Programme

‍15 octobre

10h55 - 11h00 Mot d'ouverture (Salon A)

11h00 - 12h00 Daniel Higgenbottom, Simon Fraser University (Salon A)

                         Networking silicon qubits

12h00 - 13h30 Dîner (Salle Knowlton)

13h30 - 14h15 Evgeny Moiseev, Université McGill (Salon A)

                        Tutoriel: Squeezed light generation: from classical to unconventional methods

14h15 - 14h45 Michael Hilke, Université McGill (Salon A)

                        The experimental tale of quantum computers

14h45 - 15h15 Pause-café (Salon C)

15h15 - 16h15 Quantum Question Box: The questions you always wanted to ask! (Salon A)

16h15 - 17h00 Quantum Ecosystem in Québec (Salon A)

                         Juliette Goeffrion, Calcul Québec - Introducing MonarQ : a quantum computer dedicated to research

                         Michael McGuffin, ÉTS - Some Visual Approaches to Quantum Computing

‍17h00 - 19h00 Session d'affiches et rafraîchissements (Salon C)

19h30 -             Souper INTRIQ (Salle Knowlton)

16 octobre

  9h00 - 10h00 Sarah Sheldon, IBM Quantum (Salon A)

                         Entering the era of quantum utility: what can you do with 100 qubits?

10h00 - 10h30 Pause-café (Salon C)

10h30 - 11h30 Gilles Brassard, Université de Montréal (Salon A)

                         Quantum cryptography from its humble origins to its glorious future

11h30 - 11h45 Nicolas Dalbec-Constant, Polytechnique Montréal

                         Nonlinear Dimensionality Reduction for Enhanced Unsupervised Classification in Transition Edge Sensors

11h45 - 12h00 Martin Houde, Polytechnique Montréal (Salon A)

                         Gain-induced group delay in spontaneous parametric down-conversion

12h00 - 13h30 Dîner (Salle Knowlton)

13h30 - 14h30 Présentation de projets INTRIQ (Salon A)

                          Mathieu Juan - Helium battery & vibration isolation for single-photon optomechanics

                          Bill Truong- Creating, manipulating and protecting Majorana fermions

                          Gurleen Padda - Prior-Free Amortized Quantum Communication Complexity

                          Michael Hilke - Qubits, Topology and Quantum Computing

                          Philippe St-Jean - Photonic Topological quantum walks in noisy environments

14h30 - 15h00 Pause-Café (Salon C)

15h00 - 16h00 Samuel Boutin, Microsoft Quantum (Salon A)

                         Interferometric Single-Shot Parity Measurement in InAs-Al Hybrid Devices

16h00 - 16h30 Denis Seletskiy, Polytechnique Montréal (Salon A)

                         Bright quantum light as a resource for quantum metrology

16h30               Mot de fermeture (Salon A)

‍

Conférenciers invités

Daniel Higginbottom

Simon Fraser University
Networking silicon qubits
Distributed quantum processing over local optical networks is a route to fault-tolerant quantum computing at scale and practical quantum advantage. The performance of modular, networked quantum technologies will, however, be contingent upon the quality of their light-matter interconnects. Silicon colour centres offer optically-coupled spin qubit registers as the basis for quantum networks and distributed quantum computing. Silicon is an ideal platform for commercial quantum technologies: it unites advanced photonics and microelectronics, as well as hosting long-lived spin qubits. The silicon T centre was recently discovered to combine direct telecommunications-band photonic emission, long-coherence electron and nuclear spins, and proven integration into industry-standard, CMOS-compatible, silicon-on-insulator (SOI) photonic chips at scale. In this talk I review the challenges of modular quantum computing, recent progress developing T centre devices, and present the first demonstration of entanglement between remote silicon quantum processors over an optical network.

Samuel Boutin

Microsoft Quantum
Interferometric Single-Shot Parity Measurement in InAs-Al Hybrid Devices
The fusion of non-Abelian anyons or topological defects is a fundamental operation in measurement-only topological quantum computation. In topological superconductors, this operation amounts to a determination of the shared fermion parity of Majorana zero modes. In this presentation, I will review recent work from Microsoft Quantum [1] on a device architecture that is compatible with future tests of these fusion rules. Using this architecture, we implement a single-shot interferometric measurement of fermion parity in indium arsenide-aluminum heterostructures with a gate-defined superconducting nanowire.

