Nonresonant photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave

The nonresonant Coulomb photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave is theoretically investigated. The approximation is examined when pulsewidth is considerably greater than the characteristic time of wave oscillations. The interaction of an electron and a positron with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation). An analytic expression for the nonresonant differential cross section was obtained for the range of moderately strong fields in the case relativistic and nonrelativistic energies. It is shown, that the nonresonant cross section of Coulomb photocreation of nonrelativistic pair in the field of a pulsed light wave is two times larger than the cross section of Coulomb photocreation in the absence of an external field.     

Coherent localization of two interacting carriers in one-dimensional quantum dot arrays

The coherent dynamics of two interacting carriers in one-dimensional quantum dot arrays driven by oscillating electric fields is theoretically investigated with the help of numerical calculations. The coherent localization of two electrons and that of an electron–hole pair are studied in this paper. For the two-electron case, the dynamic localization of the electrons is achieved when the Coulomb interaction is large enough. In this coherent localization, the Coulomb repulsion helps the electrons to be localized. For an electron–hole pair, although the dynamic localization of the composite particle does not occur due to charge neutrality, a different type of coherent localization can occur. These phenomena are explained by the quasienergy spectra based on Floquet analysis.     

High-frequency hopping conductivity and permittivity in compensated semiconductors

In semiconductors, high-frequency conductivity is caused by polarization reversal of the collective states of a pair of impurity atoms under the action of the random electric fields of all the impurities. A Coulomb correlation which appreciably increases the conductivity is established as a result of the statistical distribution of the particles over four levels of the diatomic system. The relaxation absorption and the permittivity of the entire pair system are calculated allowing for these statistics.     

Relativistic nonperturbative above-threshold phenomena in strong laser fields

Relativistic features of various nonperturbative above-threshold phenomena in strong laser fields are discussed and compared. This includes above-threshold ionization of multiply charged ions as well as pair production in an ultrastrong laser wave, superimposed with either a nuclear Coulomb field or another counterpropagating laser wave. For the probability of above-threshold pair production, a new scaling relation is given. Particular attention is paid to similarities among these processes, regarding the energy and angular spectra of the particles as well as the total reaction rates.     

Processes with heavy ion collisions

Some Coulomb effects in heavy ion collisions are considered. Among them the process of muon and lepton pair creation, Coulomb and unitary corrections, statistics of multiple pair production. Effects of multiple photon exchange in process of lepton pair production by linearly polarized photon on nuclei are considered. This process is used for measuring the polarization of initial photon. Relativistic muon energy loss due to the light lepton pair production in the Coulomb field are calculated. Also we consider the effects of multiple photon exchange in elastic lepton scattering on unscreened atomic field and discuss the possible experimental testing.     

Resonant electron-positron pair photoproduction on a nucleus in a pulsed light field

The resonant photoproduction of an electron-positron pair on a nucleus in the field of a pulsed light wave is studied theoretically. The approximation where the electromagnetic pulse duration is much longer than the characteristic time of wave oscillations is considered. The interaction of the electron and positron with the Coulomb potential of the nucleus is considered in the Born approximation. An analytical expression for the resonant differential cross section is derived for the range of moderately strong external fields. This cross section contains a resonant peak whose height and width are determined by the external pulsed wave characteristics. The resonant cross section for pair photoproduction on a nucleus in a pulsed laser field can exceed the corresponding cross section for pair photoproduction on a nucleus in the absence of an external field by an order of magnitude.     

Deflections of photoelectron classical trajectories in screened Coulomb potentials of H_2~+

The photoelectron momentum distribution of H+2in circularly polarized laser fields is studied based on classical trajectory calculations. We screen Coulomb potentials at different radii, and trace trajectories of an ensemble of electrons in such screened Coulomb potentials and circularly polarized laser fields. Simulations show that electron trajectories are bent by Coulomb fields, resulting in the laser-intensity-dependent drift of photoelectron momentum distributions in the laser polarization plane. This study intuitively explains how Coulomb potentials modify photoelectron momenta.     

Behaviour of gluons at high temperature

The screening of colour electric and magnetic fields and plasma oscillations in a high-temperature gluon plasma are investigated using linear response theory and self-consistent nonperturbative solutions to the Schwinger-Dyson equation. Static electric fields are screened, with

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. This result is proven to be gauge invariant in two ways: by computing π₀₀ in temporal axial, Coulomb and covariant gauges, and by computing the physical free energy of a heavy quark pair in the plasma in temporal axial gauge. To order g³ static magnetic fields are not screened.     

How composite bosons really interact

The aim of this paper is to clarify the conceptual difference which exists between the interactions of composite bosons and the interactions of elementary bosons. A special focus is made on the physical processes which are missed when composite bosons are replaced by elementary bosons. Although what is here said directly applies to excitons, it is also valid for composite bosons in other fields than semiconductor physics. We, in particular, explain how the two elementary scatterings – Coulomb and Pauli – of our many-body theory for composite excitons, can be extended to a pair of fermions which is not an Hamiltonian eigenstate – as for example a pair of trapped electrons, of current interest in quantum information.     

