November 2, 2015 10:30 AM

November 3, 2015 10:00 PM
November 2, 2015 10:30 AM

November 3, 2015 10:00 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.
For Professor Gilles Bassard’s 60th birthday, INTRIQ and the Centre de recherches mathématiques (CRM) are proud to recognize three decades of research in quantum cryptographyand two decades in quantum teleportation as well as the outstanding contributions of Professor Gilles Brassard for the emergence of the field of quantum information science with a series of scientific conferences held at Domaine ChâteauBromont and a banquet in Montréal.
Gilles Brassard received a PhD in computer science in 1979 from Cornell University, specifically in cryptography. Since then, he has been a professor at the Université de Montréal and has held the Canada Research Chair in quantum information science since 2001. His Chair has recently been renewed until the end of 2021.
Professor Brassard is interested in all aspects of quantum information science, a field that is at the crossroads of computer science and quantum mechanics. In the late 1970's, he was one of the first researchers to apply quantum mechanical principles to information processing, giving birth to the field of quantum information science at a time when it seemed more like science fiction than science.
His invention of quantum cryptography was hailed in the February 2003 issue of Technology Review, a journal published by the Massachusetts Institute of Technology, as one of the « 10 emerging technologies that will change the world ». This makes it possible to communicate in perfect secrecy under the nose of an eavesdropper who has unlimited computational power and whose technology is restricted only by the known laws of physics. This technology, which was initially considered a fringe pursuit at best, has moved from proofofprinciple prototypes to sophisticated apparatus, to commercial venture. Gilles Brassard is also one of the inventors of quantum teleportation, which is universally recognized as a fundamental cornerstone of quantum information science. In 2012, Thomson Reuters predicted that he would one day be awarded the Nobel Prize in Physics for this discovery.
In addition to being the former editorinchief of the Journal of Cryptology, Professor Brassard has authored three books that have been translated into eight languages and, according to Google Scholar, his scientific articles and books have been cited over 36,000 times. He has been awarded many honours and accolades: most notably, he was the first Canadian to be made a Fellow of the International Association for Cryptologic Research (IACR). He has also won both the Gerhard Herzberg Canada Gold Medal for Science and Engineering and the Killam Prize for Natural Sciences, generally considered to be the two most prestigious science prizes in Canada. Professor Gilles Brassard was described as « one of Canada's science superstars » by British astronomer David Darling. He is a Fellow of the Royal Society of London and holder of honorary doctorates from the ETH (Eidgenössische Technische Hochschule) of Zurich, the University of Ottawa and the Università della Svizzera italiana, Lugano. He was recently appointed Officer of the Order of Canada.
10h30  10h55 Inscription
10h55  11h00 Mots d'ouverture
11h00  12h00 Charles Bennett, IBM Thomas J. Watson Research Cente (Salon A)
Is there such a thing as private information?
12h00  13h30 Dîner (Salle 4 canards)
13h30  14h30 Christopher Fuchs, University of Massachusetts Boston (Salon A)
What Huangjun Zhu would say if he were disguised as Chris Fuchs
14h30  15h00 Pause café (Salon B)
15h00  16h00 Harry Buhrman, CWI  University of Amsterdam (Salon A)
Quantum positionbased cryptography
16h00  16h45 Nicolas Quesada, Université de Sherbrooke (Salon A)
Efficiency limits in quantum frequency conversion
16h45  17h00 Alexandre Blais, Université de Sherbrooke (Salon A)
From quantum science to quantum technologies
16h45  19h00 Session d'affiches et rafraichissements (Salon B)
19h30  Souper (Salle 4 canards)
9h00  10h00 Nicolas Gisin, Université de Genève (Salon A)
Quantum Nonlocality with Arbitrary Limited Detection Efficiency and
Measurement Dependence
10h00  10h30 Paul RaymondRobichaud, Université de Montréal (Salon A)
The tale of the Orouboros
10h30  11h30 Pause café (Salon B)
11h30  12h00 Yuval Elias, Université de Montréal (Salon A)
Algorithmic Cooling in Liquid State NMR
12h00  13h30 Dîner (Salle 4 canards)
13h30  14h15 Michael Hilke, McGill University (Salon A)
Probing localization with a qubit
14h15  14h45 Shruti Puri, Université de Sherbrooke (Salon A)
Fighting KerrInduced NonGaussianity with Squeezing
14h45  15h15 Dany LachanceQuirion, Université de Sherbrooke (Salon A)
Observation of magnon number states in
a superconducting qubit spectrum
15h15  15h20 Mots de clôture
15h40  Départ en autobus vers le restaurant Le Cercle des HEC
17h45  18h15 Cocktail au restaurant Le Cercle, HEN Montréal
18h15  Banquet
Thomas J. Watson Research Center, Yorktown Heights, NY USA
Is there such a thing as private information?
Quantum information theory originated in the practical use of quantum laws to keep classical information private, but soon grew to encompass the whole classical theory, generalizing it as powerfully as the complex numbers generalize the reals. Conceptually, private classical information sits on a silppery slope between quantum information and public information. Indeed decoherence theory suggests that the slope may be so slippery that private classical information doesn't exist: once an ebit is measured by Alice and Bob to generate a bit of classical key, the news necessarily escapes into the environment, rendering the key no longer private.
