Canada

H2 continues to provide fundamental insights into the mechanisms of intense light-matter interactions [1]. Recently, there has been significant interest in so-called light-induced conical intersections (LICI) that arise from the angle dependence of the single-photon coupling of electronic states. Analogously to regular conical intersections, electronic and nuclear motions are strongly coupled in the vicinity of LICIs. As a signature of such rovibronic dynamics, weak modulations in the angular distribution of protons emitted from H2+ have been reported [2]. More generally speaking, infrared (IR) laser pulses couple the 1sg and 2pu electronic states of H2+ typically through several pathways involving an odd number of photons [1], which can produce complex light-induced potential energy landscapes, and consequently even richer dynamics.
In this talk we will present theory and experiment to show that the full complexity of such light-induced potential energy surfaces can be uncovered using a two-step scheme [3]. In this scheme a few cycle optical pulse projects a coherent wavepacket onto the ionic state of H2 and a weak, non-ionizing, mid-infrared, and perpendicularly polarized pulse creates the light-induced potential energy landscapes upon which the H2+ wavepacket can propagate. We observe a strongly modulated angular distribution of protons which has escaped prior observation. These modulations result directly from ultrafast dynamics on the light-induced molecular potentials and can be modified by varying the amplitude, duration and phase of the mid-infrared dressing field.

[1] H. Ibrahim, C. Lefebvre, A.D. Bandrauk, A. Staudte and F. Légaré. J. Phys. B 51, 042002 (2018).
[2] A. Natan, M.R. Ware, V.S. Prabhudesai, U. Lev, B.D. Bruner, O. Heber, and P.H. Bucksbaum, Phys. Rev. Lett. 116, 143004 (2016).
[3] M. Kübel, M. Spanner, Z. Dube, A.Yu. Naumov, S. Chelkowski, A.D. Bandrauk, M.J.J. Vrakking, P.B. Corkum, D.M. Villeneuve, and A. Staudte. Nature Communications 10, 1042 (2019).

CAP Virtual Congress 2021

Signatures of light-induced potential energy surfaces in H2+ - beyond conical intersections

femtochemistry

light-induced molecular potentials

coltrims

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technical paper

The non-adiabatic coupling of nuclear and electronic degrees of freedom underlies many fundamental processes in Nature, including solar energy conversion and photosynthesis. The formation of electronic coherences by nuclear motion is a new aspect of such dynamics and requires new measurement techniques and methods of analysis. We will discuss Ultrafast Time-Resolved Xray Absorption and Time-Resolved Photoelectron Spectroscopy, powerful methods suited to addressing this problem. In particular, we present a new approach to fully separating electronic coherences from electronic population dynamics, a long-standing problem, based on the use and analysis of Time-Resolved Photoelectron Angular Distributions.

Coherent Ultrafast Electronic Dynamics in Molecules

Superconducting radiofrequency (SRF) cavities have been used for more than 50 years to increase the energy of charged particles. In Canada there are two accelerator centres which use SRF technology, i.e TRIUMF and the Canadian Light Source (CLS). The CLS was the first light source to use an SRF cavity in a storage ring from the beginning of operations in 2004. TRIUMF began developing SRF technology in 2000 which led in 2006 to the commissioning of the ISAC-II heavy ion superconducting linac for the post-acceleration of radioactive beams. More recently, the ARIEL SRF electron accelerator was installed at TRIUMF as a second driver for radioactive isotope production. In this talk, I will first give an overview of Canada’s SRF infrastructure and the underlying concepts. Then, I will briefly present how performance has globally evolved since the early days. Nowadays, state of the art niobium cavities reach fundamental limitations in terms of accelerating gradient (energy gain per unit length) and power dissipation. Increasing performance requires specialized chemical and surface treatments which must be tailored to specific cavity types and exploring materials beyond bulk niobium. I will highlight recent research highlights from TRIUMF and UVic including results from testing new surface treatments on unique multimode coaxial resonators and material science investigations using beta detected nuclear magnetic resonance (beta-NMR) and muon spin rotation and relaxation (muSR).

