November 18, 2025 10:55 AM
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November 19, 2025 4:30 PM
November 18, 2025 10:55 AM
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November 19, 2025 4:30 PM
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Hôtel Château Bromont
Hôtel Château Bromont
Opening Remarks
Pr Mathieu Juan, Institut quantique - Université de Sherbrooke
Clasical and quantum computations as tensor networks
Pr Stefanos Kourtis, Institut quantique - Université de Sherbrooke
Classical and quantum computations as tensor networks
Break
Event organized in collaboration with the RQMP and animated by Mrs. Chloé Freslon, founder of URelles
Falisha Karpati, Ph.D.
Think Differently Together: Strengthening research and innovation by embracing cognitive diversity
Louis-Philippe Lamoureux (Slides / Présentation)
Thierry Debuischert, Thales - France (postponed to Monday at 13:15 / reporté à lundi 13h15)
Closing remarks of the day
Opening remark of the day
Thierry Debuischert, Thales - France
Professor Tami Pereg-Barnea, McGill University
Dynamic topology - quantized conductance and Majoranas on wires
Professor Philippe St-Jean, Université de Montréal
Topological physics with light and matter: new horizons
Break
Louis Gaudreau, National Research Council Canada (Ottawa)
Entanglement distribution via coherent photon-to-spin conversion in semiconductor quantum dot circuits
Philippe Lamontagne, National Research Council Canada (Montréal)
Black-Box Impossibility in the Common Reference Quantum State Model
Olivier Gagnon-Gordillo, Québec quantique lead
Presentation of the Québec Quantum ecosystem
Institut quantique - Université de Sherbrooke
Classical and quantum computations as tensor networks
Tensor networks are multilinear-algebra data structures that are finding application in diverse fields of science, from quantum many-body physics to artificial intelligence. I will introduce tensor networks and illustrate how they can be used to represent classical and quantum computations. I will then motivate tensor network algorithms that perform or simulate computations in practice and demonstrate their performance on benchmarks of current interest, such as model counting and quantum circuit simulation. I will close with an outline of ongoing work and an outlook on future directions.
Institut quantique - Université de Sherbrooke
Optomechanics with a non-linear cavity
The possibility to operate massive mechanical oscillators close to or in the quantum regime has become central in fundamental sciences. LIGO is a prime example where quantum states of light are now used to further improve the sensitivity. Concretely, optomechanics relies on the use of photons to control the mechanical motion of a resonator, providing a path toward quantum states of massive objects and for the development of quantum sensors. In order to improve this control many approaches have been explored, some more complicated than others. In particular, in order to cool the mechanical motion a cavity can be used to realise side-band cooling. In general, linear cavities are favoured to allow for large photon number providing stronger cooling. I will show that, surprisingly, non-linear cavities can be used to achieve very efficient cooling at low powers. Indeed, even in the bad cavity limit, we have been able to cool a mechanical resonator from 4000 thermal phonons down 11 phonons. Currently limited by flux noise, this approach opens promising opportunities to achieve quantum control of massive resonators, an avenue to study foundational questions.
McGill University
Dynamic topology - quantized conductance and Majoranas on wires
This talk will address the issue of out-of-equilibrium topological systems. While many materials and devices produced in labs today are topological at equilibrium, it is desirable to have a knob to tune or induce topological properties. For example, if we could dynamically turn a superconductor into a topological superconductor we may create the sought after Majorana fermions which are potential building blocks of quantum bits.
In this context we will explore the possibility of perturbing quantum systems using time-periodic fields (i.e., radiation) and use the Floquet theory to characterize the driven states. We find that in topological systems, beyond the expected splitting of the spectrum into side bands, a change in the topology may occur. In the case of a topological superconductor, the driven system may develop new Majorana modes which do not exist at equilibrium and can be exchanged on a single wire. A protocol for exchanging Majoranas will be presented.
Université de Montréal
Topological physics with light and matter: new horizons
Topology is a branch of mathematics interested in geometric properties that are invariant under continuous deformation, e.g. the number of holes in an object. In the early 1980s it was demonstrated that similar topological properties can be defined for solids presenting appropriate symmetry elements. The discovery of these topological phases of matter has profoundly impacted our understanding of condensed matter, its influence ranging from better explaining the universality of the conductivity plateaus in the quantum Hall effect to developing new platforms for fault-tolerant quantum computation[i]. In the late 2000s, Duncan Haldane (co-laureate of the Nobel Prize in physics for the discovery of topological phases of matter) demonstrated that this topological physics is not restricted to condensed matter but can also emerge in artificial systems like photonic crystals through a careful engineering of their symmetry properties[ii]. Since then, these photonics platforms have proven to be an amazing resource for pushing the exploration of topological matter beyond what is physically reachable in the solid-state, leading to the emergence of a blooming field called topological photonics[iii].
In this presentation, I will describe recent experimental works based on exciton-polaritons, a hybrid light-matter quasiparticle, which have opened new horizons in topological photonics[iv]. The main advantages of polaritonic systems arise from their dual nature: their photonic part allows for tailoring well-defined topological properties in lattices of coupled microcavities and makes them inherently non-hermitian; on the other hand, their matter part gives rise to a strong Kerr-like nonlinearity and to lasing[v]. I will then discuss in more details a recent work in which we took profit of these assets to experimentally extract topological invariants - a fundamental quantity in topology - in a polaritonic analog of graphene[vi]. Importantly, this has allowed us to directly probe the topological phase transition occurring in a critically strained lattice - i.e. where Dirac cones have merged - a condition impossible to reach in the solid-state. I will conclude this presentation by discussing how topological protection can provide a powerful asset for generating and stabilizing many-body quantum states of light and matter. Such mesoscopic quantum objects are highly desirable as they would provide an extended playground for quantum simulation, sensing applications or for generating exotic states of light such as many-body entangled states[vii].
[i] M. Z. Hasan and C. L. Kane. Rev. Mod. Phys. 82, 3045 (2010)
[ii] F. D. M. Haldane and S. Raghu. Phys. Rev. Lett. 100, 013904 (2008)
[iii] T. Ozawa et al. Rev. Mod. Phys. 91, 015006 (2019)
[iv] D. D. Solnyshkov, G. Malpuech, P. St-Jean et al. Opt. Mat. Express 11, 1119 (2021)
[v] I. Carusotto and C. Ciuti. Rev. Mod. Phys. 85, 299 (2013)
[vi] P. St-Jean et al. Phys. Rev. Lett. 126, 127403 (2021)
[vii] P. Lodahl et al. Nature 541, 473 (2017)
Think Differently Together: Strengthening research and innovation by embracing cognitive diversity
This talk will cover:
Biography
Falisha Karpati, PhD is a neuroscientist turned inclusion consultant. Falisha’s work focuses on using neuroscience to build inclusive environments in academic, research, and scientific organizations. Her approach to inclusion centres on the interconnectedness of cognitive, demographic, and experiential diversity. Prior to starting her consultancy practice, she worked as the Training and Equity Advisor for Healthy Brains, Healthy Lives at McGill University.
