多光子非线性Compton散射的能量转换

研究了多光子非线性Compton散射中电子与光子的能量转换及其转换效率.结果表明:散射光子频率随电子吸收光子数n的增大而增大,随碰撞非弹性成分ξ的增大而迅速减小.在超强激光场中,当极端相对论性电子与光子发生多光子非线性Compton散射且被光场俘获时,能量转换效率趋于无限大,即电子可以从超强激光场中获得巨大的加速能量.用高速电子束入射并与光子发生多光子非线性Compton散射,是提高非线性Compton散射能量转换效率的重要途径.     

Absorption of gamma-ray photons in a vacuum neutron star magnetosphere: I. Electron-positron pair production

The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.     

The weak neutral charge and coherent photoproduction of lepton pairs

The production of e⁺e⁻ pairs in the nuclear electroweak field from intermediate energy circularly polarized photons is studied. The polarization asymmetry provides a measurement of the weak charge induced by neutral current interactions. The analysis is made for the double differential cross section corresponding to the energy spectrum and angular distribution of the outgoing positron. Predictions, within the standard model, of the parity violating asymmetry reach values near 10⁻⁴ at incident photon energies of 500 MeV and positrons in the backward hemisphere.     

Efficient Generation of Frequency-Multiplexed Entangled Single Photons

We present two schemes to generate frequency-multiplexed entangled (FME) single photons by coherently mapping photonic entanglement into and out of a quantum memory based on Raman interactions. By splitting a single photon and performing subsequent state transfer, we separate the generation of entanglement and its frequency conversion, and find that the both progresses have the characteristic of inherent determinacy. Our theory can reproduce the prominent features of observed results including pulse shapes and the condition for deterministically generating the FME single photons. The schemes are suitable for the entangled photon pairs with a wider frequency range, and could be immune to the photon loss originating from cavity-mode damping, spontaneous emission, and the dephasing due to atomic thermal motion. The sources might have significant applications in wavelength-division-multiplexing quantum key distribution.     

The effects of interactions between photon and the quark-gluon plasma on production of soft dileptons

We investigate the effects of interactions of the intermediate photons with the quark-gluon plasma on dilepton productions. The singular behaviour at the photon mass shell in the case of free photon is removed by the interactions. Instead, we find double resonance peaks near the photon mass shell due to the transverse and longitudinal modes. The effects of interactions further away fromM ²=0 is negligible and the photons effectively propagate as free particles in the plasma. The result of resummation is the enhancement of dilepton production rate, except in an extremely narrow region around each resonance peak, where its effect is to reduce the peak. The net result is more dilepton pairs come out of the plasma than in the one loop case. Both enhancement and reduction are partly due to Landau damping. Whereas the former is true over most range of the energy-momentum of the photon and is particularly prominent in region close to but not too close to the resonance peaks, the latter is effectively only true at the peaks.     

未被俘获电子对多光子非线性Compton散射能量转换效率的影响

 应用单粒子理论和电子与光子非弹性碰撞模型，研究了未被俘获电子对多光子非线性Compton散射能量转换效率的影响。结果表明，未被俘获电子使该散射的频谱展宽随入射电子速度和与电子同时作用的光子数的增大而增大，随电子与光子非弹性碰撞成分的增大而减小，从而使能量转换效率近乎与电子入射速度正比降低。用低能电子入射，能有效地减小这种损失。     

Emission of a photon by an electron in a radiation-dominant universe

The process by which a photon is emitted by an electron in a radiation-dominant universe is considered, under the assumption that an arbitrary number of pairs are produced from a vaccum. In a flat space this process is forbidden by the laws of conservation. The dependence of the probability and the mean number of created particles on the energy of the initial electron is investigated. In the limiting cases (initial electron with high or low energies), approximate expressions are found for the probability that a photon is emitted by an electron as well as for the total probability of the process, including production of photons and pairs from a vacuum. Approximate expressions are obtained for the mean number of particles that are produced in the course of inelastic scattering of an electron in the early Universe. Biy State Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 98–102, September, 1996.     

