May 13, 2025 11:00 AM
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May 14, 2025 4:30 PM
May 13, 2025 11:00 AM
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May 14, 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.
13 mai
10h55 Mot d'ouverture (Salon A)
11h00 Ulysse Chabaud, INRIA (Salon A)
Can effective descriptions of bosonic systems be considered complete?
12h00 Lunch (Knowlton room)
13h30 Honghao Fu, Concordia University (Salon A)
Optimal quantum purity amplification
14h20 Pierre Botteron, Ottawa University (Salon A)
Towards Unconditional Uncloneable Encryption
14h40 Valentin Boettcher, Université McGill (Salon A)
Emulating Non-Markovian System-Bath Dynamics with Parametrically Driven Cavities
15h00 Pause café (Salon C)
15h30 Jacob Biamonte, École de technologie supérieure S (Salon A)
Hamiltonian Ground States: A Golden Thread Connecting Physics and Computation
16h20 Ecosystème quantique (Salon A)
Mathieu Juan, Université de Sherbrooke - Reasearch plateforms at Université de Sherbrooke
Quandela - Titre à venir
17h20 Séance d'affiches (Salon C)
19h30 Souper INTRIQ (Salle Knowlton)
14 mai
9h00 Hlér Kristjánsson, Université de Montréal (Salon A)
Exponential separation in quantum query complexity of the quantum switch with respect to simulations with standard quantum circuits
9h50 Rachel Wortis, Trent University (Salon A)
Connecting entanglement growth with local integrals of motion in the disordered Fermi Hubbard model
10h30 Pause café (Salon C)
11h00 Jonathan Lavoie, Xanadu (Salon A)
Scaling and networking a modular photonic quantum computer
12h00 Dîner (Salle Knowlton)
13h30 Nicolas Delfosse, IONQ (Salon A)
Titre à venir
14h30 Sebastian Koelling, Polytechnique Montréal (Salon A)
Isotopically engineered Germanium quantum wellsfor spin qubit integration
14h55 Pause café (Salon C)
15h25 Alexandre Chénier, Université de Montréal (Salon A)
Quantized Hall Drift in a Frequency-Encoded Photonic Chern Insulator
15h45 Alexander McDonald, Université de Sherbrooke (Salon A)
Predicting the bit-flip rate of dissipative cat qubits
16h05 Evgeny Moiseev, Université McGill (Salon A)
Quantum key distribution with squeezed coherent light in photonic blockade regime
16h25 Mot de fermeture (Salon A)
Xanadu, Canada
Scaling and networking a modular photonicquantum computer
We will discuss Aurora, Xanadu's latest photonic quantum computer showcasing scaling, modularity, and networking in a fault-tolerant architecture. We will also discuss more recent breakthroughs in hardware progress.
IONQ, USA
Titre à venir
INRIA, France
Can effective descriptions of bosonic systems be considered complete?
Bosonic statistics give rise to remarkable phenomena, from the Hong–Ou–Mandel effect to Bose–Einstein condensation, with applications spanning fundamental science to quantum technologies. Modeling bosonic systems relies heavily on effective descriptions: typical examples include truncating their infinite-dimensional state space and restricting their dynamics to a simple class of Hamiltonians, such as polynomials of canonical operators, which are used to define quantum computing over bosonic modes. However, many natural bosonic Hamiltonians do not belong to this simple class, and some quantum effects harnessed by bosonic computers inherently require infinite-dimensional spaces, questioning the validity of such effective descriptions of bosonic systems. How can we trust results obtained with such simplifying assumptions to capture real effects?
Driven by the increasing importance of bosonic systems for quantum technologies, we solve this outstanding problem by showing that these effective descriptions do in fact capture the relevant physics of bosonic systems. Our technical contribution is twofold: firstly, we prove that any physical, bosonic unitary evolution can be strongly approximated by a finite-dimensional unitary evolution; secondly, we show that any finite-dimensional unitary evolution can be generated exactly by a bosonic Hamiltonian that is a polynomial of canonical operators. Beyond their fundamental significance, our results have implications for classical and quantum simulations of bosonic systems, they provide universal methods for engineering bosonic quantum states and Hamiltonians, they show that polynomial Hamiltonians do generate universal gate sets for quantum computing over bosonic modes, and they lead to an infinite-dimensional Solovay–Kitaev theorem.
Joint work with F. Arzani and R. I. Booth: arXiv:2501.13857
Postdoc, Université de Sherbrooke
Directeur: Alexandre Blais
Predicting the bit-flip rate of dissipative cat qubits
Bosonic cat qubits exhibit a favorable noise bias, exponentially suppressing bit-flip errors at the cost of a linear increase in phase-flip errors. Experimental evidence however shows that there are non-perturbative corrections the bit-flip rate whose origin remains a mystery. In this talk, we will show how a hidden symmetry in these systems can be used to analytically compute the bit-flip rate. Our non-perturbative approach provides a more accurate framework for understanding and estimating the error dynamics of cat qubits in the large cat-state regime.
Doctorant, Université de Montréal
Directeur: Philippe St-Jean
Quantized Hall Drift in a Frequency-Encoded Photonic Chern Insulator
Chern insulators are topological phases of matter with broken time-reversal symmetry. Albeit their technological interest, these phases have proven to be highly challenging to implement in photonics systems, notably due to the typically low magneto-optical response of matter at optical or near-infrared frequencies. In this presentation, I will describe an experimental work in which we realize a photonic Chern insulator, inspired by the Haldane model, using the synthetic frequency dimension of a time-modulated optical fiber loop platform. Thanks to the remarkable tunability and driven-dissipative nature of our system, we demonstrate a thorough characterization of the resulting bands’ topology. This includes band structure measurements in all regions of the topological phase diagram, extraction of the Berry curvature across the entire Brillouin zone and of the resulting Chern number associated to each band, and observation of a photonic analogue of the quantized transverse Hall conductivity. Our work paves the way to engineering backscattering-immune flow of light in frequency-multiplexed photonic systems.
