November 13, 2018 10:30 AM

November 14, 2018 3:40 PM
November 13, 2018 10:30 AM

November 14, 2018 3:40 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.
13 novembre
10h30 10h55 Inscription
10h55 11h00 Mots d'ouverture (Salon A)
11h00 12h00 Dr. Avishay Tal, Simons Institute & Stanford University (Salon A)
Oracle Separation of Quantum Polynomial Time and the Polynomial Hierarchy
12h00 13h30 Dîner (Salle 4 Canards)
13h30 14h00 Dr. Gustav Kalbe, Head of Unit, High Performance Computing &
Quantum Technologies, European Commission (Salon A)
The Quantum Technologies Flagship Initiative of the European Union
14h00 15h00 Dr. Dominique Laroche, Delft University of Technology (Salon A)
Probing the building blocks of topological qubits in
superconducting InAs nanowires
15h00 15h30 Pause café (Salon B)
15h30 16h00 Dr. Yehua Liu, Postdoc, Université de Sherbrooke (Salon A)
Neural BeliefPropagation Decoders for Quantum
ErrorCorrecting Codes
16h00 – 16h20 MarcOlivier Proulx, Master, Université d'Ottawa (Salon A)
A limit on quantum nonlocality from an information
processing principle
16h20  17h00 Thomas Szkopek, Professor, McGill University (Salon A)
An account of the commercialization of an idea
17h00  17h10 Maxime Tremblay & Alexandre ChoquettePoitevin,
Université de Sherbrooke (Salon A)
Quantum Quarter
17h00  Session d'affiches et rafraichissement (Salon B)
19h30  Souper INTRIQ (Salle Knowlton)
14 novembre
09h00  10h00 Dr. Kartiek Agarwal, Princeton University (Salon A)
Spatiotemporal quenches for fast preparation of ground states of
critical models
10h00  10h45 Alexander Maloney, Professor, McGill University (Salon A)
Quantum Information Theory, Black Holes and Spacetime
10h45  11h15 Dr. Jonathan Gross, Postdoc, Université de Sherbrooke (Salon A)
Systems illuminated by squeezed wavepacket modes
11h15  12h00 Pause café (Salon B)
12h00  13h30 Diner (Salle 4 Canards)
13h30  14h00 Yves BérubéLauzière, Professor, Université de Sherbrooke (Salon A)
QSciTech NSERCCREATE Training Program
Bridging the Gap between Quantum Science & Quantum Technologies
14h00  15h00 Johannes Pollanen, Professor, Michigan State University (Salon A)
Hybrid quantum information systems with electrons on helium
15h00  15h30 Dr. Clément Godfrin, Postdoc, Université de Sherbrooke (Salon A)
Coherent manipulation of single nuclear spin
15h30  15h40 Closing remarks
Princeton University
Spatiotemporal quenches for fast preparation of ground states of critical models
The difficulty of preparing highly entangled quantum states poses an important challenge in engineering artificial quantum systems for the purposes of computation and simulation. Adiabatic methods which slowly evolve unentangled states to entangled states are typically slow and particularly fail at criticality where the gap between eigenstates vanishes. The search for novel nonadiabatic methods for quantum state preparation is a topic of current research interest, and immense experimental relevance. I will describe the state of the art in the field and discuss our proposal(s) using spatiotemporal quenches to efficiently prepare the ground states of arbitrary interacting critical theories in one dimension and beyond.
Head of Unit
High Performance Computing & Quantum Technologies
European Commission
The Quantum Technologies FET Flagship Initiative of the European Union
The Quantum Technologies Flagship is a Future and Emerging Technologies (FET) research initiative that was launched by the EU. This largescale, longterm Flagship joins both academic and industry researchers to make scientific discoveries in the quantum field, using such innovations to help grow the economy so that Europe can resolve its current societal challenges. As a panEuropean programme with support from each of its Member States, the Quantum Technologies Flagship will continue to develop using previous European funding from the last 20 years and allow Europe to match the research implemented by its competitors on the world stage.
McGill University
Quantum Information Theory, Black Holes and Spacetime
I will describe recent progress on the relationship between quantum information theory, quantum field theory and quantum gravity. I will review the theoretical evidence that spacetime emerges from the entanglement of more fundamental quantum mechanical degrees of freedom. This evidence comes from recent advances in our understanding of quantum black holes and the holographic (AdS/CFT) correspondence. The relationship between quantum information theory, field theory and gravity has already led to new results, including new positive energy theorems in general relativity and a unified theory of renormalization group flows. If time permits, I will explain the notion that spacetime can be regarded as a (quantum) errorcorrecting code. This will be an expository talk; no advanced background aside from some elements of quantum information theory will be assumed.
Delft University of Technology
Probing the building blocks of topological qubits in superconducting InAs nanowires
Utilizing the exotic properties of nonAbelian quasiparticles, topological qubits offer an approach towards quantum computing where the information is stored nonlocally, making this an architecture resilient against most decoherence sources. Majorana bound states (MBS) arising in proximityinduced superconducting nanowires are currently the prime candidate for the implementation of such topological quantum bits. Thus far, MBS signatures chiefly relied on single electron tunnelling measurements, which lead to decoherence of the quantum information stored in the MBS through quasiparticle poisoning. In this talk, I will present a novel experimental platform where proximitized nanowire devices are coupled onchip to microwave detectors and spectrometers, allowing for measurements of the building blocks of topological qubits in a parity conserving manner. Utilizing this platform, we directly observed a transition from a 2π to a 4πperiodic Josephson radiation in InAs nanowire as a function of both magnetic field and chemical potential. This transition is consistent with the onset of MBS in the nanowires. We also performed microwave spectroscopy of the fundamental unit of a prospective topological qubit, a nanowirebased Cooper pair transistor. In addition to confirm the large tunability of this system, we were able to directly measure the population of the odd and of the even parity sector in these devices.
