The MARVEL Junior Seminar series is continuing in hybrid mode, in order to maintain in-person contacts and allow off-campus attendees to follow the seminars remotely! The MARVEL Junior Seminars aim to intensify interactions between the MARVEL Junior scientists belonging to different research groups. The seminar consists of two 25-minute presentations, followed by time for discussion.
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\r\nZacharie Waysenson
\r\nLaboratoire de Physique de l’École Normale Supérieure, Sorbonne Université
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\r\nMaria Andolfatto
\r\nLaboratory for Materials Simulations, PSI
The ultrafast motion of electrons is a frontier problem for photochemical processes, as electron motion is a key ingredient of all chemical reactions. Electronic rearrangement is also the means by which light energy is harnessed in photochemistry. The timescale for coherent electron dynamics is set by the energetic splitting of the electronic states, which in small molecular systems, is on the scale of an electron volt (eV). This sets the natural timescale for electronic motion to be few-to-sub femtosecond (fs).
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\r\nTo approach these extreme timescales, we can use short pulses of light to excite small quantum systems. For instance, the impulsive interactions between a light field and a quantum system can induce time-dependent oscillations in the charge density. Such electronic wavepacket motion (in the absence of nuclear motion) has come to be referred to as charge migration [1]. While the initial charge dynamics following impulsive excitation (or ionization) begins as purely electronic motion, this wavepacket will couple to other degrees of freedom in the system (i.e. nuclear motion or chemical dynamics) and lead to localization of the charge. The transfer of electronic charge across molecular bonds is fundamental to an understanding of charge transfer phenomena.
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\r\nThe study of these fundamental phenomena requires state-of-the-art light sources, such as the Linac Coherent Light Source (LCLS), an X-ray free electron laser (XFEL) facility which produces high-brightness, ultrashort pulses, with wavelength continuously tunable across the x-ray regime. Schemes to provide isolated, sub-femtosecond pulses from an FEL are being explored at facilities world-wide, and recently we have demonstrated such pulses at the LCLS [2]; opening the door for time-resolved measurements of ultrafast electron dynamics on their natural timescale. In my talk, I will highlight our recent developments in probing electronic motion in small molecular systems. We have employed sub-femtosecond pulses from the XFEL to study ultrafast charge dynamics in both core-excited [3,4,5] and low-lying cationic systems [6]. We are also developing nonlinear x-ray spectroscopies [7,8] to initiate and control electron dynamics. The control of coherent electron motion represents a significant step towards achieving charge-directed reactivity [9], a grand challenge for the field of attosecond science.
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\r\n[1] Cederbaum and Zobeley 1999 Chemical Physics Letters 307 205–210
\r\n[2] Duris and Li et al. 2020 Nature Photonics 14 30-36
\r\n[3] Li and Driver et al. 2022 Science 375 285-290
\r\n[4] Driver et al. 2024 Nature 632 762-767 (2024)
\r\n[5] Wang and Driver et al. Phys. Rev. X 15 011008 (2005)
\r\n[6] Driver et al. ArXiv:2411.01700
\r\n[7] O’Neal et al. 2020 Phys. Rev. Lett. 125 073203
\r\n[8] Biggs et al. 2023 Proc. Nat. Acad. Sci. 110 15597-15601
\r\n[9] F. Remacle, R. D. Levine, and M. A. Ratner 1998 Chem. Phys. Lett. 285, 25
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Please join us for the QSE Center Quantum Seminar with Robin Blume-Kohout from Sandia National Labs who will give the talk \"Assessing performance of logical operations with detector error models\" and Benoit Vermersch from Quobly and UGA who will give the talk \"Randomized measurements for large-scale quantum experiments\" on Friday April 24 from 11:30pm to 2:00pm
\r\nLocation: GR B3 30
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\r\nThe first talk will start at 11:30pm. Pizzas will be available at 12:20pm, in between talks. All PhDs, postdocs, students, group leaders, and PIs are welcome to join us.
