Quantum Optical Effects Research Articles

Electrodeposited Ceramic Superlattices

Ceramic superlattices have been produced by electrodeposition with modulation wavelengths in the range from 5 to 10 nanometers. The TlaPbbOc/TldPbeOf superlattices were deposited from a single aqueous solution at room temperature, and the layer thicknesses were galvanostatically controlled. The films showed strong preferred orientation and distinct first-order satellites around the Bragg reflections in the x-ray diffraction pattem. The modulation wavelengths calculated from the satellite spacings were in agreement with those calculated from Faraday's law. Because the modulation wavelengths are of electron mean free path dimensions, this dass of degenerate semiconductor metal-oxide superlattices may exhibit thickness-dependent quantum optical, electronic, or optoelectronic effects.

Electrodeposition of Nanomodulated Ceramic Thin Films

ABSTRACTElectrochemistry can be used for the atomic-level architecture of ceramic materials. In this report, ceramic superlattices based on the TlaPbbOc/TldPbeOf system were electrodeposited with individual layer thicknesses as thin as 3nm. The superlattices were deposited from a single aqueous solution at room temperature, and the layer thicknesses were galvanostatically controlled. Substitution of Tl2O3 into PbO2 appears to stabilize a face-centered cubic structure with an average lattice parameter of 0.536nm. The lattice parameters for the T1aPbbOc. mixed oxides vary by less than 0.3% when the Pb/Tl ratio is varied from 0.84 to 7.3. Because the modulation wavelengths are of electron mean free path dimensions, this new class of degenerate semiconductor metal-oxide superlattices may show thickness-dependent quantum optical, electronic, or optoelectronic effects.

Lead salt quantum effect structures

Lead salt (IV-VI) compounds have been grown epitaxially by a variety of growth techniques, such as molecular-beam epitaxy and hot-wall epitaxy. Recently, compositional superlattices and quantum-well heterostructures have been grown that exhibit strong quantum optical effects. These structures have been used to fabricate midinfrared diode lasers with greatly improved operating temperatures. Thus, it appears that these devices will continue to maintain a significant advantage over II-VI and III-V compound diode lasers. Doping superlattices have been made which possess enhanced minority carrier properties. Ferromagnetic ordering in PbSnTe-MnTe alloys suggests potential areas for future work in magnetic field sensitivity devices. Lead salt quantum-effect structures are included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two-state system coupled to a boson mode: Quantum dynamics and classical approximations

The relation between classical and quantum mechanical integrability is investigated for a boson mode coupled to a two-level system. Different semi-classical approximations of this system are considered which are obtained by (i) factorization of expectation values of the two-state variable and the boson, (ii) making a WKB-type approximation, (iii) replacing the boson by a classical field of constant amplitude and fixed frequency and (iv) putting the boson into a self-consistent coherent state. The results vary considerably and include cases of non-integrable and integrable classical dynamics. Quantum mechanically the system is found to satisfy a criterion of quantum mechanical integrability, which we formulate, but the separated Hamiltonian of the boson alone does not have a well-defined classical limit. Numerical results for the energy spectrum and expectation values are obtained, which show a high degree of regularity but also display overlapping avoided crossings usually associated with non-integrable Hamiltonians. The exact dynamics of the occupation probabilities of the two levels is also analysed numerically. The dependence of quantum mechanical recurrence effects (in quantum optics known as revivals) on coupling strength, frequency detuning and initial conditions is studied. The revivals are found to disappear in the case of strong coupling. The Fourier spectra of the dynamical expectation values are also calculated

High-field electroluminescence

The theoretical efficiency for the direct conversion of electrical energy into luminescent emission, that is, electroluminescence (EL), is first evaluated from thermodynamics. High-field, collisional excitation EL is then introduced and compared with low-field, minority carrier injection EL and with cathodoluminescence. Some general characteristics of thin-film high-field EL are discussed. The basic mechanism of high-field EL is reviewed. It consists of three steps occuring in sequence: generation of charge carriers, acceleration of these carriers to optical energies, and their inelastic collisions to excite luminescent centers. Ballistic, streaming and Maxwellian hot carriers are distinguished, and their distribution functions discussed. The incompatibility of large cross sections for collisional excitation and stability of the excited luminescent centers in high fields is considered, taking account of the energies of the electronic states of dopants with respect to band structure. The present understanding of the structure and electronic states of transition metal and rare earth (RE) luminescent centers in II–VI and II–VII 2 semiconductors is evaluated. Particular attention is given to probable structures of molecular dopants such as REF 3 in ZnS. Recent advances in thin-film, high-field EL are summarized. The emphasis has been on ZnS:Mn and ZnSe:Mn films sandwiched between insulating films such as Y 2O 3 and operated with a.c. voltages. All three steps of the high-field EL mechanism occur in the II–VI layer, with some carrier generation at the II–VI/insulator junction. The spatial separation of the sequential steps in contiguous layers in composite EL cells is proposed, and evidence for separation of the acceleration and collision excitation in SiO/ZnF 2:Mn/SiO cells is presented. Some quantum optical effects in thin-film EL cells are discussed. Finally, some basic problems of high-field EL are reviewed. These include: the origin of charge carriers, the distribution function of the energetic carriers, structure and energy levels of complex dopants, and sources of inefficiencies and of saturation. Possible methods for achieving higher efficiencies than the current (1%) are proposed.

Anti-correlation effects in quantum optics

Specific examples of fields which produce anti-correlation effects are considered. It is shown that for a pure Fock state, the photoelectric counting distribution is binomial, and the counting fluctuations are less than those characteristic of a pure coherent state.