Head of Applied Quantum Physics
Thales Research & Technology
Researcher
National Research Council Canada (Ottawa)
In this talk, I will present our proposed long distance entanglement distribution scheme that aims to overcome fundamental limitations present in current optical schemes. By using direct band gap semiconductor quantum dots, efficiency and heralding advantages can be exploited through photon-to-spin conversion. For this reason, materials such as GaAs are superior to Si in this type of applications. I will review current schemes to transfer polarization or time-bin encoded photonic qubits to electron spin qubits and will describe adaptations to employ heavy holes which have a number of attractive properties including g-factor tunability. Finally, I will show preliminary results on quantum dot devices using Van der Waals heterostructures which present several potential advantages such as higher confinement energies due to their atomically thin geometry, easier combination with different substrates and the possibility of encoding information in their valley degree of freedom.
Biography
Louis Gaudreau studied physics at Sherbrooke University, followed by a masters and PhD in co-supervision with Andrew Sachrajda at NRC and Alexandre Blais at Sherbrooke. During his graduate studies, Louis studied electrostatic quantum dots and realized for the first time a coupled triple quantum dot system leading to the investigation of the first exchange-only qubit. During this period he was invited to perform quantum dot experiments in Stefans Ludwig’s group at LMU in Munich. After his PhD, Louis changed fields and studied light-matter interactions by combining quantum emitters and graphene to create different hybrid systems. These experiments were done during his postdoc at ICFO in Barcelona in the nano-opto-electronics group with Frank Koppens where he was awarded the prestigious Marie-Curie fellowship. Finally, since 2015, Louis has worked as research officer at the NRC where he investigates different technologies linked to quantum information.
Researcher
National Research Council Canada (Montréal)
Black-Box Impossibility in the Common Reference Quantum State Model
We explore the cryptographic power endowed by arbitrary shared physical resources. We introduce the Common Reference Quantum State (CRQS) model, where the parties involved share a fresh entangled state at the outset of each protocol execution. This model is a natural generalization of the well-known Common Reference String (CRS) model but appears to be more powerful. In the two-party setting, a CRQS can sometimes exhibit properties associated with a Random Oracle queried once. We formalize this notion as a Weak One-Time Random Oracle (W1TRO), where we only ask of the output to have some randomness when conditioned on the input is still beyond the reach of the CRQS model. We prove that the security of W1TRO cannot be black-box reduced to any assumption that can be framed as a cryptographic game. Our impossibility result employs the simulation paradigm formalized by Wichs (ITCS ’13) and has implications for other cryptographic tasks.
- There is no universal implementation of the Fiat-Shamir transform whose security can be black-box reduced to a cryptographic game assumption. This extends the impossibility result of Bitansky et al. (TCC ’13) to the CRQS model.
- We impose severe limitations on constructions of quantum lightning (Zhandry, Eurocrypt ’19). If a scheme allows n lightning states’ serial numbers (of length m such that n > m) to be combined in such a way that the outcome has entropy, then it implies W1TRO, and thus cannot be black-box reduced to a cryptographic game assumption.
Senior Product Manager
Aspen Technology
Biography
Montreal-based quantum physicist, senior product manager, and full stack developer with strong experience building award-winning hardware and software products. Currently Senior Product Manager at Aspen Technology leading connectivity and AI inference at the Edge. Prior to Aspen Technology, I worked at Machine-To-Machine Intelligence (M2Mi) a leader in IoT Security and Management located at NASA Ames research center in the heart of Silicon Valley.
Prior to M2Mi, built SQR Technologies a belgian quantum based, hardware security startup that pioneered distributed quantum key generation. Acquired by IDQ (Switzerland). Awarded a Ph.D. in Physics (Quantum Cryptography) from the University of Brussels. Research interests include: quantum cloning, experimental quantum cryptography, quantum noise reduction, and quantum random number generation.
10h55 Mot d'ouverture (Salon A)
11h00 Nathan Wiebe, Toronto University (Salon A)
Titre à venir
12h00 Lunch (Salle Knowlton)
13h30 Cunlu Zhou, Université de Sherbrooke (Salon A)
Ancilla-Free Quantum Protocol for Thermal Green’s Functions
14h15 Gisell L. Osrio, Polytechnique Montréal (Salon A)
Generation of few-mode photon triplets in waveguides and optical fibers
14h35 Marc-Antoine Roy, Université de Sherbrooke (Salon A)
Decoding Multimode Gottesman-Kitaev-Preskill Codes with Noisy Auxiliaries
14h55 Pause café (Salon C)
15h25 Benjamin Brock, Université de Sherbrooke (Salon A)
Quantum Error Correction with High-dimensional Systems
16h30 Session Écosystème quantique (Salon A)
- Guy-Philippe Nadon, École de technologie supérieure
QuantumETS - Stimuler l'informatique quantique à l'ÉTS
17h00 Session d'affiches et rafaîchissements (Salon C)
19h30 Souper INTRIQ (Salle Knowlton)
9h00 Amanda Seedhouse, CNRS, France (Salon A)
Strategies for noisy spin-based quantum computation
10h00 Shilong Liu, Polytechnique Montréal (Salon A)
Nonlinear pulse shaper for spectro-temporal light engineering
10h30 Pause café (Salon C)
11h00 Charles Bédard, École de technologie supérieure (Salon A)
Explaining Bell Locally
11:h30 Samuel Kuypers, Université de Montréal (Salon A)
Restoring locality: The Heisenberg picture as a separable description
12h00 Lunch (Salle Knowlton)
13h30 Juanita Bocquel, Université de Sherbrooke (Salon A)
Titre à venir
14h30 Lautaro Labarca, Université de Sherbrooke (Salon A)
Quantum sensing with GKP states
14h50 Pause café (Salon C)
15h15 Tami Pereg-Barnea, Université McGill (Salon A)
Kitaev chains of fermions and bosons
16h00 Ayana Sarkar et Martin Schnee, Université de Sherbrooke (Salon A)
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
16h30 Mot de clôture (Salon A)
Chercheuse, CNRS, France
Strategies for noisy spin-based quantum computation
Single electron spins in silicon quantum dots offer a promising pathway to scalable quantum computing, leveraging compatibility with semiconductor technologies and the high tunability of electrons. However, the susceptibility of these qubits to noise remains a critical challenge. This seminar explores ongoing research into understanding and mitigating noise in spin qubit hardware, focusing on strategies to enhance qubit fidelity in a scalable manner.
Professeur, Université de Sherbrooke
Quantum Error Correction with High-dimensional Systems
Professeur, Université de Sherbrooke
Titre à venir
Professeur, Toronto University
Titre à venir
Étudiant à la maîtrise, École de technologie supérieure
Directeur: Jacob Biamonte
QuantumETS - Stimuler l'informatique quantique à l'ÉTS
Gérez un club étudiant d'informatique quantique comporte plusieurs défis. Cette présentation abordera les différentes stratégies de QuantumETS pour engager la communauté étudiante de l'ÉTS, les différents projets de QuantumETS ainsi que ses succès.
Postdoc, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
Quantum kernel methods (QKMs) offer an appealing framework for machine learning on near-term quantum computers. However, QKMs generically suffer from exponential concentration, requiring an exponential number of measurements to resolve the kernel values, with the exception of trivial (i.e., classically simulable) kernels. Here we propose a QKM that is free of exponential concentration yet remains hard to simulate classically. Our QKM utilizes the weak ergodicity-breaking many-body dynamics in the Rydberg blockade of coherently driven neutral atom arrays. We demonstrate the fundamental properties of our QKM by analytically solving an approximate toy model of its underpinning quantum dynamics, as well as by extensive numerical simulations on randomly generated datasets. We further show that the proposed kernel exhibits effective learning on real data. The proposed QKM can be implemented in current neutral atom quantum computers.