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\r\nABSTRACT:
\r\n1. \"Assessing performance of logical operations with detector error models\" - Robin Blume-Kohout
\r\nQuantum computing is rapidly transitioning from the “NISQ” paradigm in which circuits and gates are executed directly on physical qubits to a fault tolerant “FTQC” paradigm in which circuits and gates are executed on encoded, error-corrected logical qubits. We want to model errors in gates. Logic gates on physical qubits are modeled by process matrices, derived from theory or estimated from tomography. But describing logical gates on logical qubits demands a richer model — specifically, detector error models — that can describe QEC syndrome data. I’ll introduce detector error models and summarize three recent papers in which we show how to estimate detector error models from data [https://arxiv.org/abs/2504.14643], how to simulate arbitrary small Markovian errors in Clifford circuits [https://arxiv.org/abs/2504.15128], and how to generate detector error models from arbitrary circuit-level Markovian errors [https://arxiv.org/abs/2603.18457].
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\r\n2. \"Randomized measurements for large-scale quantum experiments\" - Benoit Vermersch
\r\nThe randomized measurements toolbox is now routinely used in quantum experiments to estimate fundamental quantum properties, such as entanglement [1].
\r\nWhile experimentalists appreciate the simplicity and robustness aspects of such measurement protocols, a challenge for theorists is to design strategies for overcoming statistical errors using \"cheap\" polynomial resources in system size.
\r\nIn this context, I will present recent upgrades to the randomized measurements toolbox that address this challenge for large-scale quantum states that are relevant to the field of quantum simulation. In particular, I will discuss efficient protocols for measuring entanglement [2] and performing state tomography [3].
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\r\n[1] A. Elben, S. T. Flammia, H.-Y. Huang, R. Kueng, J. Preskill, B. Vermersch, and P. Zoller, The Randomized Measurement Toolbox, Nat Rev Phys 5, 9 (2022).
\r\n[2] B. Vermersch, M. Ljubotina, J. I. Cirac, P. Zoller, M. Serbyn, and L. Piroli, Many-Body Entropies and Entanglement from Polynomially Many Local Measurements, Phys. Rev. X 14, 031035 (2024).
\r\n[3] M. Votto, M. Ljubotina, C. Lancien, J. Ignacio Cirac, P. Zoller, M. Serbyn, L. Piroli, B. Vermersch, arXiv:2507.12550
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\r\nBIOS:
\r\nRobin Blume-Kohout was born on a kitchen table in the Alaska Bush almost (but not quite) 50 years ago. Unfortunately, things went downhill thereafter. He is now the founder and codirector of Sandia’s Quantum Performance Lab (QPL), where he and his fellow malcontents dream up new ways to assess and enhance the performance of quantum computers and their components.
\r\nBenoit Vermersch is an associate professor at the University of Grenoble Alpes, member of the LPMMC currently on leave in the quantum startup Quobly Research interests include implementations of quantum processing units with cold atoms, trapped ions, superconducting qubits; measurement protocols for entanglement-related quantities, out-of-time ordered correlators, topological invariants; many-body entanglement theory; quantum networks: Light-matter interfaces, quantum state transfer protocols, waveguide quantum electrodynamics; and tensor-network numerical methods: Matrix-Product-States and DMRG,TEBD related algorithms.
Join us for a community event presenting the first outcomes of the review phase of the s’EPanouir-FLourish initiative that will take place on Monday 27th of April from 13h30-15h30. The event can also be followed online.
\r\nSince room capacity is limited, attendance on site will be first-come first-served. For logistical reasons, we kindly ask you to signal your intention to attend (on site or online) via the following link: https://forms.cloud.microsoft/e/gMCxd941Lp
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\r\nDuring this event, Nicolas Grandjean, Associate Vice President for Education (AVPE), and the chairs of the Working Groups will present the main points of the Draft Feasibility Report, which is now open for feedback from teachers, sections and students.
\r\nThe session will consist of short 5‑minute presentations for each topic, followed by time for Q&A and brief small‑group discussions. Participants will also be able to share individual feedback via an online form.
\r\nThe report can be accessed online with your EPFL e-mail.
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\r\nAgenda:
\r\n13h30 – Opening remarks
\r\n13h35 – Basic educational goals and design features
\r\n14h00 – Bachelor program: thinking deeply and engaging with complexity
\r\n14h25 – Mastery and depth in first-year core disciplines
\r\n14h50 – Resources and support
\r\n15h15 – Next steps
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\r\nWe look forward to seeing you there!
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TBA
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