Programme

23 avril

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

11h00 - 12h00 Antoine Browaeys, Université Paris-Saclay, France (Salon A)

           Many-body physics with arrays of individual atoms and optical dipoles

12h00 - 13h30 Dîner (Salle Knowlton)

13h30 - 14h15 Bertrand Reulet, Université de Sherbrooke (Salon A)

           Sensing quantum vacuum fluctuations with non-Gaussian electronic noise

14h15 - 15h00 Peter Grütter, Université McGill (Salon A)

           Spatially resolved random telegraph noise

15h00 - 15h30 Pause café (Salon C)

15h30 - 16h30 Ana Asenjo Garcia, Columbia University, USA (Salon A)

           Universal scaling laws for correlated decay of many-body quantum systems

16h30 - 16h50 Javier Martínez, Polytechnique Montréal (Salon A)

           Validation of Gaussian Boson Sampling implementations using the linear cross-entropy score

16h50 - 17h10 Pierre-Gabriel Rozon, Université McGill (Salon A)

           Optimal twirling depth for classical shadows in the presence of noise

17h10 Session d'afficher avec rafraichissements (Salon C)

19:h30 Souper INTRIQ (Salle Knowlton)

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April 24th

8h30 - 9h30 Pierre Rouchon, École des Mines, École Normale Supérieure, France (Salon A)

            Quantum Error Correction and Feedback

9h30 - 9h50 Karthik Chinni, Polytechnique Montréal (Salon A)

           Beyond the parametric approximation: pump depletion, entanglement and squeezing in macroscopic down-conversion

9h50 - 10h30 Pause café (Salon C)

10h30 - 10h50 Arthur Perret, Université de Sherbrooke (Salon A)

           Engineering the stabilization of a bosonic state

10h50 - 11h10 Vincent Reiher, Université de Sherbrooke (Salon A)

           All-electrical optimal control of the full single electron double quantum dot dynamics

11h10 - 11h55 Bill Coish, Université McGill (Salon A)

            Using neural networks for quantum dynamics and shadow tomography

12h00 - 13h30 Dîner (Salle Knowlton)

13h30 - 14h30 Alicia Bette Magann, Sandia National Labs, USA (Salon A)

           Taking a quantum control perspective on quantum algorithms

14h30 - 15h00 Lev-Arcady Sellem, Université de Sherbrooke (Salon A)

           Quantum reservoir engineering for the protection of Gottesman-Kitaev-Preskill qubits

15h00 - 15h30 Pause café (Salon C)

15h30 - 15h50 Lee Carrier-Coupal, Université de Sherbrooke (Salon A)

           Parameter estimation of quantum systems using iterative gradient-based optimization method

15h50 - 16h20 Olivier Landon-Cardinal, École de technologie supérieure (Salon A)

           Quantum information training at ÉTS‍

16h20 Mot de fermeture (Salon A)

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Conférenciers invités

Alicia Bette Magann

Truman Fellow
Sandia National Labs, USA
Taking a quantum control perspective on quantum algorithms
Quantum computers are progressing at a rapid pace. This progress brings with it significant interest in quantum algorithms research. In this talk, I will explore how quantum algorithms research can be impacted by concepts from quantum dynamics and control. I will begin by providing intuition linking these areas, and survey settings where this intuition has been used previously to fruitfully advance quantum algorithms research. I will then discuss recent works that leverage connections to different branches of quantum control theory and to quantum Zeno dynamics. I will conclude with the perspective that quantum control provides a lens through which we can view, analyze, and develop quantum algorithms into the future.

Sandia National Labs is managed and operated by NTESS under DOE NNSA contract DENA0003525. SAND2024-03940A

Pre Ana Asenjo Garcia

Columbia University, USA
Universal scaling laws for correlated decay of many-body quantum systems
A key challenge in scaling up quantum systems is the potential for correlated decay, which can significantly reduce the lifetime of states of interest.  This talk answers the following question: what is the maximal decay rate of a quantum system, and how does it scale with system size? First, we reformulate the problem of maximal decay rate into finding the ground state energy of a 2-local Hamiltonian. While finding the ground state is widely believed to be hard, it is possible to efficiently find upper and lower bounds. In particular, using ideas from quantum approximation theory and semidefinite programming relaxations, we provide analytical bounds for the maximal decay rate of generic many-body quantum systems. Our bounds are universal in that they only depend on global properties of the decoherence matrix (which describes dissipative couplings between atoms) and agnostic of the specific microscopic interactions. For many classes of physically-relevant systems, the bounds are tight, resulting in scaling laws with system size. For arrays of atoms in free space, the scaling depends only on the dimensionality and interaction range. These laws serve as upper limits on how fast any quantum state can decay, and offer valuable insights for research in quantum optics, quantum information processing, and metrology.