Postdoc, École de technologie supérieure
Directeur: Claude Crépeau
Explaining Bell Locally
In the century-long history of quantum theory, Bell’s theorem stands out among the most thought-provoking results in its foundations. It reveals a conflict between the predictions of quantum mechanics and those permitted by local hidden-variable theories. Experimental confirmations of the quantum predictions—recognized by the 2022 Nobel Prize in Physics—have reinforced the prevailing conclusion that nature is nonlocal. In sharp contrast with this orthodoxy, I show how unitary quantum theory, formulated in the Heisenberg picture following Deutsch and Hayden, provides a fully local explanation. The talk is based on my recent work: https://doi.org/10.1098/rspa.2025.0553
Professeur, Université de Sherbrooke
Ancilla-Free Quantum Protocol for Thermal Green’s Functions
Green’s functions are fundamental tools for probing strongly interacting many-body systems. They provide a compact description of particle and excitation propagation without requiring explicit wave function representations, and they encode key information about the density of states and band structure—quantities that underlie phenomena such as superconductivity, magnetism, and phase transitions. However, accurately computing Green’s functions remains a notoriously difficult task for classical computers.
In this talk, I will present a simple and noise-resilient quantum algorithm for computing both zero- and finite-temperature Green’s functions. The method requires no ancillas and relies solely on native time evolution and measurements readily available on current quantum hardware. By exploiting parity symmetry—a property satisfied by a broad class of Hamiltonians in condensed matter physics and quantum chemistry, including the Fermi–Hubbard and Heisenberg models—we construct symmetric and antisymmetric thermal states and employ a tailored quench-spectroscopy protocol to directly extract the real and imaginary parts of two-point time correlators. From these correlators, Green’s functions can be efficiently reconstructed. Moreover, the same framework extends naturally to the evaluation of out-of-time-order correlators (OTOCs).
Doctorante, Polytechnique Montréal
Directeur: Nicolas Quesada
Generation of few-mode photon triplets in waveguides and optical fibers
Photon triplet sources exhibit non-Gaussian features, a key property for applications in quantum computing and quantum information. However, spectral correlations can limit the performance and detection efficiency of these systems. Motivated by this observation, we present a theoretical analysis of the spectral properties of photon triplets generated through spontaneous third-order parametric down-conversion in waveguides. We discuss strategies to quantify such correlations and introduce key design considerations to minimize them using a dispersion engineering approach. We optimized the design of thin optical fibers using the identified criteria, finding a configuration compatible with few-mode operation. Our results show that generating spectrally decorrelated photon triplets is achievable with state-of-the-art experimental systems, a crucial step toward practical applications of photon triplet sources in quantum technologies.
Doctorant, Université de Sherbrooke
Directeur: Alexandre Blais
Quantum sensing with GKP states
In recent years, quantum metrology has seen rapid progress, and promises to significantly improve sensing capabilities for both applied and fundamental domains in physics, engineering, and biology. In all these applications, the limits of measurement sensitivity are set by the unavoidable noise in real experiments and, ultimately, by the laws of quantum mechanics. Crucially, when noise is ignored, theory predicts that quantum sensing strategies can substantially outperform classical ones. When noise is considered, however, the advantage gained by the quantum strategies over classical ones can be lost and is only preserved under specific constraints, either of time, number of probes, or type of noise. Quantum error correction can enhance the achievable accuracy of metrology protocols in the presence of noise, and its implementation is the subject of current research.
In this talk, we will introduce the basic concepts of quantum metrology for a broad physics audience. Then, we present in detail how GKP states can be used for quantum metrology, and in particular how stabilizing protocols can be used for the sensing of both quadrature displacements approaching the quantum bound of sensitivity. Finally, we give an outlook on the future of the field.
Doctorant, Université de Sherbrooke
Directeur: Baptiste Royer
Decoding Multimode Gottesman-Kitaev-Preskill Codes with Noisy Auxiliaries
In order to achieve fault-tolerant quantum computing, we make use of quantum error correction schemes designed to protect the logical information of the system from decoherence. A promising way to preserve such information is using the multimode Gottesman-Kitaev-Preskill (GKP) encoding, which encodes a single logical qubit into harmonic oscillators. This type of encoding adds redundancy in the physical system by leveraging the infinitely large Hilbert space of multiple oscillators. Such redundancy can be used to increase the distance between the logical code words, protecting the logical qubit against larger errors. Usual protocols to correct multimode GKP states are based on Steane-type quantum error correction circuits. Steane-type circuits consist of auxiliary state preparation, two-mode squeezing operations, measurements and decoding. In this work, we focus on the decoding part of these protocols. More precisely, we propose a decoder that considers the noise present on the auxiliary states. Specifically, we do so by tracking the correlations between errors on different modes spreading throughout the circuit which represents the Steane-type protocol. We show that leveraging the correlations between the measurement result and the actual error affecting the multimode GKP state enables less decoding errors. Overall, for each different multimode GKP code studied, we can increase the lifetime by at least an order of magnitude, yielding more robust quantum computation.
Doctorant, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
Quantum kernel methods (QKMs) offer an appealing framework for machine learning on near-term quantum computers. However, QKMs generically suffer from exponential concentration, requiring an exponential number of measurements to resolve the kernel values, with the exception of trivial (i.e., classically simulable) kernels. Here we propose a QKM that is free of exponential concentration yet remains hard to simulate classically. Our QKM utilizes the weak ergodicity-breaking many-body dynamics in the Rydberg blockade of coherently driven neutral atom arrays. We demonstrate the fundamental properties of our QKM by analytically solving an approximate toy model of its underpinning quantum dynamics, as well as by extensive numerical simulations on randomly generated datasets. We further show that the proposed kernel exhibits effective learning on real data. The proposed QKM can be implemented in current neutral atom quantum computers.
Postdoc, Université de Montréal
Directeur: Gilles Brassard
Restoring locality: The Heisenberg picture as a separable description
Local realism has been the subject of much discussion in modern physics, partly because our deepest theories of physics appear to contradict one another in regard to whether reality is local. According to general relativity, it is, as physical quantities (perceptible or not) in two spacelike separated regions cannot affect one another. Yet, in quantum theory, it has traditionally been thought that local realism cannot hold and that such effects do occur. This apparent discrepancy between the two theories is resolved by Everettian quantum theory, as first proven by Deutsch & Hayden. In this talk, I will explain how local realism is respected in quantum theory and review the advances in our understanding of locality since Deutsch & Hayden’s work, including the more general analysis by Raymond-Robichaud.
Professionel, Polytechnique Montréal
Directeur: Denis Seletskiy
Nonlinear pulse shaper for spectro-temporal light engineering
We present a nonlinear pulse shaping platform that enables advanced dispersion and nonlinear engineering beyond the limits of conventional linear modulation. By introducing a new degree of freedom—fractional dispersion—within a nonlinear medium, we explore pulse dynamics governed by the fractional nonlinear Schrödinger equation. Building on this concept and integrating physics-embedded deep learning and high nonlinear fiber, we achieve high-fidelity control over complex spectral–temporal shaping of supercontinuum and few-cycle light states. This nonlinear pulse shaper provides a powerful tool for programmable waveform synthesis and opens new pathways for tailored light generation and control in ultrafast optics, nonlinear dynamics, and quantum photonics.
