Generation and coherent control of pulsed quantum frequency combs

We present a method for the generation and coherent manipulation of pulsed quantum frequency combs. Until now, methods of preparing high-dimensional states on-chip in a practical way have remained elusive due to the increasing complexity of the quantum circuitry needed to prepare and process such states. Here, we outline how high-dimensional, frequency-bin entangled, two-photon states can be generated at a stable, high generation rate by using a nested-cavity, actively mode-locked excitation of a nonlinear micro-cavity. This technique is used to produce pulsed quantum frequency combs. Moreover, we present how the quantum states can be coherently manipulated using standard telecommunications components such as programmable filters and electro-optic modulators. In particular, we show in detail how to accomplish state characterization measurements such as density matrix reconstruction, coincidence detection, and single photon spectrum determination. The presented methods form an accessible, reconfigurable, and scalable foundation for complex high-dimensional state preparation and manipulation protocols in the frequency domain

Induced photon correlations through the overlap of two four-wave mixing processes in integrated cavities

Induced photon correlations are directly demonstrated by exploring two coupled nonlinear processes in an integrated device. Using orthogonally polarized modes within an integrated microring cavity, phase matching of two different nonlinear four-wave mixing processes is achieved simultaneously, wherein both processes share one target frequency mode, while their other frequency modes differ. The overlap of these modes leads to the coupling of both nonlinear processes, producing photon correlations. The nature of this process is confirmed by means of time- and power-dependent photon correlation measurements. These findings are relevant to the fundamental understanding of spontaneous parametric effects as well as single-photon-induced processes, and their effect on optical quantum state generation and control

Arbitrary Phase Access for Stable Fiber Interferometers

Well-controlled yet practical systems that give access to interference effects are critical for established and new functionalities in ultrafast signal processing, quantum photonics, optical coherence characterization, etc. Optical fiber systems constitute a central platform for such technologies. However, harnessing optical interference in a versatile and stable manner remains technologically costly and challenging. Here, degrees of freedom native to optical fibers, i.e., polarization and frequency, are used to demonstrate an easily deployable technique for the retrieval and stabilization of the relative phase in fiber interferometric systems. The scheme gives access (without intricate device isolation) to <1.3 × 10−3 π rad error signal Allan deviation across 1 ms to 1.2 h integration times for all tested phases, ranging from 0 to 2π. More importantly, the phase-independence of this stability is shown across the full 2π range, granting access to arbitrary phase settings, central for, e.g., performing quantum projection measurements and coherent pulse recombination. Furthermore, the scheme is characterized with attenuated optical reference signals and single-photon detectors, and extended functionality is demonstrated through the use of pulsed reference signals (allowing time-multiplexing of both main and reference signals). Finally, the scheme is used to demonstrate radiofrequency-controlled interference of high-dimensional time-bin entangled states. © 2021 The Authors. Laser & Photonics Reviews published by Wiley-VCH Gmb

Projected Wind Impact on Abies balsamea (Balsam fir)-Dominated Stands in New Brunswick (Canada) Based on Remote Sensing and Regional Modelling of Climate and Tree Species Distribution

The paper describes the development of predictive equations of windthrow for five tree species based on remote sensing of wind-affected stands in southwestern New Brunswick (NB). The data characterises forest conditions before, during and after the passing of extratropical cyclone Arthur, July 4–5, 2014. The five-variable logistic function developed for balsam fir (bF) was validated against remote-sensing-acquired windthrow data for bF-stands affected by the Christmas Mountains windthrow event of November 7, 1994. In general, the prediction of windthrow in the area agreed fairly well with the windthrow sites identified by photogrammetry. The occurrence of windthrow in the Christmas Mountains was prominent in areas with shallow soils and prone to localised accelerations in mean and turbulent airflow. The windthrow function for bF was subsequently used to examine the future impact of windthrow under two climate scenarios (RCP’s 4.5 and 8.5) and species response to local changes anticipated with global climate change, particularly with respect to growing degree-days and soil moisture. Under climate change, future windthrow in bF stands (2006–2100) is projected to be modified as the species withdraws from the high-elevation areas and NB as a whole, as the climate progressively warms and precipitation increases, causing the growing environment of bF to deteriorate

Correlation of Visually Evoked Functional and Blood Flow Changes in the Rat Retina Measured With a Combined OCTþERG System

PURPOSE. To correlate visually evoked functional and blood flow changes in the rat retina measured simultaneously with a combined optical coherence tomography and electroretinography system (OCTþERG). METHODS. Male Brown Norway (n ¼ 6) rats were dark adapted and anesthetized with ketamine/xylazine. Visually evoked changes in the retinal blood flow (RBF) and functional response were measured simultaneously with an OCTþERG system with 3-lm axial resolution in retinal tissue and 47-kHz image acquisition rate. Both single flash (10 and 200 ms) and flicker (10 Hz, 20% duty cycle, 1-and 2-second duration) stimuli were projected onto the retina with a custom visual stimulator, integrated into the OCT imaging probe. Total axial RBF was calculated from circular Doppler OCT scans by integrating over the arterial and venal flow. RESULTS. Temporary increase in the RBF was observed with the 10-and 200-ms continuous stimuli (~1% and~4% maximum RBF change, respectively) and the 10-Hz flicker stimuli (~8% for 1-second duration and~10% for 2-second duration). Doubling the flicker stimulus duration resulted in~25% increase in the RBF peak magnitude with no significant change in the peak latency. Single flash (200 ms) and flicker (10 Hz, 1 second) stimuli of the same illumination intensity and photon flux resulted in~23 larger peak RBF magnitude and~25% larger RBF peak latency for the flicker stimulus. CONCLUSIONS. Short, single flash and flicker stimuli evoked measureable RBF changes with larger RBF magnitude and peak latency observed for the flicker stimuli

Representative morphological OCT, Doppler OCT and OCTA images of the rat eye.

<p>(A) Cross-sectional morphological OCT image of the rat retina overlaid with Doppler OCT to show the retinal vasculature with arteries marked in red and veins–in blue color. (B-C) Volumetric 3D OCT images of the rat retina and anterior eye chamber respectively. Vascular loop is placed anterior to the eye chamber (white arrow). (D-F) Examples of OCTA images from the NFL+GCL, IPL, and OPL layers respectively.</p

Correlation between IOP and axial eye length.

<p>Linear increase of the axial eye length is detected with IOP increase (red dashed line, R square = 0.91). Data are presented as Mean ± S.E.</p

Quantification of microvascular density in NFL+GCL, IPL, and OPL at different IOP levels.

<p>Density data in both eye are represented in Mean ± S.E. with fitted polynomial function (n = 3). Recovery data in the treated eye is excluded from fitting. *Significant difference between two eyes (p<0.05).</p

Structural, functional and blood perfusion changes in the rat retina associated with elevated intraocular pressure, measured simultaneously with a combined OCT+ERG system - Fig 2

<p>Representative cross-sectional OCT images of the ONH showed progressive deformation of the ONH associated with elevated IOP (A-E). (F) ONH morphology recovered 30 minutes after loop removal.</p

Structural, functional and blood perfusion changes in the rat retina associated with elevated intraocular pressure, measured simultaneously with a combined OCT+ERG system - Fig 8

<p>(A) Representative ERG traces and the corresponding OPs at different IOP levels. Dashed line labels the onset of the visual stimulation. (B-D) Statistics of photoreceptor response, ON bipolar cell response and OPs at different IOP levels. (E and F) Normalized ON bipolar cell response and OPs related to the photoreceptor response, respectively. *Significant difference between two eyes (p<0.05). Data are presented as: Mean ± S.E.</p