Postdoc, McGill University
Directeur: Kai Wang
Quantum key distribution with squeezed coherent light in photonic blockade regime
We propose to use a special coherent squeezed state for quantum key distribution (QKD), where the interference between squeezing and displacement completely suppresses the two-photon component. We show an order of magnitude increased key generation rate with these states in prepare and measure and twin-fields QKD protocols compared to the use of coherent state.
Professeur, Concordia University
Optimal quantum purity amplification
Quantum purity amplification (QPA) offers a novel approach to counteracting the pervasive noise that degrades quantum states. We present the optimal QPA protocol for general quantum systems against global depolarizing noise, which has remained unknown for two decades. We construct and prove the optimality of our protocol, which demonstrates improved fidelity scaling compared to the best-known methods. We explore the operational interpretation of the protocol and provide simple examples of how to compile it into efficient circuits for near-term experiments. Furthermore, we conduct numerical simulations to investigate the effectiveness of our protocol in the quantum simulation of Hamiltonian evolution, demonstrating its ability to enhance fidelity even under circuit-level noise. Our findings suggest that QPA could improve the performance of quantum information processing tasks. Based on: https://arxiv.org/abs/2409.18167.
Professeur, Université de Montréal
Exponential separation in quantum query complexity of the quantum switch with respect to simulations with standard quantum circuits
Quantum theory is consistent with a computational model permitting black-box operations to be applied in an indefinite causal order, going beyond the standard circuit model of computation. The quantum switch -- the simplest such example -- has been shown to provide numerous information-processing advantages. Here, we prove that the action of the quantum switch on two n-qubit quantum channels cannot be simulated deterministically and exactly by any causally ordered quantum circuit that uses M calls to one channel and one call to the other, if M ≤ max(2,2n−1). This demonstrates an exponential separation in quantum query complexity of indefinite causal order compared to standard quantum circuits.
Professeur, École de technologie supérieure
Hamiltonian Ground States: A Golden Thread Connecting Physics and Computation
Ground states of Hamiltonians provide both a fundamental theoretical framework and a practical resource in quantum computation. Variational quantum computing harnesses effective Hamiltonian minimization by iteratively refining quantum circuit parameters through quantum-to-classical feedback loops. Alternatively, certain computational models directly implement physical Hamiltonians, leveraging natural physical processes that minimize free energy as a computational mechanism.
In this talk, I will highlight our early advances establishing the computational universality of simplified ground state models, culminating in proposals to embed applications, particularly from electronic structure problems, directly into these Hamiltonians. More recently, our research has discovered limitations regarding iterative variational approaches. Specifically, we demonstrated that intrinsic structural features of certain problem instances lead to under-parameterization, causing quantum approximate optimization to fail, thereby questioning the generalizability of earlier results. Furthermore, we identified and characterized "avalanche effects" in quantum circuit training, offering the first explicit counterexamples to the widely-held piecewise trainability conjecture. Despite these challenges, our forward-looking findings provide an optimistic trajectory. We introduced the first sufficient conditions, termed "parameter concentrations," ensuring optimized circuit parameters become independent of specific problem instances. Moreover, we proved that the variational approach represents a universal model for quantum computation, in theory.
Professeur, Université de Sherbrooke
Reasearch plateforms at Université de Sherbrooke
Doctorant, Ottawa University
Directrice: Anne Broadbent
Towards Unconditional Uncloneable Encryption
Uncloneable encryption is a cryptographic primitive which encrypts a classical message into a quantum ciphertext, such that two quantum adversaries are limited in their capacity of being able to simultaneously decrypt, given the key and quantum side-information produced from the ciphertext. Since its initial proposal and scheme in the random oracle model by Broadbent and Lord [TQC 2020], uncloneable encryption has developed into an important primitive at the foundation of quantum uncloneability for cryptographic primitives. Despite sustained efforts, however, the question of unconditional uncloneable encryption (and in particular of the simplest case, called an uncloneable bit) has remained elusive. Here, we propose a candidate for the unconditional uncloneable bit problem, and provide strong evidence that the adversary's success probability in the related security game converges quadratically as 1/2+1/(2sqrt(K)), where K represents the number of keys and 1/2 is trivially achievable. We prove this bound's validity for K ranging from 2 to 7 and demonstrate the validity up to K=17 using computations based on the NPA hierarchy. We furthermore provide compelling heuristic evidence towards the general case. In addition, we prove an asymptotic upper bound of 5/8 and give a numerical upper bound of ∼0.5980, which to our knowledge is the best-known value in the unconditional model.
Doctorant, McGill University
Directeur: Bill Coish
Emulating Non-Markovian System-Bath Dynamics with Parametrically Driven Cavities
We propose and analyze a straightforward method to realize a bosonic bath with a highly tunable spectral density using a single parametrically driven cavity. By implementing a one-dimensional long-range hopping model in the cavity highly-controllable dispersion relations can be realized. This allows a single cavity to become a modular element that emulates an environment having near-arbitrary spectral density. The spectral density is determined solely by the shape of the parametric drive signal and can be changed without altering the physical setup. Its simplicity and modularity makes this approach suitable for applications in quantum simulation or bath-engineering. Furthermore, as the bath is implemented in a single cavity the bath remains observable rather than being a black box. We provide a bound on the accuracy of the simulation of open-system observables with respect to the maximum drive frequency and losses in the cavity with emphasis on the case of power-law spectral densities \(J(\omega)\propto \omega^{s}\) with \(0\leq s\). Finally, we propose a concrete implementation using classical light in modulated fiber loops to realize a Wigner-Weiskopf model exhibiting conditional decay.