University of Massachusetts Boston
What Huangjun Zhu would say if he were disguised as Chris Fuchs
Université de Genève
Quantum Nonlocality with Arbitrary Limited Detection Efficiency and Measurement Dependence
CWI  University of Amsterdam
Quantum positionbased cryptography
On 20 July 1969, millions of people held their breath as they watched, live on television, Neil Armstrong set foot on the Moon. Yet Fox Television has reported that a staggering 20% of Americans have had doubts about the Apollo 11 mission. Could it have been a hoax staged by Hollywood studios here on Earth? Position based cryptography may offer a solution. This kind of cryptography uses the geographic position of a party as its sole credential. Normally digital keys or biometric features are used.
A central building block in positionbased cryptography is that of positionverification. The goal is to prove to a set of verifier that one is at a certain geographical location. Protocols typically assume that messages can not travel faster than the speed of light. By responding to a verifier in a timely manner one can guarantee that one is within a certain distance of that verifier. Quite recently it was shown that positionverification protocols only based on this relativistic principle can be broken by attackers who simulate being at a the claimed position while physically residing elsewhere in space.
Because of the nocloning property of quantum information (qubits) it was believed that with the use of quantum messages one could devise protocols that were resistant to such collaborative attacks. Several schemes were proposed that later turned out to be insecure. Finally it was shown that also in the quantum case no unconditionally secure scheme is possible. We will review the field of positionbased quantum cryptography and highlight some of the research currently going on in order to develop, using reasonable assumptions on the capabilities of the attackers, protocols that are secure in practice.
Professor, Université de Sherbrooke
From quantum science to quantum technologies
Postdoc, Université de Montréal
Director: Gilles Brassard
Algorithmic Cooling in Liquid State NMR
Heatbath algorithmic cooling (HBAC) employs thermalization to purify quantum systems that interact with a heat bath, such as ensembles of nuclear spins, or cold atoms in an optical lattice. When applied to spins, HBAC produces ensembles of highly polarized spins, which enhance the signal strength in nuclear magnetic resonance (NMR). According to this cooling approach, spinhalf nuclei in a constant magnetic field are considered as bits, or more precisely quantum bits, in a known probability distribution. Algorithmic steps on these bits are then translated into NMR pulse sequences using common NMR quantum computation tools. The algorithmic cooling of spins is achieved by alternately combining reversible, entropypreserving manipulations (borrowed from data compression algorithms) with selective transfer of entropy from spins to the environment.HBAC, and multicycle HBAC, were previously achieved with nuclear spins using solidstate nuclear magnetic resonance (NMR), where spin diffusion allowed some spins to relax much more rapidly than others. In the liquid state, a partial variant of HBAC, without entropy compression, was applied to the three qubits of 13Cenriched trichloroethylene, resulting in modest cooling of the spin system. Recently, we utilized gradient ascent pulse engineering (GRAPE), an optimal control algorithm, to generate pulses with high fidelity for the compression and polarization exchange (SWAP) gates. Here, we combine those pulses to implement HBAC on this 3spin system. Various cooling algorithms were applied, cooling the system beyond Shannon’s entropy bound in several different ways. In particular, in one experiment a carbon qubit was cooled by a factor of 4.61.This work is a step towards potentially integrating HBAC and other tools of NMR quantum computing into in vivo magnetic resonance spectroscopy.
Professor, McGill University
Probing localization with a qubit
We look at the dynamics of a qubit that is coupled to a disordered quantum wire. We show that we can use the time evolution of the qubit to measure the static localization properties of a disordered system. The disordered system can be an electronic gate or lead with impurities, or equivalently remote spins. We also evaluate the decoherence rate of the qubit as a function of the amount of disorder in the gate and lead.
This work is a collaboration with Mackenzie and Eleuch.
Doctorat, Université de Sherbrooke
Director: Michel PioroLadrière
Observation of magnon number states in a superconducting qubit spectrum
A magnon is a collective excitation in an ordered spin system such as a ferromagnet. Interacting with both microwave and optical light, magnons in the ferrimagnetic insulator yttrium iron garnet (YIG) are candidates for transducing quantum information between those two frequency domains. Coherent interaction between a singlemagnon excitation in a YIG sphere and a superconducting qubit has recently been demonstrated through their interaction with a common microwave cavity mode.
The dispersive limit of the magnonqubit interaction is discussed in this presentation. Magnon number states are experimentally resolved in the superconducting qubit spectrum when creating a coherent state in the magnetostatic mode. The probability distribution of magnon number states recovered from these measurements is found to agree well with the Poisson distribution expected for a coherent state.
Resolving magnon number states is a necessary ingredient for implementing a protocol in which quantum information of the qubit is encoded in the magnetostatic mode. This encoding would be the first step toward the realization of a quantum transducer between microwave and optical domains.
This work has been done in the group of Pr. Yasunobu Nakamura at the Research Center for Advanced Science and Technology of the University of Tokyo.
