May 15, 2018 10:30 AM

May 16, 2018 3:50 PM
May 15, 2018 10:30 AM

May 16, 2018 3:50 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
LouisPhilippe 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 PeregBarnea, McGill University
Dynamic topology  quantized conductance and Majoranas on wires
Professor Philippe StJean, Université de Montréal
Topological physics with light and matter: new horizons
Break
Louis Gaudreau, National Research Council Canada (Ottawa)
Entanglement distribution via coherent photontospin conversion in semiconductor quantum dot circuits
Philippe Lamontagne, National Research Council Canada (Montréal)
BlackBox Impossibility in the Common Reference Quantum State Model
Olivier GagnonGordillo, Québec quantique lead
Presentation of the Québec Quantum ecosystem
Institut quantique  Université de Sherbrooke
Classical and quantum computations as tensor networks
Tensor networks are multilinearalgebra data structures that are finding application in diverse fields of science, from quantum manybody 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 nonlinear 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 sideband cooling. In general, linear cavities are favoured to allow for large photon number providing stronger cooling. I will show that, surprisingly, nonlinear 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 outofequilibrium 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 timeperiodic 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 faulttolerant quantum computation[i]. In the late 2000s, Duncan Haldane (colaureate 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 solidstate, leading to the emergence of a blooming field called topological photonics[iii].
In this presentation, I will describe recent experimental works based on excitonpolaritons, a hybrid lightmatter 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 welldefined topological properties in lattices of coupled microcavities and makes them inherently nonhermitian; on the other hand, their matter part gives rise to a strong Kerrlike 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 solidstate. I will conclude this presentation by discussing how topological protection can provide a powerful asset for generating and stabilizing manybody 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 manybody 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. StJean et al. Opt. Mat. Express 11, 1119 (2021)
[v] I. Carusotto and C. Ciuti. Rev. Mod. Phys. 85, 299 (2013)
[vi] P. StJean 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 photontospin 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 timebin encoded photonic qubits to electron spin qubits and will describe adaptations to employ heavy holes which have a number of attractive properties including gfactor 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 cosupervision 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 exchangeonly 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 lightmatter 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 nanooptoelectronics group with Frank Koppens where he was awarded the prestigious MarieCurie 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)
BlackBox 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 wellknown Common Reference String (CRS) model but appears to be more powerful. In the twoparty setting, a CRQS can sometimes exhibit properties associated with a Random Oracle queried once. We formalize this notion as a Weak OneTime 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 blackbox 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 FiatShamir transform whose security can be blackbox 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 blackbox reduced to a cryptographic game assumption.
Senior Product Manager
Aspen Technology
Biography
Montrealbased quantum physicist, senior product manager, and full stack developer with strong experience building awardwinning 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 MachineToMachine 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.
10h30  10h55 Inscription
10h55  11h00 Mots d'ouverture (Salon A)
11h00  12h00 Max Hofheinz, Université de Sherbrooke (Salon A)
Quantum microwave devices based on inelastic
Cooperpair tunneling
12h00  13h30 Dîner (Salle 4 Canards)
13h30  14h30 John Mattsson, Ericsson Research (Salon A)
PostQuantum Cryptography in Practice
14h30  15h00 Michael Hilke, McGill University (Salon A)
Decoherence in qutrits (3qubit systems)
15h00  15h30 Sergei Studenikin, National Research Council Canada (Salon A)
Hole spin qubits in laterla GaAs/AlGaAs double quantum dots
15h30  16h00 Pause café (Salon B)
16h00  17h00 Eva DupontFerrier, Université de Sherbrooke (Salon A)
Quantum information with dopants in silicon
17h00  Session d'affiches et rafraîchissement (Salon B)
19h30  Souper INTRIQ (Salon C)
9h00  10h00 Miles Stoudenmire, Computational Quantum Physics Center (Salon A)
Classical and Quantum Machine Learning with Tensor Networks
10h00  11h00 Pause café (Salon B)
11h00  12h00 Dave Touchette, Institute for Quantum Computing (Salon A)
Interactive Quantum Information Theory
12h00  13h45 Dîner (Salle 4 Canards)
13h45  14h45 William WitczakKrempa, Université de Montréal (Salon A)
Understanding exotic magnetism through quantum entanglement
14h45  15h15 Olivier LandonCardinal, McGill University
Quantitative Tomography for Continuous Variable Quantum Systems
15h15  15h45 Charles Bédard, Université de Montréal
An Algorithmic Approach to Quantify Emergence
15h45  15h50 Mots de clôture
Ericsson Research
PostQuantum Cryptography in Practice
The last 5 years, the use of cryptography has exploded and the use of cryptography for authentication, confidentiality, and integrity protection is required even in constrained IoT environments. The use of cryptography everywhere has been enabled by new faster algorithms and security protocols combined with faster hardware. Unfortunately, a large enough quantum computer running Shor’s algorithm would practically break all commonly used public key algorithms such as RSA and ECC. Such algorithms are typically used for authentication and key exchange. NIST has just initiated PQC standardization with the goal of standardizing new asymmetric algorithms replacing RSA and ECC. The new algorithms are based on mathematical problems not affected by Shor’s algorithm (e.g. lattices, codes, multivariate, isogenies). Grover’s algorithms could theoretically break some symmetric algorithms, but it is unknown if it will ever be relevant for practical cryptanalysis. QKD, which only provides unauthenticated key exchange, will likely continue to be a niche product as postquantum cryptography running on classical computers are likely to provide excellent security to a much lower cost. In this talk we describe the current use cases of cryptography and the effects of quantum computer would affect these, the current status and challenges with postquantum cryptography running on classical computers and the role of quantum cryptography.
Université de Montréal
Understanding exotic magnetism through quantum entanglement
I’ll present 2 spin models that host unusual emergent excitations. First, the 1d Motzkin spin chain introduced by Shor et al has a solvable entangled groundstate, but a gapless excitation spectrum that is poorly understood. By using largescale Density Matrix Renormalization Group (DMRG) simulations, we find that that there are 2 lowenergy excitations with distinct and nontrivial dispersion relations. Various correlation functions and entanglement properties will be discussed. Second, I’ll discuss the Heisenberg model on the frustrated kagome lattice, which is one of the most studied and experimentally relevant models for a quantum spin liquid. Despite years of study, its solution remains under debate. Using DMRG on this model, we uncover universal features of neutral Dirac fermions in the entanglement entropy. We infer that these are the fractionalized excitations of the kagome quantum spin liquid. Such methods can be used to study other quantum states of matter, such as systems poised near a quantum critical phase transition.