Superconducting Radiofrequency Science and Technology in Canada

Inhaled hyperpolarized gas lung MRI was proven to be useful for the observation and treatment planning of several pulmonary diseases including chronic obstructive pulmonary disease, asthma, COVID-19 and lung cancer. The combined economic burden of COPD and asthma in Canada, Ontario being $5.7 billion (2011). While these statistics are alarming, they don’t fully reflect the impact on economic growth and the opportunity costs that stem from such a large number of chronically ill Canadian adults and children. Moreover, both asthma and COPD are progressive and punctuated by sudden, acute worsening of symptoms or “exacerbations” that require immediate medical care – a source of enormous stress on our healthcare system. Lung cancer caused the premature deaths of 21,100 Canadians in 2017 (with an additional 28,600 being diagnosed), accounting for 26% of all cancer related deaths in Canada. People who are diagnosed with lung cancer are most likely to survive if the tumour can be surgically removed. However, nearly 1 in 4 Canadians who have their lung tumour surgically removed have lung complications following surgery called “postoperative pulmonary complications.” Presently, there is very little effort to predict these complications. So, it is not surprising that there has been a growing interest in developing new lung imaging techniques such as hyperpolarized 129Xe MRI to better understand various disruptive pulmonary, cardiac & neurodegenerative chronic diseases. In Canada, four research sites (London, Hamilton, Toronto, and Thunder Bay) have started a 129Xe MRI program, and two other sites (Vancouver, Montreal,) are in the preparation stage. Collectively, these Canadian sites urgently need novel 129Xe MR imaging methods as well as an advanced hardware package including a static-cell xenon polarizer, RF coil asymmetric unshielded rigid transmitter and multi-channel phased array receiver. Thinking about 129Xe’s place in MRI research globally, it is known that presently, 129Xe lung MRI is translating towards a clinical tool, and it has recently been approved and used as a clinical tool in the UK and USA. This opens door for better diagnoses, treatment planning and treatment assessment of patients with chronic lung, COVID-19, cardio and neuro diseases.

Noble gas MRI: A Decade of Progress Towards Clinical Translation

In response to the needs for ventilators for critically ill Covid-19 patients a collaboration of international particle physicists, engineers, software specialists, industry and medical specialists came together to create rapidly a simple, low-cost, open-source ventilator tailored specifically for such patients. The project was initiated by Professor Cristian Galbiati, spokesperson of the DarkSide-20k experiment designed to use about 55 tons of low-radioactivity liquid Argon to search for high-mass WIMPS as Dark Matter candidate particles at the Gran Sasso underground laboratory. This experiment is a successor to the DEAP experiment and pre-cursor to the proposed ARGO experiment at SNOLAB. It was realized that the expertise in gas handling and computer control that has been developed for these experiments could be used to develop the Mechanical Ventilator Milano (MVM). The Italian group was immediately joined by Canadian scientists and engineers from TRIUMF laboratory, CNL Chalk River, SNOLAB and the McDonald Institute and other international collaborators. A prototype was working in the lab within 10 days, papers were published openly for the design, industrialized versions were developed and the collaboration won a Canadian government contract that has now resulted in the delivery of over 6000 ventilators to the Canadian stockpile following Health Canada Interim Authorization. Donation to other countries in need is another possibility under discussion. A description will be provided of how this highly motivated team pivoted their work to make a contribution to the COVID-19 pandemic.

The MVM Ventilator: Particle physicists, National Labs and Industry

In 2014 the Executive Officer of the American Physical Society (APS), Kate Kirby, created an Ad-Hoc Committee on LGBT Issues (C-LGBT) charged with reporting on the obstacles to inclusion of LGBT physicists, a term which for the purpose of this report refers to persons who self-identify as lesbian, gay, bisexual, transgender, queer, questioning, intersex, or asexual, as well as other sexual and gender minorities. The full charge was as follows: "The committee will advise the APS on the current status of LGBT issues in physics, provide recommendations for greater inclusion, and engage physicists in laying the foundation for a more inclusive physics community. More specifically, the committee will investigate LGBT representation in physics, assess the educational and professional climate in physics, recommend changes in policies and practices that impact LGBT physicists, and address other issues that affect inclusion." I will present the findings and recommendations of the C-LGBT final report, and discuss the future of APS efforts toward LGBT inclusion in physics with an intersectional lens.