Photon-assisted shot noise due to the charging effect in a quantum dot device

We have investigated the spectral density of shot noise for an ultra-small quantum dot(QD) system in the Coulomb blockade regime when irradiated with microwave fields (MWFs) by employing a nonequilibrium Green’s function technique. The shot noise is sensitive to Coulomb interaction, and the photon-assisted Coulomb blockade behaviour strongly modifies the mesoscopic transport. We have calculated the first and second derivatives of shot noise in the strong and weak coupling regimes to compare the theoretical results with existing experimental results. In the strong coupling regime, the first and second derivatives of shot noise display Fano type peak-valley structures around the charging channel 2E _c due to Coulomb interaction. When the magnitudes of the MWFs are sufficiently large, the system displays channel blockade due to photon irradiation. The photon-assisted and Coulomb blockade steps in the noise — as well as the resonant behaviour in the differential noise — are smeared by increasing temperature. The Coulomb interaction suppresses the shot noise, but the ac fields can either suppress the shot noise(balanced case) or enhance the shot noise(unbalanced case). The suppression of shot noise caused by ac fields in the balanced case is greater than that caused by Coulomb interaction in our system. Super-Poissonian shot noise may be induced due to the compound effects of strong Coulomb interaction and photon absorption-emission processes.     

Effect of Cluster Coulomb Fields on Electron Acceleration in Laser-Cluster Interaction

Single particle simulations are used to investigate electron acceleration in the laser-cluster interaction, taking into account the Coulomb fields around individual clusters. These Coulomb fields are induced from the cluster cores with positive charge when electrons escape from the cluster cores through ponderomotive push from the laser field. These Coulomb fields enable some stripped electrons to be stochastically in phases with the laser fields so that they can gain net energy from the laser efficiently. In this heating mechanism, circularly polarized lasers, larger cluster size and higher cluster densities make the acceleration more efficient.     

远程传输过程中纠缠态的破坏

将来的远程通信中,量子远程传输可能成为重要的手段之一.整个理论是基于量子纠缠态机制的.但是纠缠态是很脆弱的.当量子态被环境扰动时,纠缠态会被打破.在此文中,我们选择处在总自旋为0的纠缠态中的正负电子为例,研究纠缠态由于与背景辐射光子的康普顿散射或与电子经过的大天体的强磁场散射而破坏的概率.由于单个电子的自旋投影不是物理可观测量,而且,电子束由于带电粒子间的库仑斥力,不可能较长期保持成团的形状.因而只能每次只发射一对正负电子对,并不断重复这个过程.由于这些限制,此文研究只有理论上的意义,但是也许对将来如何选择信息传递信使的研究有帮助     

Coulomb effects in a nanoscale SINIS junction

We study a system of two superconductors connected by a small normal grain. We consider the modification of the Josephson effect by the Coulomb interaction on the grain. Coherent charge transport through the junction is suppressed by Coulomb repulsion. An optional gate electrode may relax the charge blocking and enhance the current leading to the single Cooper pair transistor effect. Temperature dependences of critical current and of the minigap induced in the normal grain by the proximity to superconductor are studied. Both temperature and Coulomb interaction suppress critical current and minigap, but their interplay may lead to the nonmonotonic and even reentrant temperature dependence.     

Effect of the Coulomb blockade of Cooper pairs on the dynamic properties of small-size Josephson junctions

The dynamics of Cooper pair tunneling under Coulomb blockade in small-size Josephson junctions is studied in terms of the resistive model. A relationship between the delay time and temperature fluctuations of the Coulomb blockade edge and the rate of rise of the voltage across the junction is derived.     

Magnetic fields and fractional statistics in boundary conformal field theory

We study conformal field theories describing two massless one-dimensional fields interacting at a single spatial point. The interactions we include are periodic functions of the bosonized fields separately plus a “magnetic” interaction that mixes the two fields. Such models arise in open-string theory and dissipative quantum mechanics and perhaps in edge state tunneling in the fractional quantized Hall effect. The partition function for such theories is a Coulomb gas with interchange phases arising from the magnetic field. These “fractional statistics” have a profound effect on the phase structure of the Coulomb gas. In this paper we present new exact and approximate results for this type of generalized Coulomb gas.     

Dynamics of a pair of electron and hole in semiconductor superlattice under an intense electric field

This paper investigates the behavior of a pair of electron and hole in semiconductor superlattice under an external electric field with the consideration of Coulomb interaction. By numerically calculating the corresponding probability in the nearest neighbor tight binding approximation, we find that the single electron (or the hole) can not be dynamically localized due to the Coulomb interaction, while the dynamic localization of exciton (the pair of the electron and hole) still exists. Moreover we find that with the increase of the intensity of electric field, the exciton can be dynamically localized more completely.     

Effect of electromagnetic environment effect on coherent and incoherent Cooper pair tunneling in superconducting C-SET

Cooper pair tunneling in voltage-biased superconducting C-SET structure is discussed with emphasis on the electromagnetic environment effect based on the self-consistent microscopic theory of Coulomb blockade in C-SET. It is shown that coherent Cooper pair tunneling survives only in the low impedance limit where charge fluctuation is large, while incoherent Cooper pair tunneling survives in both low- and high-impedance limits.     

Signatures of spin pairing in chaotic quantum dots

Coulomb blockade resonances are measured in a GaAs quantum dot in which both shape deformations and interactions are small. The parametric evolution of the Coulomb blockade peaks shows a pronounced pair correlation in both position and amplitude, which is interpreted as spin pairing. As a consequence, the nearest-neighbor distribution of peak spacings can be well approximated by a modified bimodal Wigner surmise, in which interactions are taken into account beyond the constant interaction model.     

Mesoscopic Josephson effect

In the classical Josephson effect the phase difference across the junction is well defined, and the supercurrent is reduced only weakly by phase diffusion. For mesoscopic junctions with small capacitance the phase undergoes large quantum fluctuations, and the current is also decreased by Coulomb blockade effects. We discuss the behavior of the current–voltage characteristics in a large range of parameters comprising the phase diffusion regime with coherent Josephson current as well as the supercurrent peak due to incoherent Cooper pair tunneling in the Coulomb blockade regime.