Programme

‍17 octobre 2023

10h55 Mot d'ouverture (Salon A)

11h00 Quoc Huy Vu, Léonard de Vinci Pôle Universitaire, France (Salon A)

           Public-Key Encryption with Quantum Keys

12h00 Lunch (Salle Knowlton)

13h30 Philippe Lamontagne, CNRC Montréal (Salon A)

           Recent Advances in the Bounded Quantum Storage Model

14h15 Denis Rochette, Université d'Ottawa (Salon A)

           Monogamy of highly symmetric states

14h40 Ashutosh Marwah, Université de Montréal (Salon A)

             Source correlations for QKD

15h00 Pause café (Salon C)

15h25 Kai Wang, Université McGill (Salon A)

            Non-Hermitian topological photonics in synthetic dimensions

16h10 Rigel Zifkin, Université McGill (Salon A)

           Cavity Enhancement of Diamond Defect Centers

16h30 Présentations de l'écosystème quantique

             - Jinny Plourde (Directrice, PROMPT), Sébastien Garbarino (Directeur, PRIMA) et Sylvain Nicolay (Professeur, UdeS)
                  Funding your Quantum projects

             - Lydia Vermeyden, Ddirectrice dudéveloppement des nouveaux services à la recherche, Calcul Québec
                MonarQ, quantum computing at your service

             - Jérôme Cabana, Business development Director, Mitacs
               How Mitacs Helps Accelerate Quantum Innovation

17h15 Session d'affiches avec rafraichissements (Salon C)

19h30 Souper INTRIQ (Salle Knowlton)

‍

18 octobre 2023

9h00 – Denis Seletskiy, Polytechnique Montréal (Salon A)

               Experimental quantum electrodynamics

9h45 – Baptiste Royer, Université de Sherbrooke (Salon A)

               Encoding qubits in harmonic oscillators with quantum error correction

10h30 – Pause

11h00 – Mark Friesen, University of Wisconsin-Madison, USA (Salon A)

              Strategies for enhancing the valley splitting in Si/SiGe quantum dot qubits

12h00 – Lunch

13h30 – Val Zwiller, Royal Institute of Technology, Suède (Salon A)

‍               Generation, manipulation and detection of single photons

14h30 – Pause

15h00 – Cristóbal Lledó, Université de Sherbrooke (Salon A)

                  Dispersive readout in circuit QED

15h45 - Benjamin D’Anjou, Université de Sherbrooke (Salon A)

                Predicting the onset of non-QND effects in superconducting qubit readout

16h10 - Mot de clôture

Conférenciers invités

Pr Mark Friesen

University of Wisconsin-Madison, USA

Strategies for enhancing the valley splitting in Si/SiGe quantum dot qubits

For quantum dot spin qubits, we want the first excited state of the dot to be a spin excitation. However, in Si/SiGe quantum wells, the first excited state is often a conduction-band valley excitation, with an energy splitting so small that it competes with the spin to form qubits. To overcome this challenge, special heterostructures have been engineered, including sharp interfaces and narrow quantum wells. In this talk, I show that such strategies do not solve the problem of low valley splittings. Using theoretical methods and numerical simulations, we study interface disorder, including atomic steps and SiGe random alloys. Comparing our results to experiments, we show that the latter are responsible for the wide range of valley splittings observed in experiments, even among nominally identical samples. We propose to leverage this variability by electrically controlling the dot’s position, to tune the valley splitting.

Quoc Huy Vu, PhD

Léonard de Vinci Pôle Universitaire, Research Center, France

Public-Key Encryption with Quantum Keys

In the framework of Impagliazzo's five worlds, a distinction is often made between two worlds, one where public-key encryption exists (Cryptomania), and one in which only one-way functions exist (MiniCrypt). However, the boundaries between these worlds can change when quantum information is taken into account. Recent work has shown that quantum variants of oblivious transfer and multi-party computation, both primitives that are classically in Cryptomania, can be constructed from one-way functions, placing them in the realm of quantum MiniCrypt (the so-called MiniQCrypt). This naturally raises the following question: Is it possible to construct a quantum variant of public-key encryption, which is at the heart of Cryptomania, from one-way functions or potentially weaker assumptions?

In this talk, I will present new notions of quantum public-key encryption (qPKE), i.e., public-key encryption where keys are allowed to be quantum states. I will then discuss the (im)possibility of constructing quantum PKE from different assumptions.