LGBT+ Climate in Physics (flipped)

Physics is widely recognised as a subject which often does not recognise the diversity of the societies in which it is practised. There are differences between countries, but there are many parts of the world where female participation at all levels in Physics is 20% or below. In the UK specifically, there is also low participation by some groups either ethnic groups or lower socioeconomic groups. It is clear that for Physics to be a success and to build teams to solve the key challenges in Physics, we need the participants to fully represent the diversity of the society in which they are based. 

I will present some of the activities of the Department of Physics at the University of York in the UK, in attempting to open up Physics to all. In particular, I will focus on actions intended to address gender imbalance and the recognised higher drop-out rate of women at all levels in Physics. At York, we hold Athena Swan Silver and Project Juno Champion status which are two schemes in the UK to recognise Physics departments in their equality activities. I will outline key aspects of our action plan to ensure a level playing field. These have been welcomed by all staff as they recognise issues such as work/life balance and part-time working which are of relevance to all. I will review aspects of recruiting and how avoiding unconscious bias is being put at the centre of our approach. I will review the data which shows the significance of this work and the impacts that it can achieve. 

While there are many avenues to take in tackling challenges of inclusion, outreach can play a very strong role. I will discuss some aspects of our outreach programme. We engage with many different groups, at different levels and different ages. This starts with hands-on astronomy for schoolchildren at primary level and for local scouting groups such as cubs and brownies. Our outreach programme covers more advanced material for those in the final years of high school. For example, an online nuclear physics masterclass which has proven very popular and with audiences significantly more diverse than our own student cohort. I will also provide examples like the Physics outreach stand taken to the York Pride event. Finally, I will discuss a knowledge exchange programme with two historically disadvantaged universities in South Africa, supported by the UK Global Challenges Research Fund, which has seen many students from SA visit York for hands-on training and allowed the setting up of two detector development laboratories in South Africa.

Equality and diversity in Physics: A UK perspective (flipped)

The National Research Council Canada (NRC) was contracted by Infrastructure Canada and the City of Toronto to improve the understanding of the performance of various catch basin covers under various conditions. A full scale model roadway was built 10.7 m long and 2.6 m wide in the NRC's Coastal Wave Basin and the water depth in front of the catch basin varied from 0.5 - 15 cm, the road grade was varied from 0.5 - 10.0% and the cross slope was varied from 2.0 - 4.0%. Early in the test protocol it was noted that the capacitance wire wave gauges used to measure the water depth on the roadway provided inconsistent results. In this work we will compare water depth measurements from a manual point gauge, an acoustic sensor and the capacitance wave probes. We will examine in which way each of the sensors is biased and examine the impact of those results.

Measuring water depth on an inclined road

Quantum dots embedded in photonic nanowires are highly efficient single photon generators. Integrating such sources on-chip offers enhanced stability and miniaturization; both of which are important in many applications involving quantum information processing. We demonstrate the efficient coupling of quantum light generated in a III-V photonic nanowire to a silicon-based photonic integrated circuit. This hybrid quantum photonic integrated circuit is assembled through a “pick & place” approach using a nanomanipulator in a scanning electron microscope where the nanowires are transferred individually from the growth substrate and carefully placed onto the photonic integrated circuit. The emission properties of on-chip nanowire QDs were measured using an all-fibre pump and collection technique. We demonstrate detected count rates of a million counts per second with single photon purities higher than 95 percent thus showing that using nanowires with embedded QDs coupled to on-chip photonic structures is a viable route for the fabrication of stable single photon sources.