Radiative return at NLO and the measurement of the hadronic cross-section in electron–positron annihilation

Electron–positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process and the emission of two real hard photons: . A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DANE, CLEO-C and B-meson factories. Received: 14 December 2001 / Published online: 5 April 2002     

Heralding Pure Single Photons Generated with Spontaneous Parametric Down Conversion

We investigate the possibility of generated heralding single photons via spontaneous parametric down conversion using periodically poled lithium niobate crystals with different phase-matching. We use the Schmidt decomposition to calculate the degree of entanglement of photon pairs We simulated the spectral purity, bandwidth, and the joint spectral intensity pictures of degenerate and non-degenerate photon pairs. At last, we obtain an ideal condition of the counter-propagating photons, which can be applied in the quantum communication.     

On refractive processes in strong laser field quantum electrodynamics

Refractive processes in strong-field QED are pure quantum processes, which involve only external photons and the background electromagnetic field. We show analytically that such processes occurring in a plane-wave field and involving external real photons are all characterized by a surprisingly modest net exchange of energy and momentum with the laser field, corresponding to a few laser photons, even in the limit of ultra-relativistic laser intensities. We obtain this result by a direct calculation of the transition matrix element of an arbitrary refractive QED process and accounting exactly for the background plane-wave field. A simple physical explanation of this modest net exchange of laser photons is provided, based on the fact that the laser field couples with the external photons only indirectly through virtual electron–positron pairs. For stronger and stronger laser fields, the pairs cover a shorter and shorter distance before they annihilate again, such that the laser can transfer to them an energy corresponding to only a few photons. These results can be relevant for the future experiments aiming to test strong-field QED at present and next-generation facilities.     

Exafs like oscillations in X-ray excited autoionization spectra assisted by compton process

Oscillating features have been observed in the background of the inelastic electrons excited by high energy monochromatic X-ray photons at kinetic energy above the Cr M_2,3VV Auger transition. These structures are absent when X-ray photons of are used. We suggest that these extended features are due to an autoionization process experienced by the 3p core electron assisted by a Compton scattering with the X-ray photons. Through the inelastic Compton process the incoming photons excite the core electrons towards empty states above the Fermi level in a continuous manner up to a maximum energy, which strongly depends on the incident photon energy. These excited states are modulated in energy by the crystalline structure as it has been shown by means of the EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy. These oscillating structures are compared with those obtained through electron excitation for the same Auger transition in the Extended Fine Auger Structure (EXFAS) spectroscopy.     

Measuring the photon fragmentation function at HERA

The production of final state photons in deep inelastic scattering originates from photon radiation off leptons or quarks involved in the scattering process. Photon radiation off quarks involves a contribution from the quark-to-photon fragmentation function, corresponding to the non-perturbative transition of a hadronic jet into a single, highly energetic photon accompanied by some limited hadronic activity. Up to now, this fragmentation function was measured only in electron–positron annihilation at LEP. We demonstrate by a dedicated parton-level calculation that a competitive measurement of the quark-to-photon fragmentation function can be obtained in deep inelastic scattering at HERA. Such a measurement can be obtained by studying the photon energy spectra in γ+(0+1)-jet events, where γ denotes a hadronic jet containing a highly energetic photon (the photon jet). Isolated photons are then defined from the photon jet by imposing a minimal photon energy fraction. For this so-called democratic clustering approach, we study the cross sections for isolated γ+(0+1)-jet and γ+(1+1)-jet production as well as for the inclusive isolated photon production in deep inelastic scattering.     