Professeure, Trent University
Connecting entanglement growth with local integrals of motion in the disordered Fermi Hubbard model
Generically a quantum system initialized in an unentangled state will, under unitary dynamics, rapidly become entangled, a process closely related to information transport and to thermalization. Disorder can suppress the growth of entanglement and result in memory of initial conditions. In non-interacting systems this arises from localization of single-particle states, the occupancy of which is fixed by the initial condition. In interacting systems similar conserved quantities persist, but with the added feature that they are coupled, resulting in entanglement growth which is distinct from both non-interacting localized systems and from generic ergodic systems. The Fermi Hubbard model has two degrees of freedom per site—charge and spin—and disorder may be present in both of these, with the same or differing strengths. We study this system by expanding the Hamiltonian in terms of a set of optimally localized conserved quantities with separate charge and spin character. This talk will examine the distribution of couplings between the conserved quantities and their connection with entanglement growth. We find much weaker coupling between charge and spin, relative to charge-charge and spin-spin coupling.
Associé de recherche, Polytechnique Montréal
Isotopically engineered Germanium quantum wellsfor spin qubit integration
Semiconductor spin qubits are a promising route to fabricating scalable qubits and fully integrated quantum processors. These qubits can be fabricated using manufacturing processes and infrastructure that enabled the scaling of digital circuits to billions of integrated devices over the last decades. Accordingly, this approach facilitates both the scalability to billions of qubits and the direct integration of quantum and digital electronics for hybrid classical-quantum computing on a single chip.
Unfortunately, all industrial relevant semiconductors contain spin-full atomic nuclei. Spin qubit quantum computers utilize the spin of charge carriers like electrons and holes in semiconductors for calculations and hence rely on the precise control of that spin. The random interactions of the spin forming the qubit and the nuclear spin bath of the host material is detrimental to the qubit operation creating a need for isotopically engineered semiconductors that are nuclear spin free.
Manufacturing nuclear spin free semiconducting materials creates challenges for the epitaxial growth of the respective materials, the production of suitable precursors for the growth process and the metrology of the grown materials.
In this talk we will show how we addressed these challenges and developed wafer-scale epitaxial growth of crystalline, defect free, isotopically purified nuclear spin-depleted 70Ge quantum well (QW) strained by nuclear spin-depleted 28Si70Ge barriers on standard silicon wafers. We will discuss the development of the epitaxial growth processes and highlight the supporting metrology that enables us to quantify the distribution of isotopes in our materials.
Postdoc, Université de Sherbrooke
Directeur: Stéfanos Kourtis
Titre à venir
Postdoc, Université de Montréal
Directeur: Philipppe St-Jean
Titre à venir
Doctorant, Université de Sherbrooke
Directeur: Max Hofheinz
Directional Josephson Photonics
Postdoc, McGill University
Director: Kai Wang
Quantum key distribution with squeezed coherent light in photonic blockade regime
We propose to use a special coherent squeezed state for quantum key distribution (QKD), where the interference between squeezing and displacement completely suppresses the two-photon component. We show an order of magnitude increased key generation rate with these states in prepare and measure and twin-fields QKD protocols compared to the use of coherent state.
Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Max Hofheinz
Titre à venir
Doctorant, Polytechnique Montréal
Directeur: Oussama Moutanabbir
GeSn on Si SPAD designs operating at 2 μm and beyond
Ce poster présentera deux nouvelles conceptions de SPADs GeSn sur silicium à structure horizontale, mettant en avant des approches architecturales alternatives. Il détaillera les principales considérations de conception nécessaires à l'optimisation des performances et à la fiabilité de fonctionnement, tout en décrivant la méthodologie utilisée pour démontrer ces structures. Ensuite, les défis actuels des technologies SPAD, notamment leurs limites dans le moyen infrarouge, seront abordés et des explications sur la manière dont le GeSn émerge comme un matériau prometteur pour répondre à ces problématiques seront expliquées. L'ouvrage se conclura par des perspectives sur les axes de recherche ouverts et les avancées potentielles que pourraient apporter des SPADs personnalisables et ajustables fonctionnant sur l'ensemble du spectre moyen infrarouge.
Doctorante, Université de Sherbrooke
Directeur: Bertrand Reulet
Amplitude Higgs Mode in superconducting Ti nanowires
The Higgs-Anderson mode in superconductors is known to be difficult to observe because of its weak coupling to the electromagnetic field. A recent theory [1] predicted a huge increase of this coupling in the presence of a DC supercurrent, which should translate into an anomaly in the complex conductivity at frequencies of the order of twice the superconducting gap Δ. This phenomenon has been experimentally confirmed in macroscopic NbN films exposed to THz radiations at a temperature of 5K [2].
In order to better control, and investigate in more depth Higgs mode properties, it would be very useful to be able to work at much lower frequencies, thus much lower temperature. Our experiment aims at providing such a step towards detecting and manipulating Higgs mode in a microwave circuit.
We studied Titanium samples for which 2Δ is of the order of 10-30 GHz and can be tuned with the sample thickness and temperature. We implemented a calibrated, cryogenic microwave reflectance setup, with which we measured the complex impedance vs. frequency and temperature of superconducting wires of various dimensions. In the absence of DC current we compare our results with BCS theory at equilibrium. Adding a current results in the appearance of an anomaly at frequency 2Δ on both the real and imaginary parts of the complex impedance. This feature behaves as predicted in [1], however it is much broader in frequency.
[1] A. Moor, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 118, 047001 (2017).
[2] S. Nakamura, Y. Iida, Y. Murotani, R. Matsunaga, H. Terai, and R. Shimano, Phys. Rev.Lett. 122, 257001 (2019).
