Observation of slow light in the noise spectrum of a vertical external cavity surface emitting laser

The role of coherent population oscillations is evidenced in the noise spectrum of an ultra-low noise lasers. This effect is isolated in the intensity noise spectrum of an optimized single-frequency vertical external cavity surface emitting laser. The coherent population oscillations induced by the lasing mode manifest themselves through their associated dispersion that leads to slow light effects probed by the spontaneous emission present in the non-lasing side modes.Comment: accepted for publication in Phys. Rev. Let

Randomized trial of paroxetine in end-stage COPD

Background: Although the underlying pathology is initially confined to the lungs, the associated emotional responses to chronic obstructive pulmonary disease (COPD) contribute greatly to the resulting morbidity. The objective of this study was to examine the effect of an antidepressant drug on disease-specific quality of life in patients with end-stage COPD who present significant depressive symptoms. Methods: We conducted a 12-week, randomized double- blind placebo-controlled trial of Paroxetine in which quality of life measured by the Chronic Respiratory Questionnaire (CRQ), an evaluative COPD-specific quality-oflife questionnaire, was the primary outcome. Results: 23 patients were randomized and 15 completed the trial (8 on Paroxetine; 7 on placebo). In the per-protocol analysis, we observed statistically and clinically significant improvements favoring the active treatment in 2 of the 4 domains of the CRQ: emotional function (adjusted mean difference: 1.1; 95% confidence interval [CI]: 0.0 - 2.2) and mastery (difference: 1.1; CI: 0.4 - 1.8). Dyspnea and fatigue improved, but to an extent that did not reach statistical significance. In the intention-to-treat analysis, none of the differences in CRQ scores was significant. Paroxetine was not associated to any worsening of respiratory symptoms. Conclusions: The results of this small randomized trial indicated that patients with end-stage COPD may benefit from antidepressant drug therapy when significant depressive symptoms are present. This study underlined the difficulties in conducting experimental studies in frail and elderly patients with COPD

Hybrid III-V/Silicon photonic circuits embedding generation and routing of entangled photon pairs

The demand for integrated photonic chips combining the generation and manipulation of quantum states of light is steadily increasing, driven by the need for compact and scalable platforms for quantum information technologies. While photonic circuits with diverse functionalities are being developed in different single material platforms, it has become crucial to realize hybrid photonic circuits that harness the advantages of multiple materials while mitigating their respective weaknesses, resulting in enhanced capabilities. Here, we demonstrate a hybrid III-V/Silicon quantum photonic device combining the strong second-order nonlinearity and compliance with electrical pumping of the III-V semiconductor platform with the high maturity and CMOS compatibility of the silicon photonic platform. Our device embeds the spontaneous parametric down-conversion (SPDC) of photon pairs into an AlGaAs source and their subsequent routing to a silicon-on-insulator circuitry, within an evanescent coupling scheme managing both polarization states. This enables the on-chip generation of broadband telecom photons by type 0 and type 2 SPDC from the hybrid device, at room temperature and with internal pair generation rates exceeding $10^5$ $s^{-1}$ for both types, while the pump beam is strongly rejected. Two-photon interference with 92% visibility (and up to 99% upon 5 nm spectral filtering) proves the high energy-time entanglement quality characterizing the produced quantum state, thereby enabling a wide range of quantum information applications on-chip, within an hybrid architecture merging the assets of two mature and highly complementary platforms in view of out-of-the-lab deployment of quantum technologies

Network Defence Using Attacker-Defender Interaction Modelling

Network security is still lacking an efficient system which selects a response action based on observed security events and which is capable of running autonomously. The main reason for this is the lack of an effective defence strategy. In this Ph.D., we endeavour to create such a defence strategy. We propose to model the interaction between an attacker and a defender to comprehend how the attacker’s goals affect his actions and use the model as a basis for a more refined network defence strategy. We formulate the research questions that need to be answered and we discuss, how the answers to these questions relate to the proposed solution. This research is at the initial phase and will contribute to a Ph.D. thesis in four years