This is based on joint work with Khashayar Barooti, Alex B. Grilo, Loïs Huguenin-Dumittan, Giulio Malavolta, Or Sattath and Michael Walter.

Sujet à venir

Pr Val Zwiler

Quantum Nanophotonics, dept. of Applied Physics, Royal Institute of Technology, Stockholm, Sweden

Generation, manipulation and detection of single photons

We develop quantum devices to enable the implementation of quantum technologies based on controlling light at the single photon level. Future quantum communication, computation and sensing will require high-performance quantum devices able to generate and detect light one photon at a time.

Schemes to manipulate light on-chip, based on integrated photonics are also carried out in our group. Our single photon sources based on semiconductor quantum dots can generate single photons as well as entangled photon pairs at telecom wavelengths to enable implementation of long distance quantum communication. We operate a quantum network made of deployed optical fibers in the Stockholm area and demonstrate single photon transmission and quantum key generation over 34 km.
Single photon detectors with high detection efficiency, low noise and high time resolution are major enabling techniques, our spinoff company Single Quantum develops superconducting nanowire single photon detectors with applications in quantum communication, integrated quantum circuits as well as for lidar and quantum microscopy. We will discuss these applications along with the specific detector requirements for technologies based on single photon detection. Further improvements in terms of time resolution, photon number resolution and extended detection ranges will also be discussed.

Conférencières et conférenciers de l'écosystème quantique

Jérôme Cabana

Business Development Director, Mitacs

How Mitacs Helps Accelerate Quantum Innovation

Learn more about how Mitacs is supporting the quantum ecosystems across Canada through increased funding to support international student mobility and Umbrella agreements than allow research collaborations to launch more quickly.

Jinny Plourde (PROMPT), Sébastien Garbarino (PRIMA) et Sylvain Nicolay (UdeS)

Directrice des programmes PSO, Quantique et INNOV-R, PROMPT

Directeur Infrastructure et Innovation, PRIMA

Professeur, Université de Sherbrooke (UdeS)

Fundingyour Quantum projects

We will dress a quick overview of the funding accessible through PROMPT or PRIMA for your quantum project and Pr Nicolay will present the recently funded project “Advanced Manufacturing Toolkit for Quantum Sensing and Quantum Computing”. The project aims to develop an electronic test and measurement bench to accelerate the feedback loop between the design, manufacturing, and validation of Quebec quantum technologies.

Lydia Vermeyden

Directrice dudéveloppement des nouveaux services à la recherche, Calcul Québec

MonarQ, quantum computing at your service

Calcul Québec accueillera dans les prochains mois MonarQ, un ordinateur quantique universel. Explorez les possibilités qu’amène cette acquisition et le rôle qu’elle pourrait jouer dans vos travaux de recherche.

Conférenciers INTRIQ

Benjamin D’Anjou, PhD

Professional, Université de Sherbrooke

Directeur: Alexandre Blais

Predicting the onset of non-QND effects insuperconducting qubit readout

It is generally believed that a scalable quantum processor will necessitate error correction. Many of the most promising quantum error correction protocols require that processor qubits be continually read out to identify logical errors. To be useful for error correction, it is desirable that the readout have the following properties. First, it must be performed faster than the decoherence rate of the data qubits. Second, it must leave the syndrome-readout qubits in a known state for further processing. This last condition is naturally met if the readout is quantum nondemolition (QND). Superconducting qubits coupled to microwave readout resonators constitute one of the most promising platforms to realize such a fast QND readout. However, reducing the readout time is generally achieved by driving the resonator with a high-power microwave tone. This can induce unwanted qubit transitions that leave the system in an unknown state. Predicting the onset of these unwanted transitions has been a long standing issue in the study of superconducting qubits. In this work, we show that the onset of non-QND transitions in a driven transmon qubit can be accurately predicted from a purely classical model. More precisely, we show that chaotic motion induced by the transmon nonlinearity at high drive powers shrinks the phase space area required to sustain stable qubit states [1]. We use this observation to define a "chaos-assisted critical photon number" which we find to be in surprising agreement with recent experimental results over a large range of parameters [2]. Finally, we perform fully quantum and semiclassical simulations to refine our predictions, and we propose avenues for mitigation of non-QND effects.

