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The precise characterization and control of single-electron wave functions emitted from a single-electron source are essential for advancing electron quantum optics. Here, we introduce a method for tailoring a single-electron emission distribution using energy filtering, enabling selective control of the distribution under various energy barrier conditions of the filter. The tailored electron is studied by reconstructing its Wigner distribution in the time–energy phase space using the continuous-variable tomography method. Our results reveal that the filtering cuts the portion of the distribution below the energy–barrier height of the filter in the time–energy space. While the filtering is demonstrated in a classical regime of the emitted electrons, we expect that this study significantly contributes to the design and implementation of advanced experiments toward quantum information processing based on single electrons.

Graphical Abstract:

Herein, time‐integrated and time‐resolved photoluminescence (PL) measurement experiments are performed on coupled GaAs quantum dot (QD) molecules with larger laser spot size and a single‐coupled QD molecule to investigate the dynamics of exciton states. A linearly polarized laser along the coupled direction of a laterally‐coupled GaAs QD molecule [11¯$\overset{\cdot}{1}$0] is used to determine the coupling effects of the different exciton states. For the ensemble of coupled QD molecules, the exciton PL peak shifts to lower energy (≈70 meV) and shows a linear increase in the PL intensity, demonstrating the properties of exciton states as a function of the laser excitation power. In addition, a power‐dependent redshift is observed in the single‐coupled GaAs QD molecule as a function of the excitation power; however, the two distinguished exciton states become resolved and show different power factors when the laser excitation power is linearly increased. This result clearly indicates the presence of energy transfer between the two different exciton states, X1and X2. Furthermore, when the polarized laser excitation power is increased, a coupled biexciton consisting of two different localized exciton states (X1and X2) is clearly observed, and a power‐dependent spectral redshift is detected in the exciton and biexciton states. At a high excitation power (15 I0), the decay times of the two different localized exciton states clearly show different lifetimes; and the decay time difference due to the size difference can be ignored at a low excitation power. Theoretically, the decay times of the two different exciton states, wherein the size deviation can be ignored, should be the same. Based on the results of the time‐integrated and time‐resolved PL measurements and the comparison between the ensemble and single exciton PL peaks, it is concluded that the coupling process in laterally‐coupled GaAs QD molecules is strongly supported against long‐range separation. Herein, time‐integrated and time‐resolved photoluminescence (PL) measurement experiments are performed on coupled GaAs quantum dot (QD) molecules with larger laser spot size and a single‐coupled QD molecule to investigate the dynamics of exciton states. A linearly polarized laser along the coupled direction of a laterally‐coupled GaAs QD molecule is used to determine the coupling effects of the different exciton states.

Purpose: Using the strong motion data of K-net in Japan, the continuous magnitude prediction method based on support vector machine (SVM) was studied. Design/methodology/approach: In the range of 0.5–10.0 s after the P-wave arrival, the prediction time window was established at an interval of 0.5 s. 12 P-wave characteristic parameters were selected as the model input parameters to construct the earthquake early warning (EEW) magnitude prediction model (SVM-HRM) for high-speed railway based on SVM. Findings: The magnitude prediction results of the SVM-HRM model were compared with the traditional magnitude prediction model and the high-speed railway EEW current norm. Results show that at the 3.0 s time window, the magnitude prediction error of the SVM-HRM model is obviously smaller than that of the traditional τcmethod and Pdmethod. The overestimation of small earthquakes is obviously improved, and the construction of the model is not affected by epicenter distance, so it has generalization performance. For earthquake events with the magnitude range of 3–5, the single station realization rate of the SVM-HRM model reaches 95% at 0.5 s after the arrival of P-wave, which is better than the first alarm realization rate norm required by “The Test Method of EEW and Monitoring System for High-Speed Railway.” For earthquake events with magnitudes ranging from 3 to 5, 5 to 7 and 7 to 8, the single station realization rate of the SVM-HRM model is at 0.5 s, 1.5 s and 0.5 s after the P-wave arrival, respectively, which is better than the realization rate norm of multiple stations. Originality/value: At the latest, 1.5 s after the P-wave arrival, the SVM-HRM model can issue the first earthquake alarm that meets the norm of magnitude prediction realization rate, which meets the accuracy and continuity requirements of high-speed railway EEW magnitude prediction.

The polarized micro-photoluminescence spectrum was analyzed to investigate the anisotropic localized states in a single GaAs quantum ring. An energy difference of ~0.1 meV was observed from the perpendicularly polarized spectrum measured by a pair of linear analyzers. Spectral dependence of the polarized emission was also characterized in terms of rotation and ellipticity angles using four Stokes parameters. While the rotation angle indicates the symmetric axis of an anisotropic quantum ring with a small variation (± 2°), the ellipticity angle varies from 7.4° down to –2.5°. We conclude that optical anisotropy and birefringence are induced by the crescent-like lateral shape of localized states.

