35,671 research outputs found
Quantum effects with an X-ray free electron laser
A quantum kinetic equation coupled with Maxwell's equation is used to
estimate the laser power required at an XFEL facility to expose intrinsically
quantum effects in the process of QED vacuum decay via spontaneous pair
production. A 9 TW-peak XFEL laser with photon energy 8.3 keV could be
sufficient to initiate particle accumulation and the consequent formation of a
plasma of spontaneously produced pairs. The evolution of the particle number in
the plasma will exhibit non-Markovian aspects of the strong-field pair
production process and the plasma's internal currents will generate an electric
field whose interference with that of the laser leads to plasma oscillations.Comment: 4 pages, LaTeX2
Pair creation and plasma oscillations
We describe aspects of particle creation in strong fields using a quantum
kinetic equation with a relaxation-time approximation to the collision term.
The strong electric background field is determined by solving Maxwell's
equation in tandem with the Vlasov equation. Plasma oscillations appear as a
result of feedback between the background field and the field generated by the
particles produced. The plasma frequency depends on the strength of the initial
background field and the collision frequency, and is sensitive to the necessary
momentum-dependence of dressed-parton masses.Comment: 11 pages, revteX, epsfig.sty, 5 figures; Proceedings of 'Quark Matter
in Astro- and Particlephysics', a workshop at the University of Rostock,
Germany, November 27 - 29, 2000. Eds. D. Blaschke, G. Burau, S.M. Schmid
Transport properties of a superconducting single-electron transistor coupled to a nanomechanical oscillator
We investigate a superconducting single-electron transistor capacitively
coupled to a nanomechanical oscillator and focus on the double Josephson
quasiparticle resonance. The existence of two coherent Cooper pair tunneling
events is shown to lead to pronounced backaction effects. Measuring the current
and the shot noise provides a direct way of gaining information on the state of
the oscillator. In addition to an analytical discussion of the linear-response
regime, we discuss and compare results of higher-order approximation schemes
and a fully numerical solution. We find that cooling of the mechanical
resonator is possible, and that there are driven and bistable oscillator states
at low couplings. Finally, we also discuss the frequency dependence of the
charge noise and the current noise of the superconducting single electron
transistor.Comment: 19 pages, 11 figures, published in PR
Rashba quantum wire: exact solution and ballistic transport
The effect of Rashba spin-orbit interaction in quantum wires with hard-wall
boundaries is discussed. The exact wave function and eigenvalue equation are
worked out pointing out the mixing between the spin and spatial parts. The
spectral properties are also studied within the perturbation theory with
respect to the strength of the spin-orbit interaction and diagonalization
procedure. A comparison is done with the results of a simple model, the
two-band model, that takes account only of the first two sub-bands of the wire.
Finally, the transport properties within the ballistic regime are analytically
calculated for the two-band model and through a tight-binding Green function
for the entire system. Single and double interfaces separating regions with
different strengths of spin-orbit interaction are analyzed injecting carriers
into the first and the second sub-band. It is shown that in the case of a
single interface the spin polarization in the Rashba region is different from
zero, and in the case of two interfaces the spin polarization shows
oscillations due to spin selective bound states
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