Michigan State University
Hybrid quantum information systems with electrons on helium
Electrons floating on the surface of liquid helium at low temperature were one of the first platforms proposed for quantum computation [1]. In this hybrid quantum system the surface of the liquid helium functions as a fantastically pristine substrate without the defects and imperfections that are unavoidable in almost all other material systems. Electrons placed near this liquid substrate are bound to it and float (in vacuum) about 10 nanometers above the surface. The motion of these electrons relative to the surface of the helium, as well as their spin, are quantum mechanical and form the basis for potentially new types of qubits. These qubits, if they can be realized, are predicted to be shielded from decoherence by the isolation provided by liquid helium substrate. I will describe the state of the art in the field, experimental milestones demonstrating the fantastic level of control that can be achieved in this system, and how the time is now ripe for using the hardware tool kit of circuit quantum electrodynamics for developing novel qubits from electrons on helium.
[1] P.M. Platzman and M.I. Dykman, Quantum Computing with Electrons Floating on Liquid Heilum, Science 284, 1967 (1999).
Simons Institute & Stanford University
Oracle Separation of Quantum Polynomial Time and the Polynomial Hierarchy
In their seminal paper, Bennett, Bernstein, Brassard and Vazirani [SICOMP, 1997] showed that relative to an oracle, quantum algorithms are unable to solve NPcomplete problems in subexponential time (i.e., that Grover's search is optimal in this setting).
In this work, we show a strong converse to their result. Namely, we show that, relative to an oracle, there exist computational tasks that can be solved efficiently by a quantum algorithm, but require exponential time for any algorithm in the polynomial hierarchy. (The polynomial hierarchy is a hierarchy of complexity classes that captures P, NP, coNP, and their generalizations.)
The tasks that exhibit this "quantum advantage" arise from a pseudorandomness approach initiated by Aaronson [STOC, 2010]. Our core technical result is constructing a distribution over Boolean strings that "look random" to constantdepth circuits of quasipolynomial size, but can be distinguished from the uniform distribution by very efficient quantum algorithms.
(joint work with Ran Raz)
Professor, Université de Sherbrooke
QSciTech NSERCCREATE Training Program  Bridging the Gap between Quantum Science and Quantum Technologies
The QSciTech NSERCCREATE program aims at training the next generation of quantum scientists, engineers and entrepreneurs. The program will provide integrative and targeted training to graduate students (PhD's and MSc's) in the field of quantum technologies, one of Canada's hightech economic sector of priority. The goal is to train jobready candidates so that they get the view of the whole chain of quantum technology development, encompassing basic quantum science, engineering methods, and professional skills. The training will provide engineering skills to quantum physics students and quantum awareness to engineering and computer science students. An overall view will be given of this innovative training program. The prerequisites and selection process of students, funding structure, training phases, and the targets that are expected to be reached for the coming 6 years of this new program will be presented.
Postdoc, Université de Sherbrooke
Director : Eva DupontFerrier
Coherent manipulation of single nuclear spin
Advances in experimental techniques offer physicists the opportunity to implement simple systems worth of the "gedankenexperiments" imagined by the founders of quantum theory. During the presentation, I propose to study one of these toy model systems, namely a single 3/2 nuclear spin. The presentation will start by investigating the readout process and the coherent manipulation of the 4 nuclear spin states using a single molecular magnet transistor [1,2]. These preliminary results demonstrate that we have a fully controlled 4level quantum system, a qudit, on which we recently implemented a quantum algorithm. With their state space of large dimension, qudits open fascinating experimental prospects. Protocols based on a generalization of the Ramsey interferometry to a multilevel system enable to measure, among others, the accumulation of geometric phases and of quantum gate phase [3]. As an outlook, I will display how, using a larger single nuclear spin, we could apply quantum error correction protocol [4], to obtain a selfcorrected qubit.
1 Thiele S. et al. Science 344, 1135 (2014)
2 Godfrin C. et al. Phys. Rev. Lett. 119, 187702 (2017)
3 Godfrin C. et al. accepeted to Nature partener journal quantum information.
4 Pirandola S. et al. Phys. Rev. A 77, 032309 (2008)
Postdoc, Université de Sherbrooke
Director : Alexandre Blais
Systems illuminated by squeezed wavepacket modes
Whitenoise theory is incapable of describing photoncounting measurements in the presence of thermal and squeezed noise. We accommodate such scenarios by considering an environment that includes traveling wave packets that are squeezed, deriving a hierarchy of equations similar to those used to describe traveling wave packets with fixed photon number. Squeezing introduces qualitatively different effects, however, complicating numerical solution of these hierarchies. We provide preliminary numerical analysis of the formalism and showcase its utility by calculating the resonance fluorescence of a twolevel atom in squeezed vacuum with squeezing bandwidth narrower than the atomic linewidth, a regime inaccessible to previous techniques.
Postdoc, Université de Sherbrooke
Director : David Poulin
Neural BeliefPropagation Decoders for Quantum ErrorCorrecting Codes
Beliefpropagation (BP) decoders play a vital role in modern coding theory. However, the classical design impairs their performance in quantum information processing. Inspired by an exact mapping between BP and deep neural networks, we train neural BP decoders for quantum lowdensity paritycheck codes, with a loss function tailored for the quantum setting. Training substantially improves the performance of the original BP decoders. The flexibility and adaptability of the neural BP decoders make them suitable for lowoverhead error correction in nearterm quantum devices.