Doctorante, Université de Sherbrooke
Directeur: Alexandre Blais
Titre à venir
Postdoc, Université McGill
Directeur: Kai Wang
Birefringence-induced topological effects in laser-written quantum photonics
We experimentally observe effects of topological origin imposed on quantum states of light in laser-written waveguide arrays. In particular, we demonstrate birefringence of waveguides as a powerful tool in the development of quantum photonic circuits with built-in topological protection. We find propagation-invariant quantum interference and entanglement conversion from polarization to orbital angular momentum as effects enabled and protected via tailored birefringence. Our findings may pave the way towards photonic quantum circuitry and scalable quantum computing protected and enabled by virtue of a next generation of topological photonic devices.
Doctorant, Polytechnique Montréal
Directeur: Oussama Moutanabbir
Titre à venir
Doctorant, Université de Sherbrooke
Directeur: Baptiste Royer
Reinforcement learning-enhanced hamiltonian estimation
We use reinforcement learning techniques in order to decide how to interact with a system in a relevant way to increase the knowledge of the Hamiltonian's parameters.
Postdoc, Polytechnique Montréal
Directeur: Oussama Moutanabbir
RPCVD Growth of Nuclear Spin-Free 70Ge/28Si70Ge Heterostructures on Industrial SiGe Substrates
Spin qubits based on germanium (Ge) heterostructures are promising candidates for CMOS compatible quantum processors with long coherence times. This is in part due to the advantages of hole spins in Ge, such as their large spin orbit interaction and reduced hyperfine coupling with nuclear spins. The coherence and operation of hole spin qubits in planar Ge/SiGe heterostructures are both very sensitive to the nuclear spin bath. Therefore, developing nuclear spin-depleted materials is critical to enhance the performance of these qubits. To this end, it is important to eliminate the nuclear spin-full 29Si and 73Ge in the epitaxial Ge/SiGe heterostructures.
Our group has recently demonstrated highly crystalline, defect free, isotopically purified (>99.9 at.% 70Ge) nuclear spin-depleted 70Ge quantum well (QW) heterostructures grown in a reduced pressure CVD using purified precursors (>99.9 at.% 70GeH4 and >99.99 at.% 28SiH4) on in situ grown reversed graded SiGe buffers. However, the extensive use of expensive purified precursors across the growth remained a problem. Here we demonstrate the regrowth of 70Ge QW heterostructures on easily available industrial SiGe substrates, leading to a major reduction of purified precursor consumption.
Doctorant, Université McGill
Directrice: Tami Pereg-Barnea
Titre à venir
Doctorant, Université de Sherbrooke
Directeur: Mathieu Juan
Flux-tunable resonators for cavity magnonics
Superconducting circuits can be used for various quantum technology applications, which dictate their desired behaviour under applied magnetic fields. For computing and communications, field resilience is highly prized, as stray flux should not negatively impact device operation. This is in contrast to sensing, where flux-induced decoherence is precisely the mechanism by which quantum-enhanced sensitivities can be achieved. These two requirements of sensitivity and resilience come into direct conflict when the objective is coherent interaction with magnons, the quanta of collective spin excitations. A stronger response to external fields enables a greater coupling, but cannot be so large that the photon lifetime limits device operation. Understanding the landscape of flux-tunable resonators is essential to exploring off-resonant magnon interactions.
Doctorant, Université McGill
Directeur: Hong Guo
Atomistic first-principles modeling of single donor spin-qubit
Using an impurity atom in crystal silicon as a spin-1/2 qubit has been made experimentally possible recently where the impurity atom acts as a quantum dot (QD). Quantum transport in and out of such a donor QD is in the sequential tunneling regime where a physical quantity of importance is the charging (addition) energy which measures the energy necessary for adding an electron into the donor QD. In this work, we present a first principles method to quantitatively predict the addition energy of donor QD. Using density functional theory (DFT) we determine the impurity states which serve as the basis set for subsequent exact diagonalization calculation of the many-body states and energies of the donor QD. Due to the large effective Bohr radius of the conduction electrons in Si, very large supercells containing more than 10,000 atoms, must be used to obtain accurate results. For the donor QD of a phosphorus impurity in bulk Si, the combined DFT and exact diagonalization predicts the first addition energy to be 53 meV, in good agreement with the corresponding experimental value. For the donor QD of an arsenic impurity in Si, the first addition energy is predicted to be 44.2 meV. The calculated many-body wave functions provide a vivid electronic picture of the donor QD.
Étudiant à la maîtrise, Polytechnique Montréal
Directeur: Nicolas Quesada
Photon-number moments and cumulants of Gaussian states
We develop closed-form expressions for the moments and cumulants of Gaussian states when measured in the photon-number basis. We express the photon-number moments of a Gaussian state in terms of the loop Hafnian, a function that when applied to a (0, 1)-matrix representing the adjacency of a graph, counts the number of its perfect matchings. Similarly, we express the photon-number cumulants in terms of the Montrealer, a newly introduced matrix function that when applied to a (0, 1)-matrix counts the number of Hamiltonian cycles of that graph. Based on these graph-theoretic connections, we show that the calculation of photon-number moments and cumulants are #P −hard. Moreover, we provide an exponential time algorithm to calculate Montrealers (and thus cumulants), matching well-known results for Hafnians. We then demonstrate that when a uniformly lossy interferometer is fed in every input with identical single-mode Gaussian states with zero displacement, all the odd-order cumulants but the first one are zero. Finally, we employ the expressions we derive to study the distribution of cumulants up to the fourth order for different input states in a Gaussian boson sampling setup where K identical states are fed into an ℓ-mode interferometer. We analyze the dependence of the cumulants as a function of the type of input state, squeezed, lossy squeezed, squashed, or thermal, and as a function of the number of non-vacuum inputs. We find that thermal states perform much worse than other classical states, such as squashed states, at mimicking the photon-number cumulants of lossy or lossless squeezed states.