[1] https://arxiv.org/abs/2401.09549

Sarah Sheldon

IBM Quantum
Entering the era of quantum utility: what can you do with 100 qubits?
The proven speedups of canonical quantum algorithms over their classical counterparts have motivated work towards realizing quantum computers. To achieve these speedups we need fault tolerance, which is out of reach on today’s quantum hardware. At the same time, state-of-the-art noisy quantum systems are approaching a scale and quality that is hard to simulate classically. These systems allow us to explore applications of quantum computers at a scale that was previously inaccessible and to develop heuristic methods for evaluating new quantum algorithms. At the same time error corrected systems are on the horizon, increasing the need for developing algorithms for early fault-tolerance. This talk will describe using quantum computers to study interesting problems in the near-term with error suppression and error mitigation techniques, including recent 100+ qubits experiments run on IBM Quantum systems. These first demonstrations offer insights into the types of circuits we can run successfully on quantum computers and the types of problems we will be able to access. This talk will also outline the need for quantum algorithms development and testing on near term hardware and discuss the work being done to realize useful quantum computing for different application areas.

Conférenciers de l'écosystème

Juliette Geoffrion

Analyste en informatiquequantique, Calcul Québec
Introducing MonarQ : a quantum computer dedicated to research
MonarQ, a 24-qubit superconducting quantum computer, will soon be operational at Calcul Québec. This presentation will introduce MonarQ and its integration into Calcul Québec’s existing HPC resources. We will highlight the diverse projects this cutting-edge resource can support, along with the comprehensive support Calcul Québec can offer to assist researchers in utilizing our classical and quantum resources.

Michael McGuffin

Professeur, École de technologie supérieure
Some Visual Approaches to Quantum Computing
This talk will survey a few examples from previous work of ways to visualize processes in quantum computing.  Then I'll present a drag-and-drop software prototype for simulating quantum circuits that visualizes the evolution of the state vector and the entanglement between qubits.  I'll also point out some design strategies for information visualization that might be useful in other projects.

Conférenciers INTRIQ

Denis Seletskiy

Professeur, Polytechnique Montréal
Bright quantum light as a resource for quantum metrology
Quantum light is most commonly associated with one or few-photon events, often represented as discrete electromagnetic clumps of energy with well-defined frequency. In this talk I will review our recent advances in the generation and applications of ultrabroad (few-optical-cycle) bright quantum light. The focus on the time-domain perspective, combined with macroscopic amplitudes of quantum fields, unlocks novel possibilities. Following an introduction on the generation of such light, I will highlight two such possibilities: ability of quantum light to 1) drive light-matter interaction into the non-perturbative regime [1]; and 2) exhibit "temporal phase" (formally carrier-envelope phase) correlations, opening avenue to post-selection schemes of non-Gaussian quantum states of light [2].

Bright quantum light is becoming a promising resource for novel quantum metrologies!

[1] A. Rasputnyi et al., High Harmonic Generation by Bright Squeezed Vacuum, arXiv:2403.15337 (2024).

[2] P. Cusson et al,. Carrier-Envelope Phase Correlations in Few-Cycle Bright Twin Beams, 23rd International Conference on Ultrafast Phenomena Th- 4A.4C (2024).

Evgeny Moiseev

Postdoc, Université McGill
Directeur: Kai Wang
Tutorial - Squeezed light generation: from classical to unconventional methods
Squeezed states of light play a crucial role in various fields of physics, from extreme precise sensing to quantum computations. Many platforms, from ultra-cold gases to mechanical oscillators, have generated squeezed light since its discovery. In this tutorial, I will cover an overview of squeezed light and their unique properties, with an emphasis on experimental methods, techniques, and the challenges involved in generating them.

Gilles Brassard

Professeur, Université de Montréal
Quantum cryptography from its humble origins to its glorious future

Martin Houde

Postdoc, Polytechnique Montréal
Directeur: Nicolas Quesada
Gain-induced group delay in spontaneous parametric down-conversion
Strongly-driven nonlinear optical processes such as spontaneous parametric down-conversion can produce multiphoton nonclassical beams of light which have applications in quantum information processing and sensing. In contrast to the low-gain regime, new physical effects arise in a high-gain regime due to the interactions between the nonclassical light and the strong pump driving the nonlinear process. In this talk, we describe and experimentally observe a gain-induced group delay between the multiphoton pulses generated in a high-gain type-II spontaneous parametric down-conversion source. Since the group delay introduces distinguishability between the generated photons, it will be important to compensate for it when designing quantum interference devices in which strong optical nonlinearities are required.