Professeure, Université McGill
Kitaev chains of fermions and bosons
In the first part of the talk, I will survey some recent results on shuttling Majorana fermions on wires and errors associated with disorder and noise. The second part will be devoted to bosonic Kitaev chain and its surprising Non-Hermitian connection.
Doctorant, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
Spin qubit Singlet-Triplet readout on a CMOS device made from a 300mm integrated process
Étudiant à la maîtrise, Université McGill
Directeur: Kai Wang
Optimization of Gaussian States for Twin-Field QKD
We investigate the use of squeezed displaced states in a twin-field-like quantum key distribution scheme. The interplay between squeezing and displacement in the squeezed displaced states allows for optimizing errors in two complementary bases, in contrast to one basis in the case of coherent states. We find that under special circumstances, the squeezed coherent states surpass coherent states and the superposition of vacuum and single-photon.
The states can be prepared unconditionally and are robust to losses that may open a way for more efficient and long-distance quantum key distribution schemes.
Étudiante à la maîtrise, Université de Sherbrooke
Directeur: Baptiste Royer
Bosonic Control and Error Correction with a Heavy Fluxonium Control Qubit
Bosonic quantum error-correcting codes offer a hardware-efficient avenue for QEC where information is encoded in the continuous phase-space of a single harmonic oscillator. The linear harmonic oscillator realised as the microwave modes of a superconducting cavity is controlled via a nonlinear superconducting control qubit.
Experiments on bosonic QEC are limited by bit flip errors in the control qubit, leading to low logical lifetimes of the storage cavity. Our idea is to replace the transmon with a heavy fluxonium qubit that has intrinsic protection against bit-flips. With this architecture in mind, we investigate the performance of a universal gateset, laying out the building blocks of an error-corrected bosonic quantum computer.
Étudiant à la maîtrise, Université Concordia
Directeur: Abhijeet Alase
The equilibrating behaviour of statistical systems
The many interpretations of the entropic principle leads us to believe that an abstract structure exists that can unify the different fields in which it appears. From thermodynamics and statistical mechanics, to information theory and machine learning, we are interested in the common qualities and quantities, and how we can use processes from one field in another. With this unification, we showed the well known thermodynamic relations with a simple dice simulation, even demonstrating the second law of thermodynamics in the process. We then demonstrate an important application to machine learning, specifically in the learning algorithm in Restricted Boltzmann machines. Using ideas from our previously formulated framework, we were able to recreate the phase transition in an Ising spin model system, by varying the hyperparameter related to temperature.
Doctorant, Université de Sherbrooke
Directeur: Max Hofheinz
Titre à venir
Doctorant, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
3D simulation of charge defect impact on an industrial 28 nm FD-SOI quantum dot
The emergence of cryo-electronics and quantum applications has shown that experiments involving quantum dots are highly sensitive to disorder and variability. This sensitivity offers the opportunity to detect and classify defects, evaluate process quality in detail, and guide the enhancement of robustness. We explore the 3D quantum simulation of an industrial FD-SOI quantum dot device, with and without a charge defect.
Doctorant, Université McGill
Directrice: Tami Pereg-Barnea
Titre à venir
Doctorant, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
Titre à venir
Doctorant, Université McGill
Directrice: Tami Pereg-Barnea
Lyapunov exponents in disordered non-Hermitian models
The topological origin of skin states in translation-invariant non-Hermitian systems has been established for a few years. Yet, a rigorous extension to disordered systems has remained elusive. In this work, we develop a comprehensive topological framework using the Lyapunov exponent for fully general Hatano-Nelson chains with disordered complex-valued potentials and nearest-neighbor hopping. Our approach unifies the theory of non-Hermitian Anderson localization with topologically protected directional amplification, thereby extending the bulk-boundary correspondence to a broad class of one-dimensional non-Hermitian systems. Our work opens new directions for disorder-resilient transport in photonic, optomechanical and superconducting platforms.
Doctorant, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
Titre à venir
Doctorant, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
Quantifying Material Losses in Superconducting Qubits with Microwave Resonators
Stagiaire, Université McGill
Directeur: Michael Hilke
Thermal Reorientation and Raman Signatures of Isotopically Labeled Bilayer Graphene
Graphene, a two-dimensional material composed of carbon atoms arranged in a single-layer honeycomb lattice, exhibits exceptional electronical and mechanical properties. In this study, we fabricate twisted bilayer graphene with different carbon isotopes (¹²C and ¹³C) using chemical vapor deposition (CVD). The use of isotopically distinct layers enables clear identification via Raman spectrsocopy. Upon annealing the stacked graphene from 21 °C to 250 °C, we observe an irreversible change in interlayer orientation. An increase in the relative intensity of the middle 2D′ peak (3190 cm⁻¹) in the same sampled region suggests enhanced interlayer coupling and a reorientation toward Bernal (AB) stacking. These results demonstrate how thermal treatment can be used to tune the stacking configuration in bilayer graphene.
Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Baptiste Royer
Titre à venir
Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Baptiste Royer
GKP magic state preparation with a Kerr interaction
Magic state distillation and injection is a promising strategy towards universal fault tolerant quantum computation, especially in architectures based on the bosonic Gottesman-Kitaev-Preskill (GKP) codes where non-Clifford gates remain challenging to implement. Here we address GKPmagic state preparation by studying a non-Gaussian unitary mediated by a Kerr interaction which realizes a logical gate √H_L for square GKP codes. This gate does not directly involve an auxiliary qubit and is compatible with finite energy constraints on the code. Fidelity can be further enhanced using the small-Big-small (SBS) error correction protocol and post-selection, making the scheme robust against a single photon loss event. We finally propose a circuit QED implementation to operate the Kerr interaction.
Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Mathieu Juan
Vers une transduction quantique efficace: optimisation du couplage magnétique dans un système magnéto-opto-mécanique
Une des façons d'arriver à bâtir un réseau quantique est en connectant, avec des fibres optiques, différents ordinateurs quantiques entre eux. Pour que le signal utilisé dans le frigo à dilution survive au voyage extérieur, il faut pouvoir changer son régime de fréquence ; principe appelé la transduction. Pour ce faire, un dispositif constitué d'un cantilever (système mécanique) portant un aimant (système magnétique) interagissant avec une boucle SQUID supraconductrice (système optique) est une première étape pour y arriver. Il faut ensuite pouvoir mesurer une signature mécanique de ce système, ce qui se révèle plus complexe. Le but de ce projet est d'explorer plusieurs paramètres d'optimisation pour rendre une lecture mécanique possible, que ce soit en contrôlant la distance entre l'aimant et la boucle, la taille et position de l'aimant, ou en contrôlant la nature même de l'aimant. Ces possibles optimisations constituent une étape clé vers la mise au point d’un transducteur efficace pour la communication quantique.