Doctorate, Université de Montréal
Director: Gilles Brassard
The tale of the Orouboros
Beyond "it from bit", John Archibal Wheeler, expressed his desire for a primeval ophidian selfreflexive recursive structure able to give birth to itself. What can the autological serpent impart on Boltzmann brains, the nature of information, and of causality? Is our ontology leading to an epistemology leading to the very same ontology leading to the very same epistemology? Should Jǫrmungandr fail to eat it's tail, knell Ragnarøkkr, the heterological darkness!
Postdoc, Unviersité de Sherbrooke
Director: Alexandre Blais
Efficiency limits in quantum frequency conversion
Frequency conversion is an enabling process in many quantum information protocols. In this talk we study fundamental limits to high efficiency frequency conversion imposed by time ordering corrections. Using the Magnus expansion, we argue that these corrections, which are usually considered detrimental, can be used to increase the efficiency of conversion under certain circumstances. The corrections induce a nonlinear behaviour in the probability of upconversion as a function of the pump intensity, significantly modifying the sinusoidal Rabi oscillations that are otherwise expected. Finally, by using a simple scaling argument, we explain why cascaded frequency conversion devices attenuate time ordering corrections, allowing the construction of near ideal quantum pulse gates.
Postdoc, Unviersité de Sherbrooke
Director: Alexandre Blais
Fighting KerrInduced NonGaussianity with Squeezing
Effort is being directed towards using the large Hilbert space of microwave resonators to encode quantum information. Universal quantum gates can be performed on this encoded information by using the dispersive interaction between resonators and offresonant qubits. The dispersive interaction is however valid only for small resonator photon numbers and a Kerrtype interaction emerges at moderately large powers. This leads to unwanted evolution and distortion of the resonator state and thereby logical errors. We propose to eliminate the effect of this Kerr nonlinearity by using an input squeezed vacuum on the resonator. By choosing the appropriate angle and strength of squeezing, we show that the Kerrinduced distortions in the resonator state can be removed, thereby increasing the fidelity of operations, such as creation of cat states, rotation of coherent state in phase space, QND measurement of qubit state, etc.
Doctorate, McGill University
Director: Bill Coish
Dynamic Nuclear Polarization and NuclearSpin Superradiance in 1D systems
The hyperfine coupling between an electron and many nuclear spins confined in a quantum dot can be a pathway to reach and measure high spin polarization of the nuclear spin system. Furthermore, the presence of long range coherence in the nuclear spin system could lead to the observation of nuclear spin superradiance, in which the spin flip rate is drastically enhanced.
Doctorate, McGill University
Director: Bill Coish
Hamiltonian simulation for improved state transfer and readout in cavity QED
Quantum state transfer into a memory, state shuttling over long distances via a quantum bus, and highfidelity readout are important tasks for quantum technology. Generating the Hamiltonians that realize these tasks is often challenging; inhomogeneous broadening leads to dephasing during state transfer and an insufficiently strong interaction between a qubit and a cavity used for measurement may lead to an imperfect readout. Here, we use average Hamiltonian theory to design the desired Hamiltonians in cavity QED. In particular, we present a protocol for state transfer between a qubit and a cavity. This protocol gives a high fidelity even for inhomogeneous broadening that is larger than the qubitcavity coupling. In addition, we design a timeaveraged interaction that allows for a fast quantum nondemolition readout that is Purcell insensitive. These ideas can be applied directly to novel systems coupling single spins [Viennot et al, Science 349, 408 (2015)] or spin ensembles to a microwave cavity, or magnon modes to a transmon qubit [Tabuchi et al, Science 349 405 (2015)].
Doctorate, Université de Sherbrooke
Director: Michel PioroLadrière
Integration of nanomagnets for spin rotation in quantum dots
Doctorat, Université de Sherbrooke
Director: David Poulin
Error Correction for Systems with NonAbelian Anyons
Topologically ordered systems giving rise to excitations which are nonabelian are of prime interest in terms of quantum computation, as these systems are thought to be naturally resilient against noise. There is nevertheless growing evidence that error correction will still be needed if one wishes to use such a system as a building block for a quantum computer. Difficulties in term of error correction arise from the nonabelian nature of the excitations, and very little work has been done on this topic. We present both numerical and analytical work on a faulttolerant error correction scheme for systems that give rise to nonabelian anyonic excitations.
Doctorate, McGill University
Director: Bill Coish
Maximal adaptivedecision speedups in quantumstate readout
The average time T required for highfidelity readout of quantum states can be significantly reduced via a realtime adaptive decision rule. An adaptive decision rule stops the readout as soon as a desired level of confidence has been achieved, as opposed to setting a fixed readout time tf. The performance of the adaptive decision is characterized by the "adaptivedecision speedup," tf/T. In this work, we reformulate this readout problem in terms of the firstpassage time of a particle undergoing stochastic motion. This formalism allows us to theoretically establish the maximum achievable adaptivedecision speedups for several physical twostate readout implementations. We show that for two common readout schemes (the Gaussian latching readout and a readout relying on statedependent decay), the speedup is bounded by 4 and 2, respectively, in the limit of high singleshot readout fidelity. We experimentally study the achievable speedup in a realworld scenario by applying the adaptive decision rule to a readout of the nitrogenvacancycenter (NVcenter) charge state. We find a speedup of ≈2 with our experimental parameters. In addition, we propose a simple readout scheme for which the speedup can in principle be increased without bound as the fidelity is increased. Our results should lead to immediate improvements in nanoscale magnetometry based on spintocharge conversion of the NVcenter spin, and provide a theoretical framework for further optimization of the bandwidth of quantum measurements.