Michael Hilke

Professeur: McGill University
The experimental tale of quantum computers

Nicolas Dalbec-Constant

Étudiant à la maîtrise, Polytechnique Montréal
Directeur: Nicolas Quesada
Nonlinear Dimensionality Reduction for Enhanced Unsupervised Classification in Transition Edge Sensors
We compare methods for signal classification applied to voltage traces from transition edge sensors (TES) which are photon-number resolving detectors fundamental for accessing quantum advantages in information processing, communication and metrology. We quantify the impact of numerical analysis on the distinction of such signals. Furthermore, we explore dimensionality reduction techniques to create interpretable and precise photon number embeddings. We demonstrate that the preservation of local data structures of some nonlinear methods is an accurate way to achieve unsupervised classification of TES traces. We do so by considering the Confidence that quantifies the overlap of the signal's probability distribution inside an embedding. We demonstrate that for our dataset previous methods like the signal's area and principal component analysis (PCA) can resolve up to 16 photons with Confidence above 90% while nonlinear can resolve up to 21 with the same confidence threshold. We also showcase implementations of neural networks to leverage information within local structures, aiming to increase confidence in assigning photon numbers. Finally, we demonstrate the advantage of some nonlinear methods to detect and remove outlier signals.

‍

Affiches

Aashutosh Kumar

Postdoc, École de technologie supérieure
Director: Bora Ung
Radio-Frequency Excitation for Quantum Sensing Based on Diamond NV Center Using Coplanar Waveguide Transmission Lines

Alexandre Chénier

Doctorant, Université de Montréal
Directeur: Philippe St-Jean
Titre à venir

Alexis Morel

Doctorant, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
Titre à venir

Arthur Dupré

Étudiant à la maîtrise, Université de Montréal
Directeur: Philippe St-Jean
Understanding the statistical fluctuations of a photonic field
Measuring the statistical fluctuation of an observable is done through the calculation of statistical cumulants, such as the variance. Recently, several theoretical works have shown that these statistical cumulants depend on the geometry of the sub-region of space in which they are measured. The aim of this research project is to build a quantum imaging setup for studying the evolution of intensity fluctuations in a photonic field. The first part of the project is to build a set-up for imaging one and only one pulse of entangled photons. The second is to analyze the spatial fluctuations of these single pulses. This will enable us to study the transition from the classical, Gaussian regime to the quantum, poissonian or sub-poissonian regime, and to investigate the emergence of universal laws describing the evolution of statistical cumulants. This project will provide the technical means to study the transition between the classical and quantum worlds, based on the statistical properties of measured fluctuations.

Ayana Sarkar

Postdoc, Université de Sherbrooke
Directeur: Stéfanos Kourtis
New Avenues in the Exploration of SVD Entanglement Entropy
In a recent work by Parzygnat, Takayanagi, Taki, et al. [J. High Energ. Phys. 2023, 123 (2023)], introduced a novel entanglement measure termed "SVD entanglement entropy (SVD EE)," which generalizes the standard entanglement entropy by incorporating two distinct quantum states to construct "reduced transition matrices," based on pre- and post-selection of these eigenstates. Mathematically, SVD EE extends the von Neumann entropy from density matrices to arbitrary square matrices. In the framework of quantum information, the SVD EE can be interpreted as the average number of Bell pairs distillable from intermediate states. It was also demonstrated in this work, using the transverse-field Ising model, that SVD EE increases when the two states reside in different quantum phases, suggesting its utility as a potential measure for detecting quantum phase transitions in many-body systems. Building on these foundations, we extend the investigation of SVD EE into three previously unexplored directions. First, we aim to establish a connection between the local unitary framework of SVD EE and random matrix theory, specifically through the Bures-Hall ensemble of density matrices—a context that, to the best of our knowledge, remains unexplored. Second, we explore the application of SVD EE in detection of exceptional points in the spectra of non-Hermitian quantum many-body systems. Exceptional points are special points in the parameter space where both eigenvalues and eigenstates coalesce. We begin with a simple PT-symmetric non-Hermitian Hamiltonian, performing exact analytical calculations for the SVD EE in these systems. Finally, we study the behavior of Renyi SVD EE in a paradigmatic quantum chaotic system, the coupled quantum kicked top, and compare it with known results for standard entanglement entropies.

Joint work  with Akshat Pandey, M.Sc Student, Institute for Theoretical Physics, KU Leuven. Celestijnenlaan 200D, B-3001 Leuven, Belgium.

Azin Aghdaei

Postdoc, Université de Montréal
Directeur: Philippe St-Jean
Titre à venir

Baptiste Monge

PhD student, Université de Sherbrooe
Director: Max Hofheinz
Directional Josephson Photonics
Making low-noise cryogenic amplifiers and isolators with microwave superconducting circuits is an active field of research. The key is to tune the circuit to a specific parametric process to give rise to amplification or frequency-conversion (isolation). We present here the ongoing project to elaborate an isolator with voltage-biased Josephson junctions in a superconducting transmission line.

