V. V. Ovsyankin

Nonlinear optical dynamics of semiconductor nanostructures:: feasibility of the photonic quantum gate

Abstract This paper is related to the modern branch of the nonlinear optics which is a search for and design of new media appropriate for the photonic information devices. We have studied experimentally a resonant nonlinear photoresponse of semiconductor nanostructure with GaAs/AlGaAs superlattice and determined the energy and phase relaxation rates of the free excitons in this structure. Theoretical analysis of resonant interaction of the coherent light pulses with quasi-two-dimensional nanostructure allowed us to conclude that such structures can be used for the fabrication of the photonic gates for quantum computer.

Coherent transients in semiconductor nanostructures as a basis for optical logical operations

We propose an approach to realization of all-optical logical operations based on the nonlinear dynamics of an ensemble of two-level systems (TLSs) in a coherent photonic field. Using a theoretical analysis of the behaviour of a TLS ensemble in a resonant field, we formulate requirements for dynamic characteristics of a medium suitable for implementation of a photonic gate. Experimental studies of optical dynamics and excitonic state spectra of epitaxial GaAs/AlGaAs quantum wells and superlattices has allowed us to conclude that their physical parameters make it possible to build photonic-gate matrices exceeding the transistor-based electronic switches in terms of their productive capacity by five to six orders of magnitude.

Increasing of AlGaAs/GaAs quantum well robustness to resonant excitation by lowering Al concentration in barriers

The robustness of AlGaAs/GaAs quantum well to strong resonant excitation is studied. It was found that lowering Al concentration in barriers to 3% does not influence the measured radiative linewidth of exciton resonance in the sample at low intensities. At the same time parasitic broadening of the resonance by an additional resonant illumination is strongly suppressed as compared to the quantum well with 30% of Al in barriers.

Temperature-induced delocalization of excitations in GaAs/AlAs type-II superlattices

This paper describes investigations of the photoluminescence spectra of heterostructures containing short-period type-II GaAs/AlAs superlattices grown both within the regime where the heterojunction is smoothed, and in a regime where it is not smoothed, in the temperature range 10–40 K. A quantitative analysis of the experimental data shows that the quenching of exciton luninescence in the majority of cases is characterized by a single value of the activation energy E2=8±1 meV which coincides with the value of the binding energy of an X-Γ exciton. It is concluded that the primary reason for quenching in this temperature interval is thermal dissociation of the exciton into a pair of free carriers whose delocalization is accompanied by nonradiative recombination at traps. It is observed that smoothing the heterojunction leads to an increase in the probability of quenching by 1–2 orders of magnitude on the average.

Electron-vibrational shift of f-levels in CaF2 and SrF2 crystals with Tm2+ ions

Abstract The nonparametric calculations of f-level shifts in CaF 2 : Tm 2+ and SrF 2 : Tm 2+ crystals are performed in the frame of the electron-vibrational coupling (EVC) model, thoroughly tested previously by analysis of vibronic spectra and suppression of electron transitions in these crystals. It is found that EVC is able to cause large (in few tenths of cm −1 ) level shifts provided that the Stark splitting is less than phonon spectrum width. This fact should be taken into account when analysing the rare-earth ion levels Stark splitting by phenomenological crystal-field models.

Optical vidicon based on a layered semiconductor structure: Image reading and storage

A simple device for image scanning and storage based on a semiconductor structure is proposed. The scanning and storage involve laser-beam reading. A video signal is represented by the photoelectromotive force generated by the structure. Simple experiments demonstrating that the structure proposed works as a vidicon and a storage device capable of the data storage for at least two hours are presented. A physical interpretation of the effects observed is proposed.

On experimental potentialities of correlation analysis of the inhomogeneously broadened spectra

The potentialities of the correlation technique with respect to extracting the homogeneous line profile from an inhomogeneously broadened spectrum are analyzed by computer simulation. The signal-to-noise ratio for autoconvolution of the homogeneous line profile, obtained by statistical processing of an array of realizations of the inhomogeneously broadened spectrum for different experimental conditions and different values of parameters of the system is calculated. A general form of the dependence of the signal-to-noise ratio on the magnitude of the accumulated signal is established. An interpolation formula that expresses this dependence in an analytical form is obtained and a simple procedure is proposed that allows one to plot this dependence for specific experimental situations.

Spin memory in the n-doped GaAs/AlGaAs quantum wells

The polarized luminescence spectra and kinetics of the GaAs quantum wells with excess free electrons are studied experimentally. Quantum beats between the exciton and electron spin sublevels, split by a magnetic field, are detected. The dynamics of the degree of polarization is found to contain a long component associated with slow relaxation of electron spins.