夸克-胶子等离子体中的喷注-光子转换机制(英文)

提出了一种夸克 胶子等离子体中的喷注 光子转换机制。 对于热光子而言, 在热夸克 胶子媒介中的喷注 光子转换是一个非常重要的热光子来源。 喷注可以通过次级康普顿散射和湮灭过程来实现喷注 光子转换。 此外, 还考虑了在快光子产生过程中起重要修正作用的胶子 光子贡献, 其中,核遮蔽效应和同位旋效应也被引入到了部分子模型中。We develop a jet photon conversion mechanism in the expanding quark gluon plasma. The jet photon conversion in hot quark gluon medium is a vital source of the thermal photon production. The jet converts into photons via the secondary Compton and annihilation processes in the quark gluon plasma. The gluon photons are also considered in the calculation of prompt photons which includes the effect of the shadowing and isospin of nucleus. We find that the prompt gluon photons are also an important modification to prompt photons.     

The factor of suppression of Cherenkov radiation from electron-positron pairs produced by a hard γ photon

Cherenkov radiation from electron-positron pairs produced by hard γ photons is considered. The radiation yield is shown to be suppressed when the distance between an electron and a positron is less than the wavelength. This effect depends on the γ-photon energy and radiation intensity.     

On propagation of high-energy photon in a medium in presence of an external field

The polarization tensor is calculated which originates from interaction of a photon with the electron–positron field. The effects of multiple scattering of electrons and positrons in a medium side by side with external fields are included. The corresponding general representation of polarization tensor is found in the form of two-dimensional integral. The both effects may be essential for propagation of high-energy photons in oriented single crystals.     

Nonlinear interactions with an ultrahigh flux of broadband entangled photons

We experimentally demonstrate sum-frequency generation with entangled photon pairs, generating as many as 40,000 photons per second, visible even to the naked eye. The nonclassical nature of the interaction is exhibited by a linear intensity dependence of the nonlinear process. The key element in our scheme is the generation of an ultrahigh flux of entangled photons while maintaining their nonclassical properties. This is made possible by generating the down-converted photons as broadband as possible, orders of magnitude wider than the pump. This approach can be applied to other nonlinear interactions, and may become useful for various quantum-measurement tasks.     

The stimulated Breit-Wheeler process as a source of background <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> pairs at the international linear collider

Passage of beamstrahlung photons through the bunch fields at the interaction point of the ILC determines background pair production. The number of background pairs per bunch crossing due to the Breit-Wheeler, Bethe-Heitler and Landau-Lifshitz processes is well-known. However, the Breit-Wheeler process also takes place in and is modified by the bunch fields. A full QED calculation of this stimulated Breit-Wheeler process reveals cross-section resonances due to the virtual particle reaching the mass shell. The one-loop electron self-energy in the bunch field is also calculated and included as a radiative correction. The bunch field is considered to be a constant crossed electromagnetic field with associated bunch field photons. Resonance is found to occur whenever the energy of contributed bunch field photons is equal to the beamstrahlung photon energy. The stimulated Breit-Wheeler cross-section exceeds the ordinary Breit-Wheeler cross-section by several orders of magnitude and a significantly different pair background may result.      

Photon and positron generation by ultrahigh intensity laser interaction with electron beams

This study investigates the generation of high energy photons and positrons using focused ultrahigh intensity femtosecond laser pulses on a relativistic electron beam with a set of two-dimensional particle-in-cell simulations. We consider circularly and linearly polarized, single and spatially separated double laser pulses. We model both 500 MeV and 1 GeV electron beams. Higher positron production is obtained using circularly polarized laser pulses. Using double pulses, the focusing effect of the ponderomotive force confines the electrons to a small volume, generating additional energetic photons and positrons. The positron spectral distributions are effectively modified by these variations. When the electron beam energy is doubled, the number of positrons increased, while the cutoff energy remained nearly constant.     

Dispersive photon blockade in a superconducting circuit

Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.     

等离子体波背景下的光子Berry相位

利用光学度规将强激光脉冲激发的电子等离子体波描述为有效几何背景.借助于广义相对论中弯曲时空下的Maxwell方程组得到了探针光子在等离子体中电子等离子体波背景下(被处理为有效度规)所满足的运动方程及光子的Hamilton表达式.导出了电子等离子体波对光子Berry相位贡献的解析表达式并且对光子在真空中Berry相位的修正做了数值估算. 关键词： 电子等离子体波 等离子体 Berry相位