[1] Cohen et al., PRX Quantum 4, 020312 (2023)

[2] Khezri et al., arXiv:2212.05097 (2022)

Philippe Lamontagne

Chercheur, CNRC Montréal

Recent Advances in the Bounded Quantum Storage Model

The bounded quantum storage (BQS) model is the cryptographic assumption that quantum adversaries have imited quantum storage capabilities; usually as a fraction of the number of qubits transmitted during a protocol. For a variety of tasks, the BQS assumption can replace computational assumptions based on the existence of hard problems. The BQS model is motivated by the difficulty of storing transmitted qubits for more than a few seconds with high fidelity and with the improved security properties (secrets are unconditionally hidden after the protocol ends, instead of being hard to compute).

Most research into the BQS model took place 10-15 years ago and provided an alternative to computational assumptions for generic multiparty cryptographic tasks. Recently, the BQS assumption was revisited as a way to achieve tasks that would otherwise be impossible, even using computational assumptions. This is made possible by the fact that protocols for the BQS model typically require fewer rounds of interaction than their classical counterparts. In this talk, we will present some of these new results.

Cristóbal Lledó

Postdoc, Université de Sherbrooke

Directeur: Alexandre Blais

Dispersive readout in circuit QED

Introduction to the dispersive regime and dispersive readout in circuit QED. If time allows, we will discuss recent methods for improving readout over the standard approach.

Ashutosh Marwah

Doctorant, Université de Montréal

Directeur: Frédéric Dupuis

Source correlations for QKD

Protocols in quantum cryptography often require an honest party to produce multiple independent quantum states. For example, quantum key distribution (QKD) protocols require the honest participant, Alice to produce an independently chosen quantum state from a set of states in every round of the protocol. The security proofs for these protocol rely on the fact that the quantum state produced in each round of the protocol is independent of the other rounds. However, this is a difficult property to enforce practically. All physical devices have an internal memory, which is difficult to characterise and control. This memory can cause the quantum states produced in different rounds to be correlated with one another. In this talk, we will demonstrate how a simple source preparation test can be used to bound these correlations and incorporate them in the security proof for QKD protocols.

Denis Rochette

Postdoc, Université d'Ottawa

Directrice: Anne Broadbent

Monogamy of highly symmetric states

We study the question of how highly entangled two particles can be when also entangled with other particles. In order to do so we solve optimization problems motivated by many-body physics, computational complexity and quantum cryptography. In particular, we determine the exact maximum values of the projection to the maximally entangled and antisymmetric Werner state possible for a system of size $n$. We find these optimal values by use of SDP duality and representation theory of the symmetric and orthogonal groups, and the Brauer algebra, directly relating our work to the study of entanglement in the context of Werner and isotropic states, and quantum de Finetti theorems.

Baptiste Royer

Professeur, Université de Sherbrooke

Encoding qubits in harmonic oscillators with quantum error correction

Although quantum at its fundamental level, nature appears classical on a macroscopic scale. Indeed, large objects entangle quickly with the surrounding environment, resulting in the rapid loss of individual quantum coherences. The goal of building a quantum computer with a large number of qubits is at odds with this fundamental phenomenon.  Fortunately, quantum error correction (QEC) allows us, in principle, to preserve the information indefinitely in a quantum computer at the cost of added hardware and operations, a price sometimes referred to as control overhead. In the attempts to engineer such a QEC process so far, the control overhead has created a surplus of errors that overwhelm the error correcting ability of the process itself.

In this talk, I will introduce a promising approach to quantum computers: using harmonic oscillator modes to encode qubits. Due to their large number of quantum levels and to the fact that they can be made long-lived, harmonic oscillators such as microwave cavities constitute a hardware efficient approach to QEC. I will discuss recent experimental results that demonstrate for the first time a feature at the heart of QEC: it is possible to overcome the control overhead and use a composite system to extend the lifetime of quantum information beyond the coherence time of the individual subsystems. I will also discuss different advances that allowed to achieve this milestone: improved QEC protocols, new control techniques and the use of modern reinforcement learning.

Denis Seletskiy

Professeur, Polytechnique Montréal

Experimental quantum electrodynamics

Traditional approaches to quantum optics are rooted in the reciprocal, frequency-momentum space. In this talk, I will discuss recent advances toward sub-cycle quantum optics, where, instead, quantum fields are accessed in a localized region of space-time. Both regimes will be compared side-by-side to contrast the advantages of each approach, with a particular emphasis on quantum sensing proposals [1-3] in the mid-infrared frequency range.

