Does the quantum collapse make sense? Quantum Mechanics vs Multisimultaneity in interferometer-series experiments

It is argued that the three assumptions of quantum collapse, one photon-one count, and relativity of simultaneity cannot hold together: Nonlocal correlations can depend on the referential frames of the beam-splitters but not of the detectors. New experiments using interferometers in series are proposed which make it possible to test Quantum Mechanics vs Multisimultaneity.Comment: 18 pages Latex, 2 eps figures. Archive adapted version of an article accepted for publication in Physics Letters

From continent to intra-oceanic arc: zircon xenocrysts record the crustal evolution of the Solomon island arc

The first U-Pb ages from a ca. 26–24 Ma pluton on Guadalcanal, in the intra-oceanic Solomon island arc (southwest Pacific Ocean), reveal Eocene- to Archean-aged zircon xenocrysts. Xenocryst populations at ca. 39–33 Ma and ca. 71–63 Ma correlate with previously obtained ages of supra-subduction magmatism within the arc. A ca. 96 Ma zircon population may be derived from Cretaceous ophiolite basement crust or region-wide continental rift-related magmatism. Xenocryst age populations alternate with periods of oceanic basin formation that fragmented the East Gondwana margin. Early Cretaceous to Archean zircon xenocryst ages imply continental origins and a cryptic source within the arc crust; they may have been introduced by Eocene interaction of a continental fragment with the arc, and concealed by ophiolite obduction. The data demonstrate that continentally derived zircons may be transported thousands of kilometers from their source and added to intra-oceanic arc magmas, a process likely facilitated by cyclical subduction zone advance and retreat. The findings highlight the continuum of arcs that occurs between continental and oceanic end members, and the caution with which zircons should be used to determine the provenance and setting of ancient arc terranes accreted to the continental crust

Developments towards practical free-space quantum cryptography

We describe a free space quantum cryptography system which is designed to allow continuous unattended key exchanges for periods of several days, and over ranges of a few kilometres. The system uses a four-laser faint-pulse transmission system running at a pulse rate of 10MHz to generate the required four alternative polarization states. The receiver module similarly automatically selects a measurement basis and performs polarization measurements with four avalanche photodiodes. The controlling software can implement the full key exchange including sifting, error correction, and privacy amplification required to generate a secure key

Parametric fluorescence in periodically poled silica fibres

We report the observation of quasiphase matched parametric fluorescence from a periodically poled silica fiber. A pair-photon production rate of more than 100 MHz around 1532 nm was achieved in second-order nonlinear gratings for 300 mW of pump power at 766 nm. These results are very promising for the realization of reliable all-fiber single-photon sources for quantum cryptography systems and metrology applications

Four-photon correction in two-photon Bell experiments

Correlated photons produced by spontaneous parametric down-conversion are an essential tool for quantum communication, especially suited for long-distance connections. To have a reasonable count rate after all the losses in the propagation and the filters needed to improve the coherence, it is convenient to increase the intensity of the laser that pumps the non-linear crystal. By doing so, however, the importance of the four-photon component of the down-converted field increases, thus degrading the quality of two-photon interferences. In this paper, we present an easy derivation of this nuisance valid for any form of entanglement generated by down-conversion, followed by a full study of the problem for time-bin entanglement. We find that the visibility of two-photon interferences decreases as V=1-2\rho, where \rho is, in usual situations, the probability per pulse of creating a detectable photon pair. In particular, the decrease of V is independent of the coherence of the four-photon term. Thanks to the fact that \rho can be measured independently of V, the experimental verification of our prediction is provided for two different configuration of filters.Comment: 16 pages, 4 figures; published versio

Photon bunching in parametric down-conversion with continuous wave excitation

The first direct measurement of photon bunching (g2 correlation function) in one output arm of a spontaneous-parametric-down-conversion source operated with a continuous pump laser in the single-photon regime is demonstrated. The result is in agreement with the statistics of a thermal field of the same coherence length, and shows the feasibility of investigating photon statistics with compact cw-pumped sources. Implications for entanglement-based quantum cryptography are discussed.Comment: 7 pages, 4 figures, expanded introduction and experimental details added. Accepted for publication in Phys.Rev.

Duration and nature of the end-Cryogenian (Marinoan) glaciation

The end-Cryogenian glaciation (Marinoan) is portrayed commonly as the archetype of snowball Earth, yet its duration and character remain uncertain. Here we report U-Pb zircon ages for two ash beds from widely separated localities of the Marinoan-equivalent Ghaub Formation in Namibia: 639.29 ± 0.26 Ma and 635.21 ± 0.59 Ma. These findings verify, for the first time, the key prediction of the snowball Earth hypothesis for the Marinoan glaciation, i.e., longevity, with a duration of ≥4 m.y. They also show that the nonglacial interlude of Cryogenian time spanned 20 m.y. or less and that glacigenic erosion and sedimentation, and at least intermittent open-water conditions, occurred 4 m.y. prior to termination of the Marinoan glaciation

High coherence photon pair source for quantum communication

This paper reports a novel single mode source of narrow-band entangled photon pairs at telecom wavelengths under continuous wave excitation, based on parametric down conversion. For only 7 mW of pump power it has a created spectral radiance of 0.08 pairs per coherence length and a bandwidth of 10 pm (1.2 GHz). The effectively emitted spectral brightness reaches 3.9*10^5 pairs /(s pm). Furthermore, when combined with low jitter single photon detectors, such sources allow for the implementation of quantum communication protocols without any active synchronization or path length stabilization. A HOM-Dip with photons from two autonomous CW sources has been realized demonstrating the setup's stability and performance.Comment: 12 pages, 4 figure

How the quality of a received EPR pair depends on the distances from an EPR source?

Let an EPR source which generates maximally entangled pairs be located so that it has distances $L_1$ and $L_2$ to two users. After taking into account various effects like loss of photons, deficiencies in the source and detectors, an entangled pair traveling through the channel may loose its perfect correlation due to errors in the channel. How the entanglement of the received pair depends on the above distances and the local properties of the channels used for this transmission? What is the best location of the source if we want to achieve the highest fidelity? What is the threshold distance beyond which the entanglement of the pair vanishes and becomes useless for using in teleportation. We discuss these problems for the Pauli channel which simulates the effect of optical fibers and possibly the atmosphere on the polarization-entangled photons.Comment: 10 pages, 2 figures, substantially revised, late