Hybrid Integration of III-V Nanowires Embedded with Quantum Dots on Photonic Integrated Circuits

Among solid state quantum emitter systems, semiconductor quantum dots are particularly attractive due to their high radiative quantum efficiencies [1], their strong optical coupling enabling fast [2] and arbitrary [3] qubit rotations, and their tunable emission in the range of standard telecommunication wavelengths. For applications such as quantum light sources and quantum nodes, it is essential to maximize the fidelity of the optical control process governing quantum state initialization and control. While the dephasing time tied to radiative relaxation is many orders of magnitude longer than control times achievable with subpicosecond laser pulses, resonant coupling of the electron-hole pair to phonons in the solid-state environment can still contribute to decoherence during the optical control process [2]. This decoherence channel is often referred to as excitation-induced dephasing since the impact on fidelity is dictated in part by the characteristics of the driving laser field. Here we report the demonstration of suppression of phonon-mediated decoherence through the application of frequency-swept laser pulses via adiabatic rapid passage in the strong-driving regime [4]. We also investigate the dependence of the threshold for decoherence suppression on the size and shape of the quantum dot. Our findings indicate that the use of telecom-compatible quantum dots leads to decoherence suppression at pulse areas comparable to a single Rabi oscillation period.

[1] Atature et al. Nat. Rev. Mater. 3, 38 (2018).

[2] Mathew et al. Phys. Rev. B 90, 035316 (2014).

[3] Mathew et al. Phys. Rev. B 84, 205322 (2011); Gamouras et al. J. Appl. Phys. 112, 014313 (2012); Gamouras et al. Nano Letters 13, 4666 (2013); Mathew et al. Phys. Rev. B 92, 155306 (2015).

[4] Ramachandran et al. Opt. Lett. 45, 6498 (2020).

Suppression of Phonon-Mediated Decoherence using Frequency-Swept Laser Pulses in Optically-Driven Semiconductor Quantum Emitters

In addition to being extremely sensitive sensors, nitrogen vacancies (NV) centers in diamond are an ideal showcase of quantum technologies as they work in ambient conditions. Experiments with NV centers usually involve a bulky optical system, together with a wide assortment of signal generators and samplers, which is challenging to synchronize together. Here, we perform quantum control experiments on NV centers which are much more accessible to a broader community. We achieve this by (i) miniaturizing hardware components into a magnetometer the size of Rubik’s cube and (ii) leveraging a commercial platform for control and readout. We interfaced all the quantum magnetometers signal generation and readout components with a modular control platform, thus allowing it to fully operate the sensor. We will present room-temperature results including optically detected magnetic resonance, Rabi and Ramsey oscillations of an ensemble of NV centers. In addition to democratizing complex experiments in quantum physics, our work paves the way for efficient prototyping of quantum sensors with commercial control solutions.

Les centres azote-lacune (NV) dans le diamant sont une vitrine idéale des technologies quantiques car ils fonctionnent dans des conditions ambiantes. Les expériences avec les centres NV impliquent généralement un système optique volumineux, ainsi qu'un large assortiment de générateurs de signaux et d'échantillonneurs, qu'il est difficile de synchroniser ensemble. Ici, nous réalisons des expériences de contrôle quantique sur des centres NV qui sont beaucoup plus accessibles à une plus large communauté. Nous y parvenons (i) en miniaturisant l’électronique dans un magnétomètre de la taille d'un cube Rubik et (ii) en exploitant une plateforme commerciale pour le contrôle et la lecture. Nous avons interfacé tous les composants de génération de signaux et de lecture du magnétomètre quantique avec une plateforme de contrôle modulaire, lui permettant ainsi d’opérer le capteur quantique. Nous présenterons les résultats obtenus à température ambiante, notamment la résonance magnétique détectée optiquement et les oscillations de Rabi et de Ramsey d'un ensemble de centres NV. En plus de démocratiser les expériences complexes en physique quantique, notre travail ouvre la voie à un prototypage efficace des senseurs quantiques avec des solutions de contrôle commerciales.

A portable diamond-based quantum demonstrator based on a quantum control and readout platform - Démonstrateur quantique portable à base de diamant, basé sur une plateforme de contrôle et de lecture quantique

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Signatures of light-induced potential energy surfaces in H2+ - beyond conical intersections

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