Montréal Quantum Photonics Seminar Series Abstract: When a pulse of light traverses a material, it incurs a time delay referred to as the group delay. Should the group delay experienced by photons be attributed to the time they spend as atomic excitations? However reasonable this connection may seem, it appears problematic when the frequency of the light is close to the atomic resonance, as the group delay becomes negative in this regime. To address this question, I used the cross-Kerr effect to probe the degree of atomic excitation caused by a resonant transmitted photon by measuring the phase shift on a separate beam that is weak and off-resonant. These results, over a range of pulse durations and optical depths, are consistent with the recent theoretical prediction that the mean atomic excitation time caused by a transmitted photon (as measured via the time integral of the observed phase shift) equals the group delay experienced by the light. Specifically, I measured mean atomic excitation times ranging from (−0.82 ±0.31)τ0 for the most narrowband pulse to (0.54 ±0.28)τ0 for the most broadband pulse. I report these times normalized to the non-post-selected excitation time τ0, which is equal to the scattering (absorption) probability multiplied by the atomic lifetime τsp. These results suggest that negative values taken by times such as the group delay have more physical significance than has generally been appreciated. Bio: Daniela Angulo is a physicist from Colombia who recently completed her PhD at the University of Toronto, focusing on experimental light-matter interaction. Under the supervision of Aephraim Steinberg, her research explored the behavior of photons in atomic clouds using weak measurements. She is passionate about teaching and science communication. Outside the lab, she is an avid cyclist and musician. Local J-1035 Pavillon J. A. Bombardier, Polytechnique Montréal, Montréal, Quebec, Canada

Abstract: In the talk I will try to convince you that the answer is yes. Maxwell postulated that there can be a current of electric charges in the vacuum. This was needed to turn the equations of electrostatics into a consistent set of quations forming the basis of electrodynamics. We argue that Maxwell’s current are moving virtual elementary particles and their anti-particles in the vacuum. We are using a phenomenological model treating the vacuum as a dielectric. We find this reproduces fairly well the coefficients and . We also formu­lated the story in the language of quantum field theory. G Leuchs, M Hawton and LL Sánchez-Soto, Physics 5, 179 (2023) G Leuchs, SPG Mitteilungen 70, 34 (2023) Bio : Gerd Leuchs is Director Emeritus at the Max Planck Institute for the Science of Light in Erlangen and an adjunct professor within the physics department of the University of Ottawa. After 15 years in academic research at the University of Cologne, the University of Munich and JILA in Boulder, Colorado, he worked at a Swiss optics company for five years before becoming a full professor at the University of Erlangen-Nürnberg. His scientific work includes quantum beats, photo-electron angular distributions in multiphoton ionization, quantum noise-reduced and entangled light beams and solitons in optical fibers and quantum communication protocols, focusing light beams and nanophotonics. For five years, Gerd Leuchs led the German gravitational wave detection group (1985-1989). He has been a Visiting Fellow of JILA, Feodor-Lynen Fellow of the Alexander von Humboldt Foundation, Heisenberg Fellow of the German Science Foundation and Visiting Professor at the Australian National University, at the University of Adelaide and the Laboratoire Kastler Brossel of the Ecole Normale Supérieure. He is a member of the German Physical Society, the German Society for Applied Optics, the European Physical Society, and the German Academy of Sciences Leopoldina and a Fellow of the Institute of Physics, Optica and the American Association for the Advancement of Science. He is a foreign member of the Russian Academy of Sciences. He holds honorary degrees from the Danish Technical University and Saint Petersburg State University. Over the years, he has served on several OSA committees. In 2005, he received the Quantum Electronics Prize from the European Physical Society, and in 2018, the Herbert Walther Prize jointly awarded by OSA and the German Physical Society (DPG). He won an advanced grant from the European Research Council, a megagrant from Russia, and a Julius-von-Haast Fellowship award from the Royal Society of New Zealand. With his research, Gerd Leuchs is contributing to the field of quantum technology. He is member of a number of advisory boards for quantum technology application and innovation in Germany and abroad. Local J-1035 Pavillon J. A. Bombardier, Polytechnique Montréal, Montréal, Quebec, Canada

Abstract: The talk will review the work done by the group of kinetics of nanosecond discharges of Laboratory of Plasma Physics in the direction of studying of plasma parameters and optimizing plasma chemistry. Special attention will be payed to techniques related to optics, plasma action on cell morphology and measuring of ROS produced by plasma. The capabilities of the phase imaging technique, Quadriwave Lateral Shearing Interferometry (QLSI) as a diagnostic for the plasma action on living cells will be discussed. A novel approach to calibration of ratio of two-photon Xe/O cross-sections for two-photon absorption fluorescence (TALIF) of atomic oxygen will be presented. Bio: Svetlana Starikovskaia received the Ph.D. in Plasma Physics from Moscow Institute of Physics and Technology (MIPT) in 1993, Dr.Sc. degree from Joint Institute of High Temperatures Russian Academy of Sciences in Moscow State University in 2000 and degree of Professor from MIPT in 2006. She is currently a CNRS Leading Scientific Researcher in Laboratory of Plasma Physics (LPP) and Professor at Ecole Polytechnique, Palaiseau, France. Her scientific interest involves molecular energy transfer, non-equilibrium plasma, plasma-assisted combustion, shock waves and chemical kinetics, plasma conversion of CO2, plasma-living cells interaction. Local J-1035 Pavillon J. A. Bombardier, Polytechnique Montréal, Montréal, Quebec, Canada

Abstract: Phase-change materials (PCMs) have emerged as a promising platform to modulate light in a nonvolatile manner—a reversible switching between their stable amorphous and crystalline states leads to an impressive refractive index contrast (∆n, ∆k ~1−3). The last decade has seen a growing interest in such a combination of properties for a variety of nonvolatile programmable devices, such as metasurfaces, tunable filters, phase/amplitude modulators, color pixels, thermal camouflage, photonic memories/computing, plasmonics, and more. Thus, PCMs have demonstrated outstanding versatility and integration in low-energy photonic applications. Integrated photonics, in particular, has benefited from the progress of PCMs such as Sb2Se3 and Ge2Sb2Te5 for ultra-compact phase and amplitude modulators, respectively, using all-optical and electro-thermal approaches. These low-energy devices allow small-form-factor quasi-passive silicon photonics, i.e. silicon photonics with zero-static power, yet with the ability to reconfigure actively—crucial properties in applications such as in-memory computing, optical synapses, zero-power photonic switches, trimming, and optical storage. This talk will discuss the fundamental principles and switching mechanisms of PCMs in integrated photonic platforms and the state-of-the-art achievements, current efforts, and open challenges. Bio: Carlos A. Ríos Ocampo is an Assistant Professor at the University of Maryland, College Park, where he has led the Photonic Materials & Devices groups since 2021. Before joining UMD, Carlos was a Postdoctoral Associate at MIT, received a DPhil (PhD) degree in 2017 from the University of Oxford (UK), an MSc degree in Optics and Photonics in 2013 from the KIT (Germany), and a BSc in Physics in 2010 from the University of Antioquia (Colombia). Carlos’s scientific interests focus on studying and developing new on-chip technologies driven by the synergy between nanomaterials and photonics. Local J-1035 Pavillon J. A. Bombardier, Polytechnique Montréal, Montréal, Quebec, Canada