Pr Antoine Browaeys

Institut d’Optique
Université Paris-Saclay, France
Many-body physics with arrays of individual atoms and optical dipoles
This talk will present effort to control and use the dipole interactions between cold atoms to implement spin Hamiltonians useful for quantum simulation of condensed matter or quantum optics situations. We rely on laser-cooled atomic ensembles. By exciting arrays of up to 100 atoms into Rydberg states, we make the atoms interact by the resonant dipole interaction. The system implements the XY spin ½ model, which exhibits various magnetic orders depending on the ferromagnetic or antiferromagnetic nature of the interaction. When the system is placed out of equilibrium, the interactions generate scalable spin squeezing. Analyzing the spread of correlations across the system, we measure the dispersion relation and observe the predicted anomalous behavior in the ferromagnetic case, a consequence of the dipolar interactions. Using an atomic ensemble driven on an optical transition, we also demonstrate the generation of non-classical light in a situation of super radiance.

‍Pr Pierre Rouchon

École des Mines, Ecole Normale Supérieure, France
Quantum Error Correction and Feedback
Quantum error correction relies on a feedback loop. This feedback generally corresponds to a classical controller.  From classical signals obtained  by  error-syndrome measurements (controller input), the controller produces  classical signals  (controller output) in order to correct  the errors  on  physical systems encoding  logical qubits. Quantum error correction can also exploit the dissipation associated with the phenomenon of decoherence. Called autonomous correction by physicists, it then uses feedback where the controller is a dissipative quantum auxiliary system. This talk focuses on the development of such quantum controllers to stabilize logical qubits encoded in harmonic oscillators (bosonic code). Two types of encoding will be considered: cat-qubit  encoded in  two coherent states of opposite phases (Mirrahimi-...-Devoret, NJP 2014), for which bit-flip errors induced by usual noises can be experimentally almost suppressed (Reglade-...-Leghtas, Nature 2024); GKP-qubit encoded in finite energygrid-states approximating position/impulsion Dirac combs (Gotesman-Kitaev-Preskill, PRA 2002) where, in principle, bit-flips and phase-flips could be also almost suppressed.

‍Conférenciers INTRIQ

Arthur Perret

Doctorant, Université de Sherbrooke
Directeur : Yves Bérubé-LauzièreEngineering the stabilization of a bosonic state
‍Bosonic codes area promising tool for quantum error correction, due to their efficient use of the Hilbert space. Notably, cat, GKP and binomial codes have been achieved, or surpassed, break-even in recent years. Current methods to prepare bosonic code states can however lead to large but undetectable errors.

In this work, we address bosonic code state preparation by proposing a parametrized circuit generated by the Trotter expansion of an underlying dynamical equation which has the target state as its only steady state. To ensure the target state to be an asymptotically stable point, we require the Trotter expansion to be made of a unitary evolution followed by a non-unitary one.

We find that for computational and dual basis states of rotationally symmetric codes, there exists a corresponding unitary operation that can be found analytically using only one SNAP gate. Finally, we explore two different methods based on the works of [1,2] in order to generate the desired non unitary evolution.

[1] A. Perret, Y. Bérubé-Lauzière, PRA 109 (2), 022609
[2] M. Kudra et al., arXiv:2212.12079

Bertrand Reulet

Professeur, Université de Sherbrooke
Sensing quantum vacuum fluctuations with non-Gaussian electronic noise
The statistics of electron transport in a tunnel junction is affected by fluctuations of its voltage bias, which modulates the probability for electrons to cross the junction. We exploit this phenomenon to provide a direct measurement of quantum vacuum fluctuations in the microwave domain of a resistor placed at ultra-low temperature: we show that the amplified vacuum fluctuations are correlated with the noise generated by the junction to contribute to a third moment of detected voltage fluctuations. This experiment constitutes an absolute measurement of noise, not affected by the unavoidable noise added by the detection setup.