Master, Université d'Ottawa
Director : Anne Broadbent
A limit on quantum nonlocality from an information processing principle
In their most common formulation, the axioms of quantum mechanics provide the mathematical description of quantum states, measurements and time evolution. The mathematical nature of the axioms enables us to make very precise predictions but provides little physical intuition on the quantum theory. For instance, the absence of consensus on the interpretation of the measurement process is a symptom of the lack of physical intuition in the mathematical axioms the quantum theory builds on. Nonlocality is another feature of quantum mechanics that arises from the mathematical axioms but that lacks an intuitive understanding. Indeed, quantum entanglement is known to give rise to nonlocal correlations that are not possible in a classical theory. Even though quantum correlations are stronger than classical correlations, they are still limited by the mathematical structure of quantum mechanics. Since physical limits usually emerge from physical principles, multiple principles were suggested in order to give a more physical explanation of the quantum limit on nonlocal correlations. None of these principles were able to completely rule out all superquantum correlations. In this work, we study the principle of nontrivial communication complexity (NTCC), that sets a limit on what can be done in a particular information processing setting. Nonlocal correlations that violate this principle are believed to be impossible in nature. In this work, we expand the set of superquantum correlations that are known to be ruled out by the NTCC principle, thus providing an explanation for their impossibility in quantum mechanics.
Professor, McGill University
An account of the commercialization of an idea
Through a number of serendipitous events, an idea that emerged in my laboratory  the application of graphene materials to acoustic transduction  is on the path to commercialization via the startup ORA Graphene Audio. My talk will give a first hand account of the simple physics behind the idea, and how students were able to build a hardware startup based upon it. I will highlight lessons learned through successes and failures encountered along the way.
Doctorate & Master students, Université de Sherbrooke
Directors: David Poulin & Alexandre Blais
Quantum Quarter
In this talk, we will present the Q2 project. This student project aims to bridge the gap between the quantum industries and universities by creating new career opportunities for physics and engineering students.
Postdoc, Université de Sherbrooke
Director : Glen Evenbly
Role of canting and depletedtriplet minima in superconducting spin valve structures
The trilayer and pentalayer spin valve structures are revisited to determine the behavior of pair correlations and Josephson current when the magnetic layers are canted at arbitrary angle. The two systems display markedly different behaviors in the center magnetic layer. While the trilayer generates a triplet component that is weakly affected by canting, the pentalayer tunes in singlet pair correlations depending heavily on canting. We also show that a minimum with depleted m=+/1 triplet components, rather than a 0π transition, may be observed in the current profile Ic(dF) of a trilayer spin valve. The depletedtriplet minimum (DTM) is directly attributable to a decrease of m=+/1 triplet correlations with increased thickness of the central ferromagnet, accompanied by a hidden, simultaneous sign change of the Gor'kov functions contributed from the left and right superconductors. We introduce a toy model for superconductingmagnetic proximity systems to better illuminate the behavior of individual components of the Gor'kov function and compare with a full numerical calculation.
Doctorate, McGill University
Director : Jack Sankey
Progress toward optical control of mechanical geometry
We report experimental progress toward achieving our group's recent proposal [1] to use the field inside a FabryPerot cavity to apply a spatially confined optical spring to a single lattice site of a phononic crystal. This perturbation of the otherwise pristine phononic crystal will allow an unprecedented level of optomechanical control over the shape and mass of a mechanical mode, enabling the smooth localization of the spatial distribution of oscillating mass from the centimeter scale to the micron scale. Such control over shape and effective mass has never been demonstrated, and represents an entirely unexplored avenue in the field.
Thus far, we have reliably fabricated the requisite (delicate!) mechanical structures, and observed the characteristic "phononic bandgap" (a necessary ingredient for localization). We present here the design of a rigid, vibrationisolated apparatus to measure these effects in ultrahigh vacuum. Furthermore, we show preliminary attempts at decreasing the finesse of a fibermirror in a controllable manner by etching away some of the layers forming the highreflectivity Bragg stack. Achieving a specific finesse value for our fibermirrors is necessary to assemble a fiber cavity that will generate a strong optical spring whilst displaying a sufficiently large decay rate, therefore minimizing antidamping of the phononic crystal, and facilitating cavity locking.
[1] A. Z. Barasheed et al., Phys. Rev. A 93, 053811 (2016)
Master, Université de Montréal
Director : Gilles Brassard
A wonderful combination of the parallel repetition theorem, Kolmogorov complexity and the magic square game
The classical magic square game consists of a 3x3 grid that needs to be filled with bits (0 or 1), respecting an even number of ones in each row and an odd number of ones in each column. In a 2players' version of this game, Alice and Bob each receive a trit (1, 2 or 3) and are asked to fill the corresponding row (containing an even number of ones) and column (containing an odd number of ones) respectively such that the intersection of their row and column matches, that is, it contains the same bit. With a classical strategy, they can win at most with probability 8/9. The parallel repetition theorem by Ran Raz says that if they play n repetitions in parallel of a game, the probability that they win all of the n repetitions decreases exponentially with n. This theorem can be used to prove some interesting results on the Kolmogorov complexity of Alice and Bob's answers to the magic square game. More precisely, we can show that the answer (row or column) must be uncomputable even given the respective question (the trit indicating which row or column to fill).
Postdoc, McGill University
Director : Bill Coish
Collective nuclear spins coherent effects in a quantum electron shuttle
In a spinblockade quantum dot with coherent electronnuclear spin interaction, initially polarized nuclear spins may lead to a transient boost in leakagecurrent owning to the dynamically built correlations among the nuclear spins  a reminiscent of fluorescence emission in the optical Dicke superradiance effect. We study how this correlation could manifest in an electron shuttle device where a small ”island” of nuclear spins was embedded along the shuttling path. By incorporating hyperfine flipflop effect exactly into the dissipator under a "boxmodel" setting, we qualitatively showed that how a threesteps protocol might be used to modify the nuclear spins distribution and reveal their collective coherent dynamical features.