In the concluding part of the talk, I will summarize recent advances in producing few-cycle bright one- and two-mode squeezed vacuum states approaching macroscopic photon numbers [4]. Such capabilities are poised to unlock a new era of (extreme) nonlinear quantum optics in the attosecond regime [5].  

 [1 ]Enhanced electro-optic sampling with quantum probes
   Stéphane Virally, Patrick Cusson, DVS, Phys.Rev. Lett. 127, 270504 (2021)

[2] Self-referenced subcycle metrology of quantum fields
   S. Gündoğdu, S. Virally, M.Scaglia, DVS, A.S. Moskalenko, Laser Phot. Rev. 17, 2200706 (2023)

[3] Direct measurement of Husimi-Q function of electric field in time-domain

   Sho Onoe, Stéphane Virally, DVS, arXiv:2307.13088(2023)

[4] Twin beam probe pulses for subcycle sampling of mid-IR quantum fields
   Patrick Cusson; Stéphane Virally; DVS,IRMMW-THz Conference, paper Th-PM2-5-7 (2023)

[5] 2023 Nobel Prize in Physics: Pierre Agostini, Ferenc Krausz and Anne L'Huillier. Experimental methods that generate attosecond pulses for the study of electron dynamics inmatter.

Kai Wang

Professeur, McGill University

Non-Hermitian topological photonics in synthetic dimensions

The nontrivial topological features in the energy bands of non-Hermitian systems provide promising pathways to achieve robust physical behaviors in classical or quantum open systems. Recent advances in synthesizing dimensions beyond the spatial degree of freedom, especially in photonics, have provided unprecedented flexibility in realizing lattice Hamiltonians. A synthetic-dimension approach to non-Hermitian topology can enable new opportunities for observing non-Hermitian topological effects that are difficult to achieve in other means.

In this talk, I will summarize some of our results in the experimental exploration of non-Hermitian eigenvalue topology enabled by the concept of synthetic dimensions. Specifically, a key topological feature of non-Hermitian systems is the nontrivial winding of one energy band in the complex energy plane. I will show our experimental demonstrations of the topological winding of non-Hermitian band energies, achieved by implementing non-Hermitian lattice Hamiltonians along a frequency synthetic dimension formed in a ring resonator undergoing simultaneous phase and amplitude modulations. Furthermore, with two or more non-Hermitian bands, the system can be topologically classified by nontrivial braid groups. By generalizing the experiment to two modulated ring resonators, we performed the experimental demonstration of such braid-group topology with two energy bands braiding around each other, forming nontrivial knots or links.  Our experiments also show that the topological winding or braiding can be controlled by changing the modulation waveform.

Rigel Zifkin

PhD student, McGill University

Director: Lilian Childress

Cavity Enhancement of Diamond Defect Centers

Defect centers in diamond offer a promissing spin-photon interface platform due to their atom-likespin-dependent optical transitions. In addition, their coupling to nuclear spins allows for a multitude of quantum information applications. Achieving high coupling to such emitters presents a long standing challenge to realizing a high-cooperativity cavity QED system and limits state-of-the-art realizations of entanglement protocols. By incorporating defect centers into low-loss, micron-scale optical cavities, the Purcell effect can greatly improve the emission and collection rate of coherent single photons; however, this introduces numerous experimental challenges. I will present our recent results of achieving significant excited-state lifetime reductions in a germanium-vacancy defect system coupled to a cryogenic microcavity.

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Affiches

Louis Beaudoin

Doctorant, Université de Sherbrooke

Directeur: Bertrand Reulet

Sujet à venir

Coralie Bellemare

Étudiante à la maîtrise, Polytechnique Montréal

Directeur: Oussama Moutanabbir

Sujet à venir

Justin Boddison-Chouinard

Postdoc, CNRC Ottawa

Directeur: Louis Gaudreau

Magnetotransport through a gate-defined 1D channel in monolayer WSe₂

Quantum confinement in two-dimensional (2D) transition metal dichalcogenides (TMDs) offers the opportunity to create quantum circuits that can be practical for quantum technologies. The interplay between charge carrier spin and valley, as well as the possibility to address their quantum states electrically and optically, make 2D TMDs an emerging platform for the development of quantum devices. Limited by the difficulty of achieving high quality contacts to semiconducting TMDs and the quality of the material itself, quantum transport experiments are scarce. Here, we present transport experiments focussing on quantum dots, nano-constrictions, and long 1D channels infully encapsulated monolayer tungsten diselenide (WSe₂), made possible by achieving low resistance ohmic contacts.