Doctorate, McGill University
Director: Guillaume Gervais
Critical Flow and Dissipation in a QuasiOneDimensional Superfluid
In one of the most celebrated examples of the theory of universal critical phenomena, the phase transition to the super fluid state of 4He belongs to the same three dimensional O(2) universality class as the onset of ferromagnetism in a lattice of classical spins with XY symmetry. Below the transition, the super fluid density Rho and super fluid velocity V increase as powerlaws of temperature described by a universal critical exponent constrained to be equal by scale invariance. As the dimensionality is reduced towards one dimension (1D), it is expected that enhanced thermal and quantum fluctuations preclude longrange order, thereby inhibiting super fluidity. We have measured the flow rate of liquid helium and deduced its superfluid velocity in a capillary flow experiment occurring in single ~30nm long nanopores with radii ranging down from ~20nm to ~3nm. As the pore size is reduced towards the 1D limit, we observe: i) a suppression of the pressure dependence of the superfluid velocity; ii) a temperature dependence of V that surprisingly can be wellfitted by a powerlaw with a single exponent over a broad range of temperatures; and iii) decreasing critical velocities as a function of decreasing radius for channel sizes below ~20nm, in stark contrast with what is observed in micron sized channels. We interpret these deviations from bulk behavior as signaling the crossover to a quasi1D state whereby the size of a critical topological defect is cut off by the channel radius.
Master, McGill University
Director: Lilian Childress
NV Centres to Study Magnetization Dynamics in STT Devices
Postdoc, McGill University
Director: Aashish Clerk
QubitCavity Entanglement in the Dispersive Regime: NonDemolition Measurement and Initialization
The dispersive regime of the JaynesCummings interaction between electromagnetic radiation in a cavity and a twolevel qubit has proven to be useful in many quantum information processing tasks. For example, in contemporary circuit quantum electrodynamics (cQED) architectures, the dispersive regime can be used for qubit readout and for gate operations. As the dispersive regime is derived after a frame transformation, to connect to external experimental devices the inverse frame transformation back to the lab frame is required. In this work, we show that in the lab frame the system is best described by an entangled state known as the dressed coherent state. We discuss how this results in further qubit evolution depending on both the amplitude and phase of the cavity field. In addition, we show how standard dispersive qubit readout is quantum nondemolition (QND) only in the limit of infinite measurement time, as the formation of a dressed coherent state in the qubitcavity system results in an effective qubit rotation. A protocol to correct for this, and improve qubit initialization, is also introduced.
Master, Université de Sherbrooke
Director: Bertrand Reulet
Cryogenic nanobolometer as a noise detector
Building a good quantum computer working with many qubits requieres a good understanding of the electronic noise. To understand fundamental concepts of the electronic transport, we need the right tools. A cryogenic nanobolometer is an exemple of tools able to detect electron noise without bandpass limitation. The goals of this project are to build a such device, caracterize it in a cryogenic system and optimize its use.
Doctorate, Université de Sherbrooke
Director: David Poulin
Learning the noise rate of a quantum channel
Noise is intrinsic to a quantum computation process. The theory of quantum error correction was developed to show that it is in fact possible to perform meaningful quantum computation in the presence of noise. However, it assumes a simplistic picture, where the noise on a quantum system can be modelled as the action of Pauli matrices. In such a case, the effect of the noise process on the quantum system can be encapsulated into a quantity often called the noise rate, whose value can help determine if an error correction procedure can save the computation result from the effect of noise.
An experimental scenerio is far from the simplistic picture of Pauli noise, one can imagine amplitude damping, leakage errors or even small rotations which cannot be captured by Pauli matrices. In this case, it is useful to provide a notion of a noise strength which can directly relate to the usefulness of an error correction procedure. Here, we try to come up with a measure of a noise strength for a noise process on a single qubit system. To do this, we apply machine learning techniques with a large database of quantum channels and we aim to arrive at a metric for the channel that can best describe the logical error on the quantum computation.
Doctorate, McGill University
Director: Bill Coish
Hyperfine Interactions for Hole Spins
Due to the anisotropic nature of the hyperfine coupling for hole spins in semiconductor quantum dots, these systems may show significantly longer coherence times than electron spins given the correct quantumdot geometry and magnetic field orientation. This advantage of hole spins relies on the hyperfine tensor takingon an Isinglike form. This form of the hyperfine coupling has been recently called into question with experiments [1] that have been interpreted to indicate a strong hybridization of plike and dlike components in the valence band of IIIV semiconductors. However, this interpretation relies on two assumptions: (1) That spinorbit coupling is weak in these systems compared to the anisotropic crystal field, and (2) that higherangularmomentum contributions are negligible. Assumption (1) may break down in light of the fact that the spinorbit energy is even larger than the principal gap in InAs, and assumption (2) is difficult to justify in any crystal that breaks pure rotational symmetry. Using a generalization of the grouptheoretic analysis in , we show here that relaxing either of these assumptions can restore the Isinglike nature of the hyperfine tensor, albeit for a particular choice of coupling constants. We propose a way in which to test for these dlike components using optical selection rules. Finally, we use density functional theory (D.F.T.) to estimate hyperfine couplings. In contrast to other works, we include offdiagonal elements of the spindensity operator.