Benjamin Lanthier

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Accelerating Counting Using Tensor Networks
Tensor networks are a versatile tool employed in numerous fields, spanning from classical quantum many-body system simulations to quantum circuit modeling. In this work, we'll discuss about the use of this method with p-spin models, a class of spin-glass systems, and investigate the connections between these physical systems and the SAT problem genre, more precisely  the #p-XORSAT problem. Our primary goal is to evaluate the effectiveness of tensor network contraction in evaluating the zero-temperature partition function of these systems, while examining how this efficacy varies with the number of interactions to spins ratio.

Bill Truong

Doctorant, Université McGill
Directrice: Tami Pereg-Barnea
Titre à venir

Clément Fortin

Doctorant, Université McGill
Directrice: Tami Pereg-Barnea
Non-Hermitian Topology of the Bosonic Kitaev Chain

Dominic Leclerc

Étudiant à la maîtrise, Université de Sherbrooke
Directrice: Eva Dupont-Ferrier
Cryogenic characterization of a 14 nm Nanosheet transistor for spin qubit co-integration
CMOS spin qubits are promising candidates for scaling up quantum computers due to their high coherence time and potential for co-integration with classical electronics (Cryo-CMOS) for control and read-out on the same chip. However, further investigation at cryogenic temperature of different CMOS architectures needs to be done. In this work, we present a cryogenic characterization of an industrial nMOS 14 nm Nanosheet transistor for potential spin qubit co-integration. We demonstrate that the device can be used as a classical transistor and a quantum dot at low temperatures. We show improved DC output characteristics when operating as a transistor at cryogenic temperature, excellent gate control in the quantum dot regime, and promising low level of charge noise.

Evgeny Moiseev

Postdoc, Université McGill
Directeur: Kai Wang
Connection between exceptional points and quantum non-demolishing measurements in bosonic quadratic systems
The presence of an exceptional point was considered to be an inclusive feature of systems described by effective non-Hermitian Hamiltonian. Recent research demonstrates that a fully Hermitian system with parametric gain, like single mode and two mode squeezing, encounters exceptional points. However, the physical manifestation of exceptional points in these systems is still an open question. We investigate the relationship between an exceptional point and the presence of quantum non-demolishing (QND) dynamics for quadrature operators in the dynamics of a general N-mode quadratic bosonic Hamiltonian. We derive necessary conditions for observing QND dynamics and point out when QND dynamics becomes an exceptional point.

Félix Pellerin

Doctorant, Université de Montréal
Directeur: Philippe St-Jean
Titre à venir

Felix-Gabriel Boucher-Luneau

Stagiaire, École de technologie supérieure
Directeur: Olivier Landon-Cardinal
Transpiler for MonarQ
MonarQ is a 24-qubits NISQ computer being installed at Calcul Québec, located at École de Technologie Supérieure in Montréal. The aim of the project is to design a transpiler for MonarQ using Pennylane. The the forementioned transpiler's goal is to enhance performance and ownership by reducing middleware layers and allowing extensibility over optimization and routing techniques.

François Cyrenne-Bergeron

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Max Hofheinz
Low noise amplification with a twist

Frédéric Boivin

Étudiant à la maîtrise, Université McGill
Directeur: Guillaume Gervais
Large Composite Fermion Effective Mass at Filling Factor 5/2
The growth of ultra-high mobility GaAs/Al-GaAs two-dimensional electron gas systems (2DEG) has opened a path for the exploration of a plethora of exotic quantum states. Notably, the fractional quantum Hall (FQH) effect arises when such a material is cooled to cryogenic temperatures and subjected to high magnetic fields. Among the sequence of composite fermion FQH states in the second Laudau level, the 5/2 state [1] emerges as a favorite for fundamental research and applications. Indeed, it is expected to host anyonic quasi-particles that obey non-Abelian quantum statistics [2], i.e., under an exchange of particles, the quasi-particle ground state wave-function undergoes a non-trivial transformation within the quasiparticles Hilbert’s space. Along with being of fundamental importance, this property is one of the building blocks of topologically protected (fault-tolerant) quantum computations [3]. Previous works [4] aiming to demonstrate the non- Abelian nature of the 5/2 state relied on the conventional Hall bar geometry for transport measurements, which unavoidably included edge states detrimental to the accuracy of bulk properties. Conversely, in this work [5], enabled by Corbino geometry samples, the "true bulk" thermodynamic properties are probed using a time resolved measurement scheme. As such, the specific heat data reported in this work allows the extraction of the effective mass of 5/2 composite fermions in the Fermi liquid phase and yields a large effective mass ranging from 2 to 4 times the bare electron mass.