Valentin Boettcher

Doctorant, Université McGill

Directeur: Bill Coish

Simulating a Topological Quantum Walk in Sythetic Dimensions

The framework of synthetic dimensions offers a new way to engineer physical systems. In this work, we present theoretical progress toward simulating a topological quantum walk in an open system using classical light in a system of coupled fibre loops. The model is interesting, as it features an observable tied to its topological phase taking on universal values if the structure of the environment fulfils certain requirements. The experimental platform which we propose is low cost and highly tunable. We collaborate closely with the group of Philippe St-Jean at the Université de Montréal, which works on the experimental implementation.

Nicolas Dalbec-Constant

Étudiant à la maîtrise,  Polytechnique Montréal

Directeur: Nicolas Quesada

Enhancing Photon Number Classification: A Comparative Study Using Transition Edge Sensor Signals

We present an open-source comparative study of methods for photon number classification with transition edge sensor signals. This research is motivated by the desire to improve the performance of existing systems used for quantum optics and quantum information. We attempt to quantify the impact of signal analysis on the distinction of such signals.

Additionally, the rise in popularity of open-source tools in the field of machine learning makes the implementation of such techniques easier than ever. Among these methods, the use of neural networks demonstrates significant potential due to their capacity to interpret complex signals. However, the abundant amount of design parameters can be intimidating for users without prior knowledge of the field. To bridge the gap and simplify the use of neural networks, a high-level API was created based on popular and reliable libraries such as Pytorch and Scikit-learn. The API allows users to design autoencoder models and train through user-friendly configurations. The trained models can then be loaded to efficiently process signals. This structure allows for unsupervised learning and filtering, two interesting characteristics for precise measurements.

Julien Drapeau

Étudiant à la maîtrise, Université de Sherbrooke

Directeur: Stéfanos Kourtis

Sujet à venir

Marie Frédérique Dumas et Benjamin Groleau-Paré

Étudiante et étudiant à la maîtrise, Université de Sherbrooke

Directeur: Alexandre Blais

Predicting the onset of non-QND effects in the readout of superconducting qubits

Dispersive readout of the transmon can be non-QND due to leakage of the qubit to higher excited states. Full dynamics, analysis of dressed eigenstates, Floquet theory and signature of classical chaos were used to predict onset of non-QNDness. In this work we show that these different approaches lead to the same predictions, which we compare to experiments.

Alexandre Dumont

Doctorant, Université de Sherbrooke

Directeur : Bertrand Reulet

Violation of detailed balance in microwave circuits

We investigate the violation of detailed balance, both in frequency- and time-domain of circuits driven out of equilibrium by the presence of two noise sources and probed by two microwave amplifiers. In the frequency domain we consider the heat, the cross-power and the angular momentum in the voltage plane as global metrics. We show how to relate these quantities to the scattering matrix of the circuits as well as measurements of those metrics at room temperature in circuits with various spatial and time-reversal symmetries operating between 4 and 8 GHz. In the time domain, we provide a direct probe of the violation of the detailed balance by imaging the probability current density in the voltage plane.

Yasmine Faraj

Étudiante à la maîtrise, Université de Sherbrooke

Directeur: Mathieu Juan

Quantum dots in undoped GaAs : Improving fabrication and measurements

Quantum dot devices provide excellent coherence and measurement efficiency as well as small dimensions, thus offering a promising approach for quantum computing. Nevertheless, integrating a large number of quantum dots remains challenging . This project addresses this issue by simplifying the architecture of quantum dots. Concretely, using a double quantum dot device¹ coupled to a superconducting resonator on undoped GaAs and by sending light at a chosen wavelength to create electron hole pairs, we can remove many of the components usually present in standard gate defined quantum dots. Nevertheless , some issues arise in the process, such as the difficulty to predict the behaviour of the device before and after creating charges, the efficiency of the gate’s geometry, the need for a fast and accurate readout, among others. In this work , we are exploring different solutions to some of the current limitations of quantum dot devices . Solving Poisson’s and Schrödinger’s equations for the device and studying the light matter interaction gives us a better understanding of its physical properties and the effects of the gate’s geometry on the wave function. Concerning the readout, the use of a custom made, low cost, and modular up/down conversion circuit allows a fast and accurate measurement of charge population in the device. The resonator’s quality factor will also be investigated using different fabrication methods and geometries.