Bill Coish

Professeur, Université McGill
Using neural networks for quantum dynamics and shadow tomography
I will discuss two cases where we have found neural networks to be an important practical tool. The first is in studying decoherence/dynamics for quantum systems that are well described by the "Gaudin magnet" [1]. This model precisely describes the decoherence dynamics of an electron-spin qubit interacting with a nuclear spin environment. Although the model has many symmetries (it is integrable), finding closed-form solutions for the dynamics is nevertheless highly challenging. We speculate that neural networks may soon be able to exploit these symmetries to find more efficient numerical solutions to this and other problems of integrable quantum systems. I will also discuss recent work on improving classical shadow tomography of quantum states with a neural-network ansatz [2]. By constraining results found via classical shadows to a physical representation of the underlying pure quantum state, certain features of the quantum state can be extracted more effectively than would be possible using the standard (more general) formulation of classical shadow tomography.

[1] V. Wei, A. Orfi, F. Fehse, and W. A. Coish "Finding the Dynamics of an Integrable Quantum Many-Body System via Machine Learning", Adv. Phys. Research 3, 2300078 (2023)

[2] Victor Wei, W.A. Coish, Pooya Ronagh, Christine A. Muschik "Neural-Shadow Quantum State Tomography", arXiv:2305.01078

Javier Martinez

Doctorant, Polytechnique Montréal
Directeur : Nicolas Quesada
Validation of Gaussian Boson Sampling implementations using the linear cross-entropy score
Gaussian Boson Sampling (GBS) is a promising architecture for experimentally demonstrating quantum advantage. Theoretically, there is evidence that sampling from the probability distribution of a lossless GBS experiment, either exactly or approximately, is a computationally hard task. Real-world implementations of GBS suffer from inevitable losses and other sources of noise, and their expected theoretical descriptions, i.e. their ground truth models, diverge from that of an ideal, lossless implementation. Nevertheless, it is assumed that the ground truth is sufficiently close to the ideal model, so that sampling from the corresponding probability distribution is still computationally hard. This is why the current validation techniques for GBS experiments rely on using statistical measures to show that the experimental samples really follow the ground truth models. These strategies have limitations and cannot readily verify quantum advantage claims. Rather, they are used to build up confidence in the correct functioning of the experiments. The main drawback of this approach to validation is that we cannot be sure if the ground truth distributions are computationally hard to sample from, and this opens the door to classical algorithms that exploit the noise in the ground truth models to efficiently simulate the experiments. In this work, we argue that we can avoid this issue by validating GBS implementations using their corresponding ideal distributions directly. We explain how to use a modified version of the linear cross-entropy, a measure we call the LXE score, to find reference values that may tell us how close a given GBS implementation is to its corresponding ideal model. Moreover, we analytically compute the score that would be obtained by a lossless GBS implementation.

Peter Grütter

Professeur, Université McGill
Spatially resolved random telegraph noise
Low-frequency noise due to two level fluctuations inhibits the reliability and performance of nanoscale semiconductor devices and challenges the scaling of emerging spin based quantum sensors and computers.

Here, we measure temporal two-state fluctuations of individual defects at the Si/SiO2 interface with nanometer spatial resolution using atomic force microscopy. When measured as an ensemble, the observed defects have a 1/f power spectral trend at low frequencies. The presented method and insights provide a more detailed understanding of the origins of 1/f noise in silicon-based classical and quantum devices, and could be used to develop processing techniques to reduce two-state fluctuations associated with defects.

Karthik Chinni

Postdoc, Polytechnique Montréal
Directeur : Nicolas Quesada
‍Beyond the parametric approximation: pump depletion, entanglement and squeezing in macroscopic down-conversion
We study the dynamics of the pump mode in the down-conversion Hamiltonian using the cumulant expansion method, perturbation theory, and the full numerical simulation of systems with a pump mean photon number of up to one hundred thousand. We particularly focus on the properties of the pump-mode such as depletion, entanglement, and squeezing for an experimentally relevant initial state in which the pump mode is initialized in a coherent state. Through this analysis, we obtain the short-time behavior of various quantities and derive timescales at which the above-mentioned features, which cannot be understood through the parametric approximation, originate in the system. We also provide an entanglement witness involving moments of bosonic operators that can capture the entanglement of the pump mode. Finally,we study the photon-number statistics of the pump and the signal/idler modes to understand the general behavior of these modes for experimentally relevant time scales.