Postdoc & Master, McGill University
Director : Lilian Childress
Coupling fiber microcavities and color centers in diamond
Color centers in diamond are attractive spinphoton interfaces for future quantum technologies. The nitrogen vacancy center (NV) spin is a robust qubit potentially giving access to multiqubit registers [1,2]. However, only 3% of all photons emitted by an NV can be used in remote entanglement protocols.We present our ongoing effort to couple color centers embedded in ultralowloss diamond membranes to a fully tunable optical microcavity directly interfaced with an optical fiber. The required passive and active cavity stabilisation mechanisms will be discussed, as well as our stateoftheart results for the loaded cavity finesse. At cryogenic temperatures both NV and GeV decay rates and fraction of “useful” photons will be enhanced, scaling with the cavity finesse [3]. In addition, GeV centers could also be used to improve the “Indistinguishability x Rate” figure of merit for room temperature single photon sources.
[1] E. Hogan et al., Nature 466 (2010)
[2] N. Kalb et al., Science 356 (2017)
[3] D. Riedel et al., PRX 7 (2017)
Intern, Université de Sherbrooke
Director : Max Hofheinz
Donor in Silicon Spin  Photon coupling
Postdoc, Université de Sherbrooke
Director : Alexandre Blais
Frequency and relaxation rate renormalization of driven weakly anharmonic superconducting qubits: The readout problem
Recent experiments in circuit QED with a transmon qubit have found a strong dependence of the qubit relaxation rate on readout power [Mundhada, Shankar, Narla, ZalysGeller,Girvin,Devoret, APS 2016]. We discuss a plausible mechanism that is consistent with available experimental data up to intermediate cavity occupation n_c < 5.
Master, National Research Council Canada
Director : Andrew Sachrajda
Investigation of Single Photon Emitters Based on InAsP Quantum Dots Imbedded in SiteControlled InP Nanowires
Various quantum technologies, such as quantum cryptography and quantum communication, require sources of indistinguishable single photons. InAsP quantum dots imbedded in InP nanowires are proven sources of such highpurity single photons [1]. By encapsulating the nanowires in InP tapered waveguides, the emitted photons have a Gaussian profile ideal for coupling to optical fibres [2]. Our goal is to develop a fibreonly system to collect indistinguishable single photons emitted by these quantum dots. A lensed fiber is used to map out siteselectively grown nanowires, and to perform PL experiments. This study is performed at millikelvin temperatures and in magnetic fields up to 6 T. The phonon sidebands of the emission lines are measured at different temperatures to investigate the role phonons play in photon indistinguishability. Hanbury BrownTwiss autocorrelation measurements reveal single photon emission from these dots. Magnetic field spectroscopy allows us to identify the different exciton complexes (e.g. X, X*, XX) responsible for specific emission lines in the PL spectrum and to measure their associated electron gfactors.
[1] D. Dalacu, et al. Ultraclean Emission from InAsP Quantum Dots in DefectFree Wurtzite InP Nanowires, Nano Letters, Vol. 12 (11), 59195923. (2012)
[2] G. Bulgarini, et al. Nanowire Waveguides Launching Single Photons in a Gaussian Mode for Ideal Fiber Coupling, Nano Letters, Vol. 14 (7), 41024106. (2014)
Doctorate, Université de Sherbrooke
Director : Bertrand Reulet
Exploration of the Photon Statistics of a Josephson Paramp via continuous microwave measurements
Authors: Jean Olivier Simoneau, Stéphane Virally, Christian Lupien & Bertrand Reulet
Doctorate, National Research Council Canada
Director : Andrew Sachrajda
EDSR of a single heavy hole in a lateral GaAs/AlGaAs quantum dot qubit
Single holes are attractive as spin qubits due to their advantageous properties which include a reduced hyperfine interaction, a strong spinorbit coupling for subnanosecond spin rotations, and the absence of valley complications.
Here we report single hole electric dipole spin resonance (EDSR) measurements over the 2050 GHz range taking advantage of the strong spinorbit coupling. The experiment was performed in a GaAs double quantum dot device described in [1] tuned in such way that only one of the dots contained a single heavy hole with the Fermi level of the adjacent lead positioned in between Zeeman split spin states. In this situation one hole is initialized in the lowest spin level and the current is energy blockaded. A small microwave voltage is applied to a plunger gate to mediate EDSR rotating the hole spin from the lower to the upper spin level allowing the hole to tunnel to the lead. The spin resonance is detected as an increase in current when the resonant condition is fulfilled. The second dot is used as an auxiliary tool to tune the gfactor via a strong spindependent tunnel coupling [1]. We show that gfactor can be tuned in the range of 30% by a small change of the voltage applied to the auxiliary dot plunger gate.
[1] A. Bogan et al., Phys. Rev. Lett. 120, 207701 (2018).
Doctorate, McGill University
Director : Bill Coish
Optimized polarization control in a centralspin system
In this work [1], we study the zerotemperature phase diagram and the dissipative dynamics of the centralspin system, where one “central” spin is homogeneously coupled with many “ancilla” spins. An archetypical example of this model is given by an electron spin coupled to nuclear spins in a quantum dot via hyperfine interactions. This same centralspin model has been shown to improve the efficiency of quantumannealing protocols. We establish the zerotemperature phase diagram with phases characterized by the polarization of the ancilla spins relative to the central spin. By rapidly tuning a parameter in the Hamiltonian, the ancillaspin polarization can be rapidly modified through a dissipative equilibration process mediated by the central spin.
Remarkably, we find that the dissipation rate can be optimized to minimize the time scale for polarization dynamics. These results may be important for protocols to quickly polarize nuclear spins in semiconductor quantum dots or to rapidly and efficiently equilibrate a quantum annealer.
[1] A. Ricottone, Y.N. Fang, S. Chesi and W.A. Coish, in preparation
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 sensitivity to electrostatic discharge (ESD) due to the bigger current density for the same applied voltage. 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. Following sample fabrication, two guard ring removal processes, with diamond tip scribing and laser cutting, have been investigated. On Al/Co tunnel junctions isolated by a thin aluminum oxide layer, the diamond tip scribing lead to a 93% yield for junction integrity. However, removal of the guard ring with laser cutting doesn’t remove the electrical conductivity between connections.
