogen-vacancy center in diamond
Nitrogen-vacancy center in diamond is a solid state defect qubit with
favorable coherence time up to room temperature which could be harnessed in
several quantum enhanced sensor and quantum communication applications, and has
a potential in quantum simulation and computing. The quantum control largely
depends on the intricate details about the electronic structure and states of
the nitrogen-vacancy center, radiative and non-radiative rates between these
states and the coupling of these states to external spins, electrical, magnetic
and strain fields and temperature. In this review paper it is shown how first
principles calculations contributed to understanding the properties of
nitrogen-vacancy center, and will be briefly discussed the issues to be solved
towards full \emph{ab initio} description of solid state defect qubits.Comment: 33 pages, 12 figure
First principles study of charge diffusion between proximate solid state qubits and its implications on sensor applications
Solid state qubits from paramagnetic point defects in solids are promising
platforms to realize quantum networks and novel nanoscale sensors. Recent
advances in materials engineering make possible to create proximate qubits in
solids that might interact with each other, leading to electron spin/charge
fluctuation. Here we develop a method to calculate the tunneling-mediated
charge diffusion between point defects from first principles, and apply it to
nitrogen-vacancy (NV) qubits in diamond. The calculated tunneling rates are in
quantitative agreement with previous experimental data. Our results suggest
that proximate neutral and negatively charged NV defect pairs can form an
NV--NV molecule. A tunneling-mediated model for the source of decoherence of
the near-surface NV qubits is developed based on our findings on the
interacting qubits in diamond.Comment: 4 figure
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