Étudiant à la maîtrise, Université de Sherbrooke
Directeur: Max Hofheinz
Titre à venir
Doctorant, Université McGill
Directeur: Hong Guo
Titre à venir
May 13th
10:55 Opening remarks (Salon A)
11:00 Ulysse Chabaud, INRIA (Salon A)
Can effective descriptions of bosonic systems be considered complete?
12:00 Lunch (Knowlton room)
13:30 Honghao Fu, Concordia University (Salon A)
Optimal quantum purity amplification
14:20 Pierre Botteron, Ottawa University (Salon A)
Towards Unconditional Uncloneable Encryption
14:40 Valentin Boettcher, McGill University (Salon A)
Emulating Non-Markovian System-Bath Dynamics with Parametrically Driven Cavities
15:00 Coffee break (Salon C)
15:30 Jacob Biamonte, École de technologie supérieure S (Salon A)
Hamiltonian Ground States: A Golden Thread Connecting Physics and Computation
16:20 Quantum Ecosystem session (Salon A)
Mathieu Juan, Université de Sherbrooke - Reasearch plateforms at Université de Sherbrooke
Quandela - Title to be announced
17:20 Poster session with refreshments (Salon C)
19:30 INTRIQ dinner (Knowlton room)
May 14th
9:00 Hlér Kristjánsson, Université de Montréal (Salon A)
Exponential separation in quantum query complexity of the quantum switch with respect to simulations with standard quantum circuits
9:50 Rachel Wortis, Trent University (Salon A)
Connecting entanglement growth with local integrals of motion in the disordered Fermi Hubbard model
10:30 Coffee break (Salon C)
11:00 Jonathan Lavoie, Xanadu (Salon A)
Scaling and networking a modular photonic quantum computer
12:00 Lunch (Knowlton room)
13:30 Nicolas Delfosse, IONQ (Salon A)
Title to be announced
14:30 Sebastian Koelling, Polytechnique Montréal (Salon A)
Isotopically engineered Germanium quantum wellsfor spin qubit integration
14:55 Coffee break (Salon C)
15:25 Alexandre Chénier, Université de Montréal (Salon A)
Quantized Hall Drift in a Frequency-Encoded Photonic Chern Insulator
15:45 Alexander McDonald, Université de Sherbrooke (Salon A)
Predicting the bit-flip rate of dissipative cat qubits
16:05 Evgeny Moiseev, McGill University (Salon A)
Quantum key distribution with squeezed coherent light in photonic blockade regime
16:25 Closing remarks (Salon A)
Xanadu, Canada
Scaling and networking a modular photonic quantum computer
We will discuss Aurora, Xanadu's latest photonic quantum computer show casing scaling, modularity, and networking in a fault-tolerant architecture. We will also discuss more recent breakthroughs in hardware progress.
IONQ, USA
Title to be announced
INRIA, France
Can effective descriptions of bosonic systems be considered complete?
Bosonic statistics give rise to remarkable phenomena, from the Hong–Ou–Mandel effect to Bose–Einstein condensation, with applications spanning fundamental science to quantum technologies. Modeling bosonic systems relies heavily on effective descriptions: typical examples include truncating their infinite-dimensional state space and restricting their dynamics to a simple class of Hamiltonians, such as polynomials of canonical operators, which are used to define quantum computing over bosonic modes. However, many natural bosonic Hamiltonians do not belong to this simple class, and some quantum effects harnessed by bosonic computers inherently require infinite-dimensional spaces, questioning the validity of such effective descriptions of bosonic systems. How can we trust results obtained with such simplifying assumptions to capture real effects?
Driven by the increasing importance of bosonic systems for quantum technologies, we solve this outstanding problem by showing that these effective descriptions do in fact capture the relevant physics of bosonic systems. Our technical contribution is twofold: firstly, we prove that any physical, bosonic unitary evolution can be strongly approximated by a finite-dimensional unitary evolution; secondly, we show that any finite-dimensional unitary evolution can be generated exactly by a bosonic Hamiltonian that is a polynomial of canonical operators. Beyond their fundamental significance, our results have implications for classical and quantum simulations of bosonic systems, they provide universal methods for engineering bosonic quantum states and Hamiltonians, they show that polynomial Hamiltonians do generate universal gate sets for quantum computing over bosonic modes, and they lead to an infinite-dimensional Solovay–Kitaev theorem.
Joint work with F. Arzani and R. I. Booth: arXiv:2501.13857
Postdoc, Université de Sherbrooke
Director: Alexandre Blais
Predicting the bit-flip rate of dissipative cat qubits
Bosonic cat qubits exhibit a favorable noise bias, exponentially suppressing bit-flip errors at the cost of a linear increase in phase-flip errors. Experimental evidence however shows that there are non-perturbative corrections the bit-flip rate whose origin remains a mystery. In this talk, we will show how a hidden symmetry in these systems can be used to analytically compute the bit-flip rate. Our non-perturbative approach provides a more accurate framework for understanding and estimating the error dynamics of cat qubits in the large cat-state regime.
PhD student, Université de Montréal
Director: Philippe St-Jean
Quantized Hall Drift in a Frequency-Encoded Photonic Chern Insulator
Chern insulators are topological phases of matter with broken time-reversal symmetry. Albeit their technological interest, these phases have proven to be highly challenging to implement in photonics systems, notably due to the typically low magneto-optical response of matter at optical or near-infrared frequencies. In this presentation, I will describe an experimental work in which we realize a photonic Chern insulator, inspired by the Haldane model, using the synthetic frequency dimension of a time-modulated optical fiber loop platform. Thanks to the remarkable tunability and driven-dissipative nature of our system, we demonstrate a thorough characterization of the resulting bands’ topology. This includes band structure measurements in all regions of the topological phase diagram, extraction of the Berry curvature across the entire Brillouin zone and of the resulting Chern number associated to each band, and observation of a photonic analogue of the quantized transverse Hall conductivity. Our work paves the way to engineering backscattering-immune flow of light in frequency-multiplexed photonic systems.
