Circular polarization in scattered light as a possible biomarker

Biological molecules exhibit homochirality and are optically active. Therefore, it is possible that the scattering of light by biological molecules might result in a macroscopic signature in the form of circular polarization. If this is the case, then circular polarization spectroscopy, which may be utilized in remote sensing, can offer a powerful indicator of the presence of a universal biosignature, namely homochirality. Here, we describe laboratory experiments designed to investigate this idea. We focus on photosynthetic microorganisms, and also show results from macroscopic vegetation and control minerals. In the microorganisms, we find unambiguous circular polarization associated with electronic absorption bands of the photosynthetic apparatus. Macroscopic vegetation yields a stronger and more complex signature while the control minerals produce low-levels of circular polarization unrelated to their spectra. We propose a heuristic explanation of our results, which is that the polarization is produced by circular dichroism in the material after the light has undergone its last scattering event. The results are encouraging for the use of circular polarization spectroscopy in remote sensing of a generic biomarker from space or the ground.     

An Arbitrated Proxy Blind Signature Based on Hyper Entanglement Analysis

Motivated by the hyperentangled Bell states analysis, an arbitrated quantum proxy blind signature (QPBS) scheme is developed. Four participants accomplish the task of signing and verifying via exchanging the entanglement of polarization and spatial-mode degrees of freedom. Alice blinds message and sends it to a proxy signatory David who is delegated by the original signatory Charlie. David generates a signature using the delegating code while Bob verifies the signing with the help of an arbitrator Trent. Unlike previous schemes, the verifying phase is no longer executed only by a recipient. Analysis shows that when the even numbers of blinding string always equal 1, the scheme protects the proxy blind signature against forgery and disavow while maintaining the properties of verifiability and identifiability.     

Polarization catastrophe in the polaronic Wigner crystal

We consider a three dimensional Wigner crystal of electrons lying in a host ionic dielectric. Owing to their interaction with the lattice polarization, each localized electron forms a polaron. We study the collective excitations of such a polaronic Wigner crystal at zero temperature, taking into account the quantum fluctuations of the polarization within the Feynman harmonic approximation. We show that, contrary to the ordinary electron crystal, the system undergoes a polarization catastrophe when the density is increased. An optical signature of this instability is derived, whose trend agrees with the experiments carried out in Nd-based cuprates. Received 4 July 2002 Published online 17 September 2002     

Current and strain-induced spin polarization in InGaN/GaN superlattices

The lateral current-induced spin polarization in InGaN/GaN superlattices (SLs) without an applied magnetic field is reported. The fact that the sign of the nonequilibrium spin changes as the current reverses and is opposite for the two edges provides a clear signature for the spin Hall effect. In addition, it is discovered that the spin Hall effect can be strongly manipulated by the internal strains. A theoretical work has also been developed to understand the observed strain-induced spin polarization. Our result paves an alternative way for the generation of spin polarized current.     

Probing space-time structure of new physics with polarized beams at the international linear collider

At the international linear collider large beam polarization of both the electron and positron beams will enhance the signature of physics due to interactions that are beyond the standard model. Here we review our recently obtained results on a general model-independent method of determining for an arbitary one-particle inclusive state the space-time structure of such new physics through the beam polarization dependence and angular distribution of the final state particle.      

Effect of ferroelectricity on electron transport in Pt/BaTiO3/Pt tunnel junctions

Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO3/Pt FTJ as a model system, we show that the polarization of the BaTiO3 barrier leads to a substantial drop in the tunneling conductance due to changes in the electronic structure driven by ferroelectric displacements. We find a sizable change in the transmission probability across the Pt/BaTiO3 interface with polarization reversal, a signature of the electroresistance effect. These results reveal exciting prospects that FTJs offer as resistive switches in nanoscale electronic devices.     

Mode density inside an omnidirectional mirror is heavily directional but not small

We show that ominidirectional reflection is not a sufficient signature of a photonic bandgap. Although dramatic angular redistribution takes place, the mode density of the electromagnetic field is hardly altered within the ominidirectional reflection range but rather has characteristics typical of a waveguide. The strikingly large polarization anisotropy is due to the huge dielectric contrast but not to a photonic bandgap.     