1 Pierre Lefloïc and Steve Lamoureux’s poster will present in more detail the operation of our current devices.

Clovis Farley

Étudiant à la maîtrise,  Université de Sherbrooke

Directeur: Bertrand Reulet

Sujet à venir

Élie Genois

Doctorant, Université de Sherbrooke

Directeur: Alexandre Blais

‍Combining machine learning characterization and quantum optimal control to improve superconducting qubit operations

Quantum optimal control theory offers a powerful toolbox to design pulse shapes that can realize, in numerical simulations, desired quantum operations with extremely high fidelity. When implementing these pulses in practice, however, the benefit of using optimal pulses over simple analytical forms is often greatly reduced. A significant part of this discrepancy can be attributed to failures of the numerical model to precisely capture the complete quantum dynamics generated by the control electronics. Here, we address this issue directly by building a framework where we break down the problem of realizing high-fidelity quantum operations into two parts. First, we use physics-inspired machine learning to infer an accurate model of the dynamics from experimental data. We investigate a range of trainable models from black-box neural networks to physically informative Lindblad master equation solvers. Second, we use such a trained numerical model in combination with state-of-the-art quantum optimal control to find pulse shapes that realize quantum gates with maximal accuracy given our experimental constraints. Using numerical simulations, we show the feasibility of learning from realistically available data to accurately characterize qubit dynamics and to discover high-fidelity arbitrary single-qubit gates. We then demonstrate our framework in an experimental setting by optimizing the Clifford gate set of a superconducting transmon qubit.

Jaehee Kim

Doctorant, Polytechnique Montréal

Directeur: Nicolas Quesada

Quantum circuit simulation of linear optics using fermion to qubit encoding

We propose a digital simulation protocol for the linear scattering process of distinguishable bosons based on the effectively bosonic states ofmulti-fermions. By combining this phenomenon with the transformation method of fermions and qubits such as the Jordan-Wigner transformation, we  build a protocol to simulate linear scatttering process of N photons in M modes with digital quantum computers. Our method also includes a simple and intuitive way to control the distinguishablity of bosons. We designed a quantum circuit for the simulation of Hong-Ou-Mandel dip of bosons with a discrete internal degree of freedom, which is verified by IBMQ and IonQ. 

Lautaro Labarca et Othmane Benhayoune

Doctorants, Université de Sherbrooke

Directeur: Alexandre Blais

Toolbox for Nonreciprocal dispersive models in circuit QED

To address the growing complexity of quantum processors, systematic approaches have been developed to characterize the effective low-energy quantum Hamiltonian of superconducting circuits, which consider the multimode nature of the distributed circuit, while agnostic on the specific circuit design. Here, we expand the existing toolbox to incorporate nonreciprocal elements and correlated decay rates. Our method provides effective dispersive Lindblad master equations for weakly-anharmonic superconducting qubits coupled by a generic dissipationless nonreciprocal linear system, with effective coupling parameters and decay rates written in terms of the immittance parameters characterizing the coupler. This method can be used for the design of complex superconducting quantum processors with non-trivial routing of quantum information, as well as analog quantum simulators of condensed matter systems.

Antoine Labbé

Doctorant, CNRC Ottawa

Directeur: Louis Gaudreau

Electronic transport measurements of electrostatically defined Hall bar devices in monolayer WSe2

The quest of always reaching for smaller and thinner materials has led researchers to attain the ultimate frontier when, in 2004, the first report of monolayer graphene was published. This discovery led to the creation of a new area of research, the study of two-dimensional (2D) materials and their heterostructures. These materials are composed of layers that can be isolated due to weak interlayer van der Waals forces. One of the most promising categories of 2D materials is the semiconducting transition metal dichalcogenides (TMDs). TMDs have the particularity of changing from indirect band gap semiconductors to direct band gap ones, as they are thinned down from bulk crystal to monolayer i.e. one layer of atoms, leading to a change in their optical and electrical characteristics.

One of the most promising applications of 2D semiconductors are quantum devices based on the confinement of charge carries in monolayer TMDs using electrostatic gates. Towards that goal, one of the key figures of merit of quantum devices using TMDs is the field effect mobility since it is required for efficient operation of the devices. Low mobility of 2D semiconductors is currently one of the main limiting factors to the wider use of these materials in practical applications.

In this poster, I will be presenting our latest efforts towards the investigation of the mobility as well as the quantum Hall effect in monolayer WSe2 based quantum devices that have Hall bar geometry, a standard of measurement in the field.

