Observation Of Quantum Research Articles

Observation of quantum confined excited states of GaN nanocrystals

GaN nanocrystals with an average diameter of 4.5 nm±1.6 nm were synthesized by pulsed laser ablation of a gallium metal target in a nitrogen atmosphere. Transmission electron microscopy and selected area electron diffraction confirmed the hexagonal structure and size of the nanocrystals. Optical absorption and photoluminescence spectroscopy revealed quantum confined excited states in the nanocrystalline samples with features at 4.43 eV (280 nm) and 5.47 eV (227 nm).

Carrier quantum confinement in self-orderedAlxGa1−xAsV-groove quantum wells

Observation of quantum confined states and optical anisotropy of the interband absorption in self-ordered ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ vertical quantum wells (VQW's) grown on V-grooved substrates is reported. The variation in Al composition across the VQW's was determined by parallel electron energy-loss spectroscopy. It was then employed to calculate the eigenstates of the confined carriers in these structures, with valence-band mixing included using a $4\ifmmode\times\else\texttimes\fi{}4$ $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Luttinger model. Polarized photoluminescence excitation spectra of the structure show features attributed to transitions between electron and heavy-hole or light-hole confined eigenstates, with measured energies in good agreement with the calculated ones. Polarization anisotropy associated with confined electrons and holes is evidenced by the measured spectra and explained by valence-band mixing in the (011) self-ordered quantum well.

Photoluminescence observation of quantum confined stark effect caused by band bending near the surface of etched structures with GaAs/AlGaAs wells

The interaction of electronic and excitonic states confined in quantum wells (QW) with nearby sulphur-passivated surface was studied by photoluminescence (PL). The redshift (up to 12 meV for 50A QW) and quenching (down to 10 -4 ) of QW PL line were observed with approaching of the surface closely to QW by wet etching. The predominant role of quantum-confined Stark effect (QCSE) caused by the near-surface band bending was revealed by the following observations: (1) long-range surface influence (>300A), (2) increasing of the redshift for the thicker QW's, (3) the redshift dependence on the excitation level. On the basis of QCSE theory all the parameters of depleted layer on excitation level are determined. The revealed model can be used for the explanation of the optical properties of etched nanostructures

Influence of external birefringence on quantum beats in forward scattering in Voigt configuration. The [formula omitted] sodium transition

The influence of external birefringence on a quantum beat signal measured in the forward scattering in the Voigt configuration is presented. Using the Mueller matrices formalism we have calculated the intensity of the forward scattered light for moderately thick atomic vapor. We have found experimentally that the quantum beat pattern for the sodium 3 2S 1 2 ↔3 2P 3 2 trans ition changes its phase and frequency due to the birefringence generated by either a Babinet-Soleil compensator or a quarter-wave plate. A suitable setting of the analyzer uncrossing angle and the external retardance allowed us to perform an observation of the second order quantum beats only.

Time-resolved non-linear spectroscopy of local/non-local biphonon interaction in NH 4Cl

The interaction of the 2 v 4 biphonon with the corresponding overtone of the 15N impurities in natural ammonium chloride is investigated by a time-resolved coherent picosecond technique. The observation of quantum beats evidences the splitting of the quasi-biphonon into two quasi-bound states of very close frequencies and comparable Raman intensities. The spectral and dynamical features of this doublet are measured as a function of temperature. The results indicate the important role played by the two-phonon continuum in the formation and in the coherent decay of these states.

Observation of quantum well polarization effects in the photocurrent of multilayer diodes

Large electrical polarization effects in the time photoresponse of multilayer heterostructure diodes have been observed. This phenomenon manifests itself in a displacement current spike synchronous to a dark–light transition and in an opposite spike in the light–dark one. The effect is associated with the pileup and spatial separation of photogenerated electrons and holes in the wells in the space-charge region of the diode. At a particular forward bias voltage, the conduction photocurrent is eliminated, allowing accurate measurements of this phenomenon.

Magnetic field observation of a single flux quantum by electron-holographic interferometry.

The magneitc lines of force of a single flux quantum (fluxon) penetrating a superconducting film (Pb) were observed directly and individually by the electron holography technique using the Aharonov-Bohm effect. The phase contours of the electron wave not only confirm the quantized flux value h/2e but also reveal, by phase amplification, internal structure of a single fluxon. With the film thickness \ensuremath{\lesssim}0.5 \ensuremath{\mu}m, each fluxon, after penetrating the film, fans out or makes a ssU shape returning to another point on the film surface. With thicker films, fluxons form a bundle with a flux amounting to several times h/2e.

Observation of spatial quantum beating with separated photodetectors.

When signal and idler photons produced in the process of parametric down-conversion are mixed together, and directed to two photodetectors that respond to nonoverlapping optical frequencies centered at ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}$, it is found that the joint probability of two-photon detection exhibits a modulation of the form $cos({\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{2})\ensuremath{\tau}$, where $c\ensuremath{\tau}$ is the path difference. The experimental results are well described by a simple quantum-mechanical analysis.

Quantum confined Stark shifts in MOVPE-grown GaAs-AlGaAs multiple quantum wells

We report the first observation of clear quantum confined Stark shifts in GaAs-AIGaAs quantum-well devices grown using metal-organic vapour-phase epitaxy.

Observation of high photoisomerization quantum yields for 11- CIS retinal analogs having 12-s-trans geometries

Quantum yields of cis → trans photoisomerization (φPI)_were determined for two analogs of 11- cis-retinal that are expected to have 12-s- trans geometries: 11 - cis-13 demethylretinal and 11- cis-14-methylretinal. In nonpolar solvents, φPI values for these synthetic retinals are higher than that of 11- cis-retinal, thought to exist in a 2:1 equilibrium mixture of distorted 12-s- cis and 12-s- trans conformations. The φPI results are analyzed in terms of the calculated reordering of the two lowest π,π * excited singlet states with conformational changes in the polyene.

Interelectronic-state perturbation effects on photoelectron spectra and emission quantum yields

Model calculations are carried out on the photoelectron and ion emission spectra of a hypothetical diatomic molecule in the absence and presence of intramolecular coupling between two emitting excited states B + and A + of the ion. We show that interelectronic state coupling has relatively little influence on the frequency distribution of the photoelectron spectrum while modifying considerably the optical emission spectrum. Shifts of intensity from apparent B + to apparent A + emission spectral regions are shown to occur. This result explains the observation of apparent state quantum yields different from unity for emission from [Btilde] 2Σ u + and A 2Π u states of CO2 +, as well as the discrepancy between apparent populations of these two excited states inferred from photoelectron and emission spectral intensities.

Quantum chain processes. Direct observation of high quantum yields in the direct and photosensitized excitation of tetramethyl-1,2-dioxetane

Quantum chain processes. Direct observation of high quantum yields in the direct and photosensitized excitation of tetramethyl-1,2-dioxetane