Doctorant, Université de Sherbrooke
Directeur: Bertrand Reulet
Titre à venir
Doctorant, Université McGill
Directeur: Hong Guo
Alloy Disorder and Partial Order Effects on the Bowing Parameter and Resistivity of CdZnTe Semiconductors
Cd1–xZnxTe (CZT) is an important semiconductor for applications in radiation detectors. As different concentrations of Zn, x, is alloyed into the CdTe crystal, the band gap of CZT varies with x which can be described by a bowing parameter b that is independent of x. For CZT alloys, however, the measured b appears to have a full range of values, from very small to near unity, across CZT samples fabricated by different methods, experimental conditions, and labs. Such a large variation most likely reflects the microscopic details of the CZT atomic structures. In this work, we theoretically investigated atomic arrangements in the CZT on the bowing parameter by first principles modeling and found that the large variation in the bowing parameter may arise from uneven atomic distributions in partially ordered configurations. Such configurations represent intermediate states between fully disordered and fully ordered alloy structures. In particular, the completely randomized Zn distribution gives rise to small bowing parameters, and the partially ordered structures tend to produce much higher bowing. By comparing ZnTe/CdTe interface models with completely disordered models, this work provides valuable insights into the relationship between atomic arrangements, atomic-scale inhomogeneity, and the electronic properties of CZT. Finally, the disorder-limited resistivities of the CZT alloy models are calculated and compared.
Stagiaire, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Titre à venir
Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Mathieu Juan
Titre à venir
Master student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
Characterization and Modeling of Superconducting Spiral and Linear Inductors
Radio-frequency reflectometry is a fast, sensitive and multiplexable readout technique for spin qubits. It relies on LC resonant circuits whose performance highly depends on accurate impedance matching and resonant frequency control. This poster presents the characterization of superconducting spiral and linear inductors and the development of a model linking their inductance to geometric parameters. Higher-order resonance modes were also observed, offering promising opportunities for optimizing impedance matching in high frequency-measurement circuits over a wide bandwidth.
Stagiaire, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Titre à venir
Doctorant, Université McGill
Directeur: Bill Coish
Multiparameter estimation for spin qubits with information amplification
Efficient Hamiltonian parameter estimation protocols are needed to calibrate spin qubits in semiconductor quantum dot devices. For example, two parameters (the strength of the exchange interaction and an Overhauser field gradient) must be estimated before performing a two-qubit gate for Loss-DiVincenzo (spin-½) qubits to achieve good performance. For hole-spin qubits, determining g-tensor elements is another relevant multiparameter estimation problem. We construct and analyze a protocol for information amplification that is applicable to general multiparameter estimation problems. Non-amplified strategies involve successive preparations, free evolutions, and measurements to estimate, e.g., the exchange and Overhauser gradient. In contrast, we consider a protocol involving a sequence of interlaced unitaries that amplifies information about the parameters to be estimated, in direct analogy with noise spectroscopy, where specific Fourier components of the noise spectral density can be amplified through a sequence of pi-pulses. A comparison between the entropy (parameter uncertainty) achieved through amplified and non-amplified protocols is given in Fig. 1. Entropy is favored over the variance as a measure of uncertainty when the associated probability distributions are multi-modal.
Doctorant, Université McGill
Directrice: Tami Pereg-Barnea
Learning shadows to predict quantum ground state correlations
We introduce a variational scheme inspired by classical shadow tomography to compute ground state correlations of quantum spin Hamiltonians. Shadow tomography allows for efficient reconstruction of expectation values of arbitrary observables from a bag of repeated, randomized measurements, called snapshots, on copies of the state. The prescription allows one to infer expectation values of local observables using a number snapshots that scales polynomially with system size when measurements are performed in locally random bases. Turning this around, a bag of snapshots can be considered an efficient representation of the state , particularly for estimating low-weight observables, such as terms in a local Hamiltonian needed to estimate the energy. Inspired by this, we consider a variational scheme wherein a bag of parametrized snapshots is used to represent the putative ground state of a desired local spin Hamiltonian and optimized to lower the energy with respect to it. Additional constraints in the form of positivity of reduced density matrices, motivated by work in quantum chemistry, are employed to ensure compatibility of the predicted correlations with the underlying Hilbert space. Unlike reduced density matrix approaches, learning the underlying distribution of measurement outcomes allows one to further correlations beyond those in the constrained density matrix. We show, with numerical results, that the proposed variational method can be parallelized, is efficiently simulable, and yields a more complete description of the ground state.
Doctorant, Université de Sherbrooke
Directeur: Mathieu Juan
Vector magnet control for on-chip magnonics
Postdoc, Université McGill
Directrice: Tami Pereg-Barnea
Nanoscale defects as probes of time-reversal symmetry breaking
Nanoscale defects such as nitrogen-vacancy (NV) centers serve as highly sensitive and non-invasive probes of electromagnetic fields and their fluctuations in materials, enabling detailed characterization of underlying physical phenomena. Here, we discuss how NV centers can be utilized to probe time-reversal symmetry breaking (TRSB) in low-dimensional conductors. Specifically, we show that the difference in relaxation rates Γ_+ẑ and Γ_-ẑ of NV centers initialized in the spin states mₛ = +1 and mₛ = −1, respectively, and relaxing to the ground state mₛ = 0, provides a direct probe of TRSB. This effect arises due to an asymmetry in the fluctuation spectra of left- and right-circularly polarized electromagnetic fields generated by the material. More specifically, the difference in relaxation rates is proportional to the imaginary part of the wave-vector–dependent Hall conductivity, Im[σ_xy(q, ω)], and therefore offers a means to determine the Hall viscosity. This, in turn, can distinguish between candidate fractional quantum Hall states and provide insights into the pairing angular momentum of TRSB superconductors.
Doctorant, Polytechnique Montréal
Directeur: Nicolas Quesada
Efficient Simulation of Gaussian Boson Sampling
Simulating Gaussian boson sampling on a range of hardware, from laptops to multiple GPUs.
10:55 Opening remarks (Salon A)
11:00 Nathan Wiebe, Toronto University (Salon A)
Title to be announced
12:00 Lunch (Knowlton room)
13:30 Cunlu Zhou, Université de Sherbrooke (Salon A)
Ancilla-Free Quantum Protocol for Thermal Green’s Functions
14:15 Gisell L. Osrio, Polytechnique Montréal (Salon A)
Generation of few-mode photon triplets in waveguides and optical fibers
14:35 Marc-Antoine Roy, Université de Sherbrooke (Salon A)
Decoding Multimode Gottesman-Kitaev-Preskill Codes with Noisy Auxiliaries
14:55 Coffee break (Salon C)
15:25 Benjamin Brock, Université de Sherbrooke (Salon A)
Quantum Error Correction with High-dimensional Systems
16:30 Quantum Ecosystem session (Salon A)
- Guy-Philippe Nadon, École de technologie supérieure
QuantumETS - Stimuler l'informatique quantique à l'ÉTS
17:00 Poster session with refreshments (Salon C)
19:30 INTRIQ dinner (Knowlton room)
9:00 Amanda Seedhouse, CNRS, France (Salon A)
Strategies for noisy spin-based quantum computation
10:00 Shilong Liu, Polytechnique Montréal (Salon A)
Nonlinear pulse shaper for spectro-temporal light engineering
10:30 Coffee break (Salon C)
11:00 Charles Bédard, École de technologie supérieure (Salon A)
Explaining Bell Locally
11:30 Samuel Kuypers, Université de Montréal (Salon A)
Restoring locality: The Heisenberg picture as a separable description
12:00 Lunch (Knowlton room)
13:30 Juanita Bocquel, Université de Sherbrooke (Salon A)
Title to be announced
14:30 Lautaro Labarca, Université de Sherbrooke (Salon A)
Quantum sensing with GKP states
14:50 Coffee break (Salon C)
15:15 Tami Pereg-Barnea, McGill University (Salon A)
Kitaev chains of fermions and bosons
16:00 Ayana Sarkar and Martin Schnee, Université de Sherbrooke (Salon A)
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
16:30 Closing remarks (Salon A)
Researcher, CNRS, France
Strategies for noisy spin-based quantum computation
Single electron spins in silicon quantum dots offer a promising pathway to scalable quantum computing, leveraging compatibility with semiconductor technologies and the high tunability of electrons. However, the susceptibility of these qubits to noise remains a critical challenge. This seminar explores ongoing research into understanding and mitigating noise in spin qubit hardware, focusing on strategies to enhance qubit fidelity in a scalable manner.
