Photon-energy dissipation caused by an external electric circuit in "virtual" photo-excitation processes

We consider generation of an electrical pulse by an optical pulse in the ``virtual excitation'' regime. The electronic system, which is any electro-optic material including a quantum well structure biased by a dc electric field, is assumed to be coupled to an external circuit. It is found that the photon frequency is subject to an extra red shift in addition to the usual self-phase modulation, whereas the photon number is conserved. The Joule energy consumed in the external circuit is supplied only from the extra red shift.Comment: 4 pages, 1 fugur

Quantum Langevin equations for semiconductor light-emitting devices and the photon statistics at a low-injection level

From the microscopic quantum Langevin equations (QLEs) we derive the effective semiconductor QLEs and the associated noise correlations which are valid at a low-injection level and in real devices. Applying the semiconductor QLEs to semiconductor light-emitting devices (LEDs), we obtain a new formula for the Fano factor of photons which gives the photon-number statistics as a function of the pump statistics and several parameters of LEDs. Key ingredients are non-radiative processes, carrier-number dependence of the radiative and non-radiative lifetimes, and multimodeness of LEDs. The formula is applicable to the actual cases where the quantum efficiency $\eta$ differs from the differential quantum efficiency $\eta_{d}$, whereas previous theories implicitly assumed $\eta = \eta_{d}$. It is also applicable to the cases when photons in each mode of the cavity are emitted and/or detected inhomogeneously. When $\eta_{d} < \eta$ at a running point, in particular, our formula predicts that even a Poissonian pump can produce sub-Poissonian light. This mechanism for generation of sub-Poissonian light is completely different from those of previous theories, which assumed sub-Poissonian statistics for the current injected into the active layers of LEDs. Our results agree with recent experiments. We also discuss frequency dependence of the photon statistics.Comment: 10 pages, 8 figure

An Analysis of Mutual Communication between Qubits by Capacitive Coupling

A behavior of a two qubit system coupled by the electric capacitance has been studied quantum mechanically. We found that the interaction is essentially the same as the one for the dipole-dipole interaction; i.e., qubit-qubit coupling of the NMR quantum gate. Therefore a quantum gate could be constructed by the same operation sequence for the NMR device if the coupling is small enough. The result gives an information to the effort of development of the devices assuming capacitive coupling between qubits.Comment: 8 pages, 2 figures Revised and Replaced on Apr. 8 200

Polarized light-flavor antiquarks from Drell-Yan processes of h+\vec{N}\to\vec{l^{+-}} + l^{-+} + X

We propose a formula to determine the first moment of difference between the polarized $\bar u$- and $\bar d$-quarks in the nucleon, {\it i.e.} $\Delta\bar u-\Delta \bar d$ from the Drell-Yan processes in collisions of unpolarized hadrons with longitudinally polarized nucleons by measuring outgoing lepton helicities. As coefficients in the differential cross section depend on the $u$- and $d$-quark numbers in the unpolarized hadron beam, the difference $\Delta\bar u-\Delta\bar d$ can be independently tested by changing the hadron beam. Moreover, a formula for estimating the $K$-factor in Drell-Yan processes is also suggested.Comment: 10 pages, 1 figur

A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests - thanks to the rate equation model - a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.Comment: 11 pages, 10 figure

Polarized Parton Distribution Functions in the Nucleon

Polarized parton distribution functions are determined by using world data from the longitudinally polarized deep inelastic scattering experiments. A new parametrization of the parton distribution functions is adopted by taking into account the positivity and the counting rule. From the fit to the asymmetry data A_1, the polarized distribution functions of u and d valence quarks, sea quarks, and gluon are obtained. The results indicate that the quark spin content is \Delta\Sigma=0.20 and 0.05 in the leading order (LO) and the next-to-leading-order (NLO) MS-bar scheme, respectively. However, if x dependence of the sea-quark distribution is fixed at small x by "perturbative QCD" and Regge theory, it becomes \Delta \Sigma=0.24 ~ 0.28 in the NLO. The small-x behavior cannot be uniquely determined by the existing data, which indicates the importance of future experiments. From our analysis, we propose one set of LO distributions and two sets of NLO ones as the longitudinally-polarized parton distribution functions.Comment: 51 pages, REVTeX, aps.sty, aps12.sty, epsfig.sty, prabib.sty, revtex.sty, revtex.cls, 17 eps figures. Submitted for publication. Email: [email protected]

