27,864 research outputs found
Quantum key distribution over 122 km of standard telecom fiber
We report the first demonstration of quantum key distribution over a standard
telecom fiber exceeding 100 km in length. Through careful optimisation of the
interferometer and single photon detector, we achieve a quantum bit error ratio
of 8.9% for a 122km link, allowing a secure shared key to be formed after error
correction and privacy amplification. Key formation rates of up to 1.9 kbit/sec
are achieved depending upon fiber length. We discuss the factors limiting the
maximum fiber length in quantum cryptography
Barbosa et al. Reply to ``Comment on 'Secure Communication using mesoscopic coherent states', Barbosa et al, Phys Rev Lett 90, 227901", Yuan and Shields, Phys. Rev. Lett. 94, 048901(2005)
Yuan and Shields claim that our data-encryption protocol is entirely
equivalent to a classical stream cipher utilizing no quantum phenomena. Their
claim is, indeed, false. Yuan and Shields also claim that schemes similar to
the one presented in Phys. Rev. Lett. 90, 227901 are not suitable for key
generation. This claim is also refuted. In any event, we welcome the
opportunity to clarify the situation for a wider audience.Comment: This is the co-published Reply to the Comment made by Z.L. Yuan and
A.J. Shields published in Physical Review Letters, 94 (2005
Evidence for Weyl fermions in a canonical heavy-fermion semimetal YbPtBi
The manifestation of Weyl fermions in strongly correlated electron systems is
of particular interest. We report evidence for Weyl fermions in the heavy
fermion semimetal YbPtBi from electronic structure calculations, angle-resolved
photoemission spectroscopy, magnetotransport and calorimetric measurements. At
elevated temperatures where -electrons are localized, there are triply
degenerate points, yielding Weyl nodes in applied magnetic fields. These are
revealed by a contribution from the chiral anomaly in the magnetotransport,
which at low temperatures becomes negligible due to the influence of electronic
correlations. Instead, Weyl fermions are inferred from the topological Hall
effect, which provides evidence for a Berry curvature, and a cubic temperature
dependence of the specific heat, as expected from the linear dispersion near
the Weyl nodes. The results suggest that YbPtBi is a Weyl heavy fermion
semimetal, where the Kondo interaction renormalizes the bands hosting Weyl
points. These findings open up an opportunity to explore the interplay between
topology and strong electronic correlations.Comment: 19 pages, 5 figures, Supplementary Information available with open
access at https://www.nature.com/articles/s41467-018-06782-
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