November 13th
10h30 10h55 Registration
10h55 11h00 Opening remarks (Salon A)
11h00 12h00 Dr. Avishay Tal, Simons Institute & Stanford University (Salon A)
Oracle Separation of Quantum Polynomial Time and the Polynomial Hierarchy
12h00 13h30 Lunch (Dining room  4 Canards)
13h30 14h00 Dr. Gustav Kalbe, Head of Unit, High Performance Computing &
Quantum Technologies, European Commission (Salon A)
The Quantum Technologies Flagship Initiative of the European Union
14h00 15h00 Dr. Dominique Laroche, Delft University of Technology (Salon A)
Probing the building blocks of topological qubits in
superconducting InAs nanowires
15h00 15h30 Coffee break (Salon B)
15h30 16h00 Dr. Yehua Liu, Postdoc, Université de Sherbrooke (Salon A)
Neural BeliefPropagation Decoders for Quantum
ErrorCorrecting Codes
16h00 – 16h20 MarcOlivier Proulx, Master, Université d'Ottawa (Salon A)
A limit on quantum nonlocality from an information
processing principle
16h20  17h00 Thomas Szkopek, Professor, McGill University (Salon A)
An account of the commercialization of an idea
17h00  17h10 Maxime Tremblay & Alexandre ChoquettePoitevin,
Université de Sherbrooke (Salon A)
Quantum Quarter
17h00  Poster session with refreshments (Salon B)
19h30  INTRIQ dinner (Knowlton room)
November 14th
09h00  10h00 Dr. Kartiek Agarwal, Princeton University (Salon A)
Spatiotemporal quenches for fast preparation of ground states of
critical models
10h00  10h45 Alexander Maloney, Professor, McGill University (Salon A)
Quantum Information Theory, Black Holes and Spacetime
10h45  11h15 Dr. Jonathan Gross, Postdoc, Université de Sherbrooke (Salon A)
Systems illuminated by squeezed wavepacket modes
11h15  12h00 Coffee break (Salon B)
12h00  13h30 Lunch (Dining room  4 Canards)
13h30  14h00 Yves BérubéLauzière, Professor, Université de Sherbrooke (Salon A)
QSciTech NSERCCREATE Training Program
Bridging the Gap between Quantum Science & Quantum Technologies
14h00  15h00 Johannes Pollanen, Professor, Michigan State University (Salon A)
Hybrid quantum information systems with electrons on helium
15h00  15h30 Dr. Clément Godfrin, Postdoc, Université de Sherbrooke (Salon A)
Coherent manipulation of single nuclear spin
15h30  15h40 Closing remarks
Princeton University
Spatiotemporal quenches for fast preparation of ground states of critical models
The difficulty of preparing highly entangled quantum states poses an important challenge in engineering artificial quantum systems for the purposes of computation and simulation. Adiabatic methods which slowly evolve unentangled states to entangled states are typically slow and particularly fail at criticality where the gap between eigenstates vanishes. The search for novel nonadiabatic methods for quantum state preparation is a topic of current research interest, and immense experimental relevance. I will describe the state of the art in the field and discuss our proposal(s) using spatiotemporal quenches to efficiently prepare the ground states of arbitrary interacting critical theories in one dimension and beyond.
Head of Unit
High Performance Computing & Quantum Technologies
European Commission
The Quantum Technologies FET Flagship Initiative of the European Union
The Quantum Technologies Flagship is a Future and Emerging Technologies (FET) research initiative that was launched by the EU. This largescale, longterm Flagship joins both academic and industry researchers to make scientific discoveries in the quantum field, using such innovations to help grow the economy so that Europe can resolve its current societal challenges. As a panEuropean programme with support from each of its Member States, the Quantum Technologies Flagship will continue to develop using previous European funding from the last 20 years and allow Europe to match the research implemented by its competitors on the world stage.
McGill University
Quantum Information Theory, Black Holes and Spacetime
I will describe recent progress on the relationship between quantum information theory, quantum field theory and quantum gravity. I will review the theoretical evidence that spacetime emerges from the entanglement of more fundamental quantum mechanical degrees of freedom. This evidence comes from recent advances in our understanding of quantum black holes and the holographic (AdS/CFT) correspondence. The relationship between quantum information theory, field theory and gravity has already led to new results, including new positive energy theorems in general relativity and a unified theory of renormalization group flows. If time permits, I will explain the notion that spacetime can be regarded as a (quantum) errorcorrecting code. This will be an expository talk; no advanced background aside from some elements of quantum information theory will be assumed.
Delft University of Technology
Probing the building blocks of topological qubits in superconducting InAs nanowires
Utilizing the exotic properties of nonAbelian quasiparticles, topological qubits offer an approach towards quantum computing where the information is stored nonlocally, making this an architecture resilient against most decoherence sources. Majorana bound states (MBS) arising in proximityinduced superconducting nanowires are currently the prime candidate for the implementation of such topological quantum bits. Thus far, MBS signatures chiefly relied on single electron tunnelling measurements, which lead to decoherence of the quantum information stored in the MBS through quasiparticle poisoning. In this talk, I will present a novel experimental platform where proximitized nanowire devices are coupled onchip to microwave detectors and spectrometers, allowing for measurements of the building blocks of topological qubits in a parity conserving manner. Utilizing this platform, we directly observed a transition from a 2π to a 4πperiodic Josephson radiation in InAs nanowire as a function of both magnetic field and chemical potential. This transition is consistent with the onset of MBS in the nanowires. We also performed microwave spectroscopy of the fundamental unit of a prospective topological qubit, a nanowirebased Cooper pair transistor. In addition to confirm the large tunability of this system, we were able to directly measure the population of the odd and of the even parity sector in these devices.
