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

High chemical abundances in stripped Virgo spiral galaxies

Based on a comparison of the oxygen abundances in H 2 regions in field and Virgo cluster late type spiral galaxies, Shields, Skillman, & Kennicutt (1991) suggested that the highly stripped spiral galaxies in the Virgo cluster have systematically higher abundances than comparable field galaxies. In April 1991 and May 1992 we used the blue channel spectrograph on the MMT to obtain new observations of 30 H 2 regions in Virgo spiral galaxies. These spectra cover the wavelength range from (O II) lambda 3727 to (S II) lambda 6731. We now have observed at least 4 H II regions in 9 spiral galaxies in the Virgo cluster. Combining (O II) and (O III) line strengths, we calculate the H II region oxygen abundances based on the empirical calibration of Edmunds & Pagel (1984). These observations show: (1) The stripped, low luminosity Virgo spirals (N4689, N4571) truly have abundances characteristic of much more luminous field spirals; (2) Virgo spirals which show no evidence of stripping (N4651, N4713) have abundances comparable to field galaxies; and (3) Evidence for transition galaxies (e.g., N4254, N4321), with marginally stripped disks and marginal abundance enhancements. The new observations presented here confirm the validity of the oxygen over-abundances in the stripped Virgo spirals. Shields et al. (1991) discussed two different mechanisms for producing the higher abundances in the disks of stripped galaxies in Virgo. The first is the supression of infall of near-primordial material, the second is the suppression of radial inflow of metal-poor gas. Distinguishing between the two cases will require more observations of the Virgo cluster spirals and a better understanding of which parameters determine the variation of abundance with radius in field spirals (cf., Garnett & Shields 1987)

The understated turn: Emerging interests and themes in Canadian posthumanist geography

This is the final version. Available on open access from Wiley via the DOI in this recordPosthumanist geography is a broad tradition incorporating a range of intersecting theoretical approaches including assemblage theory, actor‐network theory, new materialisms, affect theory, neo‐vitalism, political ecology, post‐phenomenology, and non‐representational theory—as well as contributions from a number of theoretically progressive subject fields such as new mobilities, relational thinking, sensory and performance studies, biosocial and biopolitics studies, and science and technology studies. The specificities of and differences between these traditions and fields aside, common to posthumanism is a scepticism of human exceptionalism. Here, the sovereign human subject is decentred, and in doing so, posthumanist work acknowledges the agencies of a full array of human and non‐human actors and forces. Recognizing that there are important “geographies to (the discipline of) geography,” this paper identifies and reviews some of the key posthumanist interests and themes that have emerged over recent years quietly and organically in Canadian geography, namely posthumanist (i) Indigenous geographies; (ii) animal and natures geographies; (iii) health, wellbeing, and disability geographies; (iv) affective and atmospheric geographies; and (v) non‐representational and creative methodologies. The paper concludes with some thoughts on the nature and strengths of Canadian posthumanist geography, and on some possibilities for future advancement

Bell-inequality violation with a triggered photon-pair source

Here we demonstrate, for the first time, violation of Bell's inequality using a triggered quantum dot photon-pair source without post-selection. Furthermore, the fidelity to the expected Bell state can be increased above 90% using temporal gating to reject photons emitted at times when collection of uncorrelated light is more probable. A direct measurement of a CHSH Bell inequality is made showing a clear violation, highlighting that a quantum dot entangled photon source is suitable for communication exploiting non-local quantum correlations.Comment: 14 pages, 4 figure

Facet recovery and light emission from GaN/InGaN/GaN core-shell structures grown by metal organic vapour phase epitaxy on etched GaN nanorod arrays

The use of etched nanorods from a planar template as a growth scaffold for a highly regular GaN/InGaN/GaN core-shell structure is demonstrated. The recovery of m-plane non-polar facets from etched high-aspect-ratio GaN nanorods is studied with and without the introduction of a hydrogen silsesquioxane passivation layer at the bottom of the etched nanorod arrays. This layer successfully prevented c-plane growth between the nanorods, resulting in vertical nanorod sidewalls (∼89.8°) and a more regular height distribution than re-growth on unpassivated nanorods. The height variation on passivated nanorods is solely determined by the uniformity of nanorod diameter, which degrades with increased growth duration. Facet-dependent indium incorporation of GaN/InGaN/GaN core-shell layers regrown onto the etched nanorods is observed by high-resolution cathodoluminescence imaging. Sharp features corresponding to diffracted wave-guide modes in angle-resolved photoluminescence measurements are evidence of the uniformity of the full core-shell structure grown on ordered etched nanorods

Gigahertz quantum key distribution with InGaAs avalanche photodiodes

We report a demonstration of quantum key distribution (QKD) at GHz clock rates with InGaAs avalanche photodiodes (APDs) operating in a self-differencing mode. Such a mode of operation allows detection of extremely weak avalanches so that the detector afterpulse noise is sufficiently suppressed. The system is characterized by a secure bit rate of 2.37 Mbps at 5.6 km and 27.9 kbps at 65.5 km when the fiber dispersion is not compensated. After compensating the fiber dispersion, the QKD distance is extended to 101 km, resulting in a secure key rate of 2.88 kbps. Our results suggest that InGaAs APDs are very well suited to GHz QKD applications.Comment: 4 pages, 4 figure

Identifying teeth and tooth fragments from digital 3D models

Dental anatomy is an essential skill for human identification in forensic odontology. With the advent of technology enabling virtual autopsies, there is scope for virtual consultation by forensic odontologists especially when the expertise is unavailable but needed in zones of conflict or disasters. This study aimed to investigate potential benefits and challenges of identifying intact and damaged teeth from 3D scanned digital models. Ten 3D tooth models – nine permanent and deciduous human teeth and one animal tooth were uploaded on a hosting platform. A 3-part survey was circulated among 60 forensic odontologists with questions about demography (P1), tooth identification of the scanned 3D models (P2) and the perceived usefulness of 3D models for tooth identification (P3). This was the first time that a survey required the identification of individual human teeth (intact or not) and animal tooth combined. The response rate for study participation was 58%. Substantial agreement among participants was seen in the determination of tooth classification (i.e., molars, premolars) or non-human and tooth within the same tooth class (i.e., lateral incisors, second molar) (both k=0.61). The least agreement (k=0.21) was seen in identification of tooth according to the FDI notation with a mean accuracy of 0.34. While most responders correctly identified the animal tooth, most incorrect responses were seen in the identifica-tion of the intact third molar. While 3D-scanned teeth have the potential to be identified virtually, fo-rensic odontologists should continuously test their skills in tooth morphology and dental anatomy of humans (damaged or not) and animals