Spin systems consisted of single electronic spin S=1 of the NV center and nearby nuclear spins I=1/2 of 13C atoms disposed in diamond lattice near the center can be used as a small register of a quantum computer or as a sensor of a magnetic field. At odd number of nuclear spins eigenvalues of the spin systems at zero external magnetic field are at least twofold degenerated (Kramers degeneration) due to time reversal invariance of the spin Hamiltonian. This degeneracy is lifted only by external magnetic field regardless of the presence of any electric (crystal) field which can also lift the degeneracy thus hindering measurement of the magnetic field. Therefore, the Kramers-degenerated spin systems can be very perspective for measurement of a local magnetic field by the NV-based single-spin quantum magnetometer. Here, we are considering analytically the simplest Kramers-degenerated spin system NV+113C consisting of a single electron spin S=1 of the NV сenter coupled by hyperfine interaction with a single nuclear spin I=1/2 of 13C atom disposed in arbitrary site of diamond lattice. Simple approximate analytical expressions are obtained for eigenvalues and eigenstates of the spin system.
Modeling of atomic structure and distribution of spin density for the NV center formed close to the surface (111) of
nano-diamond has been carried out using quantum-chemical PM3 and DFT methods. The case is considered where the
nitrogen atom of NV center is located in the near-surface atomic layer of a face (111). The relaxation of surface atoms
relative to the initial position results in N atom to be shifted from the cluster center parallel to the <111> direction by
0.16Å, and C atoms belonging to the surface layer are also shifted parallel to the <111> direction to the center by 0.18Å. As this takes place, C-C and C-N distances between relaxed atoms decrease and a graphite-like structure is formed on a
(111) crystal face. In the structure, the N atom and C atoms nearest to it lay practically in the same plane. The formed CN
bond can be considered as one-and-a-half bond. It has been found that unlike the NV center in bulk diamond for which
the spin density is located mainly on the carbon atoms, being nearest neighbors to the vacancy of the NV center, in the
case of the NV center located in immediate proximity to the surface, there is a redistribution of spin density resulting in
its major allocation in three C atoms, the nearest neighbors to the N atom, that form the first atomic layer of a surface
(111) of nano-crystal.
Quantum information technology (QIT) is extremely fast developing area strongly connected with achievements in modern physics. We present a review of recent achievements in implementation of solid-state scalable quantum processors with special emphasize on diamond-based quantum hardware.
KEYWORDS: Quantum communications, Diamond, Electrons, Sensors, Chemical species, Color centers, Information security, Luminescence, Mirrors, Interferometry
We suggest a concrete way to realize the quantum repeater protocol based on nitrogen-vacancy (NV) defects in diamond, feasible with present means of manipulating the defects.
To describe experiments on fluorescence excitation of single N-V defect centers in diamond we have used the double well potential (DWP) model which incorporates the possibility of tunneling the nitrogen atom into the vacancy both in ground and excited electronic states of the center. Fluorescence and linear absorption spectra are calculated, DWP's parameter values for N-V centers are determined and manifestations of their variations due to local diamond lattice distortions in fluorescence spectra of various single N-V centers are studied.
Fluorescence detected magnetic resonance (FDMR) coherent phenomena on single triplet-state chromophore guest molecule in low-temperature organic host matrix are analyzed within the stochastic approach to describe triplet electron spin dephasing due to frequency fluctuations Ut induced by host-matrix proton spins dynamics. Exact equations for density matrix of a molecule averaged over histories of the fluctuations Ut are constructed using the model of N random telegraph process. The equations are applied to calculate FDMR responses of a molecule to cw/pulsed MW field and to describe a wide range of available experimental data on (1) the power-broadened FDMR line shapes, (2) the FDMR nutations, (3) the FDMR Hahn echo for pentacene+p- terphenyl pair supposing the fluctuations Ut to be slow. The failure of the standard Bloch equations for this system is demonstrated and the effects of microwaves-suppressed dephasing are discussed.
Transient hole-burning and free induction decay (FID) in low-temperature ion-doped crystals are studied consistently using the model of two jump processes Ut equals Ut1 + Ut2 characterized by essentially different jump rates v1 >> v2 and distribution widths (sigma) 1 << (sigma) 2 for the impurity ion optical transition frequency fluctuations Ut due to the bulk and the frozen core spin flipping. At short pump/probe pulsewidth T and short delay time (tau) d ((tau) d, T << v2-1) the calculated hole shape is narrow with the hole width determined by Ut1 process characteristics only. The hole width in this case coincides with the calculated FID rate. At long delay (tau) d >= v2-1 the hole becomes a wide lorentzian with the halfwidth 2(sigma) 2. The theory fits well the experimental data by A. Szabo et. al. on narrow hole burning and FID in ruby under low and high magnetic fields supposing the fluctuations Ut1 to be rather slow ((sigma) 21/v21 equals 0.5).
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