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I V Ponomarev

Publications and source records attributed to I V Ponomarev.

7 recordsLinked to original sources
PubMed2006

Electrically tunable g factors in quantum dot molecular spin states.

We present a magnetophotoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g factors of different spin states that have molecular wave functions distributed over both quantum dots. We propose a phenomenological model for the change in g factor based on resonant changes in the amplitude of the wave function in the barrier due to the formation of bonding and antibonding orbitals.

Journal Article↗
PubMed2006

Coherent photonic coupling of semiconductor quantum dots.

We report a new type of coupling between quantum dot excitons mediated by the strong single-photon field in a high-finesse micropillar cavity. Coherent exciton coupling is observed for two dots with energy differences of the order of the exciton-photon coupling. The coherent coupling mode is characterized by an anticrossing with a particularly large line splitting of 250 microeV. Because of the different dispersion relations with temperature, the simultaneous photonic coupling of quantum dot excitons can be easily distinguished from cases of sequential strong coupling of two quantum dots.

Journal Article↗
PubMed2006

Optical signatures of coupled quantum dots.

An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can be understood as a superposition of charge and spin configurations of the two dots. Coulomb interactions shift the molecular resonance of the optically excited state (charged exciton) with respect to the ground state (single charge), enabling light-induced coupling of the quantum dots. This result demonstrates the possibility of optically coupling quantum dots for application in quantum information processing.

Journal Article↗
PubMed2003

Surface roughness and effective stick-slip motion.

The effect of random surface roughness on hydrodynamics of viscous incompressible liquid is discussed. When the hydrodynamic decay length (the viscous wave penetration depth) is larger than the correlation radius (size) of random surface inhomogeneities, it is possible to replace a random rough surface by effective stick-slip boundary conditions on a flat surface with two constants: the stick-slip length and the renormalization of viscosity near the boundary. The stick-slip length and the renormalization coefficient are expressed explicitly via the correlation function of random surface inhomogeneities. The stick-slip length is always negative and the effective change of viscosity near the surface is positive signifying the effective average hampering of the hydrodynamic flows by the rough surface (stick rather than slip motion). A simple hydrodynamic model illustrates general hydrodynamic results. The effective boundary parameters are analyzed numerically for Gaussian, power-law and exponentially decaying correlators with various indices. The maximum on the frequency dependence of the dissipation allows one to extract the correlation radius (characteristic size) of the surface inhomogeneities directly from, for example, experiments with torsional quartz oscillators.

Journal Article↗
PubMed2001

New class of magnetoresistance oscillations: interaction of a two-dimensional electron gas with leaky interface phonons.

We report on a new class of magnetoresistance oscillations observed in a high-mobility two-dimensional electron gas (2DEG) in GaAs-Al(x)Ga(1--x)As heterostructures. Appearing in a weak magnetic field ( B < 0.3 T) and only in a narrow temperature range ( 2 K < T < 9 K), these oscillations are periodic in 1/B with a frequency proportional to the electron Fermi wave vector, k(F). We interpret the effect as a magnetophonon resonance of the 2DEG with leaky interface-acoustic phonon modes carrying a wave vector q = 2k(F). Calculations show a few branches of such modes existing on the GaAs-Al(x)Ga(1--)xAs interface, and their velocities are in quantitative agreement with the observation.

Journal Article↗
PubMedDate not supplied

[Reconstruction of images in emission tomography].

The algorithm of back projection with filtration for exponential Radon transform leads to strong distortion for big diameter objects. The main reason for this distortion is mainly the exponential increase of errors in the quadrature formula for a weighed back projection operator. So it is sometimes more convenient to use the back Radon transform R-1 and then to correct the result, taking into account attenuation. For this purpose, the approximation formulas are given, which connect f and R-1 R mu f. An appropriate iteration reconstruction algorithm is also considered. Application exponential Radon identities for projection data analysis are also discussed.

Algorithms↗