Postdoc, McGill University
Director: Kai Wang
Quantum key distribution with squeezed coherent light in photonic blockade regime
We propose to use a special coherent squeezed state for quantum key distribution (QKD), where the interference between squeezing and displacement completely suppresses the two-photon component. We show an order of magnitude increased key generation rate with these states in prepare and measure and twin-fields QKD protocols compared to the use of coherent state.
Professor, Concordia University
Optimal quantum purity amplification
Quantum purity amplification (QPA) offers a novel approach to counteracting the pervasive noise that degrades quantum states. We present the optimal QPA protocol for general quantum systems against global depolarizing noise, which has remained unknown for two decades. We construct and prove the optimality of our protocol, which demonstrates improved fidelity scaling compared to the best-known methods. We explore the operational interpretation of the protocol and provide simple examples of how to compile it into efficient circuits for near-term experiments. Furthermore, we conduct numerical simulations to investigate the effectiveness of our protocol in the quantum simulation of Hamiltonian evolution, demonstrating its ability to enhance fidelity even under circuit-level noise. Our findings suggest that QPA could improve the performance of quantum information processing tasks. Based on: https://arxiv.org/abs/2409.18167.
Professor, Université de Montréal
Exponential separation in quantum query complexity of the quantum switch with respect to simulations with standard quantum circuits
Quantum theory is consistent with a computational model permitting black-box operations to be applied in an indefinite causal order, going beyond the standard circuit model of computation. The quantum switch -- the simplest such example -- has been shown to provide numerous information-processing advantages. Here, we prove that the action of the quantum switch on two n-qubit quantum channels cannot be simulated deterministically and exactly by any causally ordered quantum circuit that uses M calls to one channel and one call to the other, if M ≤ max(2,2n−1). This demonstrates an exponential separation in quantum query complexity of indefinite causal order compared to standard quantum circuits.
Professor, École de technologie supérieure
Hamiltonian Ground States: A Golden Thread Connecting Physics and Computation
Ground states of Hamiltonians provide both a fundamental theoretical framework and a practical resource in quantum computation. Variational quantum computing harnesses effective Hamiltonian minimization by iteratively refining quantum circuit parameters through quantum-to-classical feedback loops. Alternatively, certain computational models directly implement physical Hamiltonians, leveraging natural physical processes that minimize free energy as a computational mechanism.
In this talk, I will highlight our early advances establishing the computational universality of simplified ground state models, culminating in proposals to embed applications, particularly from electronic structure problems, directly into these Hamiltonians. More recently, our research has discovered limitations regarding iterative variational approaches. Specifically, we demonstrated that intrinsic structural features of certain problem instances lead to under-parameterization, causing quantum approximate optimization to fail, thereby questioning the generalizability of earlier results. Furthermore, we identified and characterized "avalanche effects" in quantum circuit training, offering the first explicit counterexamples to the widely-held piecewise trainability conjecture. Despite these challenges, our forward-looking findings provide an optimistic trajectory. We introduced the first sufficient conditions, termed "parameter concentrations," ensuring optimized circuit parameters become independent of specific problem instances. Moreover, we proved that the variational approach represents a universal model for quantum computation, in theory.
Professor, Université de Sherbrooke
Reasearch plateforms at Université de Sherbrooke
PhD student, Ottawa University
Director: Anne Broadbent
Towards Unconditional Uncloneable Encryption
Uncloneable encryption is a cryptographic primitive which encrypts a classical message into a quantum ciphertext, such that two quantum adversaries are limited in their capacity of being able to simultaneously decrypt, given the key and quantum side-information produced from the ciphertext. Since its initial proposal and scheme in the random oracle model by Broadbent and Lord [TQC 2020], uncloneable encryption has developed into an important primitive at the foundation of quantum uncloneability for cryptographic primitives. Despite sustained efforts, however, the question of unconditional uncloneable encryption (and in particular of the simplest case, called an uncloneable bit) has remained elusive. Here, we propose a candidate for the unconditional uncloneable bit problem, and provide strong evidence that the adversary's success probability in the related security game converges quadratically as 1/2+1/(2sqrt(K)), where K represents the number of keys and 1/2 is trivially achievable. We prove this bound's validity for K ranging from 2 to 7 and demonstrate the validity up to K=17 using computations based on the NPA hierarchy. We furthermore provide compelling heuristic evidence towards the general case. In addition, we prove an asymptotic upper bound of 5/8 and give a numerical upper bound of ∼0.5980, which to our knowledge is the best-known value in the unconditional model.
Research associate, Polytechnique Montréal
Isotopically engineered Germanium quantum wellsfor spin qubit integration
Semiconductor spin qubits are a promising route to fabricating scalable qubits and fully integrated quantum processors. These qubits can be fabricated using manufacturing processes and infrastructure that enabled the scaling of digital circuits to billions of integrated devices over the last decades. Accordingly, this approach facilitates both the scalability to billions of qubits and the direct integration of quantum and digital electronics for hybrid classical-quantum computing on a single chip.
Unfortunately, all industrial relevant semiconductors contain spin-full atomic nuclei. Spin qubit quantum computers utilize the spin of charge carriers like electrons and holes in semiconductors for calculations and hence rely on the precise control of that spin. The random interactions of the spin forming the qubit and the nuclear spin bath of the host material is detrimental to the qubit operation creating a need for isotopically engineered semiconductors that are nuclear spin free.
Manufacturing nuclear spin free semiconducting materials creates challenges for the epitaxial growth of the respective materials, the production of suitable precursors for the growth process and the metrology of the grown materials.