Analysis of reactions with polarized deuterons (II)

Criteria for a simplified analysis of polarization measurements on reactions of deuterons with light nuclei are derived. In these reactions prominent resonances appear at deuteron energies up to several MeV. The characteristic signature of such levels in polarization data can be used to determine the spin parameters of the resonant element. Methods developed in an earlier paper, dealing with isolated resonances, are supplemented to include interference terms between two or more (l, s, J) reaction matrix elements. Linear relations between expansion coefficients of different polarization quantities are given for various cases. The application of these criteria in a simple, preliminary analysis is discussed and demonstrated using experimental data available at present.     

Polarized x-ray emission from magnetized neutron stars: signature of strong-field vacuum polarization

In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein type resonance across which an x-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to a unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized x rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magnetic field and geometry.     

Kondo effect in a quantum dot coupled to ferromagnetic leads: a numerical renormalization group analysis

We investigate the effects of spin-polarized leads on the Kondo physics of a quantum dot using the numerical renormalization group method. Our study demonstrates in an unambiguous way that the Kondo effect is not necessarily suppressed by the lead polarization: While the Kondo effect is quenched for the asymmetric Anderson model, it survives even for finite polarizations in the regime where charge fluctuations are negligible. We propose the linear tunneling magnetoresistance as an experimental signature of these behaviors. We also report on the influence of spin-flip processes.     

Gamma ray burst constraints on ultraviolet Lorentz invariance violation

We present a unified general formalism for ultraviolet Lorentz invariance violation (LV) testing through electromagnetic wave propagation, based on both dispersion and rotation measure data. This allows for a direct comparison of the efficacy of different data to constrain LV. As an example we study the signature of LV on the rotation of the polarization plane of γ-rays from gamma ray bursts in a LV model. Here γ-ray polarization data can provide a strong constraint on LV, 13 orders of magnitude more restrictive than a potential constraint from the rotation of the cosmic microwave background polarization proposed by Gamboa, López-Sarrión, and Polychronakos [J. Gamboa, J. López-Sarrión, A.P. Polychronakos, Phys. Lett. B 634 (2006) 471].     

Field dependence of the longitudinal muon polarization for anomalous muonium

The constant muon polarization for anomalous muonium exhibits a peculiar field dependence which represents an easily measurable signature of anomalous muonium centers even in polycrystalline materials. Furthermore it can be used to extract information on the dynamical destruction of the state upon temperature variations and it might also be useful to investigate muonium in amorphous materials.This work has been partially supported by the Swiss National Science Foundation.     

Anomalies in the slow polarization kinetics of a ferroelectric relaxor in the temperature region of a diffuse phase transition

It is shown experimentally in the specific example of Cr-doped barium-strontium niobate that the anomalies in the infralow-frequency dielectric properties characteristic of a ferroelectric relaxor persist over the whole temperature region of the diffuse phase transition and decrease gradually with increasing temperature. Experimental data are presented on the anomalous quasi-static dielectric hysteresis loops, the slow polarization kinetics, and the anomalously broad energy-distribution spectra of potential barriers. The anomalies are a signature and a quantitative measure of the structural disorder typical of a relaxor.     

Optimization of light polarization sensitivity in QWIP detectors

The current development of QWIPs (Quantum Well Infrared Photodetectors) at III–V Lab led to the production of 20 μm pitch, mid-format and full TV-format LWIR starring arrays with excellent performances, uniformity and stability. At the present time III–V Lab, together with TOL (Thales Optronics Ltd.) and SOFRADIR (Société Française de Détecteurs Infrarouges), work on the demonstration of a 20 μm pitch, 640 × 512 LWIR focal plane array (FPA) which detects the incident IR light polarization. Manufactured objects present a strong linear polarization signature in thermal emission. It is of high interest to achieve a detector able to measure precisely the degree of linear polarization, in order to distinguish artificial and natural objects in the observed scene.In this paper, we present a theoretical investigation of the optical coupling in polarization sensitive pixels. The QWIP modeling is performed by the Finite Difference Time Domain (FDTD) method. The aim is to optimize the sensitivity to light polarization as well as the performance of the detector.     

