59 research outputs found
Experimental characterization of Gaussian quantum communication channels
We present a full experimental characterization of continuous variable
quantum communication channels established by shared entanglement together with
local operations and classical communication. The resulting teleportation
channel was fully characterized by measuring all elements of the covariance
matrix of the shared two-mode squeezed Gaussian state. From the experimental
data we determined the lower bound to the quantum channel capacity, the
teleportation fidelity of coherent states and the logarithmic negativity and
the purity of the shared state. Additionally, a positive secret key rate was
obtained for two of the established channels.Comment: 9 pages, 4 figures, submitted to Physical Review
Experimental characterization of frequency dependent squeezed light
We report on the demonstration of broadband squeezed laser beams that show a
frequency dependent orientation of the squeezing ellipse. Carrier frequency as
well as quadrature angle were stably locked to a reference laser beam at
1064nm. This frequency dependent squeezing was characterized in terms of noise
power spectra and contour plots of Wigner functions. The later were measured by
quantum state tomography. Our tomograph allowed a stable lock to a local
oscillator beam for arbitrary quadrature angles with one degree precision.
Frequency dependent orientations of the squeezing ellipse are necessary for
squeezed states of light to provide a broadband sensitivity improvement in
third generation gravitational wave interferometers. We consider the
application of our system to long baseline interferometers such as a future
squeezed light upgraded GEO600 detector.Comment: 8 pages, 8 figure
Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach
Geomagnetically induced currents (GICs) in power systems, which can lead to transformer damage over the short and the long term, are a result of space weather events and geomagnetic variations. For a long time, only high-latitude areas were considered to be at risk from these currents, but recent studies show that considerable GICs also appear in midlatitude and equatorial countries. In this paper, we present initial results from a GIC model using a thin-sheet approach with detailed surface and subsurface conductivity models to compute the induced geoelectric field. The results are compared to measurements of direct currents in a transformer neutral and show very good agreement for short-period variations such as geomagnetic storms. Long-period signals such as quiet-day diurnal variations are not represented accurately, and we examine the cause of this misfit. The modelling of GICs from regionally varying geoelectric fields is discussed and shown to be an important factor contributing to overall model accuracy. We demonstrate that the Austrian power grid is susceptible to large GICs in the range of tens of amperes, particularly from strong geomagnetic variations in the east–west direction
Morphology of the Iceland Basin Excursion from a spherical harmonics analysis and an iterative Bayesian inversion procedure of sedimentary records
Spin and magnetization effects in plasmas
We give a short review of a number of different models for treating
magnetization effects in plasmas. In particular, the transition between kinetic
models and fluid models is discussed. We also give examples of applications of
such theories. Some future aspects are discussed.Comment: 18 pages, 1 figure. To appear in Plasma Physics and Controlled
Fusion, Special Issue for the 37th ICPP, Santiago, Chil
Quantum-Dense Metrology
Quantum metrology utilizes entanglement for improving the sensitivity of
measurements. Up to now the focus has been on the measurement of just one out
of two non-commuting observables. Here we demonstrate a laser interferometer
that provides information about two non-commuting observables, with
uncertainties below that of the meter's quantum ground state. Our experiment is
a proof-of-principle of quantum dense metrology, and uses the additional
information to distinguish between the actual phase signal and a parasitic
signal due to scattered and frequency shifted photons. Our approach can be
readily applied to improve squeezed-light enhanced gravitational-wave detectors
at non-quantum noise limited detection frequencies in terms of a sub shot-noise
veto-channel.Comment: 5 pages, 3 figures; includes supplementary material
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