Professor, Université de Sherbrooke
Quantum Error Correction with High-dimensional Systems
Professor, Université de Sherbrooke
Title to be annouced
Professor, Toronto University
Title to be announced
Master student, École de technologie supérieure
Director: Jacob Biamonte
QuantumETS - Stimuler l'informatique quantique à l'ÉTS
Gérez un club étudiant d'informatique quantique comporte plusieurs défis. Cette présentation abordera les différentes stratégies de QuantumETS pour engager la communauté étudiante de l'ÉTS, les différents projets de QuantumETS ainsi que ses succès.
Postdoc, Université de Sherbrooke
Director: Stéfanos Kourtis
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
Quantum kernel methods (QKMs) offer an appealing framework for machine learning on near-term quantum computers. However, QKMs generically suffer from exponential concentration, requiring an exponential number of measurements to resolve the kernel values, with the exception of trivial (i.e., classically simulable) kernels. Here we propose a QKM that is free of exponential concentration yet remains hard to simulate classically. Our QKM utilizes the weak ergodicity-breaking many-body dynamics in the Rydberg blockade of coherently driven neutral atom arrays. We demonstrate the fundamental properties of our QKM by analytically solving an approximate toy model of its underpinning quantum dynamics, as well as by extensive numerical simulations on randomly generated datasets. We further show that the proposed kernel exhibits effective learning on real data. The proposed QKM can be implemented in current neutral atom quantum computers.
Postdoc, École de technologie supérieure
Director: Claude Crépeau
Explaining Bell Locally
In the century-long history of quantum theory, Bell’s theorem stands out among the most thought-provoking results in its foundations. It reveals a conflict between the predictions of quantum mechanics and those permitted by local hidden-variable theories. Experimental confirmations of the quantum predictions—recognized by the 2022 Nobel Prize in Physics—have reinforced the prevailing conclusion that nature is nonlocal. In sharp contrast with this orthodoxy, I show how unitary quantum theory, formulated in the Heisenberg picture following Deutsch and Hayden, provides a fully local explanation. The talk is based on my recent work: https://doi.org/10.1098/rspa.2025.0553
Professor, Université de Sherbrooke
Ancilla-Free Quantum Protocol for Thermal Green’s Functions
Green’s functions are fundamental tools for probing strongly interacting many-body systems. They provide a compact description of particle and excitation propagation without requiring explicit wave function representations, and they encode key information about the density of states and band structure—quantities that underlie phenomena such as superconductivity, magnetism, and phase transitions. However, accurately computing Green’s functions remains a notoriously difficult task for classical computers.
In this talk, I will present a simple and noise-resilient quantum algorithm for computing both zero- and finite-temperature Green’s functions. The method requires no ancillas and relies solely on native time evolution and measurements readily available on current quantum hardware. By exploiting parity symmetry—a property satisfied by a broad class of Hamiltonians in condensed matter physics and quantum chemistry, including the Fermi–Hubbard and Heisenberg models—we construct symmetric and antisymmetric thermal states and employ a tailored quench-spectroscopy protocol to directly extract the real and imaginary parts of two-point time correlators. From these correlators, Green’s functions can be efficiently reconstructed. Moreover, the same framework extends naturally to the evaluation of out-of-time-order correlators (OTOCs).
PhD student, Polytechnique Montréal
Director: Nicolas Quesada
Generation of few-mode photon triplets in waveguides and optical fibers
Photon triplet sources exhibit non-Gaussian features, a key property for applications in quantum computing and quantum information. However, spectral correlations can limit the performance and detection efficiency of these systems. Motivated by this observation, we present a theoretical analysis of the spectral properties of photon triplets generated through spontaneous third-order parametric down-conversion in waveguides. We discuss strategies to quantify such correlations and introduce key design considerations to minimize them using a dispersion engineering approach. We optimized the design of thin optical fibers using the identified criteria, finding a configuration compatible with few-mode operation. Our results show that generating spectrally decorrelated photon triplets is achievable with state-of-the-art experimental systems, a crucial step toward practical applications of photon triplet sources in quantum technologies.
PhD student, Université de Sherbrooke
Director: Alexandre Blais
Quantum sensing with GKP states
In recent years, quantum metrology has seen rapid progress, and promises to significantly improve sensing capabilities for both applied and fundamental domains in physics, engineering, and biology. In all these applications, the limits of measurement sensitivity are set by the unavoidable noise in real experiments and, ultimately, by the laws of quantum mechanics. Crucially, when noise is ignored, theory predicts that quantum sensing strategies can substantially outperform classical ones. When noise is considered, however, the advantage gained by the quantum strategies over classical ones can be lost and is only preserved under specific constraints, either of time, number of probes, or type of noise. Quantum error correction can enhance the achievable accuracy of metrology protocols in the presence of noise, and its implementation is the subject of current research.
In this talk, we will introduce the basic concepts of quantum metrology for a broad physics audience. Then, we present in detail how GKP states can be used for quantum metrology, and in particular how stabilizing protocols can be used for the sensing of both quadrature displacements approaching the quantum bound of sensitivity. Finally, we give an outlook on the future of the field.
PhD student, Université de Sherbrooke
Director: Baptiste Royer
Decoding Multimode Gottesman-Kitaev-Preskill Codes with Noisy Auxiliaries
In order to achieve fault-tolerant quantum computing, we make use of quantum error correction schemes designed to protect the logical information of the system from decoherence. A promising way to preserve such information is using the multimode Gottesman-Kitaev-Preskill (GKP) encoding, which encodes a single logical qubit into harmonic oscillators. This type of encoding adds redundancy in the physical system by leveraging the infinitely large Hilbert space of multiple oscillators. Such redundancy can be used to increase the distance between the logical code words, protecting the logical qubit against larger errors. Usual protocols to correct multimode GKP states are based on Steane-type quantum error correction circuits. Steane-type circuits consist of auxiliary state preparation, two-mode squeezing operations, measurements and decoding. In this work, we focus on the decoding part of these protocols. More precisely, we propose a decoder that considers the noise present on the auxiliary states. Specifically, we do so by tracking the correlations between errors on different modes spreading throughout the circuit which represents the Steane-type protocol. We show that leveraging the correlations between the measurement result and the actual error affecting the multimode GKP state enables less decoding errors. Overall, for each different multimode GKP code studied, we can increase the lifetime by at least an order of magnitude, yielding more robust quantum computation.
PhD student, Université de Sherbrooke
Director: Stéfanos Kourtis
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
Quantum kernel methods (QKMs) offer an appealing framework for machine learning on near-term quantum computers. However, QKMs generically suffer from exponential concentration, requiring an exponential number of measurements to resolve the kernel values, with the exception of trivial (i.e., classically simulable) kernels. Here we propose a QKM that is free of exponential concentration yet remains hard to simulate classically. Our QKM utilizes the weak ergodicity-breaking many-body dynamics in the Rydberg blockade of coherently driven neutral atom arrays. We demonstrate the fundamental properties of our QKM by analytically solving an approximate toy model of its underpinning quantum dynamics, as well as by extensive numerical simulations on randomly generated datasets. We further show that the proposed kernel exhibits effective learning on real data. The proposed QKM can be implemented in current neutral atom quantum computers.
