1,103 research outputs found
Quantum state estimation with unknown measurements
Improved measurement techniques are central to technological development and
foundational scientific exploration. Quantum optics relies upon detectors
sensitive to non-classical features of light, enabling precise tests of
physical laws and quantum-enhanced technologies such as precision measurement
and secure communications. Accurate detector response calibration for
quantum-scale inputs is key to future research and development in these cognate
areas. To address this requirement quantum detector tomography (QDT) has been
recently introduced. However, the QDT approach becomes increasingly challenging
as the complexity of the detector response and input space grows. Here we
present the first experimental implementation of a versatile alternative
characterization technique to address many-outcome quantum detectors by
limiting the input calibration region. To demonstrate the applicability of this
approach the calibrated detector is subsequently used to estimate non-classical
photon number states.Comment: 7 pages, 3 figure
Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2
We report measurements of the temperature dependent anisotropies
( and ) of both the London penetration depth
and the upper critical field of MgB. Data for
was obtained from measurements of
and on a single crystal sample using a tunnel diode
oscillator technique. was
deduced from field dependent specific heat measurements on the same sample.
and have opposite temperature dependencies, but
close to tend to a common value (). These results are in good agreement with theories
accounting for the two gap nature of MgBComment: 4 pages with figures (New version
3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover
We present reversible magnetization data of a YBa2Cu4O8 single crystal and
analyze the evidence for 3D-xy critical behavior and a magnetic field induced
3D to 1D crossover. Remarkable consistency with these phenomena is observed in
agreement with a magnetic field induced finite size effect, whereupon the
correlation length transverse to the applied magnetic field cannot grow beyond
the limiting magnetic length scale L_H. By applying the appropriate scaling
form we obtain the zero-field critical temperature, the 3D to 1D crossover, the
vortex melting line and the universal ratios of the related scaling variables.
Accordingly there is no continuous phase transition in the (H,T)-plane along
the H_c2-lines as predicted by the mean-field treatment.Comment: 8 pages, 4 figure
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