Université de Sherbrooke
Quantum information with dopants in silicon
Dopants in silicon are promising candidates for quantum information processing. They form an extremely compact and reproducible quantum system in which the nuclear spin can be used to store quantum information, while the electron spin serves as a means of interfacing nuclear spin with other quantum systems. The nuclear spin in purified silicon has set the record for coherence times in solid state qubits. Spin readout and manipulation for both electron and nuclear spins have been demonstrated, with fidelities beyond the threshold for quantum error correction protocols. But high coherence times come in pair with strong isolation from the environment, i.e. spins of dopants are difficult to address and couple together which prevents realization of two qubits gates.
I will show how integration of dopants in transistors form state of the art CMOS technology could help solve this problem. We use a splitgate transistor to electrically control two dopants connected in series and perform coherent charge exchange between them. For longer range coupling between dopants, a possibility is to use magnetic coupling of the dopants’ spins to superconducting circuits. I will show the first steps in that direction, namely the realization of high quality factor superconducting resonator, tunable in frequency by means of an embedded SQUID and which can perform under magnetic fields.
Université de Sherbrooke
Quantum microwave devices based on inelastic Cooperpair tunneling
In superconducting quantum circuits the Josephson junction is the key element because it is the only strongly nonlinear and dissipationless circuit element we know. Usually it is used in the superconducting state where it acts as a nonlinear inductor. But a small Josephson junction can be nonlinear and dissipationless also when a nonzero DC voltage below the gap is applied. In this case a Cooper pair current can flow through the junction when the energy 2eV of a tunneling Cooper pair can be dissipated in the linear circuit surrounding it, in the form of photons emitted into one or several of its modes. In this inelastic Cooperpair tunneling regime, the junction acts as a nonlinear drive on the linear circuit. We have tailored this physics into quantum microwave sources, such as single photon sources and measurement devices, such as quantum limited amplifiers. I will show that while these devices tend to be much less coherent than their counter parts using the Josephson junction in the zerovoltage state of the junction, they still allow for quantumlimited performance and more readily accept very open configurations allowing for high bandwidth.
Flatiron Institute  Center for Computational Quantum Physics (CCQ)
Classical and Quantum Machine Learning with Tensor Networks
Over the last decade, there have been enormous gains in machine learning technology primarily driven by neural networks. A major reason neural networks have outperformed older techniques is that the cost of optimizing them scales well with the size of the training dataset. But neural networks have the drawback that they are not very well understood theoretically.
Recent work by several groups has explored an alternative approach to creating machine learning model functions based on tensor networks, which are a technique developed in physics to parameterize complicated manybody quantum wavefunctions. The cost of training tensor network models scales similarly to the cost of training neural networks. In addition, their relatively simple, linear structure has provided good theoretical understanding of their properties, and underpins many powerful techniques to optimize and manipulate them.
After introducing tensor network machine learning models, I will discuss some of the techniques to optimize them and results for supervised and generative machine learning tasks. Then I will discuss a recent tensor network based proposal to formulate hybrid quantumclassical algorithms for machine learning with quantum computers.
Institute for Quantum Computing and Perimeter Institute
Interactive Quantum Information Theory
Shannon’s information theory has revolutionized our approach towards two prominent problems in unidirectional communication: source compression and noisy coding.
Over the last two decades, there has been significant progress made towards developing quantum analogues for these.
Meanwhile, an interactive information theory has also been developed over the last two decades for twoway classical communication problems, both for analogues of source compression and for noisy channel coding.
Twoway quantum communication has also been studied in depth over that span, providing unconditional quantitative quantum advantages. (Even exponential ones!)
In this talk, I will discuss the development in recent years of an interactive quantum information theory to study twoway quantum communication.
In particular, I will discuss how we can maintain quantum advantage for twoway communication over noisy quantum communication channels.
Doctorate, Université de Montréal
An Algorithmic Approach to Quantify Emergence
Fundamentally datadriven, algorithmic information theory deals equally with the description of physical systems and their underlying theories. This provides the tools to quantify when, for a complex system, new structures emerge. To familiarize the audience to the insights that algorithmic information theory brings to physics, I shall first present examples from statistical physics.
Professor, McGill University
Decoherence in qutrits (3qubit systems)
I will start with an introduction on qutrit and qudit systems (instead of 2 level systems they are 3 or more level systems) and overview their potential advantages and physical realizations, before discussing our work with Mackenzie, Eleuch and Boudreault on the peculiar decoherence properties of qutrit systems.
Postdoc, McGill Université
Quantitative Tomography for Continuous Variable Quantum Systems
We present a continuous variable tomography scheme that reconstructs the Husimi Q function (Wigner function) by Lagrange interpolation, using measurements of the Q function (Wigner function) at the Padua points, conjectured to be optimal sampling points for two dimensional reconstruction. Our approach drastically reduces the number of measurements required compared to using equidistant points on a regular grid, although reanalysis of such experiments is possible. The reconstruction algorithm produces a reconstructed function with exponentially decreasing error and quasilinear runtime in the number of Padua points. Moreover, using the interpolating polynomial of the Q function, we present a technique to directly estimate the density matrix elements of the continuous variable state, with only a linear propagation of input measurement error.
Olivier LandonCardinal, Luke C.G. Govia, and Aashish A. ClerkPhys. Rev. Lett. 120, 090501 (2018)
Senior researcher, National Research Council Canada
Hole spin qubits in laterla GaAs/AlGaAs double quantum dots
The motivation for developing the hole spin platform in GaAs is based on a list of potentially attractive features such as a predicted reduced hyperfine interaction between hole and nuclear spins, optically active direct bandgap material and an in situ tuneable effective gfactor with field orientation down to zero (useful properties for hybrid spinphotonic devices), and large spinorbit coupling for fast gate operations and spin readout. In my talk I will present our resent results on the single hole hybrid spincharge qubits, and twohole singlettriplet qubit. The single hole regime has been explored via the LandauZenerStuckelberg (LZS) interferometry which involves both spin conserving and spinflip tunneling processes. The LZS patterns evolve with microwave frequency from discreet, often referred as photon assisted tunneling or PAT, at high frequencies to continuous LZS fringes at low frequencies.
Taking LZS measurements at different magnetic fields we observe two separate sets of LZS fringes offset by the Zeeman energy [1]. In order to measure spin relaxation time T1 of a single hole spin vs magnetic field we suggest a novel singleshot technique employing charge latching mechanism [2] in combination with large spinorbit coupling for fast spinselective tunnelling and readout. Additionally, we extend our LZS measurements to the twohole regime near the (02)(11) transition. The results of the LZS interferometry of the singlettriplet spin qubit will be presented vs. detuning, magnetic field, and pulse duration.[
1] A. Bogan et al., arXiv:1711.03492 (2017); PRL (in press)
[2] S. A. Studenikin, et al., Appl. Phys. Lett. 101, 233101 (2012).