Michigan State University
Hybrid quantum information systems with electrons on helium
Electrons floating on the surface of liquid helium at low temperature were one of the first platforms proposed for quantum computation [1]. In this hybrid quantum system the surface of the liquid helium functions as a fantastically pristine substrate without the defects and imperfections that are unavoidable in almost all other material systems. Electrons placed near this liquid substrate are bound to it and float (in vacuum) about 10 nanometers above the surface. The motion of these electrons relative to the surface of the helium, as well as their spin, are quantum mechanical and form the basis for potentially new types of qubits. These qubits, if they can be realized, are predicted to be shielded from decoherence by the isolation provided by liquid helium substrate. I will describe the state of the art in the field, experimental milestones demonstrating the fantastic level of control that can be achieved in this system, and how the time is now ripe for using the hardware tool kit of circuit quantum electrodynamics for developing novel qubits from electrons on helium.
[1] P.M. Platzman and M.I. Dykman, Quantum Computing with Electrons Floating on Liquid Heilum, Science 284, 1967 (1999).
Simons Institute & Stanford University
Oracle Separation of Quantum Polynomial Time and the Polynomial Hierarchy
In their seminal paper, Bennett, Bernstein, Brassard and Vazirani [SICOMP, 1997] showed that relative to an oracle, quantum algorithms are unable to solve NPcomplete problems in subexponential time (i.e., that Grover's search is optimal in this setting).
In this work, we show a strong converse to their result. Namely, we show that, relative to an oracle, there exist computational tasks that can be solved efficiently by a quantum algorithm, but require exponential time for any algorithm in the polynomial hierarchy. (The polynomial hierarchy is a hierarchy of complexity classes that captures P, NP, coNP, and their generalizations.)
The tasks that exhibit this "quantum advantage" arise from a pseudorandomness approach initiated by Aaronson [STOC, 2010]. Our core technical result is constructing a distribution over Boolean strings that "look random" to constantdepth circuits of quasipolynomial size, but can be distinguished from the uniform distribution by very efficient quantum algorithms.
(joint work with Ran Raz)
Professor, Université de Sherbrooke
QSciTech NSERCCREATE Training Program  Bridging the Gap between Quantum Science and Quantum Technologies
The QSciTech NSERCCREATE program aims at training the next generation of quantum scientists, engineers and entrepreneurs. The program will provide integrative and targeted training to graduate students (PhD's and MSc's) in the field of quantum technologies, one of Canada's hightech economic sector of priority. The goal is to train jobready candidates so that they get the view of the whole chain of quantum technology development, encompassing basic quantum science, engineering methods, and professional skills. The training will provide engineering skills to quantum physics students and quantum awareness to engineering and computer science students. An overall view will be given of this innovative training program. The prerequisites and selection process of students, funding structure, training phases, and the targets that are expected to be reached for the coming 6 years of this new program will be presented.
Postdoc, Université de Sherbrooke
Director : Eva DupontFerrier
Coherent manipulation of single nuclear spin
Advances in experimental techniques offer physicists the opportunity to implement simple systems worth of the "gedankenexperiments" imagined by the founders of quantum theory. During the presentation, I propose to study one of these toy model systems, namely a single 3/2 nuclear spin. The presentation will start by investigating the readout process and the coherent manipulation of the 4 nuclear spin states using a single molecular magnet transistor [1,2]. These preliminary results demonstrate that we have a fully controlled 4level quantum system, a qudit, on which we recently implemented a quantum algorithm. With their state space of large dimension, qudits open fascinating experimental prospects. Protocols based on a generalization of the Ramsey interferometry to a multilevel system enable to measure, among others, the accumulation of geometric phases and of quantum gate phase [3]. As an outlook, I will display how, using a larger single nuclear spin, we could apply quantum error correction protocol [4], to obtain a selfcorrected qubit.
1 Thiele S. et al. Science 344, 1135 (2014)
2 Godfrin C. et al. Phys. Rev. Lett. 119, 187702 (2017)
3 Godfrin C. et al. accepeted to Nature partener journal quantum information.
4 Pirandola S. et al. Phys. Rev. A 77, 032309 (2008)
Postdoc, Université de Sherbrooke
Director : Alexandre Blais
Systems illuminated by squeezed wavepacket modes
Whitenoise theory is incapable of describing photoncounting measurements in the presence of thermal and squeezed noise. We accommodate such scenarios by considering an environment that includes traveling wave packets that are squeezed, deriving a hierarchy of equations similar to those used to describe traveling wave packets with fixed photon number. Squeezing introduces qualitatively different effects, however, complicating numerical solution of these hierarchies. We provide preliminary numerical analysis of the formalism and showcase its utility by calculating the resonance fluorescence of a twolevel atom in squeezed vacuum with squeezing bandwidth narrower than the atomic linewidth, a regime inaccessible to previous techniques.
Postdoc, Université de Sherbrooke
Director : David Poulin
Neural BeliefPropagation Decoders for Quantum ErrorCorrecting Codes
Beliefpropagation (BP) decoders play a vital role in modern coding theory. However, the classical design impairs their performance in quantum information processing. Inspired by an exact mapping between BP and deep neural networks, we train neural BP decoders for quantum lowdensity paritycheck codes, with a loss function tailored for the quantum setting. Training substantially improves the performance of the original BP decoders. The flexibility and adaptability of the neural BP decoders make them suitable for lowoverhead error correction in nearterm quantum devices.
