Extension of coherent response time is a desired goal in the field of all-optical information processing implemented in classical and quantum ways. Here we demonstrate how spin-dependent stimulated photon echo can be used to extend decay time of coherent signal from exciton ensemble. We experimentally studied photon echoes from excitons in a model single InGaAs/GaAs quantum well subject to transverse magnetic field. Field-induced quantum beats lead to oscillation of exciton population between bright and long-lived dark excitons. As a result, photon echo decays much longer with decay time attaining dark exciton lifetime in case of non-oscillatory regime.

Localized excitons in two-dimensional (2D) materials are considered promising sources of single photons on demand. The photon indistinguishability as a key figure of merit for quantum information processing is strongly influenced by the coupling of charge excitations to lattice vibrations of the surrounding semiconductor material. Here, we quantify the impact of exciton-acoustic-phonon interaction and cavity quantum electrodynamics effects on photon indistinguishability in a Hong-Ou-Mandel setup by solving fully quantum-mechanical equations for a coupled quantum dot-cavity-phonon system including non-Markovian effects. We find a strong reduction of indistinguishability compared to 3D systems due to increased exciton-phonon coupling efficiency. Moreover, we show that the coherence properties of photons are significantly influenced by the finite phonon lifetime in the surrounding material giving rise to pure dephasing. If these limitations are overcome, localized excitons in 2D semiconductors can become a new avenue for quantum light sources.

Direct bandgap semiconductors possess a unique attribute: the presence of a free exciton state with a high total oscillator strength. This property makes them highly promising for applications in ultrafast optical signal processing and optical computing. One such protocol for optical computing is based on four-wave mixing (FWM). In this study, the nonlinear optical effect in polycrystalline thin films of halide perovskite MAPbI(3) (MA(+) = CH3NH3+) at low temperatures is demonstrated. Through analyzing the spectroscopy of the FWM signal, studying the photoluminescence excitation spectra, and comparing the findings with results from MAPbI3 single crystals, it has been discovered that the strongest nonlinear response is observed at the free exciton resonance and in the region of shallow defect states. Surprisingly, the presence of FWM in cross-linear excitation geometry has been observed, indicating potential involvement of other nonlinear or many-body effects. The observations of FWM with free excitons even in highly defective MAPbI3 thin films demonstrate the robustness of the exciton resonance and highlight the practical prospects for utilizing this material in optical computing.

Compositional engineering of the optical properties of hybrid organic-inorganic lead halide perovskites is crucial for the realization of efficient solar cells and light-emitting devices. We study the effect of band gap fluctuations on coherent exciton dynamics in a mixed FA0.9Cs0.1PbI2.8Br0.2 perovskite crystal by using photon echo spectroscopy. We reveal a narrow homogeneous exciton line width of 16 μeV at a temperature of 1.5 K. The corresponding exciton coherence time T2 = 83 ps is exceptionally long due to the localization of excitons at the scale of tens to hundreds of nanometers. From spectral and temperature dependences of the two- and three-pulse photon echo decay, we conclude that for low-energy excitons pure decoherence associated with elastic scattering on phonons is comparable with the exciton lifetime, while for excitons with higher energies, inelastic scattering to lower energy states via phonon emission dominates.

Halide perovskites show great potential for a variety of optoelectronic applications. The presence of robust exciton resonance in these materials makes them promising for use in information photonics. In this paper, we demonstrate the possibility of writing and delayed reading of the optical coherence in halide perovskite by the spontaneous (two-pulse) photon echo in ${\mathrm{MAPbI}}_{3}$ (${\mathrm{MA}}^{+}$ = ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}^{+}$) lead-halide perovskite single crystal on picosecond time scales. The spectral and polarimetric measurements of the photon echo signal confirm the free excitonic origin of the excitation under study. Observed relatively long dephasing time, high exciton oscillator strength, and weakly pronounced excitation-induced dephasing make halide perovskites a promising media for applications.

We have studied experimentally spin-dependent photon echoes from excitons in an InGaAs/GaAs quantum well subject to a transverse magnetic field (Voigt geometry). Larmor precession of the spins of the electron and heavy hole in an exciton leads to a periodic transfer of coherence between bright and dark exciton states. The increase in dephasing time due to the transition to the dark states could be useful for coherent control development. A comprehensive analysis shows a good agreement between a four-wave mixing experiment and the predictions of a theoretical treatment based on a five-level exciton model comprising a ground state and two pairs of bright and dark states. The extracted optical dephasing time of bright and dark excitons is equal to 30 and 130 ps, respectively. Exploiting the photon echo reveals evidence of electron Larmor precession with in-plane g factor |ge| = 0.44 +/- 0.05 and heavy hole precession as well. The precession frequency of the latter depends nonlinearly on the applied magnetic field, and the corresponding g factor reaches a value of |gh,& BOTTOM;| & AP; 0.3 at B = 6 T. Estimates for the heavy hole g-factor spreading as well as the isotropic exchange interaction constant are provided.

Halide perovskites show great potential for a variety of optoelectronic applications. The presence of robust exciton resonance in these materials makes them promising for use in information photonics. In this paper, we demonstrate the possibility of writing and delayed reading of the optical coherence in halide perovskite by the spontaneous (two-pulse) photon echo in MAPbI(3) (MA(+) = CH3NH3+) lead-halide perovskite single crystal on picosecond time scales. The spectral and polarimetric measurements of the photon echo signal confirm the free excitonic origin of the excitation under study. Observed relatively long dephasing time, high exciton oscillator strength, and weakly pronounced excitation-induced dephasing make halide perovskites a promising media for applications.