Postdoc, Université de Sherbrooke
Director: Glen Evenbly
Selecting initial states from Genetic Tempering for efficient Monte Carlo sampling
An alternative to Monte Carlo techniques requiring large sampling times is presented here. Ideas from a genetic algorithm are used to select the best initial states from many independent, parallel MetropolisHastings iterations that are run on a single graphics processing unit. This algorithm represents the idealized limit of the parallel tempering method and, if the threads are selected perfectly, this algorithm converges without any Monte Carlo iterationsalthough some are required in practice. Models tested here (Ising, antiferromagnetic Kagome, and randombond Ising) are sampled quickly with a small uncertainty that is free from autocorrelation.
[1] T.E. Baker, arXiv:1801.09379
Doctorate, McGill University
Director: Jack Sankey
Progress toward optical control of mechanical geometry
We report progress toward creating a tunable, localized mechanical mode in a phononic crystal using radiation pressure from light [1]. Specifically, we describe fabrication techniques producing consistently 100 nm to 300 nm thick stoichiometric SiN freestanding crystals with an area as large as 20 mm², up to 2750 crystal unit cells, and tethers as narrow as ~ 1 μm. We interferometrically measure Brownian motion of these crystals and identify a phononic bandgap required for laserinduced localization experiments (with a ratio of gap width to midgap frequency as high as 0.8), consistent with COMSOL simulations. We expect a localization length of ~ 1 unit cell for our optimal devices. We first attempt to localize the bandedge mode by modifying its mechanical frequency via a positiondependent bolometric force. Here, we use a lowfinesse FabryPérot cavity formed by the tip of an optical fiber and a Ptcoated phononic crystal. The position of the phononic crystal modulates the bolometric force, thereby creating a bolometric spring when slightly detuned from the cavity resonance. We measure a 9% decrease in the bandedge mode frequency by augmenting the input power by a factor of 5, before blowing up the device due to heat absorption or antidamping. To avoid this, we are now shifting the experiment toward using radiation pressure from light instead, by placing a phononic crystal inside a fiber cavity. We discuss design considerations for such a cavity.
[1] A. Z. Barasheed et al., Phys. Rev. A 93, 053811 (2016).
Doctorate, Université de Sherbrooke
Director: Michel PioroLadrière
Silicon Platform for quantum Dot Spin Qubits
Doctorate, Université de Sherbrooke
Director: Alexandre Blais
Nanowire Superinductance Fluxonium Qubit
Disordered superconducting materials provide a new capability to implement novel circuit designs due to their high kinetic inductance. Here, we realize a fluxonium qubit in which a long NbTiN nanowire shunts a single Josephson junction. We explain the measured fluxonium energy spectrum with a nonperturbative theory accounting for the multimode structure of the device in a large frequency range. Making use of multiphoton Raman spectroscopy, we address forbidden fluxonium transitions and observe multilevel AutlerTownes splitting. Finally, we measure lifetimes of several excited states ranging from T1 = 620 ns to T1 = 20 μs, by applying consecutive πpulses between multiple fluxonium levels. Our measurements demonstrate that NbTiN is a suitable material for novel superconducting qubit designs.
Doctorate, McGill University
Ultrashort Optomechanical FabryPerot Cavities
We report progress toward creating a wavelengthscale, flexural FabryPerot cavity comprising a flat mirror and a ~90 nm thick SiN membrane. Using this structure as a "compound input mirror" of a 10cmlong highfinesse optical cavity, we show that we can tune the optomechanical coupling from purely dispersive to purely dissipative. With the incorporation of a fiber mirror in the membrane's etch pit, this system could also enable "membraneinthemiddle" optomechanical systems having cavity lengths comparable to telecom laser wavelengths  a feature more commonly associated with onchip systems – wherein the optomechanical coupling rate would be significantly larger than that of existing free space or fiber cavity systems.
Doctorate, McGill University
Director: Bill Coish
Improving preparation and readout fidelity of spinqubits in gated quantum dots
Postdoc, Université de Sherbrooke
Director: Bertrand Reulet
NonGaussian microwave field generation by a tunnel junction
Quantum nature of voltage fluctuations across a tunnel junction have been demonstrated in previous works [1][2]. The generated states of the E.M. field (One and two modes squeezed vacuum) are only characterized by second order voltage correlators (covariances). In this project we go a step farther with the generation of nongaussian states, characterized by third order voltage correlators (coskewnesses), by photoassisting the tunnel junction at three time the detection frequency. In this poster, I show preliminary results in the classical regime (hf<kT), where the junction is adiabatically driven. I'll show that the probability density in the phasespace defined by the two quadradures of the measured voltage have a third order rotational symmetry. I'll also identify several contributions to the third order voltage correlator, such as feedback by the environment. This measurement validates our experimental setup, for future measurements in the quantum limit (hf>kT).
[1] G. Gasse, C. Lupien, and B. Reulet, Phys. Rev. Lett. 111, 2013
[2] J.C. Forgues, C. Lupien, and B. Reulet, Phys. Rev. Lett. 113, 2014
Master, Université de Sherbrooke
Director: Michel PioroLadrière
Frequencytunable 3D Microwave Resonator for Coherent Control of Large NV Ensembles
Nitrogenvacancy color centers in diamond show promise as highsensitivity vector magnetometers, due to their excellent room temperature coherence time, and the ability to address them using optical and microwave pulses (Optically Detected Magnetic Resonance). One way to increase the sensitivity of measurements is to use large ensembles of NV⁻ centers to gain a statistical advantage; however, this requires the ability to apply an uniform microwave field to the whole ensemble. Combining optical excitation and readout with uniform microwave excitation in the same device has been shown to be challenging in past experimental realizations. Here, we report the development of a threedimensional, reentrant microwave resonator geometry which allows uniform (0.3% RMS error in field amplitude) and frequencytunable (300 MHz tuning range) microwave excitation on macroscopic (~3mm³) volumes, as well as laser excitation and photoluminescence measurement. We also show results of ODMR measurements of a large (>10¹² spins) NV⁻ ensemble. This work will be used in an enhancedsensitivity roomtemperature magnetometer, but could also be applied to any experiments measuring spin resonance on large samples.
Doctorate, Université de Sherbrooke
Director: Bertrand Reulet
PhotoAssisted Dynamical Coulomb Blockade
The P(E) theory has proven itself a powerful tool for explaining transport through a tunnel junction exhibiting Dynamical Coulomb Blockade (DCB), describing DCB as an inelastic exchange of photons between the tunneling electrons and their electromagnetic environment. Although very efficient, that theory does not detail in a clear way how the dynamical response of the environment influences DCB i.e. how the feedback of the interaction between the electromagnetic environment and a tunneling electron impacts the following ones. This experiment, using ac excitation, aims at unveiling this dynamical aspect of DCB.
