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The electronic and spin properties of different nanocrystals of carbon are studied. The properties of these cluster systems are modeled in terms of the ab initio (Hartree–Fock) and semiempirical (PM3, AM1) quantum-chemical methods. The calculations are performed for different carbon nanocluster systems: defect-free and with [NV]– centers, hydrogen passivated (C38H42, C71H84, C86H78), and with a free (unpassivated) surface (C38, C71, C86). The spin properties of unhydrated nanoclusters were studied for the first time. The structure of all the clusters under study was optimized using the total energy minimization principle. It is shown that, in the case of hydrated carbon nanocrystals passivated by hydrogen atoms, diamond-like clusters are formed. The atomic structure of an unpassivated nanocrystal depends on the number of atoms in the cluster, as well as on its initial geometrical parameters. In some cases, clusters with a fullerene-like surface are formed. In hydrogen-passivated diamond nanocrystals with [NV]– centers, the spin density is localized at the nuclei of C atoms nearest to the center vacancies. For the unpassivated counterparts, the spin density is localized at the nuclei of C atoms forming the surface of the corresponding nanocrystal. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Optically detectable magnetic resonance spectra were measured for ensembles of NV-centers in CVD diamonds with different 13C contents. The obtained spectra were described using a model based on the spin Hamiltonian. The magnitude of the magnetic field applied to the sample was estimated using the constructed model and experimental data. [ABSTRACT FROM AUTHOR]

Quantum chemical modeling using the Hartree–Fock theory level HF-3c/MINIS/MINIS11 (d)(Cl)/def2-SV(P) ECP(Pt) considering intermolecular interaction within the ORCA 5.03 software package was employed to study the electronic structure and binding energy of cisplatin, quinine, and fullerenol adducts and their three-component systems. Analysis of the total energies of the systems and the calculated energy diagrams of the highest occupied and lowest unoccupied molecular orbitals for the initial components and the molecular ensembles formed by them indicated the probable stability of their combinations. The synergistic effects were examined and the prospects for using the three-component cisplatin–quinine–fullerenol C60(OH)24 system in cancer chemotherapy were discussed. [ABSTRACT FROM AUTHOR]

The procedure of quantum measurement—unambiguous discrimination—of four two-mode coherent states of the optical field which are of interest for information transmission by the optical communication channel is studied. It is shown that complex conjugation of the amplitude of one of the modes leads to better discriminability between the states. An interferometric scheme for unambiguous discrimination between such states is proposed and the probability of successful discrimination is found. Applications of the considered set of states in quantum cryptography, quantum teleportation, and optical communication with a high level of losses are discussed. [ABSTRACT FROM AUTHOR]

Attack of unambiguous state discrimination on the line of quantum key distribution using time coding based on protocols BB84 and B92 is studied. Probabilities of discriminating all signal states in the quantum communication channel are obtained. The corresponding quantum measurement parameters are established. [ABSTRACT FROM AUTHOR]

We present a new view at simulating the VCSEL spectrum based on stochastic version of the widely used SFM model [1]. In comparison to the existing results [2], our method provides not only wavelengths and relative linewidths of lasing spikes but also the full spectrum. We show that it captures all known features such as polarization switching [3], four-wave-mixing (FWM) spike [4], and relaxation oscillations [5]. [ABSTRACT FROM AUTHOR]

The results of the experimental study of the effect of optical feedback (OF) on intensity fluctuations at a selected polarization in a single-mode vertical-cavity surface-emitting laser (VCSEL) are presented. The aim of this study is to look for conditions of enhancement of the level of polarization noise for possible use as a source of randomness for fast random bit generation. It is shown for several VCSEL examples that strong optical feedback can lead to an increase polarization noise, the amplitude and frequency band of which is sufficient for the efficient generation of random bits at a speed of several Gbit/s. This approach makes it possible to implement a fairly compact and structurally simple high-speed random bit generator. [ABSTRACT FROM AUTHOR]

Individual electron–nuclear spin systems in solids are promising platforms for implementation of second-generation quantum technologies. The recognized leader among such systems is the negatively charged nitrogen–vacancy color center (NV center) in diamond with hyperfine coupling to nuclear spins of carbon-13 (13C), which are widely used as a quantum memory in emerging quantum technologies because of their weak interaction with the environment. Recently, pairs of 13C–13C nuclei (dimers) in diamond with NV centers have been proposed and actively studied for this purpose because they have extremely long coherence times (minutes at room temperature) in the singlet state. The eigenstates of the spin Hamiltonian of the NV–13C–13C system were found and used to calculate the probabilities of EPR transitions between nuclear-spin sublevels of NV-center states with electron spin projections mS = 0 and mS = –1. The obtained expressions form the basis for choosing the optimal parameters of microwave and radiofrequency pulses transforming a particular dimer into the singlet state. An example of such a prediction for a specific NV–13C–13C spin system using data for the spatial positions of the 13C spins and the internal spin–spin couplings obtained earlier by quantum chemistry methods is presented. [ABSTRACT FROM AUTHOR]