Postdoc, Université de Sherbrooke
Director: Bertrand Reulet
The Noise Thermal Impedance
We have developed a technique to probe heat relaxation times of the electron gaz. We applied it to study a metallic wire as a test. From those measurements we were able to separate two regimes where the heat relaxation is due to different phenomenons. We distinguished between an electronphonon regime and a diffusion regime and extracted the associated relaxation times and there dependence on temperature.
Postdoc, Université d'Ottawa
Director: Anne Broadbent
Topological Invariants for Abelian Reduced Spaces of Multiparticle Quantum States
We present a mathematical framework to study geometry and topology of quotients for multiparticle quantum systems. In particular, we are interested in geometrical and topological properties of abelian symplectic reduced spaces of pure multipartite states, as complex projective spaces, which are acted upon in a Hamiltonian fashion by maximal tori of the semisimple compact Local Unitary Lie groups. We discuss that the existing geometrical methods equip us with a powerful set of tools to compute topological invariants for these reduced spaces. More precisely, given the components in the moment (Kirwan) polytope for multiqubits, we utilize a recursive wallcrossing formula for the Poincar\'e polynomials and Euler characteristics of abelian symplectic quotients and as some examples we elaborate the procedure for quantum systems with two and three qubits in their pure states and propose an algorithm for a general rqubits.
Doctorate, Université de Sherbrooke
Directors: Denis Morris, Michel PioroLadrière
Vectorial magnetometry with NV centers
Doctorate, Université de Sherbrooke
Director: Bertrand Reulet
Photon statistics of shot noise measured using a Josephson parametric amplifier
Quantum measurements are very sensitive to external noise sources. Such measurements require careful amplification chain design so as not to overwhelm the signal with extraneous noise. A quantumlimited amplifier, like the Josephson parametric amplifier (paramp), is thus an ideal candidate for this purpose. We used a paramp to investigate the quantum noise of a tunnel junction. This measurement scheme allowed us to improve upon previous observations of shot noise by an order of magnitude in terms of noise temperature. With this setup, we have measured the second and fourth cumulants of current fluctuations generated by the tunnel junction within a 40 MHz bandwidth around 6 GHz. From theses measurements, we deduce the variance of the photon number fluctuations for various bias schemes of the junction. In particular, we investigate the regime where the junction emits pairs of photons.
Doctorate, McGill University
Director: Bill Coish
Magnetotransport in topological Kondo insulators
For Professor Gilles Bassard’s 60th birthday, INTRIQ and the Centre de recherches mathématiques (CRM) are proud to recognize three decades of research in quantum cryptographyand two decades in quantum teleportation as well as the outstanding contributions of Professor Gilles Brassard for the emergence of the field of quantum information science with a series of scientific conferences held at Domaine ChâteauBromont and a banquet in Montréal.
Gilles Brassard received a PhD in computer science in 1979 from Cornell University, specifically in cryptography. Since then, he has been a professor at the Université de Montréal and has held the Canada Research Chair in quantum information science since 2001. His Chair has recently been renewed until the end of 2021.
Professor Brassard is interested in all aspects of quantum information science, a field that is at the crossroads of computer science and quantum mechanics. In the late 1970's, he was one of the first researchers to apply quantum mechanical principles to information processing, giving birth to the field of quantum information science at a time when it seemed more like science fiction than science.
His invention of quantum cryptography was hailed in the February 2003 issue of Technology Review, a journal published by the Massachusetts Institute of Technology, as one of the « 10 emerging technologies that will change the world ». This makes it possible to communicate in perfect secrecy under the nose of an eavesdropper who has unlimited computational power and whose technology is restricted only by the known laws of physics. This technology, which was initially considered a fringe pursuit at best, has moved from proofofprinciple prototypes to sophisticated apparatus, to commercial venture. Gilles Brassard is also one of the inventors of quantum teleportation, which is universally recognized as a fundamental cornerstone of quantum information science. In 2012, Thomson Reuters predicted that he would one day be awarded the Nobel Prize in Physics for this discovery.
In addition to being the former editorinchief of the Journal of Cryptology, Professor Brassard has authored three books that have been translated into eight languages and, according to Google Scholar, his scientific articles and books have been cited over 36,000 times. He has been awarded many honours and accolades: most notably, he was the first Canadian to be made a Fellow of the International Association for Cryptologic Research (IACR). He has also won both the Gerhard Herzberg Canada Gold Medal for Science and Engineering and the Killam Prize for Natural Sciences, generally considered to be the two most prestigious science prizes in Canada. Professor Gilles Brassard was described as « one of Canada's science superstars » by British astronomer David Darling. He is a Fellow of the Royal Society of London and holder of honorary doctorates from the ETH (Eidgenössische Technische Hochschule) of Zurich, the University of Ottawa and the Università della Svizzera italiana, Lugano. He was recently appointed Officer of the Order of Canada.