In this talk we will show how we addressed these challenges and developed wafer-scale epitaxial growth of crystalline, defect free, isotopically purified nuclear spin-depleted 70Ge quantum well (QW) strained by nuclear spin-depleted 28Si70Ge barriers on standard silicon wafers. We will discuss the development of the epitaxial growth processes and highlight the supporting metrology that enables us to quantify the distribution of isotopes in our materials.
PhD student, McGill University
Director: Bill Coish
Emulating Non-Markovian System-Bath Dynamics with Parametrically Driven Cavities
We propose and analyze a straightforward method to realize a bosonic bath with a highly tunable spectral density using a single parametrically driven cavity. By implementing a one-dimensional long-range hopping model in the cavity highly-controllable dispersion relations can be realized. This allows a single cavity to become a modular element that emulates an environment having near-arbitrary spectral density. The spectral density is determined solely by the shape of the parametric drive signal and can be changed without altering the physical setup. Its simplicity and modularity makes this approach suitable for applications in quantum simulation or bath-engineering. Furthermore, as the bath is implemented in a single cavity the bath remains observable rather than being a black box. We provide a bound on the accuracy of the simulation of open-system observables with respect to the maximum drive frequency and losses in the cavity with emphasis on the case of power-law spectral densities \(J(\omega)\propto \omega^{s}\) with \(0\leq s\). Finally, we propose a concrete implementation using classical light in modulated fiber loops to realize a Wigner-Weiskopf model exhibiting conditional decay.
Professor, Trent University
Connecting entanglement growth with local integrals of motion in the disordered Fermi Hubbard model
Generically a quantum system initialized in an unentangled state will, under unitary dynamics, rapidly become entangled, a process closely related to information transport and to thermalization. Disorder can suppress the growth of entanglement and result in memory of initial conditions. In non-interacting systems this arises from localization of single-particle states, the occupancy of which is fixed by the initial condition. In interacting systems similar conserved quantities persist, but with the added feature that they are coupled, resulting in entanglement growth which is distinct from both non-interacting localized systems and from generic ergodic systems. The Fermi Hubbard model has two degrees of freedom per site—charge and spin—and disorder may be present in both of these, with the same or differing strengths. We study this system by expanding the Hamiltonian in terms of a set of optimally localized conserved quantities with separate charge and spin character. This talk will examine the distribution of couplings between the conserved quantities and their connection with entanglement growth. We find much weaker coupling between charge and spin, relative to charge-charge and spin-spin coupling.
Postdoc, Université de Sherbrooke
Director: Stéfanos Kourtis
Title to be announced
Postdoc, Université de Montréal
Director: Philipppe St-Jean
Title to be announced
PhD student, Université de Sherbrooke
Director: Max Hofheinz
Directional Josephson Photonics
Postdoc, McGill University
Director: Kai Wang
Quantum key distribution with squeezed coherent light in photonic blockade regime
We propose to use a special coherent squeezed state for quantum key distribution (QKD), where the interference between squeezing and displacement completely suppresses the two-photon component. We show an order of magnitude increased key generation rate with these states in prepare and measure and twin-fields QKD protocols compared to the use of coherent state.
Master student, Université de Sherbrooke
Director: Max Hofheinz
Title to be announced
PhD student, Polytechnique Montréal
Director: Oussama Moutanabbir
GeSn on Si SPAD designs operating at 2 μm and beyond
Ce poster présentera deux nouvelles conceptions de SPADs GeSn sur silicium à structure horizontale, mettant en avant des approches architecturales alternatives. Il détaillera les principales considérations de conception nécessaires à l'optimisation des performances et à la fiabilité de fonctionnement, tout en décrivant la méthodologie utilisée pour démontrer ces structures. Ensuite, les défis actuels des technologies SPAD, notamment leurs limites dans le moyen infrarouge, seront abordés et des explications sur la manière dont le GeSn émerge comme un matériau prometteur pour répondre à ces problématiques seront expliquées. L'ouvrage se conclura par des perspectives sur les axes de recherche ouverts et les avancées potentielles que pourraient apporter des SPADs personnalisables et ajustables fonctionnant sur l'ensemble du spectre moyen infrarouge.
PhD student, Université de Sherbrooke
Director: Bertrand Reulet
Amplitude Higgs Mode in superconducting Ti nanowires
The Higgs-Anderson mode in superconductors is known to be difficult to observe because of its weak coupling to the electromagnetic field. A recent theory [1] predicted a huge increase of this coupling in the presence of a DC supercurrent, which should translate into an anomaly in the complex conductivity at frequencies of the order of twice the superconducting gap Δ. This phenomenon has been experimentally confirmed in macroscopic NbN films exposed to THz radiations at a temperature of 5K [2].
In order to better control, and investigate in more depth Higgs mode properties, it would be very useful to be able to work at much lower frequencies, thus much lower temperature. Our experiment aims at providing such a step towards detecting and manipulating Higgs mode in a microwave circuit.
We studied Titanium samples for which 2Δ is of the order of 10-30 GHz and can be tuned with the sample thickness and temperature. We implemented a calibrated, cryogenic microwave reflectance setup, with which we measured the complex impedance vs. frequency and temperature of superconducting wires of various dimensions. In the absence of DC current we compare our results with BCS theory at equilibrium. Adding a current results in the appearance of an anomaly at frequency 2Δ on both the real and imaginary parts of the complex impedance. This feature behaves as predicted in [1], however it is much broader in frequency.
[1] A. Moor, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 118, 047001 (2017).
[2] S. Nakamura, Y. Iida, Y. Murotani, R. Matsunaga, H. Terai, and R. Shimano, Phys. Rev.Lett. 122, 257001 (2019).