The "germanium-vacancy" (GeV) center in diamond can be used as Temperature Sensors. The idea of GeV-based thermometry is based on optical measurements of the spectral shift of the zero-phonon line and its spectral width as a function of temperature changes. At the same time optical characteristics of GeV center which is located near-surface could be modified by formation of defect states in the band gap based on surface impurities and dangling bonds. The electronic structure of the GeV center determines its optical properties. The goal of this study was to investigate comparatively the geometric characteristics and electronic structure of the GeV center in the volume and near-surface (100) of nanodiamond in cluster approximation. It was shown for the first time that formation of isolated dangling bond on the (100) diamond surface leads to formation of unoccupied state in the band gap in vicinity of 1 eV, which is located on the distance of 1.9 eV of conduction band edge. This state in the band gap may influence optical properties of GeV in diamond. [ABSTRACT FROM AUTHOR]

The spatio-temporal correlation properties of a pseudo-thermal light source with nano- and microsecond time resolution are studied on the basis of algorithms that take into account the features of a high-speed time-resolving matrix of single-photon detectors. It is shown that the change in the degree of second-order coherence of radiation scattered on a rotating disk with irregularities of different scales can be represented using a nonlinear hyperbolic mapping. The change in coherence during the transition of the generated photon flux from coherent to pseudothermal is studied based on the presented method. [ABSTRACT FROM AUTHOR]

A method of vector magnetometry implemented using a single NV–13C spin system in diamond is proposed. The method is based on a priori knowledge of the hyperfine interaction characteristics and on the presence of experimentally measured line positions in the optically detectable magnetic resonance spectrum of such a system. The method was experimentally tested on an NV–13C system in which a 13C atom was located in the third coordination sphere of the NV-center. [ABSTRACT FROM AUTHOR]

The effect of a magnetic field on the luminescence from an ensemble of NV-centers in diamond was studied experimentally and theoretically. It was found that the intensity of infrared luminescence associated with transitions between singlet levels of NV-centers showed a pronounced increase in a near-zero magnetic field. The influence of the power and polarization of the laser radiation on the amplitude and shape of the revealed local maximum in the IR-luminescence of NV-centers was investigated. An eight-level photophysical model of an NV-center in the presence of an arbitrarily directed magnetic field was constructed and used as a basis to calculate the intensity of the luminescence emitted by an ensemble of NV-centers in both the visible and infrared spectral regions. It was shown that a phenomenological allowance for cross relaxation of NV-centers between each other and with other diamond paramagnetic centers within the framework of this model allows the experimentally observed fluorescence features of an ensemble of NV-centers in the presence of weak magnetic fields to be described. [ABSTRACT FROM AUTHOR]

The relationship between the photoluminescence intensity of the ensemble of NV centers in diamond and external magnetic field was studied. The magnetic spectra exhibit two resonances. The broader one has a width of 20 G and its amplitude is independent of the polarization of the incident radiation. The narrow resonance with a width of 4 G is found to be polarization dependent and is only visible if the direction of magnetic field is more or less perpendicular to the laser light polarization. To describe the appearance of these resonances we have modified the 8-level model of the NV center by taking into account the cross-relaxation between the ground-state spin of the center and other surrounding electronic spins (those of differently aligned NV centers, substitutional N spins etc.). [ABSTRACT FROM AUTHOR]

Abstract: The photoluminescence intensity of the ensemble of NV centers in diamond at weak magnetic field was studied. Two resonances were revealed in the region of weak magnetic fields: the first resonance with a width of the order of 20 G, and the second resonance with a width of the order of 180 G. The presence of these optical resonances makes it possible to propose a new concept for creating magnetic field sensors based on a diamond with an ensemble of NV centers without the use of a microwave field. [ABSTRACT FROM AUTHOR]

The possibility of using the long-lived entangled state between the emitter and field near the band edge of the density of states of a photonic crystal to create an efficient generator of single photons is considered. The generator can be efficiently excited by incoherent pumping, excludes simultaneous generation of two photons, and ensures a high probability of extracting the photon into a specified mode. [ABSTRACT FROM AUTHOR]

Quantum trajectories are crucial to understanding the evolution of open systems. We consider an open cavity mode undergoing up and down multistate quantum jumps due to the emission and absorption of photons. We prove that among all subtrajectories, starting simultaneously from different photon number states, only one survives a long single-run evolution. A random Fock state terminating the subtrajectory becomes known for the ergodic case via the key-the processed record of the input and output photocounts, and the trajectory duration. Based on this result, we propose a robust protocol to infer the Fock state, a valuable resource for quantum applications.