Time reversal constraint limits unidirectional photon emission in slow-light photonic crystals

Photonic crystal waveguides are known to support C-points - point-like polarisation singularities with local chirality. Such points can couple with dipole-like emitters to produce highly directional emission, from which spin-photon entanglers can be built. Much is made of the promise of using slow-light modes to enhance this light-matter coupling. Here we explore the transition from travelling to standing waves for two different photonic crystal waveguide designs. We find that time-reversal symmetry and the reciprocal nature of light places constraints on using C-points in the slow-light regime. We observe two distinctly different mechanisms through which this condition is satisfied in the two waveguides. In the waveguide designs we consider, a modest group-velocity of $v_g \approx c/10$ is found to be the optimum for slow-light coupling to the C-points.Comment: 16 pages, 4 figure

1. First of the feathers: soldiers and suffragettes 2. Flight and refuge - Folkestone welcomes all

1. It is 1918 and the fight for female suffrage has been partly won. A woman reflects on her own role, campaigning for votes for women, while handing out white feathers to young men on Folkestone Leas during World War 1. This immersive dramatization will explore the possible motivation behind women’s political action between 1914 and 1918, and the impact this had on a generation of men. Suffrage campaigners often disagreed on strategy and policy, and their political views ranged from liberal pacificism to enthusiasm for eugenic selection. School participants will take opposite sides in these highly contentious debates, as the suffragette demands their support, and wants to know why some of them are not in uniform. 2.An exhibition at Folkestone Museum and curated by a local sixth form student, based on research into the Belgian refugee presence in Folkestone during WW1. The exhibition asks why an event so fundamental to our local history remains unknown to so many? Exploring the extent to which the Folkestone community welcomed their neighbours from across the channel in a time of need, the exhibition draws parallels with the modern day immigration crisis, helping to assess how our response to refugees may have changed

Nanofocusing in SOI-based hybrid plasmonic metal slot waveguides

Abstract: Through a process of efficient dielectric to metallic waveguide mode conversion, we calculate a >400-fold field intensity enhancement in a silicon photonics compatible nanofocusing device. A metallic slot waveguide sits on top of the silicon slab waveguide with nanofocusing being achieved by tapering the slot width gradually. We evaluate the conversion between the numerous photonic modes of the planar silicon waveguide slab and the most confined plasmonic mode of a 20 x 50 nm2 slot in the metallic film. With an efficiency of ~80%, this system enables remarkably effective nanofocusing, although the small amount of inter-mode coupling shows that this structure is not quite adiabatic. In order to couple photonic and plasmonic modes efficiently, in-plane focusing is required, simulated here by curved input grating couplers. The nanofocusing device shows how to efficiently bridge the photonic micro-regime and the plasmonic nano-regime whilst maintaining compatibility with the silicon photonics platform

Boundary restriction for negative emotional images is an example of memory amplification

We investigated whether boundary restriction—misremembering proximity to traumatic stimuli—is a form of memory amplification and whether re-experiencing trauma plays a role in boundary restriction errors. In four experiments, subjects viewed a series of traumatic photographs. Later, subjects identified the photographs they originally saw among distracters that could be identical, close-up, or wide-angled versions of the same photographs. Subjects also completed measures of mood, analogue PTSD symptoms, phenomenological experience of intrusions, and processing style. Across experiments, subjects were more likely to incorrectly remember the photographs as having extended boundaries: boundary extension. Despite this tendency, the extent to which subjects re-experienced traumatic aspects of the photographs predicted how often they incorrectly remembered the photographs as having narrower boundaries: boundary restriction. Our data suggest that although boundary extension is more common, boundary restriction is related to individual differences in coping mechanisms post-trauma. These results have theoretical implications for understanding how people remember trauma.Australian Research Council ARC DP14010266

Room temperature plasmon laser by total internal reflection

Plasmon lasers create and sustain intense and coherent optical fields below light's diffraction limit with the unique ability to drastically enhance light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications. However, these important applications require room temperature operation, which remains a major hurdle. Here, we report a room temperature semiconductor plasmon laser with both strong cavity feedback and optical confinement to 1/20th of the wavelength. The strong feedback arises from total internal reflection of surface plasmons, while the confinement enhances the spontaneous emission rate by up to 20 times.Comment: 8 Page, 2 Figure

Anomalous Stark Shifts in Single Vertically Coupled Pairs of InGaAs Quantum Dots

Vertically coupled Stranski Krastanow QDs are predicted to exhibit strong tunnelling interactions that lead to the formation of hybridised states. We report the results of investigations into single pairs of coupled QDs in the presence of an electric field that is able to bring individual carrier levels into resonance and to investigate the Stark shift properties of the excitons present. Pronounced changes in the Stark shift behaviour of exciton features are identified and attributed to the significant redistribution of the carrier wavefunctions as resonance between two QDs is achieved. At low electric fields coherent tunnelling between the two QD ground states is identified from the change in sign of the permanent dipole moment and dramatic increase of the electron polarisability, and at higher electric fields a distortion of the Stark shift is attributed to a coherent tunnelling effect between the ground state of the upper QD and the excited state of the lower QD.Comment: Conference paper for QD2004 3 figure

Tailored quantum dots for entangled photon pair creation

We compare the asymmetry-induced exchange splitting delta_1 of the bright-exciton ground-state doublet in self-assembled (In,Ga)As/GaAs quantum dots, determined by Faraday rotation, with its homogeneous linewidth gamma, obtained from the radiative decay in time-resolved photoluminescence. Post-growth thermal annealing of the dot structures leads to a considerable increase of the homogeneous linewidth, while a strong reduction of the exchange splitting is simultaneously observed. The annealing can be tailored such that delta_1 and gamma become comparable, whereupon the carriers are still well confined. This opens the possibility to observe polarization entangled photon pairs through the biexciton decay cascade.Comment: 4 pages, 4 figure

"The Score Matters": Wide Variations in Predictive Performance of 18 Paediatric Track and Trigger Systems

Objective: To compare the predictive performance of 18 Paediatric Early Warning Systems (PEWS) in predicting critical deterioration. / Design: Retrospective case-controlled study. PEWS values were calculated from existing clinical data and the area under the receiver operator characteristic curve (AUROC) compared. / Setting: UK tertiary referral children’s hospital. / Patients: Patients without a ‘do not attempt resuscitation’ order admitted between 1st January 2011 and 31st December 2012. All patients on paediatric wards who suffered a critical deterioration event were designated ‘cases’ and matched with a control closest in age who was present on the same ward at the same time. / Main outcome measures: Respiratory and/or cardiac arrest, unplanned transfer to paediatric intensive care and/or unexpected death. / Results: Twelve ‘scoring’ and 6 ‘trigger’ systems were suitable for comparative analysis. 297 case events in 224 patients were available for analysis. 244 control patients were identified for the 311 events. Three PEWS demonstrated better overall predictive performance with an AUROC of 0.87 or greater. Comparing each system to the highest performing PEWS with Bonferroni’s correction for multiple comparisons resulted in statistically significant differences for 13 systems. Trigger systems performed worse than scoring systems, occupying the 6 lowest places in the AUROC rankings. / Conclusion: There is considerable variation in the performance of published PEWS and as such the choice of PEWS has the potential to be clinically important. Trigger based systems performed poorly overall but it remains unclear what factors determine optimum performance. More complex systems did not necessarily demonstrate improved performance