10h30  10h55 Registration
10h55  11h00 Opening remarks
11h00  12h00 Charles Bennett, IBM Thomas J. Watson Research Cente (Salon A)
Is there such a thing as private information?
12h00  13h30 Lunch (Dining room)
13h30  14h30 Christopher Fuchs, University of Massachusetts Boston (Salon A)
What Huangjun Zhu would say if he were disguised as Chris Fuchs
14h30  15h00 Coffee break (Salon B)
15h00  16h00 Harry Buhrman, CWI  University of Amsterdam (Salon A)
Quantum positionbased cryptography
16h00  16h45 Nicolas Quesada, Université de Sherbrooke (Salon A)
Efficiency limits in quantum frequency conversion
16h45  17h00 Alexandre Blais, Université de Sherbrooke (Salon A)
From quantum science to quantum technologies
16h45  19h00 Poster session with refreshments (Salon B)
19h30  Dinner (Dining room)
6h30  8h30 Breakfast (Dining room)
8h00  8h55 Check out
9h00  10h00 Nicolas Gisin, Université de Genève (Salon A)
Quantum Nonlocality with Arbitrary Limited Detection Efficiency and
Measurement Dependence
10h00  10h30 Paul RaymondRobichaud, Université de Montréal (Salon A)
The tale of the Orouboros
10h30  11h30 Coffe break and Poster session (Salon B)
11h30  12h00 Yuval Elias, Université de Montréal (Salon A)
Algorithmic Cooling in Liquid State NMR
12h00  13h30 Lunch (Dining room)
13h30  14h15 Michael Hilke, McGill University (Salon A)
Probing localization with a qubit
14h15  14h45 Shruti Puri, Université de Sherbrooke (Salon A)
Fighting KerrInduced NonGaussianity with Squeezing
14h45  15h15 Dany LachanceQuirion, Université de Sherbrooke (Salon A)
Observation of magnon number states in
a superconducting qubit spectrum
15h15  15h20 Closing remarks
15h40  Departure of the chartered bus to Le Cercle restaurant at HEC
17h45  18h15 Meet and Greet at Restaurant Le Cercle, HEC Montréal
18h15  Banquet
Thomas J. Watson Research Center, Yorktown Heights, NY USA
Is there such a thing as private information?
Quantum information theory originated in the practical use of quantum laws to keep classical information private, but soon grew to encompass the whole classical theory, generalizing it as powerfully as the complex numbers generalize the reals. Conceptually, private classical information sits on a silppery slope between quantum information and public information. Indeed decoherence theory suggests that the slope may be so slippery that private classical information doesn't exist: once an ebit is measured by Alice and Bob to generate a bit of classical key, the news necessarily escapes into the environment, rendering the key no longer private.
University of Massachusetts Boston
What Huangjun Zhu would say if he were disguised as Chris Fuchs
Université de Genève
Quantum Nonlocality with Arbitrary Limited Detection Efficiency and Measurement Dependence
CWI  University of Amsterdam
Quantum positionbased cryptography
On 20 July 1969, millions of people held their breath as they watched, live on television, Neil Armstrong set foot on the Moon. Yet Fox Television has reported that a staggering 20% of Americans have had doubts about the Apollo 11 mission. Could it have been a hoax staged by Hollywood studios here on Earth? Position based cryptography may offer a solution. This kind of cryptography uses the geographic position of a party as its sole credential. Normally digital keys or biometric features are used.
A central building block in positionbased cryptography is that of positionverification. The goal is to prove to a set of verifier that one is at a certain geographical location. Protocols typically assume that messages can not travel faster than the speed of light. By responding to a verifier in a timely manner one can guarantee that one is within a certain distance of that verifier. Quite recently it was shown that positionverification protocols only based on this relativistic principle can be broken by attackers who simulate being at a the claimed position while physically residing elsewhere in space.
Because of the nocloning property of quantum information (qubits) it was believed that with the use of quantum messages one could devise protocols that were resistant to such collaborative attacks. Several schemes were proposed that later turned out to be insecure. Finally it was shown that also in the quantum case no unconditionally secure scheme is possible. We will review the field of positionbased quantum cryptography and highlight some of the research currently going on in order to develop, using reasonable assumptions on the capabilities of the attackers, protocols that are secure in practice.
