Overcoming phonon-induced dephasing for indistinguishable photon sources

Reliable single photon sources constitute the basis of schemes for quantum communication and measurement based quantum computing. Solid state single photon sources based on quantum dots are convenient and versatile but the electronic transitions that generate the photons are subject to interactions with lattice vibrations. Using a microscopic model of electron-phonon interactions and a quantum master equation, we here examine phonon-induced decoherence and assess its impact on the rate of production, and indistinguishability, of single photons emitted from an optically driven quantum dot system. We find that, above a certain threshold of desired indistinguishability, it is possible to mitigate the deleterious effects of phonons by exploiting a three-level Raman process for photon production

Classical and quantum cross-section for black hole production in particle collisions

We suggest a simple model to study the problem of the black hole production in particle collisions. The cross-section for the classical and quantum production is analysed within this model. In particular, the possibility to form a black hole in collision of low energy particles (or at large impact parameter) via the quantum tunneling mechanism is pointed out. It is found that, in this model, the geometric cross-section gives a good estimate for the production at low and high energies. We also reconsider the arguments in favor of exponential suppression for the production of trans-Planckian black hole and conclude that no such suppression in fact appears. Analyzing the probability for the black hole production we point out on the importance of the backreaction and reevaluate the contribution of the black hole formed in gravitational collapse to the Euclidean path integral.Comment: 14 pages; v2: comment on gravitational radiation corrected, lower energy regime more emphasize

Production of a sterile species via active-sterile mixing: an exactly solvable model

The production of a sterile species via active-sterile mixing in a thermal medium is studied in an exactly solvable model. The \emph{exact} time evolution of the sterile distribution function is determined by the dispersion relations and damping rates $\Gamma_{1,2}$ for the quasiparticle modes. These depend on \wtg = \Gamma_{aa}/2\Delta E, with $\Gamma_{aa}$ the interaction rate of the active species in absence of mixing and $\Delta E$ the oscillation frequency in the medium without damping. \wtg \ll1,\wtg \gg 1 describe the weak and strong damping limits respectively. For \wtg\ll1, \Gamma_1 = \Gamma_{aa}\cos^2\tm ; \Gamma_{2}=\Gamma_{aa}\sin^2\tm where \tm is the mixing angle in the medium and the sterile distribution function \emph{does not} obey a simple rate equation. For \wtg \gg 1, $\Gamma_1= \Gamma_{aa}$ and \Gamma_2 = \Gamma_{aa} \sin^22\tm/4\wtg^2, is the sterile production rate. In this regime sterile production is suppressed and the oscillation frequency \emph{vanishes} at an MSW resonance, with a breakdown of adiabaticity. These are consequences of quantum Zeno suppression. For active neutrinos with standard model interactions the strong damping limit is \emph{only} available near an MSW resonance \emph{if} $\sin\theta \lesssim \alpha_w$ with $\theta$ the vacuum mixing angle. The full set of quantum kinetic equations for sterile production for arbitrary \wtg are obtained from the quantum master equation. Cosmological resonant sterile neutrino production is quantum Zeno suppressed relieving potential uncertainties associated with the QCD phase transition.Comment: To appear in Phys. Rev.

Entanglement production in Quantized Chaotic Systems

Quantum chaos is a subject whose major goal is to identify and to investigate different quantum signatures of classical chaos. Here we study entanglement production in coupled chaotic systems as a possible quantum indicator of classical chaos. We use coupled kicked tops as a model for our extensive numerical studies. We find that, in general, presence of chaos in the system produces more entanglement. However, coupling strength between two subsystems is also very important parameter for the entanglement production. Here we show how chaos can lead to large entanglement which is universal and describable by random matrix theory (RMT). We also explain entanglement production in coupled strongly chaotic systems by deriving a formula based on RMT. This formula is valid for arbitrary coupling strengths, as well as for sufficiently long time. Here we investigate also the effect of chaos on the entanglement production for the mixed initial state. We find that many properties of the mixed state entanglement production are qualitatively similar to the pure state entanglement production. We however still lack an analytical understanding of the mixed state entanglement production in chaotic systems.Comment: 16 pages, 5 figures. To appear in Pramana:Journal of Physic

Cronin Effect and High-p_T Suppression in pA Collisions

We review the predictions of the theory of Color Glass Condensate for gluon production cross section in p(d)A collisions. We demonstrate that at moderate energies, when the gluon production cross section can be calculated in the framework of McLerran-Venugopalan model, it has only partonic level Cronin effect in it. At higher energies/rapidities corresponding to smaller values of Bjorken x quantum evolution becomes important. The effect of quantum evolution at higher energies/rapidities is to introduce suppression of high-p_T gluons slightly decreasing the Cronin enhancement. At still higher energies/rapidities quantum evolution leads to suppression of produced gluons at all values of p_T.Comment: 32 pages, 8 figures, v2: extended and improved discussion, references adde