Raman scattering from GaP nanowires

A complete Raman study of GaP nanowires is presented. By comparison with the Raman spectra of GaP bulk material, microcrystals and nanoparticles, we give evidence that the Raman spectrum is affected by the one-dimensional shape of the nanowires. The Raman spectrum is sensitive to the polarization of the laser light. A specific shape of the overtones located between 600 and 800 cm^-1 is actually a signature of the nanowires. Some phonon confinement and thermal behavior is also observed for nanowires.     

Ultrastrong light-matter coupling regime with polariton dots

The regime of ultrastrong light-matter interaction has been investigated theoretically and experimentally, using zero-dimensional electromagnetic resonators coupled with an electronic transition between two confined states of a semiconductor quantum well. We have measured a splitting between the coupled modes that amounts to 48% of the energy transition, the highest ratio ever observed in a light-matter coupled system. Our analysis, based on a microscopic quantum theory, shows that the nonlinear polariton splitting, a signature of this regime, is a dynamical effect arising from the self-interaction of the collective electronic polarization with its own emitted field.     

Electron correlations, spontaneous magnetization and momentum density in quantum dots

The magnetization of quantum dots (QDs) is discussed in terms of a relatively simple but exactly solvable model Hamiltonian. The model predicts oscillations in spin polarization as a function of dot radius for a fixed electron density. These oscillations in magnetization are shown to yield distinct signature in the momentum density of the electron gas, suggesting the usefulness of momentum resolved spectroscopies for investigating the magnetization of dot systems. We also present variational quantum Monte Carlo calculations on a square dot containing 12 electrons in order to gain insight into correlation effects on the interactions between like and unlike spins in a QD.     

Scanning tunneling microscopy chemical signature of point defects on the MoS2(0001) surface

Using ab initio calculations, we have studied the modification of the electronic structure of the MoS2(0001) surface by several point defects: a surface S vacancy and different transition metal atoms substituting a S atom (Pd, Au, Fe, and V). With a S vacancy, a gap state appears with weight mostly on the Mo and S atoms surrounding the vacancy. The substitutional atoms of complete d band (Pd and Au) do not present magnetic polarization and slightly modify the DOS near the Fermi energy. On the other hand, the incomplete d band atoms (Fe and V) present spin polarization and modify significantly the states near the band edges. From calculated STM images and STS curves, we show that this chemical signature can be measured and used to characterize the surface defects of the substrate which are suitable nucleation centers for nanocluster growth.     

Wavelength-Tunable Rectangular Pulses Generated from All-Fiber Mode-Locked Laser Based on Semiconductor Saturable Absorber Mirror

The wavelength-tunable rectangular mode-locking operation is demonstrated in an all-fiber laser based on semiconductor saturable absorber mirror.As the dissipative soiiton resonance signature,the puJse duration varies from 580 ps to 2.1 ns as a function of the increasing pump power.Correspondingly,the maximum pulse energy is9.11 nJ.Moreover,it is found that the wavelength tunable operation with a range of approximately 10 nm could be obtained by properly adjusting the polarization controllers.The characteristics of the rectangular pulses at different wavelengths are similar to each other.The demonstration of the wavelength tunable rectangular pulses would be beneficial to some applications for many fields such as spectroscopy and sensing research.     

Quantitative Surface Chirality Detection with Sum Frequency Generation Vibrational Spectroscopy: Twin Polarization Angle Approach

介绍了一种新的表面和频振动光谱方法: 定量手性检测中的双偏振角方法. 一般来讲表面光谱信号中非手性项贡献最强,而纯界面手性信号要比非手性信号弱两到三个数量级. 因此在和频振动光定量测量和分析界面手性的贡献问题上存在困难. 在和频振动光谱的双偏振角方法中,通过固定入射红外光偏振方向,并同时改变入射可见光和初涉和频信号光的偏振角进行测量. 这样所得到的偏振依赖的和频振动光谱信号能够直接给出界面手性贡献的特征,并 且能够用于准确测量界面的手性和非手性贡献. 对双偏振角方法进行了描述,并且通过S和R手性的柠檬烯空