Larmor precession of the quasiparticle spin about a transverse magnetic field leads to the oscillations in the spontaneous photon echo signal due to the shuffling of the optical coherence between optically accessible (bright) and inaccessible (dark) states. Here we report on a new non-oscillating photon echo regime observed in the presence of non-equal dephasing rates of bright and dark states. This regime enables the observation of the long-living dark optical coherence. As a simple mechanical analogy, we suggest a charged particle moving in the magnetic field through the medium with anisotropic viscous friction. We demonstrate the dark coherence retrieval in the spontaneous photon echo from excitons in the InGaAs/GaAs quantum well.

The article is devoted to circuit simulation of functional units of a magnetoelectric current sensor. The magnetoelectric current sensor is designed to measure the current in electrical circuits of direct or alternating current in electrical engineering. The advantages of the developed magnetoelectric current sensors over existing analogs are higher sensitivity, lower power consumption, wide dynamic range of the output voltage, and better linearity of the output characteristics. In the course of the simulation, a model of the OA MCP6024-E/ST microcircuit from Microchip Technology Inc. was used, which is used as a signal amplifier for a magnetoelectric sensing element in a current sensor. Simulation of the signal generation unit, peak detector and linear amplifier was carried out. Circuitry solutions were proposed to improve the parameters of existing current sensors. Solutions have been found to ensure the temperature stability of the sensor. The developed magnetoelectric current sensors can be manufactured using integral technology and become a significant competitor to the traditional Hall effect sensors.

In this work, we studied the photon echo from heavy-hole excitons in a thin InGaAs/GaAs quantum well. To analyze the results, we used the model of an ensemble of two-level systems. The model allows us to describe the temporal profile and the moment of arrival of the echo signal, as well as the echo amplitude decay with increasing delay between pulses. In addition, excitation-induced dephasing effect was observed, that was beyond the limits of applicability of the model.

Exciton-polaritons in planar waveguides are of great interest for application in polariton circuits due to the large polariton group velocity in the plane of the waveguide. We demonstrate the ability to control the exciton-polariton coupling by light in an AlGaAs-based planar waveguide with GaAs/AlGaAs quantum well. The transition between strong and weak coupling regimes observed with increasing light intensity is explained by the increase in exciton mode losses due to the quantum well charging. This assumption is confirmed by the reflection spectroscopy with resonant illumination.

The article deals with the issues of bringing the heads of legal entities to criminal liability for failure to perform the duties of a tax agent. At the same time, the motive of the crime, which is mandatory and enshrined in the law, is personal interest. The courts assess the content of this concept differently, which leads to different court decisions in this area. The uncertainty of the concept of «personal interest» leads to the violation of human rights and is one of the corruption factors in law enforcement.

Coherent dynamics of excitons in single InGaAs/GaAs quantum well was investigated experimentally. In order to carry out this study a three-pulse setup capable of measuring time-resolved four-wave mixing was build. Measured signal consists of two distinguishable components of similar amplitude corresponding to the fast decaying free polarization decay and the long-lived primary photon echo, which proves comparability of homogenous and inhomogeneous broadenings of the exciton resonance.

We study the influence of optical selection rules and polarization splittings on properties of exciton polaritons in a planar AlGaAs waveguide containing embedded GaAs quantum wells. We demonstrate that transverse electric and transverse magnetic modes couple differently with light- and heavy-hole quantum well excitons, which leads to distinct polarization splittings of the resulting polariton modes. The experimental data are in good agreement with modeling based on theoretical data for the optical selection rules for quantum well excitons.

We study optically the coherent evolution of trions and excitons in a delta-doped 3.5-nm-thick ZnO/Zn-0.91 Mg0.09O multiple quantum well by means of time-resolved four-wave mixing at a temperature of 1.5 K. Employing spectrally narrow picosecond laser pulses in the x((3)) regime allows us to address differently localized trion and exciton states, thereby avoiding many-body interactions and excitation-induced dephasing. The signal in the form of photon echoes from the negatively charged A excitons (T-A, trions) decays with coherence times varying from 8 up to 60 ps, depending on the trion energy: more strongly localized trions reveal longer coherence dynamics. The localized neutral excitons decay on the picosecond time scale with coherence times up to T-2 = 4.5 ps. The coherent dynamics of the XB exciton and T-B trion are very short (T-2 < 1 ps), which is attributed to the fast energy relaxation from the trion and exciton B states to the respective A states. The trion population dynamics is characterized by the decay time T-1, rising from 30 to 100 ps with decreasing trion energy.

We study the coherent dynamics of localized excitons in 100 periods of 2.5-nm-thick (In,Ga) N/GaN quantum wells with 7.5% indium concentration, measured with spectroscopic resolution through two-pulse and threepulse photon echoes at the temperature of 1.5 K. A long-lived coherent exciton dynamics is observed in the (In,Ga)N quantum wells: When the laser photon energy is tuned across the 43-meV-wide inhomogeneously broadened resonance line, the coherence time T-2 varies between 45 and 255 ps, increasing with stronger exciton localization. The corresponding narrow homogeneous linewidths ranging from 5.2 to 29 mu eV as well as the relatively weak exciton-phonon interaction (0.7 mu eV/K) confirm a strong, quantum-dot-like exciton localization in a static disordered potential inside the (In, Ga) N quantum well layers.

We report an experimental study of the nonlinear response of single GaAs/AlGaAs quantum well. It was shown that bleaching effect manifested as reversible exciton spectral lines broadening can be suppressed by additional above-barrier illumination.

Autocorrelation measurements are used to reveal the spectral diffusion time scale in the single photon emission of a GaN interface fluctuation quantum dot. Typical characteristic diffusion times of such QDs are revealed to be of nanosecond order. The excitation power dependence of the diffusion rate is also investigated, whereby an increase in the diffusion rate with increasing excitation power is observed. This result provides information on experimental conditions that will be required for the generation of indistinguishable photons.