Lee Carrier-Coupal

Doctorant, Univerisité de Sherbrooke
Directeur : Yves Bérubé-Lauzière
Parameter estimation of quantum systems using iterative gradient-based optimization method
The characterization of quantum systems is important as it allows us to acquire information about these systems such as their properties and behavior. The characterization of quantum devices is equally important, as they are subject to imperfections during their fabrication; it is therefore crucial to verify that these quantum devices function adequately. Otherwise, they will not be able to function to their full capacity. For this presentation, we will focus on a specific aspect of characterization, namely parameter estimation. The parameters contained in the equation of dynamics that determines the behavior of a quantum device need to be determined in order to properly model its operation. We will show that it is possible to determine the optimal value of these parameters that best reflects the observations made of the system using iterative optimization methods based on the gradient.

Lev-Arcady Sellem

Postdoc, Université de Sherbrooke
Directeur : Alexandre Blais et Baptiste Royer
Quantum reservoir engineering for the protection of Gottesman-Kitaev-Preskill qubits
At first sight, dissipative processes are the source of quantum decoherence and limit the time scale over which a given system can be controlled. On the other hand, from a control point of view, the availability of dissipative processes also opens new avenues, in particular regarding the stabilization of quantum systems. This strategy, known as quantum reservoir engineering, can be traced back to the seminal work of Alfred Kastler on optical pumping.

We will present how to exploit quantum reservoir engineering to stabilize and control Gottesman-Kitaev-Preskill (GKP) qubits - a bosonic encoding exploiting exotic states of light or matter to reduce the hardware cost of quantum error correction. Our approach relies on nonlinear modular interactions with a dissipative auxiliary system to autonomously stabilize the GKP code. This approach robustly suppresses local noise processes; unlike previous proposals, it also suppresses the propagation of noise from the auxiliary system used for dissipation engineering itself. In a state-of-the-art experimental setup based on superconducting circuits, we estimate that the encoded qubit lifetime could extend several orders of magnitude beyond break-even.

Olivier Landon-Cardinal

Professeur, École de technologie supérieur - ÉTS
Quantum information training at ÉTS
Overview of undergraduate and graduate developments in quantum information training at ÉTS from January 2021 to today.

Pierre-Gabriel Rozon

Doctorant, Université McGill
Directrice : Tami Pereg-Barnea
Optimal twirling depth for classical shadows in the presence of noise*
The classical shadows protocol represents an efficient strategy for estimating properties of an unknown state ρ using a finite number of copies and measurements. In its original form, it involves twirling the state with unitaries randomly selected from a fixed ensemble and measuring the twirled state in a predetermined basis. To compute local properties of the system, it has been demonstrated that optimal sample complexity (the minimal number of required copies) is remarkably achieved when unitaries are drawn from shallow-depth circuits composed of local entangling gates, as opposed to purely local (zero-depth) or global twirling (infinite-depth) ensembles.

In this presentation, I will discuss an improvement of these ideas by considering the sample complexity as a function of the circuit's depth, in the presence of noise. Noise is bound to be present in any experimental implementation of such shallow-depth circuits, which has important implications for determining the optimal twirling ensemble. Under fairly general conditions, I will: i) show that any single-site noise can be accounted for using a depolarizing noise channel with an appropriate damping parameter, f; ii) discuss thresholds fth at which optimal twirling reduces to local twirling for arbitrary operators; iii) conduct a similar analysis for nth-order Renyi entropies (where n is greater than or equal to 2); and iv) provide a meaningful upper bound, tmax , on the optimal circuit depth for any finite noise strength f. This upper bound applies to all operators and entanglement entropy measurements. These thresholds strongly constrain the search for optimal strategies to implement the classical shadows protocol and can be easily tailored to the experimental system at hand.

*The authors acknowledge funding support from NSERC,FRQNT, INTRIQ, the Spin Chain Bootstrap Project through DOE-BES and the Quantum Telescope Project through DOE-HEP.

Vincent Reiher

Doctorant, Université de Sherbrooke
Directeur : Yves Bérubé-Lauzière
All-electrical optimal control of the full single electron double quantum dot dynamics
The single electron double quantum dot (DQD) with micromagnets described in [1] is a highly versatile architecture and an extremely promising candidate for the physical implementation of a qubit. Although electrical control of the electron charge states in such a device has long been standard, direct spin manipulation requires oscillating magnetic fields which are impractical experimentally. This difficulty can be circumvented through electric dipole spin resonance (EDSR) which allows electron spin state manipulations via AC electric fields in such devices [2].

We present a gradient ascent control approach based onthe GOAT algorithm [3] which combines standard electrical control of the charge states with electrical spin state manipulation through EDSR to yield an all electrical control scheme for the full state space of the DQD using low parameter smooth pulses to synthesize arbitrary operations on the device.