2D photonic-crystal optomechanical nanoresonator

We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8 % over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265 nm-thick membrane, is used to form a compact microcavity involving the suspended nano-membrane as end mirror. The resulting cavity has a waist size smaller than 10 $\mu$m and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane

Networks of nonlinear superconducting transmission line resonators

We investigate a network of coupled superconducting transmission line resonators, each of them made nonlinear with a capacitively shunted Josephson junction coupling to the odd flux modes of the resonator. The resulting eigenmode spectrum shows anticrossings between the plasma mode of the shunted junction and the odd resonator modes. Notably, we find that the combined device can inherit the complete nonlinearity of the junction, allowing for a description as a harmonic oscillator with a Kerr nonlinearity. Using a dc SQUID instead of a single junction, the nonlinearity can be tuned between 10 kHz and 4 MHz while maintaining resonance frequencies of a few gigahertz for realistic device parameters. An array of such nonlinear resonators can be considered a scalable superconducting quantum simulator for a Bose-Hubbard Hamiltonian. The device would be capable of accessing the strongly correlated regime and be particularly well suited for investigating quantum many-body dynamics of interacting particles under the influence of drive and dissipation.Comment: 18 pages, 3 figure

Photothermal infrared thermography applied to the identification of thin layer thermophysical properties

Abstract: The aim of the present work is the thermal non-destructive characterisation of layers at the surface of metals. The sample is sinusoidally heated by means of an argon ion laser and a focal plane array infrared camera (CEDIP IRC 320-4 LW) is used to measure the temperature variations at the surface of the layer. A numerical lock-in procedure allows the detection of very weak temperature variations at the surface of the sample, down to a few mK when working from the acquisition of hundreds of images, yielding amplitude and absolute phase maps for modulation frequencies ranging from 0.1 Hz to 1000 Hz. An inverse procedure uses the Gauss-Newton parameter estimation method, in order to identify the thermal conductivity and the optical absorption coefficient of the layer. Confidence intervals on the parameters can also be estimated by the inverse procedure. More particular attention is devoted to the study of the sensitivity coefficients, as functions of the frequency range and of the radial range along the profiles, in order to optimise the identification procedure

Heterogeneous integration and precise alignment of InP-based photonic crystal lasers to complementary metal-oxide semiconductor fabricated silicon-on-insulator wire waveguides

The integration of two-dimensional III-V InP-based photonic crystal and silicon wire waveguides is achieved through an accurate alignment of the two optical levels using mix-and-match deep ultraviolet (DUV)/electron beam lithography. The adhesively bonded structures exhibit an enhancement of light emission at frequencies where low group velocity modes of the photonic crystal line defect waveguides occur. Pulsed laser operation is obtained from these modes at room temperature under optical pumping. The laser light is coupled out of the Si waveguide via grating couplers directly to single mode fiber

Conceptually driven and visually rich tasks in texts and teaching practice: the case of infinite series

The study we report here examines parts of what Chevallard calls the institutional dimension of the students’ learning experience of a relatively under-researched, yet crucial, concept in Analysis, the concept of infinite series. In particular, we examine how the concept is introduced to students in texts and in teaching practice. To this purpose, we employ Duval's Theory of Registers of Semiotic Representation towards the analysis of 22 texts used in Canada and UK post-compulsory courses. We also draw on interviews with in-service teachers and university lecturers in order to discuss briefly teaching practice and some of their teaching suggestions. Our analysis of the texts highlights that the presentation of the concept is largely a-historical, with few graphical representations, few opportunities to work across different registers (algebraic, graphical, verbal), few applications or intra-mathematical references to the concept's significance and few conceptually driven tasks that go beyond practising with the application of convergence tests and prepare students for the complex topics in which the concept of series is implicated. Our preliminary analysis of the teacher interviews suggests that pedagogical practice often reflects the tendencies in the texts. Furthermore, the interviews with the university lecturers point at the pedagogical potential of: illustrative examples and evocative visual representations in teaching; and, student engagement with systematic guesswork and writing explanatory accounts of their choices and applications of convergence tests