Professor, Université de Sherbrooke
From quantum science to quantum technologies
Postdoc, Université de Montréal
Director: Gilles Brassard
Algorithmic Cooling in Liquid State NMR
Heatbath algorithmic cooling (HBAC) employs thermalization to purify quantum systems that interact with a heat bath, such as ensembles of nuclear spins, or cold atoms in an optical lattice. When applied to spins, HBAC produces ensembles of highly polarized spins, which enhance the signal strength in nuclear magnetic resonance (NMR). According to this cooling approach, spinhalf nuclei in a constant magnetic field are considered as bits, or more precisely quantum bits, in a known probability distribution. Algorithmic steps on these bits are then translated into NMR pulse sequences using common NMR quantum computation tools. The algorithmic cooling of spins is achieved by alternately combining reversible, entropypreserving manipulations (borrowed from data compression algorithms) with selective transfer of entropy from spins to the environment.HBAC, and multicycle HBAC, were previously achieved with nuclear spins using solidstate nuclear magnetic resonance (NMR), where spin diffusion allowed some spins to relax much more rapidly than others. In the liquid state, a partial variant of HBAC, without entropy compression, was applied to the three qubits of 13Cenriched trichloroethylene, resulting in modest cooling of the spin system. Recently, we utilized gradient ascent pulse engineering (GRAPE), an optimal control algorithm, to generate pulses with high fidelity for the compression and polarization exchange (SWAP) gates. Here, we combine those pulses to implement HBAC on this 3spin system. Various cooling algorithms were applied, cooling the system beyond Shannon’s entropy bound in several different ways. In particular, in one experiment a carbon qubit was cooled by a factor of 4.61.This work is a step towards potentially integrating HBAC and other tools of NMR quantum computing into in vivo magnetic resonance spectroscopy.
Professor, McGill University
Probing localization with a qubit
We look at the dynamics of a qubit that is coupled to a disordered quantum wire. We show that we can use the time evolution of the qubit to measure the static localization properties of a disordered system. The disordered system can be an electronic gate or lead with impurities, or equivalently remote spins. We also evaluate the decoherence rate of the qubit as a function of the amount of disorder in the gate and lead.
This work is a collaboration with Mackenzie and Eleuch.
Doctorat, Université de Sherbrooke
Director: Michel PioroLadrière
Observation of magnon number states in a superconducting qubit spectrum
A magnon is a collective excitation in an ordered spin system such as a ferromagnet. Interacting with both microwave and optical light, magnons in the ferrimagnetic insulator yttrium iron garnet (YIG) are candidates for transducing quantum information between those two frequency domains. Coherent interaction between a singlemagnon excitation in a YIG sphere and a superconducting qubit has recently been demonstrated through their interaction with a common microwave cavity mode.
The dispersive limit of the magnonqubit interaction is discussed in this presentation. Magnon number states are experimentally resolved in the superconducting qubit spectrum when creating a coherent state in the magnetostatic mode. The probability distribution of magnon number states recovered from these measurements is found to agree well with the Poisson distribution expected for a coherent state.
Resolving magnon number states is a necessary ingredient for implementing a protocol in which quantum information of the qubit is encoded in the magnetostatic mode. This encoding would be the first step toward the realization of a quantum transducer between microwave and optical domains.
This work has been done in the group of Pr. Yasunobu Nakamura at the Research Center for Advanced Science and Technology of the University of Tokyo.
Doctorate, Université de Montréal
Director: Gilles Brassard
The tale of the Orouboros
Beyond "it from bit", John Archibal Wheeler, expressed his desire for a primeval ophidian selfreflexive recursive structure able to give birth to itself. What can the autological serpent impart on Boltzmann brains, the nature of information, and of causality? Is our ontology leading to an epistemology leading to the very same ontology leading to the very same epistemology? Should Jǫrmungandr fail to eat it's tail, knell Ragnarøkkr, the heterological darkness!
Postdoc, Unviersité de Sherbrooke
Director: Alexandre Blais
Efficiency limits in quantum frequency conversion
Frequency conversion is an enabling process in many quantum information protocols. In this talk we study fundamental limits to high efficiency frequency conversion imposed by time ordering corrections. Using the Magnus expansion, we argue that these corrections, which are usually considered detrimental, can be used to increase the efficiency of conversion under certain circumstances. The corrections induce a nonlinear behaviour in the probability of upconversion as a function of the pump intensity, significantly modifying the sinusoidal Rabi oscillations that are otherwise expected. Finally, by using a simple scaling argument, we explain why cascaded frequency conversion devices attenuate time ordering corrections, allowing the construction of near ideal quantum pulse gates.
Postdoc, Unviersité de Sherbrooke
Director: Alexandre Blais
Fighting KerrInduced NonGaussianity with Squeezing
Effort is being directed towards using the large Hilbert space of microwave resonators to encode quantum information. Universal quantum gates can be performed on this encoded information by using the dispersive interaction between resonators and offresonant qubits. The dispersive interaction is however valid only for small resonator photon numbers and a Kerrtype interaction emerges at moderately large powers. This leads to unwanted evolution and distortion of the resonator state and thereby logical errors. We propose to eliminate the effect of this Kerr nonlinearity by using an input squeezed vacuum on the resonator. By choosing the appropriate angle and strength of squeezing, we show that the Kerrinduced distortions in the resonator state can be removed, thereby increasing the fidelity of operations, such as creation of cat states, rotation of coherent state in phase space, QND measurement of qubit state, etc.
Doctorate, McGill University
Director: Bill Coish
Dynamic Nuclear Polarization and NuclearSpin Superradiance in 1D systems
The hyperfine coupling between an electron and many nuclear spins confined in a quantum dot can be a pathway to reach and measure high spin polarization of the nuclear spin system. Furthermore, the presence of long range coherence in the nuclear spin system could lead to the observation of nuclear spin superradiance, in which the spin flip rate is drastically enhanced.