Postdoc, Université de Montréal
Director: Gilles Brassard
Restoring locality: The Heisenberg picture as a separable description
Local realism has been the subject of much discussion in modern physics, partly because our deepest theories of physics appear to contradict one another in regard to whether reality is local. According to general relativity, it is, as physical quantities (perceptible or not) in two spacelike separated regions cannot affect one another. Yet, in quantum theory, it has traditionally been thought that local realism cannot hold and that such effects do occur. This apparent discrepancy between the two theories is resolved by Everettian quantum theory, as first proven by Deutsch & Hayden. In this talk, I will explain how local realism is respected in quantum theory and review the advances in our understanding of locality since Deutsch & Hayden’s work, including the more general analysis by Raymond-Robichaud.
Professional, Polytechnique Montréal
Director: Denis Seletskiy
Nonlinear pulse shaper for spectro-temporal light engineering
We present a nonlinear pulse shaping platform that enables advanced dispersion and nonlinear engineering beyond the limits of conventional linear modulation. By introducing a new degree of freedom—fractional dispersion—within a nonlinear medium, we explore pulse dynamics governed by the fractional nonlinear Schrödinger equation. Building on this concept and integrating physics-embedded deep learning and high nonlinear fiber, we achieve high-fidelity control over complex spectral–temporal shaping of supercontinuum and few-cycle light states. This nonlinear pulse shaper provides a powerful tool for programmable waveform synthesis and opens new pathways for tailored light generation and control in ultrafast optics, nonlinear dynamics, and quantum photonics.
Professor, McGill University
Kitaev chains of fermions and bosons
In the first part of the talk, I will survey some recent results on shuttling Majorana fermions on wires and errors associated with disorder and noise. The second part will be devoted to bosonic Kitaev chain and its surprising Non-Hermitian connection.
PhD student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
Spin qubit Singlet-Triplet readout on a CMOS device made from a 300mm integrated process
Master student, McGill University
Director: Kai Wang
Optimization of Gaussian States for Twin-Field QKD
We investigate the use of squeezed displaced states in a twin-field-like quantum key distribution scheme. The interplay between squeezing and displacement in the squeezed displaced states allows for optimizing errors in two complementary bases, in contrast to one basis in the case of coherent states. We find that under special circumstances, the squeezed coherent states surpass coherent states and the superposition of vacuum and single-photon.
The states can be prepared unconditionally and are robust to losses that may open a way for more efficient and long-distance quantum key distribution schemes.
Master student, Université de Sherbrooke
Director: Baptiste Royer
Bosonic Control and Error Correction with a Heavy Fluxonium Control Qubit
Bosonic quantum error-correcting codes offer a hardware-efficient avenue for QEC where information is encoded in the continuous phase-space of a single harmonic oscillator. The linear harmonic oscillator realised as the microwave modes of a superconducting cavity is controlled via a nonlinear superconducting control qubit.
Experiments on bosonic QEC are limited by bit flip errors in the control qubit, leading to low logical lifetimes of the storage cavity. Our idea is to replace the transmon with a heavy fluxonium qubit that has intrinsic protection against bit-flips. With this architecture in mind, we investigate the performance of a universal gateset, laying out the building blocks of an error-corrected bosonic quantum computer.
Master student, Concordia University
Director: Abhijeet Alase
The equilibrating behaviour of statistical systems
The many interpretations of the entropic principle leads us to believe that an abstract structure exists that can unify the different fields in which it appears. From thermodynamics and statistical mechanics, to information theory and machine learning, we are interested in the common qualities and quantities, and how we can use processes from one field in another. With this unification, we showed the well known thermodynamic relations with a simple dice simulation, even demonstrating the second law of thermodynamics in the process. We then demonstrate an important application to machine learning, specifically in the learning algorithm in Restricted Boltzmann machines. Using ideas from our previously formulated framework, we were able to recreate the phase transition in an Ising spin model system, by varying the hyperparameter related to temperature.
PhD student, Université de Sherbrooke
Director: Max Hofheinz
Title to be announced
PhD student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
3D simulation of charge defect impact on an industrial 28 nm FD-SOI quantum dot
The emergence of cryo-electronics and quantum applications has shown that experiments involving quantum dots are highly sensitive to disorder and variability. This sensitivity offers the opportunity to detect and classify defects, evaluate process quality in detail, and guide the enhancement of robustness. We explore the 3D quantum simulation of an industrial FD-SOI quantum dot device, with and without a charge defect.
PhD student, McGill University
Director: Tami Pereg-Barnea
Title to be announced
PhD student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
Title to be announced
PhD student, McGill University
Director: Tami Pereg-Barnea
Lyapunov exponents in disordered non-Hermitian models
The topological origin of skin states in translation-invariant non-Hermitian systems has been established for a few years. Yet, a rigorous extension to disordered systems has remained elusive. In this work, we develop a comprehensive topological framework using the Lyapunov exponent for fully general Hatano-Nelson chains with disordered complex-valued potentials and nearest-neighbor hopping. Our approach unifies the theory of non-Hermitian Anderson localization with topologically protected directional amplification, thereby extending the bulk-boundary correspondence to a broad class of one-dimensional non-Hermitian systems. Our work opens new directions for disorder-resilient transport in photonic, optomechanical and superconducting platforms.
PhD student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
Title to be announced
PhD student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
Quantifying Material Losses in Superconducting Qubits with Microwave Resonators
Intern, McGill University
Director: Michael Hilke
Thermal Reorientation and Raman Signatures of Isotopically Labeled Bilayer Graphene
Graphene, a two-dimensional material composed of carbon atoms arranged in a single-layer honeycomb lattice, exhibits exceptional electronical and mechanical properties. In this study, we fabricate twisted bilayer graphene with different carbon isotopes (¹²C and ¹³C) using chemical vapor deposition (CVD). The use of isotopically distinct layers enables clear identification via Raman spectrsocopy. Upon annealing the stacked graphene from 21 °C to 250 °C, we observe an irreversible change in interlayer orientation. An increase in the relative intensity of the middle 2D′ peak (3190 cm⁻¹) in the same sampled region suggests enhanced interlayer coupling and a reorientation toward Bernal (AB) stacking. These results demonstrate how thermal treatment can be used to tune the stacking configuration in bilayer graphene.
Master student, Université de Sherbrooke
Director: Baptiste Royer
Title to be announced
Master student, Université de Sherbrooke
Director: Baptiste Royer
GKP magic state preparation with a Kerr interaction
Magic state distillation and injection is a promising strategy towards universal fault tolerant quantum computation, especially in architectures based on the bosonic Gottesman-Kitaev-Preskill (GKP) codes where non-Clifford gates remain challenging to implement. Here we address GKPmagic state preparation by studying a non-Gaussian unitary mediated by a Kerr interaction which realizes a logical gate √H_L for square GKP codes. This gate does not directly involve an auxiliary qubit and is compatible with finite energy constraints on the code. Fidelity can be further enhanced using the small-Big-small (SBS) error correction protocol and post-selection, making the scheme robust against a single photon loss event. We finally propose a circuit QED implementation to operate the Kerr interaction.
