A. P. Nizovtsev

Single spin states in a defect center resolved by optical spectroscopy

Individual paramagnetic defect centers in diamond nanocrystals have been investigated by low-temperature high-resolution optical spectroscopy. Narrow fluorescence excitation spectral lines have been found, indicating transitions between individual spin sublevels. Spectral diffusion is explained by cross relaxation among spin sublevels and by the presence of excited electrons in the conduction band of diamond. The relaxation times are in the millisecond range. The system may be useful for quantum information processing with individual electron spins.

Spectroscopy of Single N-V Centers in Diamond

Over the past few years, the detection of single N-V centers in diamond has attracted much interest, since it is expected to lead to innovative applications in various domains of quantum information. The N-V center in diamond is a defectconsisting of a substitutional nitrogen atom adjacent to a carbon-atom vacancy. The optical transition between the 3A ground state and the 3E excited state has a very high quantum efficiency allowing single defect spectroscopy. Because of the paramagnetic nature of the ground electronic state, single N-V defects are believed to be promising candidates for solid state quantum computation. To date, however, the photophysics of the defect is not entirely understood. The existence of a singlet metastable state 1A was challenged in a series of papers reporting hole-burning, optically detected magnetic resonance and single molecule experiments. We present here an overview of recent low and room temperature data, indicating the important role of a metastable state of the defect in single center experiments.

Theoretical study of hyperfine interactions and optically detected magnetic resonance spectra by simulation of the C291[NV]-H172 diamond cluster hosting nitrogen-vacancy center

Single nitrogen-vacancy (NV) centers in diamond coupled to neighboring nuclear spins are promising candidates for room-temperature applications in quantum information processing, quantum sensing and metrology. Here we report on a systematic density functional theory simulation of hyperfine coupling of the electronic spin of the NV center to individual 13C nuclear spins arbitrarily disposed in the H-terminated C291[NV]-H172 cluster hosting the NV center. For the ‘families’ of equivalent positions of the 13C atom in diamond lattices around the NV center we calculated hyperfine characteristics. For the first time the data are given for a system where the 13C atom is located on the NV center symmetry axis. Electron paramagnetic resonance transitions in the coupled electron–nuclear spin system 14NV-13C are analyzed as a function of the external magnetic field. Previously reported experimental data from Dreau et al (2012 Phys. Rev. B 85 134107) are described using simulated hyperfine coupling parameters.

Spectroscopy on single N–V defect centers in diamond: tunneling of nitrogen atoms into vacancies and fluorescence spectra

Abstract Experiments on fluorescence excitation of single N–V defect centers in diamond are described in terms of 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, DWPs 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.

On “anomalous” free induction decay rate

Abstract Generalized non-markovian master equations, which take into account the nonvanishing bath correlation time τ c , are used to explain the “anomalous” (which cannot be described by the well-known Bloch master equations) behaviour of the optical free induction decay recently observed by DeVoe and Brewer [Phys. Rev. Lett. 50 (1983) 1269] for the Pr 3+ : LaF 3 at T ≃ 1.6 K. We found τ c = 5 μs to be the best fit of our theory to the above experiment provided that T 1 = 100 μs, T 2 = 24 μs. New experimental tests of the non-markovian relaxation theory are proposed.

Generalised non-linear optical master equations taking into account the correlation time of relaxational perturbations

Generalised master equations in two equivalent forms, namely differential master equations (DME) and integro-differential master equations (IDME), are obtained. Both differ from the Bloch ones in that they take into account the density matrix dynamics during the correlation time tau C of the relaxational perturbations. On the basis of these equations, the non-linear optical problems of high-power radiation absorption, the resonance fluorescence spectrum and the free induction decay signal are discussed.

Model systems and photo-kinetics of single N-V defect centers in diamond

Fluorescence excitation method of single molecule spectroscopy has been applied recently to study individual nitrogen-vacancy (N-V) defect centers in diamond. These objects are of great interest owing to the proposal to build quantum computer at /sup 13/C nuclear spins neighboring the N-V center. Based on new spectroscopic information we have developed simple models of the N-V center and used them to describe a wide range of experiments dealing both with single centers and with their ensembles. The first model emphasizes possible tunneling of N atom into vacancy and describes that in terms of double well potentials. The second model takes into account the spin-triplet character of the ground electronic state of the center and allows to describe a variety of fluorescence detected magnetic resonance phenomena.

Stochastic theory of narrow hole-burning in low-temperature dilute ruby

Abstract Transient hole-burning in low-temperature impurity-ion crystals is studied using the model of two jump processes Ut = Ut1 + Ut2 (the random telegraph process Ut1 and the uncorrelated jump process Ut2 with a Lorentzian distribution of possible values) characterised by essentially different jump rates v1 ⪢ v2 and distribution widths σ1 ⪡ σ2 for the impurity ion optical transition frequency fluctuations Ut due to the bulk and the frozen core host nuclear spins flipping. At short pump/probe pulse width T and short delay time τd(τd, T ⪡ v2−1) the calculated hole shape is narrow with the hole width determined by the Ut1 process characteristic only while at long delay τd ≥ v2−1 it becomes a wide Lorentzian with the haftwidth 2σ2. The theory fits the experimental data of Szabo et al. well on narrow hole burning in ruby under low and high magnetic field, supposing the fluctuations Ut1 to be rather slow ( σ 2 1 v 2 1 = 0.5 ).

Kramers-degenerated NV+113C spin systems in diamond: analytical description

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.

ELASTIC MODULES AND LOW-FREQUENCY OSCILLATIONS OF ISOLATED CARBON NANOTUBES

Institute for Nuclear Problems, BSU, Bobruiskaya 11, 220050 Minsk, Belarus Iinstitute of Physical Organic Chemistry NASB Surganova 13, 220072 Minsk, Belarus alexp@ifoch.bas-net.by Belarusian State University of Informatics and Radioelectronics P. Browka 6, 220013 Minsk, Belarus vadimka@vadimka.com Al-Balqa Applied University, P.O. Box 204,1Amman 11953, Jordan B.I. Stepanov Institute of Physics NASB, Nezavisimosti Ave. 68, 220072 Minsk, Belarus