Infra-red Divergences in Light-Front QED and Coherent State Basis

We present a next to leading order calculation of electron mass renormalization in Light-Front Quantum Electrodynamics (LFQED) using old-fashioned time ordered perturbation theory (TOPT). We show that the true infrared divergences in $\delta m^2$ get canceled up to $O(e^4)$ if one uses coherent state basis instead of fock basis to calculate the transition matrix elements.Comment: 44 pages,11 figure

Phonon bottleneck in the low-excitation limit

The phonon-bottleneck problem in the relaxation of two-level systems (spins) via direct phonon processes is considered numerically in the weak-excitation limit where the Schroedinger equation for the spin-phonon system simplifies. The solution for the relaxing spin excitation p(t), emitted phonons n_k(t), etc. is obtained in terms of the exact many-body eigenstates. In the absence of phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the bottleneck plateau p_\infty > 0 with strongly damped oscillations, the frequency being related to the spin-phonon splitting Delta at the avoided crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 but in the case of strong bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is nonexponential. Inhomogeneous broadening exceeding Delta partially alleviates the bottleneck and removes oscillations of p(t). The line width of emitted phonons, as well as Delta, increase with the strength of the bottleneck, i.e., with the concentration of spins.Comment: 16 PR pages, 14 Figure captions, submitted to PRB. The whole text does dot fit here. Please, get the correct file from http://www.lehman.edu/faculty/dgaranin/Bottleneck2.pd

Towards Microscopic Understanding of the Phonon Bottleneck

The problem of the phonon bottleneck in the relaxation of two-level systems (spins) to a narrow group of resonant phonons via emission-absorption processes is investigated from the first principles. It is shown that the kinetic approach based on the Pauli master equation is invalid because of the narrow distribution of the phonons exchanging their energy with the spins. This results in a long-memory effect that can be best taken into account by introducing an additional dynamical variable corresponding to the nondiagonal matrix elements responsible for spin-phonon correlation. The resulting system of dynamical equations describes the phonon-bottleneck plateau in the spin excitation, as well as a gap in the spin-phonon spectrum for any finite concentration of spins. On the other hand, it does not accurately render the lineshape of emitted phonons and still needs improving.Comment: 13 Phys. Rev. pages, 5 figure captions (7 figures

Sub-Natural Linewidth Single Photons from a Quantum Dot

The observation of quantum dot resonance fluorescence enabled a new solid-state approach to generating single photons with a bandwidth almost as narrow as the natural linewidth of a quantum dot transition. Here, we operate in the Heitler regime of resonance fluorescence to generate sub-natural linewidth and high-coherence quantum light from a single quantum dot. The measured single-photon bandwidth exhibits a 30-fold reduction with respect to the radiative linewidth of the QD transition and the single photons exhibit coherence properties inherited from the excitation laser. In contrast, intensity-correlation measurements reveal that this photon source maintains a high degree of antibunching behaviour on the order of the transition lifetime with vanishing two-photon scattering probability. This light source will find immediate applications in quantum cryptography, measurement-based quantum computing and, in particular, deterministic generation of high-fidelity distributed entanglement among independent and even disparate quantum systems

THE SOCIO-DEMOGRAPHIC CORRELATIONS OF PSYCHOLOGICAL CAPITAL

The definition and content of psychological capital is not unitary in the professional literature. Research carried out in this subject is directed at exploring cause-result correlations between certain personal psychological constructs and one of the aspects of labour productivity. In our research the positive, psychology based concept of Psychological Capital (PsyCap) defined by Luthans et al (2007a) is used. This concept consists of four components: self-efficacy, optimism, hope and resiliency which are measured by the Psychological Capital Questionnaire (PsyCap) invented by them.The present paper is a pilot study using the Psychological Capital Questionnaire for the first time in Hungary. Within its framework the Psychological capital questionnaire is applied for the job starters with a business qualification in higher education by examining the socio-demographic correlations (gender, studies, labour market characteristics). The main constraints of the examination are the cross-section layout of the research and few elements in the sample, which limit our cause and effect conclusions. On the basis of the significant results Psychological Capital is considered to determine success in finding a job, earning a good salary and being satisfied with the career alike when employing job starting graduates with a business qualification at the beginning of their career in the labour market

Three and Four-Body Interactions in Spin-Based Quantum Computers

In the effort to design and to construct a quantum computer, several leading proposals make use of spin-based qubits. These designs generally assume that spins undergo pairwise interactions. We point out that, when several spins are engaged mutually in pairwise interactions, the quantitative strengths of the interactions can change and qualitatively new terms can arise in the Hamiltonian, including four-body interactions. In parameter regimes of experimental interest, these coherent effects are large enough to interfere with computation, and may require new error correction or avoidance techniques.Comment: 5 pages incl. 4 figures. To appear in Phys. Rev. Lett. For an expanded version including detailed calculations see http://xxx.lanl.gov/abs/cond-mat/030201

Entanglement between the future and past in the quantum vacuum

We note that massless fields within the future and past light cone may be quantized as independent systems. We show that the vacuum is an entangled state of these systems, exactly mirroring the known entanglement between the spacelike separated Rindler wedges. We describe a detector which exhibits a thermal response to the vacuum when switched on at t=0. The feasibility of experimentally detecting this effect is discussed.Comment: 4 pages, 1 figur

Quantization Of Cyclotron Motion and Quantum Hall Effect

We present a two dimensional model of IQHE in accord with the cyclotron motion. The quantum equation of the QHE curve and a new definition of filling factor are also given.Comment: 13 Pages, Latex, 1 figure, to appear in Europhys. Lett. September 199

Photon Orbital Angular Momentum in Astrophysics

Astronomical observations of the orbital angular momentum of photons, a property of electromagnetic radiation that has come to the fore in recent years, have apparently never been attempted. Here, I show that measurements of this property of photons have a number of astrophysical applications.Comment: 17 pages plus two figure

Corrections to Fermi's Golden Rule in ϕ→KKˉ\phi \to K\bar{K} Decays

We analyze the decays $\phi \to K\bar{K}$ utilizing a formulation of transition rates which explicitly exhibits corrections to Fermi's Golden Rule. These corrections arise in systems in which the phase space and/or matrix element varies rapidly with energy, as happens in $\phi \to K\bar{K}$, which is just above threshold. We show that the theoretical corrections resolve a puzzling $5\sigma$ discrepancy between theory and experiment for the branching ratio $R = \Gamma (\phi \to K^+K^-)/\Gamma(\phi \to K^0\bar{K}^0)$