A new pairwise kernel for biological network inference with support vector machines

International audienceBACKGROUND: Much recent work in bioinformatics has focused on the inference of various types of biological networks, representing gene regulation, metabolic processes, protein-protein interactions, etc. A common setting involves inferring network edges in a supervised fashion from a set of high-confidence edges, possibly characterized by multiple, heterogeneous data sets (protein sequence, gene expression, etc.). RESULTS: Here, we distinguish between two modes of inference in this setting: direct inference based upon similarities between nodes joined by an edge, and indirect inference based upon similarities between one pair of nodes and another pair of nodes. We propose a supervised approach for the direct case by translating it into a distance metric learning problem. A relaxation of the resulting convex optimization problem leads to the support vector machine (SVM) algorithm with a particular kernel for pairs, which we call the metric learning pairwise kernel. This new kernel for pairs can easily be used by most SVM implementations to solve problems of supervised classification and inference of pairwise relationships from heterogeneous data. We demonstrate, using several real biological networks and genomic datasets, that this approach often improves upon the state-of-the-art SVM for indirect inference with another pairwise kernel, and that the combination of both kernels always improves upon each individual kernel. CONCLUSION: The metric learning pairwise kernel is a new formulation to infer pairwise relationships with SVM, which provides state-of-the-art results for the inference of several biological networks from heterogeneous genomic data

Fusion product diagnostics planned for Large Helical Device deuterium experiment

Deuterium experiment on the Large Helical Device (LHD) is now being planned at the National Institute for Fusion Science. The fusion product diagnostics systems currently considered for installation on LHD are described in this paper. The systems will include a time-resolved neutron yield monitor based on neutron gas counters, a time-integrated neutron yield monitor based on activation techniques, a multicollimator scintillation detector array for diagnosing spatial distribution of neutron emission rate, 2.5 MeV neutron spectrometer, 14 MeV neutron counter, and prompt γ-ray diagnostics

Number-phase-squeezed few-photon state generated from squeezed atoms

This paper develops a method of manipulating the squeezed atom state to generate a few-photon state whose phase or photon-number fluctuations are prescribed at our disposal. The squeezed atom state is a collective atomic state whose quantum fluctuations in population difference or collective dipole are smaller than those of the coherent atom state. It is shown that the squeezed atom state can be generated by the interaction of atoms with a coherent state of the electromagnetic field, and that it can be used as a tunable source of squeezed radiation. A variety of squeezed states, including the photon-number squeezed state and the phase squeezed state, can be produced by manipulating the atomic state. This is owing to the fact that quantum-statistical information of the atomic state is faithfully transferred to that of the photon state. Possible experimental situations to implement our theory are discussed.Comment: 17 pages, RevTex, 14 figures, using epsf.sty, title is changed, discussion about dissipation is added, accepted for publication in Physical Review

Tolerância para resíduos de EBDCs em culturas com geração fitogênica de CS2.

Neste trabalho foram utilizados três métodos para análise de ditiocarbamatos em amostras testemunha de mamão das variedades Golden, Sunrise solo e Tainung. Os mamões foram cultivados em áreas experimentais sem utilização, durante todo o ciclo da cultura, de agrotóxicos ou fertilizantes sulfurados. O CS2 foi quantificado por espectrofotometria e por cromatografia gasosa utilizando detector fotométrico de chama no modo enxofre, tanto no método por headspace quanto por partição em iso-octano. Todos os métodos forneceram resultados positivos de CS2 no mamão, independentemente da variedade avaliada. As concentrações de CS2 observadas foram comparadas com o limite máximo de resíduos de etilenobis(ditiocarbamatos)(EBDCs), estabelecido na Comunidade Européia em 0,05mg kg-1. A probabilidade de ser encontrada uma amostra de mamão com concentração de CS2 igual ou acima de 0,05 mg kg-1 foi de 12 % pelo método de iso-octano, 55% pelo método de headspace e 94 % pelo método espectrofotométrico. Desse modo, os resíduos de EBDCs quantificados como CS2, devem ser cuidadosamente interpretados em culturas com geração fitogênica de CS2, pois a presença deste não confirma a utilização de fungicidas EBDCs