Master, Université d'Ottawa
Director : Anne Broadbent
A limit on quantum nonlocality from an information processing principle
In their most common formulation, the axioms of quantum mechanics provide the mathematical description of quantum states, measurements and time evolution. The mathematical nature of the axioms enables us to make very precise predictions but provides little physical intuition on the quantum theory. For instance, the absence of consensus on the interpretation of the measurement process is a symptom of the lack of physical intuition in the mathematical axioms the quantum theory builds on. Nonlocality is another feature of quantum mechanics that arises from the mathematical axioms but that lacks an intuitive understanding. Indeed, quantum entanglement is known to give rise to nonlocal correlations that are not possible in a classical theory. Even though quantum correlations are stronger than classical correlations, they are still limited by the mathematical structure of quantum mechanics. Since physical limits usually emerge from physical principles, multiple principles were suggested in order to give a more physical explanation of the quantum limit on nonlocal correlations. None of these principles were able to completely rule out all superquantum correlations. In this work, we study the principle of nontrivial communication complexity (NTCC), that sets a limit on what can be done in a particular information processing setting. Nonlocal correlations that violate this principle are believed to be impossible in nature. In this work, we expand the set of superquantum correlations that are known to be ruled out by the NTCC principle, thus providing an explanation for their impossibility in quantum mechanics.
Professor, McGill University
An account of the commercialization of an idea
Through a number of serendipitous events, an idea that emerged in my laboratory  the application of graphene materials to acoustic transduction  is on the path to commercialization via the startup ORA Graphene Audio. My talk will give a first hand account of the simple physics behind the idea, and how students were able to build a hardware startup based upon it. I will highlight lessons learned through successes and failures encountered along the way.
Doctorate & Master students, Université de Sherbrooke
Directors: David Poulin & Alexandre Blais
Quantum Quarter
In this talk, we will present the Q2 project. This student project aims to bridge the gap between the quantum industries and universities by creating new career opportunities for physics and engineering students.
Postdoc, Université de Sherbrooke
Director : Glen Evenbly
Role of canting and depletedtriplet minima in superconducting spin valve structures
The trilayer and pentalayer spin valve structures are revisited to determine the behavior of pair correlations and Josephson current when the magnetic layers are canted at arbitrary angle. The two systems display markedly different behaviors in the center magnetic layer. While the trilayer generates a triplet component that is weakly affected by canting, the pentalayer tunes in singlet pair correlations depending heavily on canting. We also show that a minimum with depleted m=+/1 triplet components, rather than a 0π transition, may be observed in the current profile Ic(dF) of a trilayer spin valve. The depletedtriplet minimum (DTM) is directly attributable to a decrease of m=+/1 triplet correlations with increased thickness of the central ferromagnet, accompanied by a hidden, simultaneous sign change of the Gor'kov functions contributed from the left and right superconductors. We introduce a toy model for superconductingmagnetic proximity systems to better illuminate the behavior of individual components of the Gor'kov function and compare with a full numerical calculation.
Doctorate, McGill University
Director : Jack Sankey
Progress toward optical control of mechanical geometry
We report experimental progress toward achieving our group's recent proposal [1] to use the field inside a FabryPerot cavity to apply a spatially confined optical spring to a single lattice site of a phononic crystal. This perturbation of the otherwise pristine phononic crystal will allow an unprecedented level of optomechanical control over the shape and mass of a mechanical mode, enabling the smooth localization of the spatial distribution of oscillating mass from the centimeter scale to the micron scale. Such control over shape and effective mass has never been demonstrated, and represents an entirely unexplored avenue in the field.
Thus far, we have reliably fabricated the requisite (delicate!) mechanical structures, and observed the characteristic "phononic bandgap" (a necessary ingredient for localization). We present here the design of a rigid, vibrationisolated apparatus to measure these effects in ultrahigh vacuum. Furthermore, we show preliminary attempts at decreasing the finesse of a fibermirror in a controllable manner by etching away some of the layers forming the highreflectivity Bragg stack. Achieving a specific finesse value for our fibermirrors is necessary to assemble a fiber cavity that will generate a strong optical spring whilst displaying a sufficiently large decay rate, therefore minimizing antidamping of the phononic crystal, and facilitating cavity locking.
[1] A. Z. Barasheed et al., Phys. Rev. A 93, 053811 (2016)
Master, Université de Montréal
Director : Gilles Brassard
A wonderful combination of the parallel repetition theorem, Kolmogorov complexity and the magic square game
The classical magic square game consists of a 3x3 grid that needs to be filled with bits (0 or 1), respecting an even number of ones in each row and an odd number of ones in each column. In a 2players' version of this game, Alice and Bob each receive a trit (1, 2 or 3) and are asked to fill the corresponding row (containing an even number of ones) and column (containing an odd number of ones) respectively such that the intersection of their row and column matches, that is, it contains the same bit. With a classical strategy, they can win at most with probability 8/9. The parallel repetition theorem by Ran Raz says that if they play n repetitions in parallel of a game, the probability that they win all of the n repetitions decreases exponentially with n. This theorem can be used to prove some interesting results on the Kolmogorov complexity of Alice and Bob's answers to the magic square game. More precisely, we can show that the answer (row or column) must be uncomputable even given the respective question (the trit indicating which row or column to fill).
Postdoc, McGill University
Director : Bill Coish
Collective nuclear spins coherent effects in a quantum electron shuttle
In a spinblockade quantum dot with coherent electronnuclear spin interaction, initially polarized nuclear spins may lead to a transient boost in leakagecurrent owning to the dynamically built correlations among the nuclear spins  a reminiscent of fluorescence emission in the optical Dicke superradiance effect. We study how this correlation could manifest in an electron shuttle device where a small ”island” of nuclear spins was embedded along the shuttling path. By incorporating hyperfine flipflop effect exactly into the dissipator under a "boxmodel" setting, we qualitatively showed that how a threesteps protocol might be used to modify the nuclear spins distribution and reveal their collective coherent dynamical features.