Marie Lafontaine

Stagiaire, Polytechnique Montréal

Directeur: Nicolas Quesada

Any Value of the Second Order Coherence Function can be Associated with a Single-Mode Gaussian State

In quantum optics, the second-order coherence function, the g^{(2)} function, is a useful measurement to describe the quantum behaviour of a light source. For instance, it is often assumed that a value close to 0 implies a single-photon source, while a value close to 1 is more consistent with a source with classical behaviour.

The g^{(2)} function has positive and real values and can be calculated for each quantum state. Hence, it cannot ensure the state type of the source output since more than two states could have the same g^{(2)} value.

To prove this point, we were able to find single-mode Gaussian states, states that have a Gaussian Wigner function, for any g^{(2)} value. We chose to work with those states since they are the most easily produced in the lab.

To do so, we wrote an optimization algorithm using the library Mr. Mustard. Single-mode Gaussian states are generated and then optimized by the optimization module to get a wanted g^{(2)} value. From this work, we found that a g^{(2)} value close to 0 could also imply a specific single-mode Gaussian state source and not only a single-photon source.

Louis Lamoureux

Étudiant à la maîtrise, CNRC Ottawa

Directeur : Louis Gaudreau

Trapping photo-carriers in undoped accumulation-mode quantum dots using an on-chip microwave resonator for charge readout

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 populating the quantum dots does not require ohmic contact reservoirs, source/drain bias, or external atomic dopants. Therefore, the number of gates can be reduced and the fabrication process can be simplified. Moreover, this 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.

Benjamin Lanthier

Étudiant à la maîtrise, Unviersité 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 the SAT problems genre, more precisely the #3-XORSAT. This project's goal is to study the efficacy of the tensor network contraction in counting the number of solutions of #3-XORSAT instances as a function of the number of clauses to variables ratio.

Ivan Martinez

Doctorant, Université McGill

Directeur: Bill Coish

Sujet à venir

Maxime Massoudzadegan

Doctorant, Université de Sherbrooke

Directeur: Bertrand Reulet

Transport measurements using Megagauss facility

The pseudo-gap is a phase that is still poorly understood but that could reveal important information about the origin of HTc superconductivity. In order to provide information on the pseudo-gap phase, we want to measure quantum oscillations (QO) in the hole-doped cuprates YBCO at low temperature. These measurements will help us to characterise the fundamental state of the pseudo-gap phase, in particular its Fermi surface which is still under debate in the community. To study the pseudo-gap phase at low temperature in YBCO, we need an intense magnetic field of the order of 150T to suppress superconductivity. To reach this extreme magnetic field, we need the Megagauss facility. Also, to measure QO, we need to perform transport measurements in the the harsh Megagauss environment: intense magnetic field, high dB/dt (2μs to reach the maximum field), presence of high voltage and the explosion of the single-wire coil... To realise measurements, sample signal to noise ratio improvement was mandatory. By working on the noise attenuation, the acquisition circuit... we succeeded for the first time to measure a superconducting transition of a cuprate. Thanks to the signal improvement, we now have a clear view of the last issues that we need to get over. We observe that the sample warm up during a shoot: it heat from 4.2K to 30K for a 140T shot. We also found that the heating depends on samples size. To reduce the effect of heating we will reduce the samples size by using FIB technique. This will also show if there is an underlying heating effect or not.

Evgeny Moiseev

Postdoc, Université McGill

Directeur: Kai Wang

Swallowtail singularities in two-mode squeezing of light

We report that swallowtail, a rich degeneracy morphology, can naturally exist in dynamics governedby a bosonic quadratic Hamiltonian (BQH) with asymmetric losses. The swallowtail is one of the elementary catastrophes in Arnold’s ADE classification that appears in different branches of physics from acoustic to attosecond generation. In contrast to the recent observation of swallowtail degeneracy in non-Hermitian systems, the origin of the underlying degeneracy in BQH is the fundamental particle-hole symmetry bosonic particles. We discuss the classification of swallowtail degeneracy and how it can be implemented with optical parametric oscillators.