The photoelectrochemical characteristics of p-InAlP grown on GaAs were investigated to exploit the potential of that material future as a photocathode in solar water splitting. The flat band potential was measured, and electrochemical impedance spectroscopy was performed to propose an equivalent circuit model and circuit elements fitted for charge transport analysis. Low photocatalytic activity was attributed to the band alignment with the water redox level. Since the valence band of InAlP is close to the water oxidation level, it causes inefficient hole transport to the counter electrode and the accumulation of holes in the photocathode.

Utilizing Sb-based bulk epilayers on large-scale low-cost substrates such as GaAs for fabricating infrared (IR) photodetectors is presently attracting significant attention worldwide. For this study, three sample series of GaAsxSb1−x, In1−xGaxSb, and InAsxSb1−xwith different compositions were grown on semi-insulating GaAs substrates by using molecular beam epitaxy (MBE) and appropriate InAs quantum dots (QDs) as a defect-reduction buffer layer. Photoluminescence (PL) signals from these samples were observed over a wide IR wavelength range from 2 μm to 12 μm in agreement with the expected bandgap, including bowing effects. In particular, interband PL signals from InAsxSb1−xand In1−xGaxSb samples even at room temperature show promising potential for IR photodetector applications.

We investigate the highly efficient terahertz nonlinearity exhibited by n-type GaAs crystals under metallic metamaterials. An intense THz field applied to the metamaterials leads to impact ionization in the GaAs substrate, which emits electroluminescence in the near-infrared region. Even for a similar THz field strength, n-type GaAs emits near-infrared photons more efficiently than semi-insulating GaAs. We analyzed the luminescence lineshapes and intensity as a function of the excitation field strength, using Fermi–Dirac statistics and the density of states in the conduction band to quantify electron density and locate the Fermi level after the relaxation of excited hot electrons.

We found that optical Aharonov–Bohm oscillations in a single GaAs/GaAlAs quantum ring can be controlled by excitation intensity. With a weak excitation intensity of 1.2 kW cm–2, the optical Aharonov–Bohm oscillation period of biexcitons was observed to be half that of excitons in accordance with the period expected for a two-exciton Wigner molecule. When the excitation intensity is increased by an order of magnitude (12 kW cm–2), a gradual deviation of the Wigner molecule condition occurs with decreased oscillation periods and diamagnetic coefficients for both excitons and biexcitons along with a spectral shift. These results suggest that the effective orbit radii and rim widths of electrons and holes in a single quantum ring can be modified by light intensity via photoexcited carriers, which are possibly trapped at interface defects resulting in a local electric field.

It is critical to determine whether a site has potential damage in real-time after an earthquake occurs, which is a challenge in earthquake disaster reduction. Here, we propose a real-time Earthquake Potential Damage predictor(EPDor) based on predicting peak ground velocities (PGVs) of sites. The EPDor is composed of three parts: (1) predicting the magnitude of an earthquake and PGVs of triggered stations based on the machine learning prediction models; (2) predicting the PGVs at distant sites based on the empirical ground motion prediction equation; (3) generating the PGV map through predicting the PGV of each grid point based on an interpolation process of weighted average based on the predicted values in (1) and (2). We apply the EPDor to the 2022 MS6.9 Menyuan earthquake in Qinghai Province, China to predict its potential damage. Within the initial few seconds after the first station is triggered, the EPDor can determine directly whether there is potential damage for some sites to a certain degree. Hence, we infer that the EPDor has potential application for future earthquakes. Meanwhile, it also has potential in Chinese earthquake early warning system.

We have investigated the effects of carrier localization on the migration-enhancing time in a wetting layer (WL) of quantum dots (QDs) grown by using the migration-enhanced epitaxy (MEE) growth technique. The WL photoluminescence (PL) intensity of QD sample grown with a longer migration-enhancing time remained strong even at low excitation densities. The PL decay time at the WL peak was longer for the MEE-grown QD with a longer migration-enhancing time. Moreover, the decay times of MEE-grown QDs across the WL’s PL band were longer at longer wavelengths. We conclude that the localization effect in the WL intensifies as the migration-enhancing time is increased.

We report on the optical and structural characterization of InSb QDs in InAs matrix, grown on InAs (100) substrates, for infrared photodetection. InSb has 7% lattice mismatch with InAs forming strained QDs, which are promising for longwave IR applications, due to their type-II band alignment. This report contains material development results of InSb QDs for increasing their emission wavelength towards long-wave IR region. Samples were grown by two techniques of MBE and MOVPE, with different InSb coverage on InAs (100) substrates. Structures grown by MBE reveal QD related photoluminescence at 4 m. AFM investigations of the MBE grown structures showed uncapped dots of ~ 35 nm in size and ~ 3 nm in height, with a density of about 2 x 1010cm-2. Cross-section TEM investigations of buried InSb layers grown by MBE showed coherently strained QDs for nominal InSb coverage in the range of 1.6 - 2 monolayers (MLs). Layers with InSb coverage more than 2MLs contain relaxed QDs with structural defects due to large amount of strain between InSb and InAs. Samples with such large dots did not show any InSb related luminescence. The MOVPE grown InSb samples exhibit a strong QD related emission between 3.8 to 7.5 m, depending on the amount of InSb coverage and other growth parameters. We report the longest wavelength observed so far in this material system.