PhD student, Université de Sherbrooke
Director: Alexandre Blais
Title to be announced
Postdoc, McGill University
Director: Kai Wang
Birefringence-induced topological effects in laser-written quantum photonics
We experimentally observe effects of topological origin imposed on quantum states of light in laser-written waveguide arrays. In particular, we demonstrate birefringence of waveguides as a powerful tool in the development of quantum photonic circuits with built-in topological protection. We find propagation-invariant quantum interference and entanglement conversion from polarization to orbital angular momentum as effects enabled and protected via tailored birefringence. Our findings may pave the way towards photonic quantum circuitry and scalable quantum computing protected and enabled by virtue of a next generation of topological photonic devices.
PhD student, Polytechnique Montréal
Director: Oussama Moutanabbir
Title to be announced
PhD student, Université de Sherbrooke
Director: Baptiste Royer
Reinforcement learning-enhanced hamiltonian estimation
We use reinforcement learning techniques in order to decide how to interact with a system in a relevant way to increase the knowledge of the Hamiltonian's parameters.
Postdoc, Polytechnique Montréal
Director: Oussama Moutanabbir
RPCVD Growth of Nuclear Spin-Free 70Ge/28Si70Ge Heterostructures on Industrial SiGe Substrates
Spin qubits based on germanium (Ge) heterostructures are promising candidates for CMOS compatible quantum processors with long coherence times. This is in part due to the advantages of hole spins in Ge, such as their large spin orbit interaction and reduced hyperfine coupling with nuclear spins. The coherence and operation of hole spin qubits in planar Ge/SiGe heterostructures are both very sensitive to the nuclear spin bath. Therefore, developing nuclear spin-depleted materials is critical to enhance the performance of these qubits. To this end, it is important to eliminate the nuclear spin-full 29Si and 73Ge in the epitaxial Ge/SiGe heterostructures.
Our group has recently demonstrated highly crystalline, defect free, isotopically purified (>99.9 at.% 70Ge) nuclear spin-depleted 70Ge quantum well (QW) heterostructures grown in a reduced pressure CVD using purified precursors (>99.9 at.% 70GeH4 and >99.99 at.% 28SiH4) on in situ grown reversed graded SiGe buffers. However, the extensive use of expensive purified precursors across the growth remained a problem. Here we demonstrate the regrowth of 70Ge QW heterostructures on easily available industrial SiGe substrates, leading to a major reduction of purified precursor consumption.
PhD student, McGill University
Director: Tami Pereg-Barnea
Title to be announced
PhD student, Université de Sherbrooke
Director: Mathieu Juan
Flux-tunable resonators for cavity magnonics
Superconducting circuits can be used for various quantum technology applications, which dictate their desired behaviour under applied magnetic fields. For computing and communications, field resilience is highly prized, as stray flux should not negatively impact device operation. This is in contrast to sensing, where flux-induced decoherence is precisely the mechanism by which quantum-enhanced sensitivities can be achieved. These two requirements of sensitivity and resilience come into direct conflict when the objective is coherent interaction with magnons, the quanta of collective spin excitations. A stronger response to external fields enables a greater coupling, but cannot be so large that the photon lifetime limits device operation. Understanding the landscape of flux-tunable resonators is essential to exploring off-resonant magnon interactions.
PhD student, McGill University
Director: Hong Guo
Atomistic first-principles modeling of single donor spin-qubit
Using an impurity atom in crystal silicon as a spin-1/2 qubit has been made experimentally possible recently where the impurity atom acts as a quantum dot (QD). Quantum transport in and out of such a donor QD is in the sequential tunneling regime where a physical quantity of importance is the charging (addition) energy which measures the energy necessary for adding an electron into the donor QD. In this work, we present a first principles method to quantitatively predict the addition energy of donor QD. Using density functional theory (DFT) we determine the impurity states which serve as the basis set for subsequent exact diagonalization calculation of the many-body states and energies of the donor QD. Due to the large effective Bohr radius of the conduction electrons in Si, very large supercells containing more than 10,000 atoms, must be used to obtain accurate results. For the donor QD of a phosphorus impurity in bulk Si, the combined DFT and exact diagonalization predicts the first addition energy to be 53 meV, in good agreement with the corresponding experimental value. For the donor QD of an arsenic impurity in Si, the first addition energy is predicted to be 44.2 meV. The calculated many-body wave functions provide a vivid electronic picture of the donor QD.
Master student, Polytechnique Montréal
Director: Nicolas Quesada
Photon-number moments and cumulants of Gaussian states
We develop closed-form expressions for the moments and cumulants of Gaussian states when measured in the photon-number basis. We express the photon-number moments of a Gaussian state in terms of the loop Hafnian, a function that when applied to a (0, 1)-matrix representing the adjacency of a graph, counts the number of its perfect matchings. Similarly, we express the photon-number cumulants in terms of the Montrealer, a newly introduced matrix function that when applied to a (0, 1)-matrix counts the number of Hamiltonian cycles of that graph. Based on these graph-theoretic connections, we show that the calculation of photon-number moments and cumulants are #P −hard. Moreover, we provide an exponential time algorithm to calculate Montrealers (and thus cumulants), matching well-known results for Hafnians. We then demonstrate that when a uniformly lossy interferometer is fed in every input with identical single-mode Gaussian states with zero displacement, all the odd-order cumulants but the first one are zero. Finally, we employ the expressions we derive to study the distribution of cumulants up to the fourth order for different input states in a Gaussian boson sampling setup where K identical states are fed into an ℓ-mode interferometer. We analyze the dependence of the cumulants as a function of the type of input state, squeezed, lossy squeezed, squashed, or thermal, and as a function of the number of non-vacuum inputs. We find that thermal states perform much worse than other classical states, such as squashed states, at mimicking the photon-number cumulants of lossy or lossless squeezed states.
Master student, Université de Sherbrooke
Director: Max Hofheinz
Title to be announced
PhD student, McGill University
Director: Hong Guo
Title to be announced