Postdoc & Master, McGill University
Director : Lilian Childress
Coupling fiber microcavities and color centers in diamond
Color centers in diamond are attractive spinphoton interfaces for future quantum technologies. The nitrogen vacancy center (NV) spin is a robust qubit potentially giving access to multiqubit registers [1,2]. However, only 3% of all photons emitted by an NV can be used in remote entanglement protocols.We present our ongoing effort to couple color centers embedded in ultralowloss diamond membranes to a fully tunable optical microcavity directly interfaced with an optical fiber. The required passive and active cavity stabilisation mechanisms will be discussed, as well as our stateoftheart results for the loaded cavity finesse. At cryogenic temperatures both NV and GeV decay rates and fraction of “useful” photons will be enhanced, scaling with the cavity finesse [3]. In addition, GeV centers could also be used to improve the “Indistinguishability x Rate” figure of merit for room temperature single photon sources.
[1] E. Hogan et al., Nature 466 (2010)
[2] N. Kalb et al., Science 356 (2017)
[3] D. Riedel et al., PRX 7 (2017)
Intern, Université de Sherbrooke
Director : Max Hofheinz
Donor in Silicon Spin  Photon coupling
Postdoc, Université de Sherbrooke
Director : Alexandre Blais
Frequency and relaxation rate renormalization of driven weakly anharmonic superconducting qubits: The readout problem
Recent experiments in circuit QED with a transmon qubit have found a strong dependence of the qubit relaxation rate on readout power [Mundhada, Shankar, Narla, ZalysGeller,Girvin,Devoret, APS 2016]. We discuss a plausible mechanism that is consistent with available experimental data up to intermediate cavity occupation n_c < 5.
Master, National Research Council Canada
Director : Andrew Sachrajda
Investigation of Single Photon Emitters Based on InAsP Quantum Dots Imbedded in SiteControlled InP Nanowires
Various quantum technologies, such as quantum cryptography and quantum communication, require sources of indistinguishable single photons. InAsP quantum dots imbedded in InP nanowires are proven sources of such highpurity single photons [1]. By encapsulating the nanowires in InP tapered waveguides, the emitted photons have a Gaussian profile ideal for coupling to optical fibres [2]. Our goal is to develop a fibreonly system to collect indistinguishable single photons emitted by these quantum dots. A lensed fiber is used to map out siteselectively grown nanowires, and to perform PL experiments. This study is performed at millikelvin temperatures and in magnetic fields up to 6 T. The phonon sidebands of the emission lines are measured at different temperatures to investigate the role phonons play in photon indistinguishability. Hanbury BrownTwiss autocorrelation measurements reveal single photon emission from these dots. Magnetic field spectroscopy allows us to identify the different exciton complexes (e.g. X, X*, XX) responsible for specific emission lines in the PL spectrum and to measure their associated electron gfactors.
[1] D. Dalacu, et al. Ultraclean Emission from InAsP Quantum Dots in DefectFree Wurtzite InP Nanowires, Nano Letters, Vol. 12 (11), 59195923. (2012)
[2] G. Bulgarini, et al. Nanowire Waveguides Launching Single Photons in a Gaussian Mode for Ideal Fiber Coupling, Nano Letters, Vol. 14 (7), 41024106. (2014)
Doctorate, Université de Sherbrooke
Director : Bertrand Reulet
Exploration of the Photon Statistics of a Josephson Paramp via continuous microwave measurements
Authors: Jean Olivier Simoneau, Stéphane Virally, Christian Lupien & Bertrand Reulet
Doctorate, National Research Council Canada
Director : Andrew Sachrajda
EDSR of a single heavy hole in a lateral GaAs/AlGaAs quantum dot qubit
Single holes are attractive as spin qubits due to their advantageous properties which include a reduced hyperfine interaction, a strong spinorbit coupling for subnanosecond spin rotations, and the absence of valley complications.
Here we report single hole electric dipole spin resonance (EDSR) measurements over the 2050 GHz range taking advantage of the strong spinorbit coupling. The experiment was performed in a GaAs double quantum dot device described in [1] tuned in such way that only one of the dots contained a single heavy hole with the Fermi level of the adjacent lead positioned in between Zeeman split spin states. In this situation one hole is initialized in the lowest spin level and the current is energy blockaded. A small microwave voltage is applied to a plunger gate to mediate EDSR rotating the hole spin from the lower to the upper spin level allowing the hole to tunnel to the lead. The spin resonance is detected as an increase in current when the resonant condition is fulfilled. The second dot is used as an auxiliary tool to tune the gfactor via a strong spindependent tunnel coupling [1]. We show that gfactor can be tuned in the range of 30% by a small change of the voltage applied to the auxiliary dot plunger gate.
[1] A. Bogan et al., Phys. Rev. Lett. 120, 207701 (2018).
Doctorate, McGill University
Director : Bill Coish
Optimized polarization control in a centralspin system
In this work [1], we study the zerotemperature phase diagram and the dissipative dynamics of the centralspin system, where one “central” spin is homogeneously coupled with many “ancilla” spins. An archetypical example of this model is given by an electron spin coupled to nuclear spins in a quantum dot via hyperfine interactions. This same centralspin model has been shown to improve the efficiency of quantumannealing protocols. We establish the zerotemperature phase diagram with phases characterized by the polarization of the ancilla spins relative to the central spin. By rapidly tuning a parameter in the Hamiltonian, the ancillaspin polarization can be rapidly modified through a dissipative equilibration process mediated by the central spin.
Remarkably, we find that the dissipation rate can be optimized to minimize the time scale for polarization dynamics. These results may be important for protocols to quickly polarize nuclear spins in semiconductor quantum dots or to rapidly and efficiently equilibrate a quantum annealer.
[1] A. Ricottone, Y.N. Fang, S. Chesi and W.A. Coish, in preparation
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 sensitivity to electrostatic discharge (ESD) due to the bigger current density for the same applied voltage. 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. Following sample fabrication, two guard ring removal processes, with diamond tip scribing and laser cutting, have been investigated. On Al/Co tunnel junctions isolated by a thin aluminum oxide layer, the diamond tip scribing lead to a 93% yield for junction integrity. However, removal of the guard ring with laser cutting doesn’t remove the electrical conductivity between connections.