Doctorate, Université de Sherbrooke
Director: David Poulin
chflow  A software tool for quantum error correction and noise characterization
Arbitraryprecision control of quantum systems is a lofty goal due to the sensitivity of quantum states to environmental influences that manifest themselves as errors in a quantum algorithm. Quantum error correction and, in general, faulttolerant schemes have been invented to guarantee reliable quantum computation in the presence of noise. However, in most cases they have been developed assuming a simplified error model corresponding to probabilistic application of Pauli operators. While Pauli noise models are convenient for demonstrating proof of concepts, many quantum processes are poorly approximated by the Pauli errors. Nevertheless, it is crucial to have precise estimates of the quality and quantity of hardware resources required for a quantum algorithm before attempting to build a physical realization. Inspired by this requirement, we have developed a software tool, called "chflow", (available online on GitHub), that provides numerical estimates of the performance of an error correction scheme under different noise processes. Concretely, the software tool can be applied to study the response of any stabilizer error correction scheme under any completely positive trace preserving (CPTP) noise process. Simulations of quantum error correction with generic noise processes are quite resource intensive. However, these could be avoided if the noise on the logical information can be accurately estimated using some parameter(s) of the physical noise model. In the work of [arXiv:1711.04736], it has been observed that standard error metrics can only provide very coarse estimates of the noise on the logical information. The tools in "chflow" use machine learning techniques to derive new operational definitions of noise strength in physical processes that help provide better estimates of the noise on the logical information than previously known metrics.
Doctorate, McGill University
Director: Bill Coish
FirstPrinciples Hyperfine Tensors in Si and GaAs
Electron (hole) spins confined to semiconductor nanostructures interact with the nuclear spins making up the nanostructure via the hyperfine interaction. It is important to understand the hyperfine interaction so that first, the decoherence it causes can be limited, and second, to use the induced dynamics to our advantage. We have used densityfunctional theory (DFT) to calculate the wavefunctions of the states at the conductionband minima and valenceband maximum in GaAs and Si so that we may evaluate the hyperfine constants for electrons and holes in these materials. This method allows us to include noncollinear terms and compute effects of the nuclearorbital interaction. For the electrons in silicon and GaAs, our results are consistent with past experiments only when the fullyrelativistic hyperfine operator is considered. For holes, we find that the form of the hyperfine Hamiltonian in the heavyhole subspace is Isinglike which can yield interesting benefits such as driving the system to motionalaveraging regime with an applied inplane magnetic field, which limits the hyperfine interaction's ability to induce decoherence on the hole spin.
Professional, Université de Sherbrooke
Director: Bertrand Reulet
NonGaussian Current Fluctuations in a Short Diffusive Conductor
We report the measurement of the third moment of current fluctuations in a short metallic wire at low temperature. The data are deduced from the statistics of voltage fluctuations across the conductor using a careful determination of environmental contributions. Our results at low bias agree very well with theoretical predictions for coherent transport with no fitting parameter. By increasing the bias voltage we explore the crossover from elastic to inelastic transport.
Master, Université de Sherbrooke
Director: Michel PioroLadrière
FanOut Process on 28nm FDSOI CMOS structure for Cryogenic Characterisation
The compatibility of silicon qubits with CMOS technology shows great promise for cointegration of quantum systems with classical control and readout systems for large scale integration [12]. To achieve cointegration, the behaviour of classical MOS structure at cryogenic temperature needs to be investigate as solid state quantum systems need to operate at such temperature. Since these devices are fabricated within STMicroelectronics multi projects wafers, the devices size and location makes them hard to connect for cryogenic characterization. To overcome this issue we present here a BackEnd Of Line (BEOL) FanOut process on a CMOS advanced structure for cointegration to facilitate cryogenic characterisation. This process is compatible with flip chip using an interposer as an alternative to wire bonding.
Master, Université de Sherbrooke
Director: Michel PioroLadrière
Use of a guard ring as an ESD protection component for tunnel junctions
Modern electronic fabrication processes allow to make nanoscale devices. However, the small size of those devices increases their sensibility to electrostatic discharge (ESD). In many cases, it becomes challenging to manipulate and characterize samples without damaging them especially when many preparation steps are required before the final experiment. Therefore, the use of a guard ring that shorts every connection on the samples can protect them when used with simple ESD precautions. The guard ring can then be removed after the preparation process with a diamond tip when the samples are adequately grounded. On Al/Co tunnel junctions that can tolerate only a maximum tension of a few volts, it has been possible to achieve a yield of 93% throughout the preparation process which includes dicing and wire bonding. The effect of sharp edges in the junction design has also been investigated but the geometry of the junctions doesn’t influence ESD occurrences when the work functions of the metals are similar.
Postdoc, Université de Sherbrooke
Director: Michel PioroLadrière
Qmag and QMSat : Prototyping Diamond Based Magnetometry for On Ground and Space Geophysics
Doctorate, Université de Sherbrooke
Director: Alexandre Blais
Qubit Parity Measurement by Parametric Driving in Circuit QED
Multiqubit parity measurements are essential to quantum error correction. Current realizations of these measurements often rely on ancilla qubits, a method that is sensitive to faulty twoqubit gates and which requires significant experimental overhead. We introduce a hardwareefficient multiqubit parity measurement exploiting the bifurcation dynamics of a parametrically driven nonlinear oscillator. This approach takes advantage of the resonator's parametric oscillation threshold which is a function of the joint parity of dispersively coupled qubits, leading to highamplitude oscillations for one parity subspace and no oscillation for the other. We present analytical and numerical results for two and fourqubit parity measurements with highfidelity readout preserving the parity eigenspaces. Moreover, we discuss a possible realization which can be readily implemented with the current circuit QED experimental toolbox. These results could lead to significant simplifications in the experimental implementation of quantum error correction, and notably of the surface code.
Master, Université de Sherbrooke
Director: Alexandre Blais
Hardware Efficient Schemes for Quantum Computation with Photonic Cat States
Fault tolerant quantum computing protocols require thousands of physical qubits per logical qubit in order to carry out quantum computations in the presence of unknown noise processes. The resulting overhead of physical qubits presents a daunting challenge for experimental realization of a large scale, faulttolerant, quantum computer. However, a better understanding of the noise inflicting the hardware elements can help significantly reduce the overhead for fault tolerance. Precisely, systems with biased noise can be used to improve standard error correction schemes, with a small overhead. A particularly attractive candidate for such a system with highly biased noise is using stabilized microwavephoton cat states. We will present cat state stabilization schemes and discuss how photonic noise processes affect the underlying quantum information in this framework. Moreover, we examine the performance of a simple 5qubit repetition code with these stabilized cat states and compare it with the wellknown 5qubit code using standard Fock states and their unbiased noise. The tradeoff between fidelity of encoded information and the associated overhead is better in the first case which highlights the potential advantage of optimizing error correction for biased noise in cat states. Further investigations on fault tolerant quantum computation schemes optimized for cat states’ error model could exhibit a reduced resource overhead compared to schemes for unbiased noise.