[1] Benito, M. and Mi, X. and Taylor, J. M. and Petta,J. R. and Burkard, G. Phys. Rev. B 96, 235434 (2017)

[2] Benito, M. and Croot, X. and Adelsberger, C. and Putz, S. and Mi, X. and Petta, J. R. and Burkard, G. Phys. Rev. B 1 00, 125430(2019)

[3] Machnes, S. and Assémat, E. and Tannor, D. and Wilhelm, F. K. Phys Rev. Letters 120, 150401 (2018)

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Affiches

Alex Chapple

Doctorant, Université de Sherbrooke
Directeur : Alexandre Blais
Sujet à venir

Amin Lakhal

Étudiant à la maîtrise, Polytechnique Montréal
Directeur : Denis Seletskiy
Optical spectroscopy of thermal current fluctuations detected via quantum interference of absorption pathways in centrosymmetric semiconductors
We propose a time-resolved optical measurement scheme for sampling transient thermal currents inside a bulk centrosymmetric semiconductor. The technique relies on spontaneous emission of second harmonic light, triggered by four-wave mixing between a pulsed below-gap optical excitation and a spontaneous intraband polarization. This all-optical technique requires neither contact nor bias fields, making it an innovative experimental method for exploring thermal and quantum fluctuations in the solid state in a non-invasive manner. Theoretical estimates bracket signal in the range of 0.1 to 1 relative to the shot noise of the probe, motivating experimental implementations of the proposal.

Amir Hosein Esmaeili

Doctorant, Université de Sherbrooke
Directeur : Max Hofheinz
Precise Phase-Locked Voltage Bias for Josephson Photonics Devices
Josephson photonics devices use voltage-biased Josephson junctions to generate and measure microwave quantum signals. In these devices, the energy of a tunneling Cooper-pair, 2eV, where V is the voltage applied to the junction, is transferred to one or several microwave photons. Noise of the voltage bias, therefore, causes phase noise on the devices, limiting the performance of some devices and making others impossible. So far, in our research group, voltage sources with 5Ohm output impedance have been implemented and reach an effective noise temperature of 20mK corresponding to a voltage noise of approximately 2 pV/sqrt(Hz).

The goal of this project is to reduce voltage noise even further and control the phase associated with the time integral of voltage, to enable new Josephson photonics devices. We will explore a way to use Shapiro steps where an external clock signal is applied to Josephson junctions to generate extremely precise voltages. The SI definition of the volt is based on this working principle since 1990.

We will then use this device to explore power other Josephson photonics devices.

Amirali Ekhteraei

Étudiant à la maîtrise, Université McGill
Directeur : Kai Wang
Sujet à venir

Arthur Dupré

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

Arthur Perret

Doctorant, Université de Sherbrooke
Directeur : Yves Bérubé-Lauzière
Sujet à venir

Benjamin Lanthier

Étudiant à la maîtrise, Université de Sherbrooke
Directeur : Stéfanos Kourtis
Accelerating Counting Using Tensor Networks
Tensor networks are a versatile tool employed in numerous fields, spanning from classical quantum many-body system simulations to quantum circuit modeling. In this work, we'll discuss about the use of this method with 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.

Coralie Bellemare

Étudiante à la maîtrise, Polytechnique Montréal
Directeur : Oussama Moutanabbir
Toward Silicon-Integrated SWIR Single-Photon Detectors

Catarina Castro and Félix Wilhelmy

Étudiante et étudiant à la maîtrise, ÉTS
Directeur : Olivier Landon-Cardinal
‍Robustesse des classificateurs quantiques face aux attaques adverses
‍Évaluer la robustesse des réseaux neuronaux formés en utilisant l'informatique quantique contre les attaques adverses et comparer leur résilience et leurs performances à celles formées par des méthodologies informatiques classiques.

Dominic Leclerc

Étudiant à la maîtrise, Université de Sherbrooke
Directrice : Éva Dupont-Ferrier
Sujet à venir

Étienne Pilon

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

Evgeny Moiseev

Postdoc, Université McGill
Directeur : Kai Wang
Exceptional swallowtail degeneracies in driven-dissipative two-modesqueezing
We explore the structure of exceptional manifolds for the dynamics of two modes governed by a general bosonic quadratic Hamiltonian (BQH).

We find that the space of degeneracy morphology forms a swallowtail structure \cite{arnol2003catastrophe} if the pseudo-Hermitician symmetry of the underlying non-Hermitian dynamics is broken.  