Master student, Université de Sherbrooke
Director: Mathieu Juan
Vers une transduction quantique efficace: optimisation du couplage magnétique dans un système magnéto-opto-mécanique
Une des façons d'arriver à bâtir un réseau quantique est en connectant, avec des fibres optiques, différents ordinateurs quantiques entre eux. Pour que le signal utilisé dans le frigo à dilution survive au voyage extérieur, il faut pouvoir changer son régime de fréquence ; principe appelé la transduction. Pour ce faire, un dispositif constitué d'un cantilever (système mécanique) portant un aimant (système magnétique) interagissant avec une boucle SQUID supraconductrice (système optique) est une première étape pour y arriver. Il faut ensuite pouvoir mesurer une signature mécanique de ce système, ce qui se révèle plus complexe. Le but de ce projet est d'explorer plusieurs paramètres d'optimisation pour rendre une lecture mécanique possible, que ce soit en contrôlant la distance entre l'aimant et la boucle, la taille et position de l'aimant, ou en contrôlant la nature même de l'aimant. Ces possibles optimisations constituent une étape clé vers la mise au point d’un transducteur efficace pour la communication quantique.
PhD student, Université de Sherbrooke
Director: Bertrand Reulet
Title to be announced
PhD student, McGill University
Director: Hong Guo
Alloy Disorder and Partial Order Effects on the Bowing Parameter and Resistivity of CdZnTe Semiconductors
Cd1–xZnxTe (CZT) is an important semiconductor for applications in radiation detectors. As different concentrations of Zn, x, is alloyed into the CdTe crystal, the band gap of CZT varies with x which can be described by a bowing parameter b that is independent of x. For CZT alloys, however, the measured b appears to have a full range of values, from very small to near unity, across CZT samples fabricated by different methods, experimental conditions, and labs. Such a large variation most likely reflects the microscopic details of the CZT atomic structures. In this work, we theoretically investigated atomic arrangements in the CZT on the bowing parameter by first principles modeling and found that the large variation in the bowing parameter may arise from uneven atomic distributions in partially ordered configurations. Such configurations represent intermediate states between fully disordered and fully ordered alloy structures. In particular, the completely randomized Zn distribution gives rise to small bowing parameters, and the partially ordered structures tend to produce much higher bowing. By comparing ZnTe/CdTe interface models with completely disordered models, this work provides valuable insights into the relationship between atomic arrangements, atomic-scale inhomogeneity, and the electronic properties of CZT. Finally, the disorder-limited resistivities of the CZT alloy models are calculated and compared.
Intern, Université de Sherbrooke
Director: Stéfanos Kourtis
Title to be announced
Master student, Université de Sherbrooke
Director: Mathieu Juan
Title to be announced
PhD Student, McGill University
Director: Bill Coish
Multiparameter estimation for spin qubits with information amplification
Efficient Hamiltonian parameter estimation protocols are needed to calibrate spin qubits in semiconductor quantum dot devices. For example, two parameters (the strength of the exchange interaction and an Overhauser field gradient) must be estimated before performing a two-qubit gate for Loss-DiVincenzo (spin-½) qubits to achieve good performance. For hole-spin qubits, determining g-tensor elements is another relevant multiparameter estimation problem. We construct and analyze a protocol for information amplification that is applicable to general multiparameter estimation problems. Non-amplified strategies involve successive preparations, free evolutions, and measurements to estimate, e.g., the exchange and Overhauser gradient. In contrast, we consider a protocol involving a sequence of interlaced unitaries that amplifies information about the parameters to be estimated, in direct analogy with noise spectroscopy, where specific Fourier components of the noise spectral density can be amplified through a sequence of pi-pulses. A comparison between the entropy (parameter uncertainty) achieved through amplified and non-amplified protocols is given in Fig. 1. Entropy is favored over the variance as a measure of uncertainty when the associated probability distributions are multi-modal.
Master student, Université de Sherbrooke
Director: Eva Dupont-Ferrier
Characterization and Modeling of Superconducting Spiral and Linear Inductors
Radio-frequency reflectometry is a fast, sensitive and multiplexable readout technique for spin qubits. It relies on LC resonant circuits whose performance highly depends on accurate impedance matching and resonant frequency control. This poster presents the characterization of superconducting spiral and linear inductors and the development of a model linking their inductance to geometric parameters. Higher-order resonance modes were also observed, offering promising opportunities for optimizing impedance matching in high frequency-measurement circuits over a wide bandwidth.
Undergrade intern, Université de Sherbrooke
Director: Stéfanos Kourtis
Title to be announced
PhD student, McGill University
Director: Tami Pereg-Barnea
Learning shadows to predict quantum ground state correlations
We introduce a variational scheme inspired by classical shadow tomography to compute ground state correlations of quantum spin Hamiltonians. Shadow tomography allows for efficient reconstruction of expectation values of arbitrary observables from a bag of repeated, randomized measurements, called snapshots, on copies of the state. The prescription allows one to infer expectation values of local observables using a number snapshots that scales polynomially with system size when measurements are performed in locally random bases. Turning this around, a bag of snapshots can be considered an efficient representation of the state , particularly for estimating low-weight observables, such as terms in a local Hamiltonian needed to estimate the energy. Inspired by this, we consider a variational scheme wherein a bag of parametrized snapshots is used to represent the putative ground state of a desired local spin Hamiltonian and optimized to lower the energy with respect to it. Additional constraints in the form of positivity of reduced density matrices, motivated by work in quantum chemistry, are employed to ensure compatibility of the predicted correlations with the underlying Hilbert space. Unlike reduced density matrix approaches, learning the underlying distribution of measurement outcomes allows one to further correlations beyond those in the constrained density matrix. We show, with numerical results, that the proposed variational method can be parallelized, is efficiently simulable, and yields a more complete description of the ground state.
PhD student, Université de Sherbrooke
Director: Mathieu Juan
Vector magnet control for on-chip magnonics
Postdoc, McGill University
Director: Tami Pereg-Barnea
Nanoscale defects as probes of time-reversal symmetry breaking
Nanoscale defects such as nitrogen-vacancy (NV) centers serve as highly sensitive and non-invasive probes of electromagnetic fields and their fluctuations in materials, enabling detailed characterization of underlying physical phenomena. Here, we discuss how NV centers can be utilized to probe time-reversal symmetry breaking (TRSB) in low-dimensional conductors. Specifically, we show that the difference in relaxation rates Γ_+ẑ and Γ_-ẑ of NV centers initialized in the spin states mₛ = +1 and mₛ = −1, respectively, and relaxing to the ground state mₛ = 0, provides a direct probe of TRSB. This effect arises due to an asymmetry in the fluctuation spectra of left- and right-circularly polarized electromagnetic fields generated by the material. More specifically, the difference in relaxation rates is proportional to the imaginary part of the wave-vector–dependent Hall conductivity, Im[σ_xy(q, ω)], and therefore offers a means to determine the Hall viscosity. This, in turn, can distinguish between candidate fractional quantum Hall states and provide insights into the pairing angular momentum of TRSB superconductors.
PhD student, Polytechnique Montréal
Director: Nicolas Quesada
Efficient Simulation of Gaussian Boson Sampling
Simulating Gaussian boson sampling on a range of hardware, from laptops to multiple GPUs.