Master, Université de Sherbrooke
Director: Michel PioroLadrière
Micromagnet induced spinorbit coupling for Majorana modes
Majorana fermions are topologically protected quasiparticles that appear at the end of unidimensional semiconducting wires with large spinorbit coupling and induced superconductivity. While recent implementations mostly rely on nanowires with large intrinsic spinorbit coupling, these approaches offer poor control on properties such as the length of the wire and the confinement potential. Here, versatile designs consisting of a micromagnet arrays are explored to engineer the spinorbit coupling in a two dimensional electron gas. On one hand we find, suitable conditions for the experimental observation of Majorana fermions in gallium arsenide and silicon through numerical simulations. On the other hand, we present first experimental steps toward direct measurement of the spinorbit coupling induced by a single magnet in a magnetic focusing setup.
Master, Université de Sherbrooke
Director: David Poulin
A tensor network approach to coding theory
This work is based on two recent developments in information theory and manybody physics. The first one being the introduction of capacity achieving error correcting codes named polar codes by Erdal Arikan in 2009 and the second one being the introduction of branching MERA by Glen Evenbly and Guifre Vidal in 2014. Later in the same year, it has been shown by Andy Ferris and David Poulin that the task of decoding can be map to contracting a tensor network. Therefore, it is possible to design an efficient decoder by finding an efficiently contractable tensor network. Based on that idea, it was possible to generalize polar codes to a broad family of codes called branching MERA codes that we can decode in an efficient manner using the so called successive cancellation decoder. Here we present the methods and software that we developed in order to analyse codes in that family and the underlying theory that allows us to link error correcting codes and tensor networks.
10h30  10h55 Registration
10h55  11h00 Opening remarks (Salon A)
11h00  12h00 Max Hofheinz, Université de Sherbrooke (Salon A)
Quantum microwave devices based on inelastic
Cooperpair tunneling
12h00  13h30 Lunch (Dining room  4 Canards)
13h30  14h30 John Mattsson, Ericsson Research (Salon A)
PostQuantum Cryptography in Practice
14h30  15h00 Michael Hilke, McGill University(Salon A)
Decoherence in qutrits (3qubit systems)
15h00  15h30 Sergei Studenikin, National Research Council Canada (Salon A)
Hole spin qubits in laterla GaAs/AlGaAs double quantum dots
15h30  16h00 Coffee break (Salon B)
16h00  17h00 Eva DupontFerrier, Université de Sherbrooke (Salon A)
Quantum information with dopants in silicon
17h00  Poster sesson with refreshments (Salon B)
19h30  INTRIQ dinner (Salon C)
9h00  10h00 Miles Stoudenmire, Computational Quantum Physics Center (Salon A)
Classical and Quantum Machine Learning with Tensor Networks
10h00  11h00 Coffee break (Salon B)
11h00  12h00 Dave Touchette, Institute for Quantum Computing (Salon A)
Interactive Quantum Information Theory
12h00  13h45 Lunch (Dining room  4 Canards)
13h45  14h45 William WitczakKrempa, Université de Montréal (Salon A)
Understanding exotic magnetism through quantum entanglement
14h45  15h15 Olivier LandonCardinal, McGill University
Quantitative Tomography for Continuous Variable Quantum Systems
15h15  15h45 Charles Bédard, Université de Montréal
An Algorithmic Approach to Quantify Emergence
15h45  15h50 Closing remarks
Ericsson Research
PostQuantum Cryptography in Practice
The last 5 years, the use of cryptography has exploded and the use of cryptography for authentication, confidentiality, and integrity protection is required even in constrained IoT environments. The use of cryptography everywhere has been enabled by new faster algorithms and security protocols combined with faster hardware. Unfortunately, a large enough quantum computer running Shor’s algorithm would practically break all commonly used public key algorithms such as RSA and ECC. Such algorithms are typically used for authentication and key exchange. NIST has just initiated PQC standardization with the goal of standardizing new asymmetric algorithms replacing RSA and ECC. The new algorithms are based on mathematical problems not affected by Shor’s algorithm (e.g. lattices, codes, multivariate, isogenies). Grover’s algorithms could theoretically break some symmetric algorithms, but it is unknown if it will ever be relevant for practical cryptanalysis. QKD, which only provides unauthenticated key exchange, will likely continue to be a niche product as postquantum cryptography running on classical computers are likely to provide excellent security to a much lower cost. In this talk we describe the current use cases of cryptography and the effects of quantum computer would affect these, the current status and challenges with postquantum cryptography running on classical computers and the role of quantum cryptography.
Université de Montréal
Understanding exotic magnetism through quantum entanglement
I’ll present 2 spin models that host unusual emergent excitations. First, the 1d Motzkin spin chain introduced by Shor et al has a solvable entangled groundstate, but a gapless excitation spectrum that is poorly understood. By using largescale Density Matrix Renormalization Group (DMRG) simulations, we find that that there are 2 lowenergy excitations with distinct and nontrivial dispersion relations. Various correlation functions and entanglement properties will be discussed. Second, I’ll discuss the Heisenberg model on the frustrated kagome lattice, which is one of the most studied and experimentally relevant models for a quantum spin liquid. Despite years of study, its solution remains under debate. Using DMRG on this model, we uncover universal features of neutral Dirac fermions in the entanglement entropy. We infer that these are the fractionalized excitations of the kagome quantum spin liquid. Such methods can be used to study other quantum states of matter, such as systems poised near a quantum critical phase transition.
Université de Sherbrooke
Quantum information with dopants in silicon
Dopants in silicon are promising candidates for quantum information processing. They form an extremely compact and reproducible quantum system in which the nuclear spin can be used to store quantum information, while the electron spin serves as a means of interfacing nuclear spin with other quantum systems. The nuclear spin in purified silicon has set the record for coherence times in solid state qubits. Spin readout and manipulation for both electron and nuclear spins have been demonstrated, with fidelities beyond the threshold for quantum error correction protocols. But high coherence times come in pair with strong isolation from the environment, i.e. spins of dopants are difficult to address and couple together which prevents realization of two qubits gates.
I will show how integration of dopants in transistors form state of the art CMOS technology could help solve this problem. We use a splitgate transistor to electrically control two dopants connected in series and perform coherent charge exchange between them. For longer range coupling between dopants, a possibility is to use magnetic coupling of the dopants’ spins to superconducting circuits. I will show the first steps in that direction, namely the realization of high quality factor superconducting resonator, tunable in frequency by means of an embedded SQUID and which can perform under magnetic fields.
Université de Sherbrooke
Quantum microwave devices based on inelastic Cooperpair tunneling
In superconducting quantum circuits the Josephson junction is the key element because it is the only strongly nonlinear and dissipationless circuit element we know. Usually it is used in the superconducting state where it acts as a nonlinear inductor. But a small Josephson junction can be nonlinear and dissipationless also when a nonzero DC voltage below the gap is applied. In this case a Cooper pair current can flow through the junction when the energy 2eV of a tunneling Cooper pair can be dissipated in the linear circuit surrounding it, in the form of photons emitted into one or several of its modes. In this inelastic Cooperpair tunneling regime, the junction acts as a nonlinear drive on the linear circuit. We have tailored this physics into quantum microwave sources, such as single photon sources and measurement devices, such as quantum limited amplifiers. I will show that while these devices tend to be much less coherent than their counter parts using the Josephson junction in the zerovoltage state of the junction, they still allow for quantumlimited performance and more readily accept very open configurations allowing for high bandwidth.