[1] R. Willett, J. P. Eisenstein, H. L. Störmer, D. C. Tsui, A. C. Gossard and J. H. English, Phys. Rev. Lett. 59, 1776 (1987)
[2] G. Moore and N. Read, Nucl. Phys. B 360, 362 (1991)
[3] C. Nayak, S. H. Simon, A. Stern, M. Freedman and S. Das Sarma, Rev. Mod. Phys. 80, 1083 (2008)
[4] W. E. Chickering, J. P. Eisenstein, L. N. Pfeiffer and K. W. West, Phys. Rev. B 87, 075302 (2013)
[5] M. Petrescu, Z. Berkson-Korenberg, S. Vijayakrishnan, K. W. West, L. N. Pfeiffer and G. Gervais, Nat. Commun. 14, 7250 (2023)

Gabriel Demontigny

Doctorant, Polytechnique Montréal
Directeur: Denis Seletskiy
Field-Sensitive Detection of fs-Pulses in the Mid-Infrared Using Sub-Cycle Electron Tunneling
A recent advancement in photonics is the use of electron tunneling to directly detect the electric field of an optical pulse. Since tunneling through a nano-gap is a highly nonlinear process with respect to the electric field applied, the created electron bursts emitted are shorter than the period of oscillation of the optical field applied. Thus, these bursts of electron can probe the electric field of an incoming wave on a sub-cycle scale. Due to the nature of the tunneling process, the mid-infrared spectral region has an advantage for efficient electron transport. In this work, we will present our advancement in the field resolved detection of mid-infrared pulses, towards the detection of quantum states of light.

Jean-Baptiste Bertrand

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Baptiste Royer
Simulation of bosonic qubits using tensor networks
Creating qubits that are resilient to errors is a necessary step in creating quantum computers. A very promising way of accomplishing this is to encode qubits into the large Hilbert space of quantum harmonic oscillators. This idea leads to a whole class of Quantum Error Correcting codes (QEC codes) called bosonic codes. Many popular codes exists but the work here presented mainly focuses on GKP (Gottesman-Kitaev-Preskill) codes. When developing such codes, it is essentiel to be able to know how they perform under different noise models. However, the useful large Hilbert space harmonic oscillators here becomes a problem as system with even just a few oscillators rapidly become very challenging to simulate. Here, we propose a combination of different methods that would enable fast simulation of large bosonic systems. Namely, we discuss the uses of tensors networks, the selection of a simulation (the BP+ basis), and the use Monte-Carlo simulation (MC). We also present a few preliminary simulation results using these techniques.

Jérémy Peltier

Doctorant, Université de Montréal
Directeur: Philippe St-Jean
Anomalous Quantum Hall Effect for Light in Photonic Crystals
The ability to emulate exotic states of matter with light has open the door to the realization of topological phases of matter that are very difficult to study in the solid-state. Here, we investigate photonic crystals with a deformed honeycomb lattice. This deformation induces artificial gauge fields at the Dirac points such that we can have effective electric and/or magnetic fields (depending on the deformation) acting on the light in the crystal. Using the simulation module MPB (Mit Photonic Bands), we observe Landau levels and the anomalous Hall effect for light, i.e. a non-reciprocal displacement of a light wavepacket. For the latter, we also show that the direction of the Hall deviation depends on the circular polarization of the light. In the near future, we envision harnessing this chiral routing of light for entangling remote solid-state impurities.

Jonathan Pelletier

Doctorant, Université de Sherbrooke
Directeur: Baptiste Royer
Enlarging the GKP stabilizer group for enhanced noise protection
Encoding a qubit in a larger Hilbert space of an oscillator is an efficient way to protect its quantum information against decoherence [1]. The Gottesman-Kitaev-Preskill (GKP) code [2] is a promising example where the usage of quantum error correction has been shown to enhance the lifetime of the qubit [3]. Up to now, a lot of effort has been put into the preparation and stabilization of the GKP state [4], but not so much into the computations using the GKP code. In this work, we search for the optimal physical implementation of a logical circuit, when it is affected by noise. We find that the larger gaussian stabilizer group allows one to choose between logically equivalent physical operations. As a result, we propose an algorithm that selects the optimal physical operation to perform a prescribed Clifford gate in such a way that the resulting state is less prone to loss errors.

Julien Drapeau

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Variational Quantum Counting
Counting problems are computationally hard to solve, even with state-of-the-art classical devices. Approximate solutions to such problems are of practical relevance to several applications of current interest, like probabilistic reasoning, network reliability, and statistical physics. A general procedure for approximatively solving counting problems using Variational Quantum Algorithms (VQAs), near-term quantum-classical algorithms suggested to achieve quantum advantage, is introduced. This approach relies on the relationship between random sampling and approximate counting to find an exponential count with only a polynomial number of samples.