By breaking the pseudo-Hermitician symmetry with asymetric losses for two modes, we construct trajectories around the exceptional line that leads to the non-trivial eigenvalue topology of the two modes.

Finally, we discuss the classification of swallowtail degeneracy and how it can be implemented with an optical parametric oscillator.

Félix Pellerin

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

Fnu Naveen

Doctorant, Université de Sherbrooke
Directrice : Éva Dupont-Ferrier
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. Our goal is to design and fabricate superconducting CPW NbN resonatorson silicon, which we measure in the single photon regime (SPR).

Ivan Martinez

Doctorant, Université McGill
Directeur : Bill Coish
Driving an Ising system into a topological magnon insulator
Topological magnon insulators are two-dimensional systems with an ordered magnetic ground state and gapped bosonic magnetic excitations (magnons). In the presence of an out-of-plane Dzyaloshinskii-Moriya interaction (DMI), a two-dimensional magnetic system may support excitations corresponding to bands of one-magnon and two-magnon modes. These bands may be topologically non-trivial (characterized by non-zero Chern numbers) and therefore these systems support chiral magnon edge states. Recently, Ref. [1] studied magnetic systems where the (otherwise trivial) single-magnon and two-magnon bands are hybridized by in-plane DMI, resulting in a topologically non-trivial band structure. We aim to find magnetic systems in which such hybridization between (initially trivial) bands having a different magnon number is achieved by driving the system with time-dependent electromagnetic fields. The resulting bands may have non-zero Chern numbers that can be modified by varying the relative phase between ac magnetic fields driven at two distinct frequencies.

Jérémy Peltier

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

Joffrey Rivard

Doctorant, Université de Sherbrooke
Directrice : Éva Dupont-Ferrier
Gate reflectometry measurements on industrial CMOS devices using superconducting spiral inductors
An advantage of creating spin qubits in silicon is their compatibility with industrial CMOS scalable platforms, making it easier to improve the scalability and manufacturing of spin qubits [1]. However, the conventional technique for spin readout, involving the utilization of a single electron transistor positioned near the quantum dot for charge sensing, introduces a significant constraint on the scalability of spin qubits. In that regard, charge sensing by radio frequency reflectometry appears as a superior readout method. Working with the same gate as the one controlling the qubits, this method not only offers a more compact design [2,3,4], but also improves measurement speed and limits the 1/f noise by working in a radio frequency range.

To demonstrate the compatibility of reflectometry measurements with CMOS technologies, we present charge sensing gate-based reflectometry measurements on a variety of transistor architectures with high potential for implementing scalable spin qubits on a 300mm wafer. These architectures include FinFET, Gate all-around, and FDSOI silicon nanowires. We also extend this technique to probe disruptive technologies such as single carbon nanotube transistors. We employ superconducting spiral inductors to achieve a higher quality factor, better impedance matching and improved frequency range, thereby mitigating differences in impedance between devices.

Jonathan Pelletier

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

Laurine Marian

Doctorante, Université de Sherbrooke
Directeur : Bertrand Reulet
Sujet à venir

Lautaro Labarca

Doctorant, Université de Sherbrooke
Directeur : Alexandre Blais
Estimation of isotropic displacement with GKP states
We explore the use of stabilized GKP states as sensor states for the estimation of isotropic Gaussian displacement. Using ideas and methods from QEC and GKP stabilization we show how the estimation limit achievable with Gaussian states and operations can be beaten. In particular, our protocol implements a phase estimation measurement while preserving the number of photons in the cavity.

Marc-Antoine Roux

Doctorant, Université de Sherbrooke
Directrice : Éva Dupond-Ferrier
From zero to hero: booting up a spin qubit quantum processor in a flash
Spin qubits make a good quantum processor because they have a long coherence time and are compatible with the fabrication processes of the semiconductor industry. However, extensive tuning is required to achieve the highest gate and readout fidelities needed for quantum computation. I will present FPGA tools, developed with Keysight’s Quantum Engineering Toolkit, made specifically for quantum dot tuning. I will describe how those tools enable faster and easier tuning. Specifically, I show that some parts of the tuning process can be done 8.6 times faster.

Mona Arabmohammadi

Doctorante, Université de Sherbrooke
Directeur : Max Hofheinz
High-Frequency Quantum-Limited Amplifier
Gaining a better understanding of quantum phenomena and furthering the development of next-generation technologies is heavily dependent on obtaining accurate measurements. One of the most difficult tasks is to enhance the signal-to-noise ratio. Usually, quantum response signals have very low energy, sometimes only a few photons. Therefore, the transmitting power must also be at this low level to prevent the qubit transition to higher-energy states, which would disrupt its role as a two-state system. In many applications, such as reading a qubit, where we need to amplify the signal while adding the minimum noise, the use of a quantum-limited amplifier is essential.