Flatiron Institute  Center for Computational Quantum Physics (CCQ)
Classical and Quantum Machine Learning with Tensor Networks
Over the last decade, there have been enormous gains in machine learning technology primarily driven by neural networks. A major reason neural networks have outperformed older techniques is that the cost of optimizing them scales well with the size of the training dataset. But neural networks have the drawback that they are not very well understood theoretically.
Recent work by several groups has explored an alternative approach to creating machine learning model functions based on tensor networks, which are a technique developed in physics to parameterize complicated manybody quantum wavefunctions. The cost of training tensor network models scales similarly to the cost of training neural networks. In addition, their relatively simple, linear structure has provided good theoretical understanding of their properties, and underpins many powerful techniques to optimize and manipulate them.
After introducing tensor network machine learning models, I will discuss some of the techniques to optimize them and results for supervised and generative machine learning tasks. Then I will discuss a recent tensor network based proposal to formulate hybrid quantumclassical algorithms for machine learning with quantum computers.
Institute for Quantum Computing and Perimeter Institute
Interactive Quantum Information Theory
Shannon’s information theory has revolutionized our approach towards two prominent problems in unidirectional communication: source compression and noisy coding.
Over the last two decades, there has been significant progress made towards developing quantum analogues for these.
Meanwhile, an interactive information theory has also been developed over the last two decades for twoway classical communication problems, both for analogues of source compression and for noisy channel coding.
Twoway quantum communication has also been studied in depth over that span, providing unconditional quantitative quantum advantages. (Even exponential ones!)
In this talk, I will discuss the development in recent years of an interactive quantum information theory to study twoway quantum communication.
In particular, I will discuss how we can maintain quantum advantage for twoway communication over noisy quantum communication channels.
Doctorate, Université de Montréal
An Algorithmic Approach to Quantify Emergence
Fundamentally datadriven, algorithmic information theory deals equally with the description of physical systems and their underlying theories. This provides the tools to quantify when, for a complex system, new structures emerge. To familiarize the audience to the insights that algorithmic information theory brings to physics, I shall first present examples from statistical physics.
Professor, McGill University
Decoherence in qutrits (3qubit systems)
I will start with an introduction on qutrit and qudit systems (instead of 2 level systems they are 3 or more level systems) and overview their potential advantages and physical realizations, before discussing our work with Mackenzie, Eleuch and Boudreault on the peculiar decoherence properties of qutrit systems.
Postdoc, McGill Université
Quantitative Tomography for Continuous Variable Quantum Systems
We present a continuous variable tomography scheme that reconstructs the Husimi Q function (Wigner function) by Lagrange interpolation, using measurements of the Q function (Wigner function) at the Padua points, conjectured to be optimal sampling points for two dimensional reconstruction. Our approach drastically reduces the number of measurements required compared to using equidistant points on a regular grid, although reanalysis of such experiments is possible. The reconstruction algorithm produces a reconstructed function with exponentially decreasing error and quasilinear runtime in the number of Padua points. Moreover, using the interpolating polynomial of the Q function, we present a technique to directly estimate the density matrix elements of the continuous variable state, with only a linear propagation of input measurement error.
Olivier LandonCardinal, Luke C.G. Govia, and Aashish A. ClerkPhys. Rev. Lett. 120, 090501 (2018)
Senior researcher, National Research Council Canada
Hole spin qubits in laterla GaAs/AlGaAs double quantum dots
The motivation for developing the hole spin platform in GaAs is based on a list of potentially attractive features such as a predicted reduced hyperfine interaction between hole and nuclear spins, optically active direct bandgap material and an in situ tuneable effective gfactor with field orientation down to zero (useful properties for hybrid spinphotonic devices), and large spinorbit coupling for fast gate operations and spin readout. In my talk I will present our resent results on the single hole hybrid spincharge qubits, and twohole singlettriplet qubit. The single hole regime has been explored via the LandauZenerStuckelberg (LZS) interferometry which involves both spin conserving and spinflip tunneling processes. The LZS patterns evolve with microwave frequency from discreet, often referred as photon assisted tunneling or PAT, at high frequencies to continuous LZS fringes at low frequencies.
Taking LZS measurements at different magnetic fields we observe two separate sets of LZS fringes offset by the Zeeman energy [1]. In order to measure spin relaxation time T1 of a single hole spin vs magnetic field we suggest a novel singleshot technique employing charge latching mechanism [2] in combination with large spinorbit coupling for fast spinselective tunnelling and readout. Additionally, we extend our LZS measurements to the twohole regime near the (02)(11) transition. The results of the LZS interferometry of the singlettriplet spin qubit will be presented vs. detuning, magnetic field, and pulse duration.[
1] A. Bogan et al., arXiv:1711.03492 (2017); PRL (in press)
[2] S. A. Studenikin, et al., Appl. Phys. Lett. 101, 233101 (2012).
Postdoc, Université de Sherbrooke
Director: Glen Evenbly
Selecting initial states from Genetic Tempering for efficient Monte Carlo sampling
An alternative to Monte Carlo techniques requiring large sampling times is presented here. Ideas from a genetic algorithm are used to select the best initial states from many independent, parallel MetropolisHastings iterations that are run on a single graphics processing unit. This algorithm represents the idealized limit of the parallel tempering method and, if the threads are selected perfectly, this algorithm converges without any Monte Carlo iterationsalthough some are required in practice. Models tested here (Ising, antiferromagnetic Kagome, and randombond Ising) are sampled quickly with a small uncertainty that is free from autocorrelation.
[1] T.E. Baker, arXiv:1801.09379
Doctorate, McGill University
Director: Jack Sankey
Progress toward optical control of mechanical geometry
We report progress toward creating a tunable, localized mechanical mode in a phononic crystal using radiation pressure from light [1]. Specifically, we describe fabrication techniques producing consistently 100 nm to 300 nm thick stoichiometric SiN freestanding crystals with an area as large as 20 mm², up to 2750 crystal unit cells, and tethers as narrow as ~ 1 μm. We interferometrically measure Brownian motion of these crystals and identify a phononic bandgap required for laserinduced localization experiments (with a ratio of gap width to midgap frequency as high as 0.8), consistent with COMSOL simulations. We expect a localization length of ~ 1 unit cell for our optimal devices. We first attempt to localize the bandedge mode by modifying its mechanical frequency via a positiondependent bolometric force. Here, we use a lowfinesse FabryPérot cavity formed by the tip of an optical fiber and a Ptcoated phononic crystal. The position of the phononic crystal modulates the bolometric force, thereby creating a bolometric spring when slightly detuned from the cavity resonance. We measure a 9% decrease in the bandedge mode frequency by augmenting the input power by a factor of 5, before blowing up the device due to heat absorption or antidamping. To avoid this, we are now shifting the experiment toward using radiation pressure from light instead, by placing a phononic crystal inside a fiber cavity. We discuss design considerations for such a cavity.
