13,537 research outputs found
Robust and Scalable Scheme to Generate Large-Scale Entanglement Webs
We propose a robust and scalable scheme to generate an -qubit state
among separated quantum nodes (cavity-QED systems) by using linear optics and
postselections. The present scheme inherits the robustness of the Barrett-Kok
scheme [Phys. Rev. A {\bf 71}, 060310(R) (2005)]. The scalability is also
ensured in the sense that an arbitrarily large -qubit state can be
generated with a quasi-polynomial overhead . The
process to breed the states, which we introduce to achieve the scalability,
is quite simple and efficient, and can be applied for other physical systems.Comment: 5 pages, 3 figure
Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature
We present a high-resolution microwave spectrometer to measure the
frequency-dependent complex conductivity of a superconducting thin film near
the critical temperature. The instrument is based on a broadband measurement of
the complex reflection coefficient, , of a coaxial transmission
line, which is terminated to a thin film sample with the electrodes in a
Corbino disk shape. In the vicinity of the critical temperature, the standard
calibration technique using three known standards fails to extract the strong
frequency dependence of the complex conductivity induced by the superconducting
fluctuations. This is because a small unexpected difference between the phase
parts of for a short and load standards gives rise to a large
error in the detailed frequency dependence of the complex conductivity near the
superconducting transition. We demonstrate that a new calibration procedure
using the normal-state conductivity of a sample as a load standard resolves
this difficulty. The high quality performance of this spectrometer, which
covers the frequency range between 0.1 GHz and 10 GHz, the temperature range
down to 10 K, and the magnetic field range up to 1 T, is illustrated by the
experimental results on several thin films of both conventional and high
temperature superconductors.Comment: 13 pages, 14 figure
Discrete derivatives and symmetries of difference equations
We show on the example of the discrete heat equation that for any given
discrete derivative we can construct a nontrivial Leibniz rule suitable to find
the symmetries of discrete equations. In this way we obtain a symmetry Lie
algebra, defined in terms of shift operators, isomorphic to that of the
continuous heat equation.Comment: submitted to J.Phys. A 10 Latex page
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