Multiple Quantum Wells for P T -Symmetric Phononic Crystals

We demonstrate that the parity-time symmetry for sound is realized in laser-pumped multiple-quantum-well structures. Breaking of the parity-time symmetry for the phonons with wave vectors corresponding to the Bragg condition makes the structure a highly selective acoustic wave amplifier. Single-mode distributed feedback phonon lasing is predicted for structures with realistic parameters.Fil: Poshakinskiy, A.V.. Ioffe Institute; RusiaFil: Poddubny, A.N.. Ioffe Institute; RusiaFil: Fainstein, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

Carrier relaxation in Si/SiO2_2 quantum dots

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots in SiO$_2$ has been considered. Interaction of confined holes with optical phonons has been studied. The Huang-Rhys factor is calculated for such transitions. The probability of intraband transition of a confined hole emitting several optical phonons is estimated.Comment: 8 pages, 2 figures, submitted as an extended abstract to the E-MRS Spring Meeting 200

Magnon polaron formed by selectively coupled coherent magnon and phonon modes of a surface patterned ferromagnet

Strong coupling between two quanta of different excitations leads to the formation of a hybridized state which paves a way for exploiting new degrees of freedom to control phenomena with high efficiency and precision. A magnon polaron is the hybridized state of a phonon and a magnon, the elementary quanta of lattice vibrations and spin waves in a magnetically-ordered material. A magnon polaron can be formed at the intersection of the magnon and phonon dispersions, where their frequencies coincide. The observation of magnon polarons in the time domain has remained extremely challenging because the weak interaction of magnons and phonons and their short lifetimes jeopardize the strong coupling required for the formation of a hybridized state. Here, we overcome these limitations by spatial matching of magnons and phonons in a metallic ferromagnet with a nanoscale periodic surface pattern. The spatial overlap of the selected phonon and magnon modes formed in the periodic ferromagnetic structure results in a high coupling strength which, in combination with their long lifetimes allows us to find clear evidence of an optically excited magnon polaron. We show that the symmetries of the localized magnon and phonon states play a crucial role in the magnon polaron formation and its manifestation in the optically excited magnetic transients

Resonant Photonic Quasicrystalline and Aperiodic Structures

We have theoretically studied propagation of exciton-polaritons in deterministic aperiodic multiple-quantum-well structures, particularly, in the Fibonacci and Thue-Morse chains. The attention is concentrated on the structures tuned to the resonant Bragg condition with two-dimensional quantum-well exciton. The superradiant or photonic-quasicrystal regimes are realized in these structures depending on the number of the wells. The developed theory based on the two-wave approximation allows one to describe analytically the exact transfer-matrix computations for transmittance and reflectance spectra in the whole frequency range except for a narrow region near the exciton resonance. In this region the optical spectra and the exciton-polariton dispersion demonstrate scaling invariance and self-similarity which can be interpreted in terms of the ``band-edge'' cycle of the trace map, in the case of Fibonacci structures, and in terms of zero reflection frequencies, in the case of Thue-Morse structures.Comment: 13 pages, 9 figures, submitted to Phys. Rev.

Atom-mediated spontaneous parametric down-conversion in periodic waveguides

We propose the concept of atom-mediated spontaneous parametric down-conversion, in which photon-pair generation can take place only in the presence of a single two-level emitter, relying on the bandgap evanescent modes of a nonlinear periodic waveguide. Using a guided signal mode, an evanescent idler mode, and an atom-like emitter with the idler’s transition frequency embedded in the structure, we find a heralded excitation mechanism, in which the detection of a signal photon outside the structure heralds the excitation of the embedded emitter. We use a rigorous Green’s function quantization method to model this heralding mechanism in a 1D periodic waveguide and determine its robustness against losses

Analogue simulation of two-body quantum dynamics with classical setup

info:eu-repo/semantics/publishe

Simulation of two-boson bound states using arrays of driven-dissipative coupled linear optical resonators

We present a strategy based on two-dimensional arrays of coupled linear optical resonators to investigate the two-body physics of interacting bosons in one-dimensional lattices. In particular, we want to address the bound pairs in topologically nontrivial Su-Schrieffer-Heeger arrays. Taking advantage of the driven-dissipative nature of the resonators, we propose spectroscopic protocols to detect and tomographically characterize bulk doublon bands and doublon edge states from the spatially resolved transmission spectra, and to highlight Feshbach resonance effects in two-body collision processes. We discuss the experimental feasibility using state-of-the-art devices, with a specific eye on arrays of semiconductor micropillar cavities.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Surface brightens up Si quantum dots: direct bandgap-like size-tunable emission

Colloidal semiconductor quantum dots (QDs) constitute a perfect material for ink-jet printable large area displays, photovoltaics, light-emitting diode, bio-imaging luminescent markers and many other applications. For this purpose, efficient light emission/absorption and spectral tunability are necessary conditions. These are currently fulfilled by the direct bandgap materials. Si-QDs could offer the solution to major hurdles posed by these materials, namely, toxicity (e.g., Cd-, Pb- or As-based QDs), scarcity (e.g., QD with In, Se, Te) and/or instability. Here we show that by combining quantum confinement with dedicated surface engineering, the biggest drawback of Si—the indirect bandgap nature—can be overcome, and a ‘direct bandgap’ variety of Si-QDs is created. We demonstrate this transformation on chemically synthesized Si-QDs using state-of-the-art optical spectroscopy and theoretical modelling. The carbon surface termination gives rise to drastic modification in electron and hole wavefunctions and radiative transitions between the lowest excited states of electron and hole attain ‘direct bandgap-like’ (phonon-less) character. This results in efficient fast emission, tunable within the visible spectral range by QD size. These findings are fully justified within a tight-binding theoretical model. When the C surface termination is replaced by oxygen, the emission is converted into the well-known red luminescence, with microsecond decay and limited spectral tunability. In that way, the ‘direct bandgap’ Si-QDs convert into the ‘traditional’ indirect bandgap form, thoroughly investigated in the past