[1] A. Z. Barasheed et al., Phys. Rev. A 93, 053811 (2016).
Doctorate, Université de Sherbrooke
Director: Michel PioroLadrière
Silicon Platform for quantum Dot Spin Qubits
Doctorate, Université de Sherbrooke
Director: Alexandre Blais
Nanowire Superinductance Fluxonium Qubit
Disordered superconducting materials provide a new capability to implement novel circuit designs due to their high kinetic inductance. Here, we realize a fluxonium qubit in which a long NbTiN nanowire shunts a single Josephson junction. We explain the measured fluxonium energy spectrum with a nonperturbative theory accounting for the multimode structure of the device in a large frequency range. Making use of multiphoton Raman spectroscopy, we address forbidden fluxonium transitions and observe multilevel AutlerTownes splitting. Finally, we measure lifetimes of several excited states ranging from T1 = 620 ns to T1 = 20 μs, by applying consecutive πpulses between multiple fluxonium levels. Our measurements demonstrate that NbTiN is a suitable material for novel superconducting qubit designs.
Doctorate, McGill University
Ultrashort Optomechanical FabryPerot Cavities
We report progress toward creating a wavelengthscale, flexural FabryPerot cavity comprising a flat mirror and a ~90 nm thick SiN membrane. Using this structure as a "compound input mirror" of a 10cmlong highfinesse optical cavity, we show that we can tune the optomechanical coupling from purely dispersive to purely dissipative. With the incorporation of a fiber mirror in the membrane's etch pit, this system could also enable "membraneinthemiddle" optomechanical systems having cavity lengths comparable to telecom laser wavelengths  a feature more commonly associated with onchip systems – wherein the optomechanical coupling rate would be significantly larger than that of existing free space or fiber cavity systems.
Doctorate, McGill University
Director: Bill Coish
Improving preparation and readout fidelity of spinqubits in gated quantum dots
Postdoc, Université de Sherbrooke
Director: Bertrand Reulet
NonGaussian microwave field generation by a tunnel junction
Quantum nature of voltage fluctuations across a tunnel junction have been demonstrated in previous works [1][2]. The generated states of the E.M. field (One and two modes squeezed vacuum) are only characterized by second order voltage correlators (covariances). In this project we go a step farther with the generation of nongaussian states, characterized by third order voltage correlators (coskewnesses), by photoassisting the tunnel junction at three time the detection frequency. In this poster, I show preliminary results in the classical regime (hf<kT), where the junction is adiabatically driven. I'll show that the probability density in the phasespace defined by the two quadradures of the measured voltage have a third order rotational symmetry. I'll also identify several contributions to the third order voltage correlator, such as feedback by the environment. This measurement validates our experimental setup, for future measurements in the quantum limit (hf>kT).
[1] G. Gasse, C. Lupien, and B. Reulet, Phys. Rev. Lett. 111, 2013
[2] J.C. Forgues, C. Lupien, and B. Reulet, Phys. Rev. Lett. 113, 2014
Master, Université de Sherbrooke
Director: Michel PioroLadrière
Frequencytunable 3D Microwave Resonator for Coherent Control of Large NV Ensembles
Nitrogenvacancy color centers in diamond show promise as highsensitivity vector magnetometers, due to their excellent room temperature coherence time, and the ability to address them using optical and microwave pulses (Optically Detected Magnetic Resonance). One way to increase the sensitivity of measurements is to use large ensembles of NV⁻ centers to gain a statistical advantage; however, this requires the ability to apply an uniform microwave field to the whole ensemble. Combining optical excitation and readout with uniform microwave excitation in the same device has been shown to be challenging in past experimental realizations. Here, we report the development of a threedimensional, reentrant microwave resonator geometry which allows uniform (0.3% RMS error in field amplitude) and frequencytunable (300 MHz tuning range) microwave excitation on macroscopic (~3mm³) volumes, as well as laser excitation and photoluminescence measurement. We also show results of ODMR measurements of a large (>10¹² spins) NV⁻ ensemble. This work will be used in an enhancedsensitivity roomtemperature magnetometer, but could also be applied to any experiments measuring spin resonance on large samples.
Doctorate, Université de Sherbrooke
Director: Bertrand Reulet
PhotoAssisted Dynamical Coulomb Blockade
The P(E) theory has proven itself a powerful tool for explaining transport through a tunnel junction exhibiting Dynamical Coulomb Blockade (DCB), describing DCB as an inelastic exchange of photons between the tunneling electrons and their electromagnetic environment. Although very efficient, that theory does not detail in a clear way how the dynamical response of the environment influences DCB i.e. how the feedback of the interaction between the electromagnetic environment and a tunneling electron impacts the following ones. This experiment, using ac excitation, aims at unveiling this dynamical aspect of DCB.
Doctorate, Université de Sherbrooke
Director: David Poulin
chflow  A software tool for quantum error correction and noise characterization
Arbitraryprecision control of quantum systems is a lofty goal due to the sensitivity of quantum states to environmental influences that manifest themselves as errors in a quantum algorithm. Quantum error correction and, in general, faulttolerant schemes have been invented to guarantee reliable quantum computation in the presence of noise. However, in most cases they have been developed assuming a simplified error model corresponding to probabilistic application of Pauli operators. While Pauli noise models are convenient for demonstrating proof of concepts, many quantum processes are poorly approximated by the Pauli errors. Nevertheless, it is crucial to have precise estimates of the quality and quantity of hardware resources required for a quantum algorithm before attempting to build a physical realization. Inspired by this requirement, we have developed a software tool, called "chflow", (available online on GitHub), that provides numerical estimates of the performance of an error correction scheme under different noise processes. Concretely, the software tool can be applied to study the response of any stabilizer error correction scheme under any completely positive trace preserving (CPTP) noise process. Simulations of quantum error correction with generic noise processes are quite resource intensive. However, these could be avoided if the noise on the logical information can be accurately estimated using some parameter(s) of the physical noise model. In the work of [arXiv:1711.04736], it has been observed that standard error metrics can only provide very coarse estimates of the noise on the logical information. The tools in "chflow" use machine learning techniques to derive new operational definitions of noise strength in physical processes that help provide better estimates of the noise on the logical information than previously known metrics.