Marc-Antoine Roy

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Baptiste Royer
Teleportation-based quantum error correction of multimode Gottesman-Kitaev-Preskill states
In order to achieve fault-tolerant quantum computing, we must make use of quantum error correction (QEC) schemes designed to protect the physical information from decoherence [1]. The multimode Gottesman-Kitaev-Preskill (GKP) encoding is a clever way to encode a single logical qubit into many physical oscillators [2]. This type of encoding adds redundancy in our system by utilizing the infinitely large Hilbert space of many quantum harmonic oscillators. Usual protocols to correct multimode GKP states are based on Steane-type correction circuits, consisting of quadrature-quadrature operations [3]. However, these interactions do not preserve the shape of the gaussian envelope describing our GKP, distorting it and injecting more energy into the system. This leads to enhanced errors on the GKP state we wish to correct, decreasing greatly the logical lifetime of our state [4]. In this work, we propose a continuous-variable qubit teleportation method, consisting uniquely of passive gaussian transformation [5]. Using this circuit, we can effectively correct our multimode GKP state while keeping its envelope intact, bringing us closer to a fault-tolerant QEC code.

[1] J. Preskill, Quantum 2, 79 (2018)
[2] D. Gottesman, A. Kitaev, and J. Preskill, Phys. Rev. A 64, 012310 (2001)
[3] B. Royer, S. Singh, and S. Girvin, PRX Quantum 3, 010335 (2022)
[4] K. Noh, C. Chamberland, and F. G. Brandão, PRX Quantum 3, 010315 (2022)
[5] C. Weedbrook, S. Pirandola, R. García-Patrón, N. J. Cerf, T. C. Ralph, J. H. Shapiro, and S. Lloyd, Phys. Rev. A 84, 621 (2012)

Marie-Frédérique Dumas

Étudiante à la maîtrise, Université de Sherbrooke
Directeur: Alexandre Blais
Unified picture of measurement induced ionization in the transmon, Part I
Dispersive readout in circuit QED the enables fast and high-fidelity measurements that are essential for quantum computation. However, it is a common experimental observation that increasing the measurement drive amplitude to even moderate values leads to quantum non-demolition and low-fidelity readout. Recent theoretical work suggests that this is due to ionization of the qubit to higher-energy excited states by the drive. In this poster, I present a tool to compute the critical photon numbers at which the qubit ionizes. This tool also provides new insight on the mechanisms at play depending on the system's parameters such as the qubit-resonator frequency detuning.

Martin Schnee

Doctorant, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Early-time signatures of Quantum Many-body Scars in survival probability decay
We show that unconventional relaxation dynamics of special initial states in one dimensional arrays of Rydberg atoms produce non-generic decay of the initial-state survival probability at early times. Using the PXP hamiltonian as a minimal model of the Rydberg blockade, we prove that the early-time survival probability for states exhibiting quantum many-body scarring decays at a characteristic rate, whose finite-size scaling is determined solely by scars. We numerically investigate the effects of both revival-enhancing and ergodicity-restoring perturbations and find results consistent with the limiting cases of integrable and ergodic dynamics, respectively. Since the survival probability is easily accessible experimentally at early times, our findings enable us to probe the presence of scars at time scales much shorter than that of thermalization.

Mengfan Jiang

Master student, McGill University
Director: Kai Wang
Design of Optical Metasurface for Quantum State Discrimination
This study presents a method to design a metasurface for N-photon polarization state discrimination using quantum state discrimination principles. The metasurface distinguishes photon polarization states by directing photons to different diffraction orders. Starting with initial parameters, the S-matrix is calculated using Rigorous Coupled-Wave Analysis (RCWA) to compute the success probability. NLopt is then used to optimize this probability, and the optimized parameters are used to design the metasurface for efficient polarization state discrimination.

Mostafa-Fouad Youssef

Doctorant, École de technologie supérieure
Directeur: Bora Ung
Biphoton Quantum State Tomography and Spin-orbit conversion in the C+L Telecom Bands
High-dimensional quantum states offer the promise of enhancing information capacity in quantum communications. Towards that goal, we here characterize a fiber-based system with the generation and transmission of biphotons in the telecom C+L bands and capable of converting photons with low-dimensional spin subspace to a high-dimensional orbital angular momentum (OAM) subspace (from -5 to +5 topological charge). We experimentally confirm that Bell’s inequality is violated with a CHSH value of 2.43. The reconstructed density matrix through polarization quantum state tomography (QST) indicates a fidelity of 92 %, a purity of 86 % and concurrence of 84 % are achieved. The spin (polarization) to OAM conversion through spatial light modulator (SLM) is shown to yield a conversion efficiency of 41.5 %. This work is a step towards achieving multidimensional entanglement and high-dimensional quantum key distribution at standard fiber telecom wavelengths.

