Waveguiding without a waveguide: Local‐mode exciton polaritons in multiple quantum wells

Exciton polaritons are considered in infinite multiple quantum wells which are periodic except that one well (impurity) has a different well width from the others (host). Under certain circumstances it is possible to have a long‐lived exciton‐polariton mode localized about the impurity. From the viewpoint of the electromagnetic field, this corresponds to waveguide modes in the vicinity of an exciton resonance in such structures. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71327/2/APPLAB-66-8-994-1.pd

Selective spin coupling through a single exciton

We present a novel scheme for performing a conditional phase gate between two spin qubits in adjacent semiconductor quantum dots through delocalized single exciton states, formed through the inter-dot Foerster interaction. We consider two resonant quantum dots, each containing a single excess conduction band electron whose spin embodies the qubit. We demonstrate that both the two-qubit gate, and arbitrary single-qubit rotations, may be realized to a high fidelity with current semiconductor and laser technology.Comment: 5 pages, 3 figures; published version, equation formatting improved, references adde

Plasmon dispersion in metal nanoparticle chains from angle-resolved scattering

We present angle and frequency resolved optical extinction measurements to determine the dispersion relation of plasmon modes on Ag and Au nanoparticle chains with pitches down to 75 nm. The large splitting between transverse and longitudinal modes and the band curvature are inconsistent with reported electrostatic near-field models, and confirm that far-field retarded interactions are important, even for $\lambda/5$-sized structures. The data imply that lower propagation losses, larger signal bandwidth and larger maximum group velocity then expected can be achieved for wave vectors below the light line. We conclude that for the design of optical nanocircuits coherent far-field couplings across the entire circuit need to be considered, even at subwavelength feature sizes.Comment: 4 pages, 4 figures, colo

3D Quantitative Damage Characterization in the Coating of a Metal Substrate with Terahertz Waves

In this study, terahertz (THz) reflective imaging is applied to characterize damage in the coating on metal substrates. The coating was initially scratched, and after aging, different damage mechanisms have occurred. Since the coating is optically thin (compared to the wavelengths within the THz spectrum), the THz echoes will partially or totally overlap, which makes it difficult to reconstruct the damaged coating structure. THz frequency-wavelet domain deconvolution is applied to resolve the overlapping echoes. Based on the observed features in the deconvoluted THz signals, three types of damage, including corrosion, the appearance of blisters and delamination, are successfully identified. The corrosion area is located in the middle of the scratch, and the delamination occurs around the scratch. In the blister area, no delamination is observed, but the swelling of the coating is clearly revealed. Moreover, quantitative information in depth is also obtained by analyzing the deconvoluted data. The thickness of the delamination and the thickness of the coating in both the normal (undamaged) and blister areas can be calculated. 3D imaging results shown in Fig. 1 clearly exhibit the thickness distribution across the whole coating plane, which also highlights the features of the different damage mechanisms

Radiative Lifetimes of Single Excitons in Semiconductor Quantum Dots- Manifestation of the Spatial Coherence Effect

Using time correlated single photon counting combined with temperature dependent diffraction limited confocal photoluminescence spectroscopy we accurately determine, for the first time, the intrinsic radiative lifetime of single excitons confined within semiconductor quantum dots. Their lifetime is one (two) orders of magnitude longer than the intrinsic radiative lifetime of single excitons confined in semiconductor quantum wires (wells) of comparable confining dimensions. We quantitatively explain this long radiative time in terms of the reduced spatial coherence between the confined exciton dipole moment and the radiation electromagnetic field.Comment: 4 pages, 3 figure

A note on the photoluminescence decay of thermalized excitons in quantum structures: Many-bond model

The temperature dependence of the photoluminescence decay time associated with the radiative decay of a thermalized exciton population in a quantum well or wire is shown to be independent of the number of exciton bands involved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31170/1/0000069.pd

Off-diagonal disorder model for exciton polaritons in layered media. Disorder-induced origin of radiative widths

Excitons in an infinite layered dipolar medium, such as a layered crystal or a multiple-quantum-well stack, with perfect periodicity exhibit a vanishing radiative width due to the requirement of energy-momentum conservation. Using a polariton model with off-diagonal disorder and a configuration-averaging technique, we show how deviations from the ideal case, specifically in the form of weak departures from perfect periodicity, and the resulting breaking of full translational invariance, give rise to a nonvanishing radiative width.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31260/1/0000166.pd

Alkali Metal Adsorbates on W(110): Ionic, Covalent, or Metallic?

The photoemission signal from the first atomic layer of W(110) is used to assess the nature of the interaction between the surface atoms of the metal substrate and the adsorbates Na, K, and Cs for coverages up to 1 atomic layer. Our results indicate that there is little or no charge transfer from the alkali metal to the W surface, even in the limit of low coverage. The satellite structure of the photoemission lines of the outermost p shell of the alkali metals confirms this conclusion. While contrary to the conventional picture of alkali-metal-charge donation, these findings fully support recent theoretical calculations