Doctorate, McGill University
Director: Bill Coish
FirstPrinciples Hyperfine Tensors in Si and GaAs
Electron (hole) spins confined to semiconductor nanostructures interact with the nuclear spins making up the nanostructure via the hyperfine interaction. It is important to understand the hyperfine interaction so that first, the decoherence it causes can be limited, and second, to use the induced dynamics to our advantage. We have used densityfunctional theory (DFT) to calculate the wavefunctions of the states at the conductionband minima and valenceband maximum in GaAs and Si so that we may evaluate the hyperfine constants for electrons and holes in these materials. This method allows us to include noncollinear terms and compute effects of the nuclearorbital interaction. For the electrons in silicon and GaAs, our results are consistent with past experiments only when the fullyrelativistic hyperfine operator is considered. For holes, we find that the form of the hyperfine Hamiltonian in the heavyhole subspace is Isinglike which can yield interesting benefits such as driving the system to motionalaveraging regime with an applied inplane magnetic field, which limits the hyperfine interaction's ability to induce decoherence on the hole spin.
Professional, Université de Sherbrooke
Director: Bertrand Reulet
NonGaussian Current Fluctuations in a Short Diffusive Conductor
We report the measurement of the third moment of current fluctuations in a short metallic wire at low temperature. The data are deduced from the statistics of voltage fluctuations across the conductor using a careful determination of environmental contributions. Our results at low bias agree very well with theoretical predictions for coherent transport with no fitting parameter. By increasing the bias voltage we explore the crossover from elastic to inelastic transport.
Master, Université de Sherbrooke
Director: Michel PioroLadrière
FanOut Process on 28nm FDSOI CMOS structure for Cryogenic Characterisation
The compatibility of silicon qubits with CMOS technology shows great promise for cointegration of quantum systems with classical control and readout systems for large scale integration [12]. To achieve cointegration, the behaviour of classical MOS structure at cryogenic temperature needs to be investigate as solid state quantum systems need to operate at such temperature. Since these devices are fabricated within STMicroelectronics multi projects wafers, the devices size and location makes them hard to connect for cryogenic characterization. To overcome this issue we present here a BackEnd Of Line (BEOL) FanOut process on a CMOS advanced structure for cointegration to facilitate cryogenic characterisation. This process is compatible with flip chip using an interposer as an alternative to wire bonding.
Master, Université de Sherbrooke
Director: Michel PioroLadrière
Use of a guard ring as an ESD protection component for tunnel junctions
Modern electronic fabrication processes allow to make nanoscale devices. However, the small size of those devices increases their sensibility to electrostatic discharge (ESD). In many cases, it becomes challenging to manipulate and characterize samples without damaging them especially when many preparation steps are required before the final experiment. Therefore, the use of a guard ring that shorts every connection on the samples can protect them when used with simple ESD precautions. The guard ring can then be removed after the preparation process with a diamond tip when the samples are adequately grounded. On Al/Co tunnel junctions that can tolerate only a maximum tension of a few volts, it has been possible to achieve a yield of 93% throughout the preparation process which includes dicing and wire bonding. The effect of sharp edges in the junction design has also been investigated but the geometry of the junctions doesn’t influence ESD occurrences when the work functions of the metals are similar.
Postdoc, Université de Sherbrooke
Director: Michel PioroLadrière
Qmag and QMSat : Prototyping Diamond Based Magnetometry for On Ground and Space Geophysics
Doctorate, Université de Sherbrooke
Director: Alexandre Blais
Qubit Parity Measurement by Parametric Driving in Circuit QED
Multiqubit parity measurements are essential to quantum error correction. Current realizations of these measurements often rely on ancilla qubits, a method that is sensitive to faulty twoqubit gates and which requires significant experimental overhead. We introduce a hardwareefficient multiqubit parity measurement exploiting the bifurcation dynamics of a parametrically driven nonlinear oscillator. This approach takes advantage of the resonator's parametric oscillation threshold which is a function of the joint parity of dispersively coupled qubits, leading to highamplitude oscillations for one parity subspace and no oscillation for the other. We present analytical and numerical results for two and fourqubit parity measurements with highfidelity readout preserving the parity eigenspaces. Moreover, we discuss a possible realization which can be readily implemented with the current circuit QED experimental toolbox. These results could lead to significant simplifications in the experimental implementation of quantum error correction, and notably of the surface code.
Master, Université de Sherbrooke
Director: Alexandre Blais
Hardware Efficient Schemes for Quantum Computation with Photonic Cat States
Fault tolerant quantum computing protocols require thousands of physical qubits per logical qubit in order to carry out quantum computations in the presence of unknown noise processes. The resulting overhead of physical qubits presents a daunting challenge for experimental realization of a large scale, faulttolerant, quantum computer. However, a better understanding of the noise inflicting the hardware elements can help significantly reduce the overhead for fault tolerance. Precisely, systems with biased noise can be used to improve standard error correction schemes, with a small overhead. A particularly attractive candidate for such a system with highly biased noise is using stabilized microwavephoton cat states. We will present cat state stabilization schemes and discuss how photonic noise processes affect the underlying quantum information in this framework. Moreover, we examine the performance of a simple 5qubit repetition code with these stabilized cat states and compare it with the wellknown 5qubit code using standard Fock states and their unbiased noise. The tradeoff between fidelity of encoded information and the associated overhead is better in the first case which highlights the potential advantage of optimizing error correction for biased noise in cat states. Further investigations on fault tolerant quantum computation schemes optimized for cat states’ error model could exhibit a reduced resource overhead compared to schemes for unbiased noise.
Master, Université de Sherbrooke
Director: Michel PioroLadrière
Micromagnet induced spinorbit coupling for Majorana modes
Majorana fermions are topologically protected quasiparticles that appear at the end of unidimensional semiconducting wires with large spinorbit coupling and induced superconductivity. While recent implementations mostly rely on nanowires with large intrinsic spinorbit coupling, these approaches offer poor control on properties such as the length of the wire and the confinement potential. Here, versatile designs consisting of a micromagnet arrays are explored to engineer the spinorbit coupling in a two dimensional electron gas. On one hand we find, suitable conditions for the experimental observation of Majorana fermions in gallium arsenide and silicon through numerical simulations. On the other hand, we present first experimental steps toward direct measurement of the spinorbit coupling induced by a single magnet in a magnetic focusing setup.
Master, Université de Sherbrooke
Director: David Poulin
A tensor network approach to coding theory
This work is based on two recent developments in information theory and manybody physics. The first one being the introduction of capacity achieving error correcting codes named polar codes by Erdal Arikan in 2009 and the second one being the introduction of branching MERA by Glen Evenbly and Guifre Vidal in 2014. Later in the same year, it has been shown by Andy Ferris and David Poulin that the task of decoding can be map to contracting a tensor network. Therefore, it is possible to design an efficient decoder by finding an efficiently contractable tensor network. Based on that idea, it was possible to generalize polar codes to a broad family of codes called branching MERA codes that we can decode in an efficient manner using the so called successive cancellation decoder. Here we present the methods and software that we developed in order to analyse codes in that family and the underlying theory that allows us to link error correcting codes and tensor networks.