This research project aims to develop and characterize a quantum-limited amplifier operating at high frequencies using Inelastic Cooper Pair Tunneling Amplification (ICTA). The term "high frequency" refers to the amplifier’s operational range, and in this context, it ranges from 75 to 110 GHz, which is the upper limit of available microwave components, including the cryogenic amplifier. The necessity of a quantum-limited amplifier at these frequencies may not be apparent for industrial applications but is crucial for various scientific research areas, including particle physics (e.g., axion detection), high-frequency quantum computing, and radio astronomy.

One might wonder why we prefer ICTA over Parametric Amplification (PA). As discussed, in the previous chapter, PA requires a microwave source and specialized tuning for the pump frequency, which complicates the design, especially at high frequencies and adds to the cost. In contrast, ICTA offers a simpler solution, by adjusting the voltage bias, we can enhance the energy of Cooper pairs without the need for complex tuning components. Additionally, increasing the operating frequency is straightforward by raising the DC voltage, making it easier to control. Therefore, this research focuses on exploring the potential of a high-frequency quantum-limited amplifier utilizing inelastic Cooper pair tunneling.

Noah Pinkney

Étudiant à la maîtrise, Université McGill
Directeur : Bill Coish
Hardware-aware quantum process tomography via Bayesian inference
The Pauli transfer matrix can be experimentally determined by quantum process tomography, where measurements of an exponentially large number of observables subject to an exponentially large number of initial conditions completely characterize the quantum process. We present an analytic description of incoherent error sources affecting electron spin-qubits on a double quantum-dot device to solve for the Pauli transfer matrix. With this complete description of the dynamics, we apply Bayesian inference techniques to adaptively quantify the error sources in our model with the fewest possible measurements. In doing so, we establish a protocol for efficient, hardware-aware quantum process tomography.

Othmane Benhayoune Khadraoui

Doctorant, Université de Sherbrooke
Directeur : Alexandre Blais
Toolbox for nonreciprocal dispersive models in circuit QED
We provide a systematic method for constructing effective dispersive Lindblad master equations to describe weakly-anharmonic superconducting circuits 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 article extends the foundational work of Solgun et al. [1] for linear reciprocal couplers described by an impedance response. Here, we expand the existing toolbox to incorporate nonreciprocal elements, account for direct stray coupling between immittance ports, circumvent potential singularities, and include collective dissipative effects that arise from interactions with external common environments. We illustrate the use of our results with a circuit of weakly-anharmonic Josephson junctions coupled to a multiport nonreciprocal environment and a dissipative port. The results obtained here 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.
[1] F. Solgun, D. P.DiVincenzo, and J. M. Gambetta, Simple impedance response formulas for the dispersive interaction rates in the effective hamiltonians of low anharmonicity superconducting qubits, IEEE Transactions on Microwave Theory and Techniques 67,928 (2019)

Pascal Obled-Bureau

Doctorant, Université de Sherbrooke
Directeur : Baptiste Royer
Error protected operation on superconduting cavities using dissipation engineering

Philippe Gigon

Stagiaire, Université de Sherbrooke
Directeur : Alexandre Blais
Many Mode Floquet Formalism and Application to Fluxonium Lambda Gate
In this work, we investigate Many Mode Floquet Theory (MMFT) and its applications to superconducting qubits in the presence of multiple drives. We demonstrate how the combined use of MMFT and numerical Schrieffer-Wolff or Kolmogorov-Arnold-Moser perturbation theory provides valuable insights into frequency collisions that occur when driving a system with multiple drive tones. Additionally, we propose a method for obtaining the effective dynamics of the system using the Floquet-Shirley matrix. By applying these tools, we explore the Lambda system and illustrate the emergence of coherent Raman transitions between the uncoupled states |g⟩ and |e⟩ within our framework. Furthermore, we analyze the fluxonium qubit as an example, extracting the drive frequency required to implement a Lambda-like gate between two states without direct coupling. Our toolbox offers a faster alternative to full-time simulations and enables a deeper understanding of multi-drive control problems.

