3,872 research outputs found
MDI-QKD: Continuous- versus discrete-variables at metropolitan distances
In a comment, Xu, Curty, Qi, Qian, and Lo claimed that discrete-variable (DV)
measurement device independent (MDI) quantum key distribution (QKD) would
compete with its continuous-variable (CV) counterpart at metropolitan
distances. Actually, Xu et al.'s analysis supports exactly the opposite by
showing that the experimental rate of our CV protocol (achieved with practical
room-temperature devices) remains one order of magnitude higher than their
purely-numerical and over-optimistic extrapolation for qubits, based on
nearly-ideal parameters and cryogenic detectors (unsuitable solutions for a
realistic metropolitan network, which is expected to run on cheap
room-temperature devices, potentially even mobile). The experimental rate of
our protocol (expressed as bits per relay use) is confirmed to be two-three
orders of magnitude higher than the rate of any realistic simulation of
practical DV-MDI-QKD over short-medium distances. Of course this does not mean
that DV-MDI-QKD networks should not be investigated or built, but increasing
their rate is a non-trivial practical problem clearly beyond the analysis of Xu
et al. Finally, in order to clarify the facts, we also refute a series of
incorrect arguments against CV-MDI-QKD and, more generally, CV-QKD, which were
made by Xu et al. with the goal of supporting their thesis.Comment: Updated reply to Xu, Curty, Qi, Qian and Lo (arXiv:1506.04819),
including a point-to-point rebuttal of their new "Appendix E: Addendum
Philosophy Enters the Optics Laboratory: Bell's Theorem and its First Experimental Tests (1965-1982)
This paper deals with the ways that the issue of completing quantum mechanics
was brought into laboratories and became a topic in mainstream quantum optics.
It focuses on the period between 1965, when Bell published what now we call
Bell's theorem, and 1982, when Aspect published the results of his experiments.
I argue that what was considered good physics after Aspect's experiments was
once considered by many a philosophical matter instead of a scientific one, and
that the path from philosophy to physics required a change in the physics
community's attitude about the status of the foundations of quantum mechanics.Comment: 57 pages, accepted by Studies in History and Philosophy of Modern
Physic
Historical and interpretative aspects of quantum mechanics: a physicists' naive approach
Many theoretical predictions derived from quantum mechanics have been
confirmed experimentally during the last 80 years. However, interpretative
aspects have long been subject to debate. Among them, the question of the
existence of hidden variables is still open. We review these questions, paying
special attention to historical aspects, and argue that one may definitively
exclude local realism on the basis of present experimental outcomes. Other
interpretations of Quantum Mechanics are nevertheless not excluded.Comment: 30 page
Casimir forces and non-Newtonian gravitation
The search for non-relativistic deviations from Newtonian gravitation can
lead to new phenomena signalling the unification of gravity with the other
fundamental interactions. Various recent theoretical frameworks indicate a
possible window for non-Newtonian forces with gravitational coupling strength
in the micrometre range. The major expected background in the same range is
attributable to the Casimir force or variants of it if dielectric materials,
rather than conducting ones, are considered. Here we review the measurements of
the Casimir force performed so far in the micrometre range and how they
determine constraints on non-Newtonian gravitation, also discussing the
dominant sources of false signals. We also propose a geometry-independent
parameterization of all data in terms of the measurement of the constant c. Any
Casimir force measurement should lead, once all corrections are taken into
account, to a determination of the constant c which, in order to assess the
accuracy of the measurement, can be compared with its more precise value known
through microscopic measurements. Although the last decade of experiments has
resulted in solid demonstrations of the Casimir force, the situation is not
conclusive with respect to being able to discover new physics. Future
experiments and novel phenomenological analysis will be necessary to discover
non-Newtonian forces or to push the window for their possible existence into
regions of the parameter space which theoretically appear unnatural.Comment: Also available at http://www.iop.org/EJ/abstract/1367-2630/8/10/23
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