Nicolas Mekhaël

Master student, Université de Sherbrooke
Director: Baptiste Royer
GKP Code Simulation in the Zak Basis
Bosonic codes allow the storage of quantum information using the infinite Hilbert space of a quantum harmonic oscillator.One of those error correction codes is the GKP code which can correct small quadrature shifts. GKP codewords are periodic and spread far into phase space making classical simulations of such schemes challenging in the conventional Fock basis. Indeed, large state vectors are needed to represent GKP states with high fidelity. Here, we explore a novel basis from which we can simulate such states. The Zak basis used in this project is ideal to represent periodic states and has the potential to reduce state vector sizes in classical simulation.

Nicolas-Ivan Gonzalez-Mora

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Mathieu Juan
Titre à venir

Noah Pinkney

Étudiant à la maîtrise, Université McGill
Directeur: Bill Coish
Titre à venir

Pierre Lefloïc

Doctorant, Université de Sherbrooke
Directeur: Mathieu Juan
Photoinitialization of quantum dots in undoped GaAs
Scaling up gate-defined quantum dot systems is hampered by the rapid growth in the number of control gates. To tackle this challenge, we propose a novel scheme, in which the quantum dots are created from optically generated charges trapped beneath accumulation gates.

By shining an above-the-gap laser light onto an undoped GaAs substrate, we demonstrate that it is possible to create and separate electron-hole pairs to form quantum dots with one of the two polarities. By pairing this technique with a superconducting coplanar waveguide resonator for the charge readout, we achieve a working many-charge double quantum dot device with controllable interdot charge exchange. The device, comprised of only two plunger gates and one tunnel coupling gate, shows that the initialization of quantum dots does not require reservoirs, source/drain bias, ohmic contacts, or doping. Therefore, the number of gates can be reduced and the fabrication process can be simplified. Moreover, this new method can be applied to a wide range of semiconductor quantum dot systems.

Such a hybrid device is the first step towards a more scalable design for quantum dot arrays. It is also a good starting point for quantum transducing thanks to the optical–matter–microwave interaction.

Robert Gerstner

Étudiant à la maîtrise, Université McGill
Directeur: Bill Coish
Titre à venir

Roya Radgohar

Postdoc, Université de Sherbrooke
Directeur: Stéfanos Kourtis
The Knapsack problem: a quantum Metropolis algorithm
We study the knapsack problem which is a combinatorial optimization problem with variety applications in real-world scenarios such as cryptography, job scheduling and optimizing of food orders. In the knapsack problem, a bag with maximum weight capacity and a set of items, each with an associated value and weight, are specified. The aim is to find a subset of items that maximizes the total value while ensuring the total weight is less than the maximum weight capacity. This problem is known as an NP-hard problem, for which finding efficient classical solutions is challenging. Motivated by circuit implementation of Szegedy’s quantization of the Metropolis-Hasting Walk, we develop a quantum algorithm that exploits non-classical properties of quantum walks to solve the Knapsack problem. We implement our algorithm on the noiseless QASM simulator in the Qiskit library, running on a classical computer. Our numerical results demonstrate that the Quantum Metropolis-Hastings algorithm provides better solutions for some instances compared to its classical counterparts. These findings suggest a new approach for tackling problem instances that are difficult to solve by classical algorithms.

Samuel Wolski

Doctorant, Université de Sherbrooke
Directeur: Mathieu Juan
Kinetic inductance in NbN microwave resonators

Sara Turcotte

Doctorante, Université de Sherbrooke
Directeur: Baptiste Royer
Titre à venir

Shilong Liu

Postdoc, Polytechnique Montréal
Directeur: Denis Seletskiy
Physics-informed machine learning for engineering arbitrary spectro-temporal light states
In this study, we introduce an innovative approach for engineering spectral-temporal states using a physics-informed convolutional neural network (P-CNN). A hybrid network structure for P-CNN is constructed by integrating the Wigner function encompassing both spectral and temporal information with a convolutional neural network. An experimental versatile platform incorporates dispersion and nonlinearity components to train two P-CNNs predicting the spectral-temporal dynamics, such as high-order soliton, dispersion wave, as well as few-cycle laser pulse. The P-CNN regime provides a powerful method to shape arbitrary pulse states and thus applies in quantum and nonlinear optics.