Pierre Lefloïc

Doctorant, Université de Sherbrooke
Directeur : Mathieu Juan
Photoinitialization of quantum dots in undoped GaAs
‍Scaling  up gate-defined quantum dot systems is hampered by the rapid growth in the  number of control gates. To tackle this challenge, we propose a novel scheme,  in which the quantum dots are created from optically generated charges trapped beneath accumulation gates. By shining an above-the-gap laser light onto an undoped GaAs substrate, we demonstrate that it is possible to create and separate electron-hole pairs to form quantum dots with one of the two polarities. By pairing this technique  with a superconducting coplanar waveguide resonator for the charge readout [1-3], we achieve a working many-charge double quantum dot device with  controllable interdot charge exchange. The device, comprised of only two plunger gates and one tunnel coupling gate, shows that the initialization of quantum dots does not require reservoirs, source/drain bias, ohmic contacts, or doping. Therefore, the number of gates can be reduced and the fabrication  process can be simplified. Moreover, this new method can be applied to a wide range of semiconductor quantum dot systems. Such a hybrid device is the first step towards a more scalable design for quantum dot arrays. It is also a good starting point for quantum transducing thanks to the optical–matter–microwave interaction.

Richard Samuel

Stagiaire, ÉTS
Directeur : Olivier Landon-Cardinal
Developing a Penny Lane plugin to interface with MonarQ

Rogalle Alexandre

Doctorant, Université de Sherbrooke
Directeur : Max Hofheinz
Cascaded microwave photomultiplier based on voltage-biased Josephson Junctions
Single photon detectors are an essential component in many quantum communication and computation schemes as well as for fundamental physics such as the search for dark matter candidates, such as dark photons or axions. While a wide range of single photon detectors is available commercially in the optical domain, there are not yet many options in the microwave range. We propose an effective and flexible device that offers wide bandwidth and high dynamics. This detector uses Josephson junctions (JJ) to photomultiply an incoming photon into several outgoing photons. To do this, we bias the junction with voltage, which allows for energy gain due to inelastic tunneling of Cooper pairs. A microwave burst at the output of this device would then indicate a photon at the input. However, a single device does not allow for sufficient gain to detect such a burst with linear amplifiers. To increase the photomultiplication gain, two options are available: directly increasing the photon-number gain of the  photomultiplication process or cascading 2 photomultipliers. Our theoretical analyses indicates that the latter option promises a lower rate of false positives (dark rate). We present here the operating principle and the initial measurement results. The device is not fully optimized yet, but we have observed photomultiplication up to 25, which is enough to read out the multiplier with linear amplifiers.

Roya Radgohar

Postdoc, Université de Sherbrooke
Directeur : Stéfanos Kourtis
Optimal noisy quantum transport on complex networks
Environment-assisted quantum transport has been experimentally and theoretically detected in many simple networks. Regarding the key role of optimal transport process in natural and man-made quantum complex systems, it is of crucial importance to investigate how transfer efficiency on quantum complex networks subjected to environmental noise is affected by network topology. Motivated by the remarkable efficiency of exciton transport within photosynthetic systems (light-harvesting complexes) in the initial stages of photosynthesis, we define the total population transferred to the trapping site as transfer efficiency. We generalize Markovian Lindblad master equation to describe the dynamics of transport process in presence of dephasing environment through complex networks. Our numerical results demonstrate that the most efficient transfer demands a delicate balance between the system Hamiltonian and pure dephasing induced by environment that strongly depends on the network structure. We show that the robustness of optimal transport against dephasing noise is also affected by network structure such that Erdös-Rényi, as well as scale-free networks with shorter average path length are more robust than their corresponding regular networks with longer average path length.

Thomas Royer

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

Valentin Boettcher

Doctorant, Université McGill
Directeur : Bill Coish
Sujet à venir

Yasmine Faraj

Étudiante à la maîtrise, Université de Sherbrooke
Directeur : Mahieu Juan
Quantum dots in undoped GaAs : Industrialization and improvements
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 attempts to address this issue by simplifying the architecture of gate-defined quantum dots [1]. Using a fabrication process more fit for industrialization, a second generation of devices has been made in collaboration with the National Research Council (NRC). However, some issues arose in the process. In order to prepare the fabrication of the next generation of devices, we address in this work some of the issues by optimizing the design and the measurement of the device, and by exploring different fabrication methods to improve the quality factor of the resonator.

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

Yuming Niu

Étudiant à la maîtrise, Université McGill
Directeur : Kai Wang
Sujet à venir

Zoé McIntyre

Doctorante, Université McGill
Directeur : Bill Coish
Sujet à venir