There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

/pdf/the-observation-of-gravitational-waves-from-a-binary-black-58srpupgg9.pdf

The Observation of Gravitational Waves from a Binary Black Hole Merger

From the Publisher: 
The accessible presentation of this book gives both a general view of the entire computer vision enterprise and also offers sufficient detail to be able to build useful applications. Users learn techniques that have proven to be useful by first-hand experience and a wide range of mathematical methods. A CD-ROM with every copy of the text contains source code for programming practice, color images, and illustrative movies. Comprehensive and up-to-date, this book includes essential topics that either reflect practical significance or are of theoretical importance. Topics are discussed in substantial and increasing depth. Application surveys describe numerous important application areas such as image based rendering and digital libraries. Many important algorithms broken down and illustrated in pseudo code. Appropriate for use by engineers as a comprehensive reference to the computer vision enterprise.

Computer vision : a modern approach = 计算机视觉 : 一种现代的方法

Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

/pdf/terabit-free-space-data-transmission-employing-orbital-47zsgn5cdx.pdf

Terabit free-space data transmission employing orbital angular momentum multiplexing

Recently, Chen et al. [Phys. Rev. A 84, 033835 (2011)] reported observation of anticorrelated photon coincidences in a Mach-Zehnder interferometer whose input light came from a mode-locked Ti:sapphire laser that had been rendered spatially incoherent by passage through a rotating ground-glass diffuser. They provided a quantum-mechanical explanation of their results, which ascribes the anticorrelation to two-photon interference. They also developed a classical-light treatment of the experiment and showed that it was incapable of explaining the anticorrelation behavior. Here we show that semiclassical photodetection theory, i.e., classical electromagnetic fields plus photodetector shot noise, does indeed explain the anticorrelation found by Chen et al. The key to our analysis is properly accounting for the disparate time scales associated with the laser's pulse duration, the speckle-correlation time, the interferometer's differential delay, and the duration of the photon-coincidence gate. Our result is consistent with the long-accepted dictum that laser light which has undergone linear-optical transformations is classical-state light, so that the quantum and semiclassical theories of photodetection yield quantitatively identical results for its measurement statistics. The interpretation provided by Chen et al. for their observations implicitly contradicts that dictum.

Comment on “Observation of anticorrelation in incoherent thermal light fields”

A quantum communication architecture is being developed for
long-distance, high-fidelity transmission and storage of
Greenberger-Horne-Zeilinger states. This system uses an
ultrabright narrowband source of polarization-entangled photons
plus trapped-atom quantum memories, and it is compatible with
long-distance transmission over standard telecommunication fiber.
An error model for the preceding architecture is derived, and the
use of quantum error correction or entanglement purification
protocols to improve the performance of this quantum communication
system is also discussed.

/pdf/error-models-and-error-mitigation-for-long-distance-high-2luz2ejmnb.pdf

Error models and error mitigation for long-distance high-fidelity quantum secret sharing

In 2011, Nair published a no-go theorem for quantum radar target detection [Phys. Rev. A 84 , 032312 (2011)]. He showed, under fairly general assumptions, that a coherent-state radar’s error probability was within a factor of two of the best possible quantum performance for the pure-loss (no background radiation) channel whose roundtrip radar-to-target-to-radar transmissivity κ satisﬁes κ ≪ 1. We introduce ﬁrst-photon radars (FPRs) to circumvent and beat Nair’s performance limit. FPRs transmit a periodic sequence of pulses, each containing N S photons on average, and perform ideal direct detection (photon counting at unit quantum eﬃciency and no dark counts) on the returned radiation from each transmission until at least one photon has been detected or a pre-set maximum of M pulses has been transmitted. They decide a target is present if and only if they detect one or more photons. We consider both quantum (each transmitted pulse is a number state) and classical (each transmitted pulse is a coherent state) FPRs, and we show that their error-probability exponents are nearly identical when κ ≪ 1. With the additional assumption that κN S ≪ 1, we ﬁnd that their advantage in error-probability exponent over Nair’s performance limit grows to 3 dB as M → ∞ . However, because FPRs’ pulse-repetition period must exceed the radar-to-target-to-radar propagation delay, their use in standoﬀ sensing of moving targets will likely employ κN S ∼ 1 and M ∼ 10 and achieve ∼ 2 dB advantage. Our work constitutes a new no-go theorem for quantum radar target detection.

First-photon target detection: Beating Nair's pure-loss performance limit

The use of ultrashort (femtosecond duration) light pulses for line-of-sight free-space optical (FSO) communication through fog is receiving increasing attention. Assuming that the transmitter power is low enough to preclude nonlinear interactions, and that scattering-induced multipath spread is less than the reciprocal of the scattering-induced Doppler spread, it is shown that the average transmitter-to-receiver fractional energy transfer of an ultrafast FSO system cannot exceed that of a quasimonochromatic (nanosecond pulse duration) system operating at the optimum wavelength within the ultrafast system’s spectrum. Thus, an ultrashort-pulse system is not a solution for high-data-rate FSO communication through fog, because, at best, it will reproduce on average the energy-transfer performance of a wavelength-optimized quasimonochromatic system.

Quasi-monochromatic bound on ultrashort light-pulse transmission through fog.

The binary (one-bit-per-photon) encoding that most existing quantum key distribution (QKD) protocols employ puts a fundamental limit on their achievable key rates, especially under high channel loss conditions associated with long-distance fiber-optic or satellite-to-ground links. Inspired by the pulse-position-modulation (PPM) approach to photon-starved classical communications, we design and demonstrate the first PPM-QKD, whose security against collective attacks is established through continuous-variable entanglement measurements that also enable a novel decoy-state protocol performed conveniently in post processing. We achieve a throughput of 8.0 Mbit/s (2.5 Mbit/s for loss equivalent to 25 km of fiber) and secret-key capacity up to 4.0 bits per detected photon, thus demonstrating the significant enhancement afforded by high-dimensional encoding. These results point to a new avenue for realizing high-throughput satellite-based or long-haul fiber-optic quantum communications beyond their photon-reception-rate limits.

Jeffrey H. Shapiro

Papers

Comment on “Observation of anticorrelation in incoherent thermal light fields”

Error models and error mitigation for long-distance high-fidelity quantum secret sharing

First-photon target detection: Beating Nair's pure-loss performance limit

Quasi-monochromatic bound on ultrashort light-pulse transmission through fog.

Photon-efficient quantum cryptography with pulse-position modulation