Suman Jyoti De

Postdoc, Université McGill
Directrice: Tami Pereg-Barnea
Magnon transmission across 𝜈=1⁢|−1|⁢1 monolayer graphene junction as a probe of electronic structure
We study magnon transmission across gate-controlled junctions in the 𝑛=0 manifold of Landau levels in monolayer graphene in the presence of both spin and valley Zeeman fields. Specifically, we consider the 1⁢|−1|⁢1 sandwich geometry. The nature of the interfaces between regions of different filling turns out to be crucial for magnon transmission. Using the Hartree-Fock approximation, we find that either the spin or the valley degrees of freedom of the occupied one-body states rotate across the interfaces. If the interfaces exhibit spin rotation, then magnon transmission is suppressed at high energies, while if the interfaces have valley rotation, then magnon transmission becomes perfect at high energies. The valley Zeeman coupling, which arises from partial alignment with the encapsulating boron nitride, is independent of perpendicular magnetic field 𝐵, while the spin Zeeman and other anisotropic couplings scale linearly with 𝐵. This allows the tuning of the relative strength of the valley Zeeman coupling in situ by varying 𝐵, which can drive phase transitions of the interfaces between spin-rotated and valley-rotated phases, leading to magnon transmission being either vanishing or perfect at high energies. Our analysis [1], along with the experimental measurements, can be used to determine the anisotropic couplings in the sample.

[1] Suman Jyoti De, Sumathi Rao and Ganpathy Murthy, PhysRevB. 110, 085417(2024)

Talia Martz-Oberlander

Doctorante, Université McGill
Directeur: Guillaume Gervais
Flip-chip gating for studying quantum Hall states in pristine ultra-high mobility 2DEGs
Electrostatic gating is a necessity for controlling and probing semiconductor systems. With interest in ultra-high mobility semiconductors and more fragile low-dimensional systems, preserving qualities such as charge carrier mobility is key to enabling future research. One innovative method for preserving pristine materials is to employ a mechanical assembly to gate two-dimensional electron gases (2DEGs) in GaAs/AlGaAs wafers. In this flip-chip device, metallic gates are deposited via lithography onto a separate sapphire substrate that is mechanically held on to the semiconductor of interest. The enables control of the current in a 2DEG via field effect for quantum interference measurements. Flip-chips offer a number of advantages, namely that they facilitate the reuse of semiconductor wafers in the case of gate malfunction or allow for movement of the gates should the original placement fall on a low-quality region of the material of interest [1]. Secondly, flip-chips avoid any contamination or mobility-degradation from chemicals or cleaning processes involved in traditional lithography. Thirdly, by avoiding direct deposition of materials on the wafers we avoid strain on the GaAs crystal due to disparities in thermal contraction as the device is cooled to millikelvins. Finally, we avoid charge traps by replacing traditional dielectric materials, such as oxides, between the semiconductor and the gates with a vacuum in a flip-chip device. By preserving the high mobility of 2DEGs, our flip-chip devices enable further study of fragile quantum Hall states. In this paper we will present results on gating a 2DEG with mobility as high as 25 ×106 cm2/Vs and will discuss further progress in making Fabry-Perot interferometer designs for the fractional quantum Hall regime.

[1] Y. Jang Chung, K. W. Baldwin, K. W. West, et al. Spatial Mapping of Local Density Variations in Two-dimensional Electron Systems Using Scanning Photoluminescence. Nano Lett. 19 (3), 1908-1913 (2019)
[2] Bennaceur, K., Schmidt, B., Gaucher, S. et al. Mechanical Flip-Chip for Ultra-High Electron Mobility De-vices. Sci. Rep. 5, 13494 (2015)

Thomas Royer

Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Mathieu Juan
Protecting superconducting quantum devices from infrared noise
Al-AlOx-Al Josephon junction-based devices can be impaired by quasiparticle poisoning, caused by "infrared noise" in the 80 - 100 GHz range. This noise is present due to the blackbody radiation of higher temperature stages in a dilution fridge going down to the mixing stage. Conventional RLC microwave filters do not protect against this type of noise, as their functionning starts to break down at higher frequencies. The usual way of protecting against infrared noise is using coaxial filter with an infrared-absorbing dielectric. However, the materials used also absorb the in-band frequencies, leading to degradation of signal. An alternative cavity-waveguide based filter, the HERD filter, was proposed in 2022. We altered the design in the hopes of improving performances. The poster will present the changes to the filter, the reason for them, and the performance of these second generation HERD filters.

Yuming Niu

Doctorant, Université McGill
Directeur: Kai Wang
Titre à venir

Zoé McIntyre

Doctorante, Université McGill
Directeur: Bill Coish
Titre à venir