Manuel Munoz

Postdoc, Université de Sherbrooke

Directeur: Alexandre Blais

A quantum-inspired approximation algorithm for MaxCut

It has been conjectured that near-term quantum computers might offer a speedup in solving combinatorial optimization problems. Much work has been done exploring the extent to which this goal can be achieved via variational quantum algorithms, without very conclusive answers. A side product of this effort has been the construction of quantum-inspired algorithms. Improved or novel classical algorithms which exploit special structures of the problems under study unveiled by their quantum counterparts. In this work we focus on the MaxCut problem and inspired by the solution unitaries  obtained with certain adaptive variational algorithms, we introduce a new quantum-inspired approximation algorithm for this problem. This algorithm is polynomial in the input both in time and space. We study its performance on different families of graphs and provide copious evidence that, for graphs up to 200 nodes, our algorithm produces a better approximated solution than the best classical algorithm, that of Goemans and Williamson.

Naveen Nehra

Doctorant, Unviersité de Sherbrooke

Directeur: Max Hofheinz

Sujet à venir

Gabriel Ouellet

Étudiant à la maîtrise, Université de Sherbrooke

Directrice: Éva Dupont-Ferrier

High-Q superconducting NbN resonators

High quality factor microwave resonators are essential in photon detectors, quantum-limited amplifiers and other superconducting circuit devices. This project aim to design, fabricate on a silicon wafer and measure in the quantum regime NbN superconducting 2D coplanar waveguide (CPW) resonators.

Félix Pellerin

Doctorant, Université de Montréal

Directeur: Philippe St-Jean

Wavefunction tomography in topological dimer chains with long-range couplings

Arthur Perret

Doctorant, Université de Sherbrooke

Directeur: Yves Bérubé-Lauzière

Sujet à venir

Noah Pinkney

Étudiante à la maîtrise, Université McGill

Directeur: Bill Coish

Efficient Quantum Process Tomography via Bayesian Inference

In order to fully characterize a process undergone by a quantum system, the map sending all possible initial states to their respective final states (called the Pauli transfer matrix) can be experimentally determined by quantum process tomography, where a brute-force measurement of an exponentially large number of final observables subject to an exponentially large number of initial conditions elucidates the process completely. For spin-qubit systems where a model for error sources is known a priori, an analytic description of the process matrix can be used to efficiently characterize the dynamics of the system with a number of preparations and measurements that scales only linearly. We will present this analytic characterization of the process matrix for a model two-qubit electron spin system subject to a magnetic field gradient and Heisenberg exchange coupling, and we will highlight the applications of this model to benchmarking quantum gates for spin qubits in quantum dots.

Roya Radgohar

Postdoc, Unviersité de Sherbrooke

Directeur: Stéfanos Kourtis

Stability of Majorana bound states in presence of non-Markovian noise

We studied the dynamics of Majorana box qubits in the presence of non-Markovian environment by performing analytical calculations of the decoherence parameter. We investigated the impact of long-range pairing interactions within the Kitaev pwave superconductors on this parameter. Our findings demonstrate that these interactions decrease the transition amplitude from zero-energy level to excited states, leading to a reduction of decoherence parameter. This outcome proposes a practical approach for creating Majorana qubits that exhibit high resilience against non-Markovian noise.

Thomas Royer

Étudiant à la maîtrise, Université de Sherbrooke

Directeur: Mathieu Juan

Sujet à venir

Martin Schnee

Doctorant, Université de Sherbrooke

Directeur: Stéfanos Kourtis

Sujet à venir

Bill Truong

Doctorant, Université McGill

Directrice: Tami Pereg-Barnea

Sujet à venir

Victor Wei

Stagiaire, Université McGill

Directeur: Bill Coish

Neural network quantum state for learning dynamics and state reconstruction

We present two of our recent works on using neural network quantum state ansatz to help learning properties of a quantum system. The first work studies the dynamics of the Gaudin magnet (“central-spin model”) using machine-learning methods. We use a neural-network representation (restricted Boltzmann machine) to obtain accurate representations of the ground state and of the low-lying excited states of the Gaudin-magnet Hamiltonian through a variational Monte Carlo calculation. From the low-lying eigenstates, we find the non-perturbative dynamic transverse spin susceptibility, describing the linear response of a central spin to a time-varying transverse magnetic field in the presence of a spin bath. In the second work, we present “neural–shadow quantum state tomography” (NSQST)—an alternative neural network-based QST protocol that uses infidelity as the loss function. The infidelity is estimated using the classical shadows of the target state. Infidelity is a natural choice for training loss, benefiting from the proven measurement sample efficiency of the classical shadow formalism. We numerically demonstrate the advantage of NSQST at learning the relative phases of three target quantum states of practical interest, as well as the advantage over direct shadow estimation.