Axon Guidance: Ephrins at WRK on the Midline

Recent findings indicate that the embryonic motor neurons act as gatekeepers to regulate midline crossing during development of the nematode Caenorhabditis elegans. The newly identified protein WRK-1 and ephrins cooperate to prevent longitudinal axons from crossing the midline

Photonic crystal fibre source of photon pairs for quantum information processing

We demonstrate two key components for optical quantum information processing: a bright source of heralded single photons; and a bright source of entangled photon pairs. A pair of pump photons produces a correlated pair of photons at widely spaced wavelengths (583 nm and 900 nm), via a $\chi^{(3)}$ four-wave mixing process. We demonstrate a non-classical interference between heralded photons from independent sources with a visibility of 95%, and an entangled photon pair source, with a fidelity of 89% with a Bell state.Comment: 4 pages, 3 figure

An All Optical Fibre Quantum Controlled-NOT Gate

We report the first experimental demonstration of an optical controlled-NOT gate constructed entirely in fibre. We operate the gate using two heralded optical fibre single photon sources and find an average logical fidelity of 90% and an average process fidelity of 0.83<F<0.91. On the basis of a simple model we are able to conclude that imperfections are primarily due to the photon sources, meaning that the gate itself works with very high fidelity.Comment: 4 pages, 4 figures, comments welcom

Intrinsically narrowband pair photon generation in microstructured fibres

In this paper we study the tailoring of photon spectral properties generated by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is to produce intrinsically narrow-band photons and hence to achieve high non-classical interference visibility and generate high fidelity entanglement without any requirement for spectral filtering, leading to high effective detection efficiencies. We show unfiltered Hong-Ou-Mandel interference visibilities of 77% between photons from the same PCF, and 80% between separate sources. We compare results from modelling the PCF to these experiments and analyse photon purities.Comment: 23 pages, 17 figures, Comments Welcom

Multicolor quantum metrology with entangled photons

Entangled photons can be used to make measurements with an accuracy beyond that possible with classical light. While most implementations of quantum metrology have used states made up of a single colour of photons, we show that entangled states of two colours can show supersensitivity to optical phase and path-length by using a photonic crystal fibre source of photon pairs inside an interferometer. This setup is relatively simple and robust to experimental imperfections. We demonstrate sensitivity beyond the standard quantum limit and show super-resolved interference fringes using entangled states of two, four, and six photons.Comment: 8 pages, 7 figure

Changes in undergraduate student alcohol consumption as they progress through university

BACKGROUND: Unhealthy alcohol use amongst university students is a major public health concern. Although previous studies suggest a raised level of consumption amongst the UK student population there is little consistent information available about the pattern of alcohol consumption as they progress through university. The aim of the current research was to describe drinking patterns of UK full-time undergraduate students as they progress through their degree course. METHOD: Data were collected over three years from 5895 undergraduate students who began their studies in either 2000 or 2001. Longitudinal data (i.e. Years 1–3) were available from 225 students. The remaining 5670 students all responded to at least one of the three surveys (Year 1 n = 2843; Year 2 n = 2219; Year 3 n = 1805). Results: Students reported consuming significantly more units of alcohol per week at Year 1 than at Years 2 or 3 of their degree. Male students reported a higher consumption of units of alcohol than their female peers. When alcohol intake was classified using the Royal College of Physicians guidelines [1] there was no difference between male and females students in terms of the percentage exceeding recommended limits. Compared to those who were low level consumers students who reported drinking above low levels at Year 1 had at least 10 times the odds of continuing to consume above low levels at year 3. Students who reported higher levels of drinking were more likely to report that alcohol had a negative impact on their studies, finances and physical health. Consistent with the reduction in units over time students reported lower levels of negative impact during Year 3 when compared to Year 1. CONCLUSION: The current findings suggest that student alcohol consumption declines over their undergraduate studies; however weekly levels of consumption at Year 3 remain high for a substantial number of students. The persistence of high levels of consumption in a large population of students suggests the need for effective preventative and treatment interventions for all year groups

Generation of UV light from microstructural fibers pumped with a femtosecond 800 NM oscillator.

Microstructured fibers have been shown to be an excellent media for nonlinear optical interactions due to small core size, long interaction length and unusual dispersion properties. Supercontinuum generation with just oscillator pumping is one of the manifestations of such properties [l]. The supercontinuum is typically observed in the fundamental mode even in the multimode PCFs. Another interesting observation is the generation of distinct frequency bands when pumping the PCF at 1550 nm [2]. The color generation was observed in the visible region exiting the fiber in single higher-order modes different for each color. Here we report the observation of the upconversion of the femtosecond 800 nm pulses from a commercial Ti:Sapphire oscillator to the UV frequency range, Fig. 1. It is unambiguously observed that the nonlinear mechanism is distinct from that of the supercontinuum generation and the UV generation occurs starting from the higher-order mode at the fundamental wavelength and yielding a very high-order mode in the UV

Control of visible harmonic generation using polarization in photonic crystal fibers

The polarization state of the input pulses to a segment of microstructured fiber controls the harmonic generation yielding specific frequencies depending on of the input state