Doctorate, McGill University
Director: Bill Coish
Hamiltonian simulation for improved state transfer and readout in cavity QED
Quantum state transfer into a memory, state shuttling over long distances via a quantum bus, and highfidelity readout are important tasks for quantum technology. Generating the Hamiltonians that realize these tasks is often challenging; inhomogeneous broadening leads to dephasing during state transfer and an insufficiently strong interaction between a qubit and a cavity used for measurement may lead to an imperfect readout. Here, we use average Hamiltonian theory to design the desired Hamiltonians in cavity QED. In particular, we present a protocol for state transfer between a qubit and a cavity. This protocol gives a high fidelity even for inhomogeneous broadening that is larger than the qubitcavity coupling. In addition, we design a timeaveraged interaction that allows for a fast quantum nondemolition readout that is Purcell insensitive. These ideas can be applied directly to novel systems coupling single spins [Viennot et al, Science 349, 408 (2015)] or spin ensembles to a microwave cavity, or magnon modes to a transmon qubit [Tabuchi et al, Science 349 405 (2015)].
Doctorate, Université de Sherbrooke
Director: Michel PioroLadrière
Integration of nanomagnets for spin rotation in quantum dots
Doctorat, Université de Sherbrooke
Director: David Poulin
Error Correction for Systems with NonAbelian Anyons
Topologically ordered systems giving rise to excitations which are nonabelian are of prime interest in terms of quantum computation, as these systems are thought to be naturally resilient against noise. There is nevertheless growing evidence that error correction will still be needed if one wishes to use such a system as a building block for a quantum computer. Difficulties in term of error correction arise from the nonabelian nature of the excitations, and very little work has been done on this topic. We present both numerical and analytical work on a faulttolerant error correction scheme for systems that give rise to nonabelian anyonic excitations.
Doctorate, McGill University
Director: Bill Coish
Maximal adaptivedecision speedups in quantumstate readout
The average time T required for highfidelity readout of quantum states can be significantly reduced via a realtime adaptive decision rule. An adaptive decision rule stops the readout as soon as a desired level of confidence has been achieved, as opposed to setting a fixed readout time tf. The performance of the adaptive decision is characterized by the "adaptivedecision speedup," tf/T. In this work, we reformulate this readout problem in terms of the firstpassage time of a particle undergoing stochastic motion. This formalism allows us to theoretically establish the maximum achievable adaptivedecision speedups for several physical twostate readout implementations. We show that for two common readout schemes (the Gaussian latching readout and a readout relying on statedependent decay), the speedup is bounded by 4 and 2, respectively, in the limit of high singleshot readout fidelity. We experimentally study the achievable speedup in a realworld scenario by applying the adaptive decision rule to a readout of the nitrogenvacancycenter (NVcenter) charge state. We find a speedup of ≈2 with our experimental parameters. In addition, we propose a simple readout scheme for which the speedup can in principle be increased without bound as the fidelity is increased. Our results should lead to immediate improvements in nanoscale magnetometry based on spintocharge conversion of the NVcenter spin, and provide a theoretical framework for further optimization of the bandwidth of quantum measurements.
Doctorate, McGill University
Director: Guillaume Gervais
Critical Flow and Dissipation in a QuasiOneDimensional Superfluid
In one of the most celebrated examples of the theory of universal critical phenomena, the phase transition to the super fluid state of 4He belongs to the same three dimensional O(2) universality class as the onset of ferromagnetism in a lattice of classical spins with XY symmetry. Below the transition, the super fluid density Rho and super fluid velocity V increase as powerlaws of temperature described by a universal critical exponent constrained to be equal by scale invariance. As the dimensionality is reduced towards one dimension (1D), it is expected that enhanced thermal and quantum fluctuations preclude longrange order, thereby inhibiting super fluidity. We have measured the flow rate of liquid helium and deduced its superfluid velocity in a capillary flow experiment occurring in single ~30nm long nanopores with radii ranging down from ~20nm to ~3nm. As the pore size is reduced towards the 1D limit, we observe: i) a suppression of the pressure dependence of the superfluid velocity; ii) a temperature dependence of V that surprisingly can be wellfitted by a powerlaw with a single exponent over a broad range of temperatures; and iii) decreasing critical velocities as a function of decreasing radius for channel sizes below ~20nm, in stark contrast with what is observed in micron sized channels. We interpret these deviations from bulk behavior as signaling the crossover to a quasi1D state whereby the size of a critical topological defect is cut off by the channel radius.
Master, McGill University
Director: Lilian Childress
NV Centres to Study Magnetization Dynamics in STT Devices
Postdoc, McGill University
Director: Aashish Clerk
QubitCavity Entanglement in the Dispersive Regime: NonDemolition Measurement and Initialization
The dispersive regime of the JaynesCummings interaction between electromagnetic radiation in a cavity and a twolevel qubit has proven to be useful in many quantum information processing tasks. For example, in contemporary circuit quantum electrodynamics (cQED) architectures, the dispersive regime can be used for qubit readout and for gate operations. As the dispersive regime is derived after a frame transformation, to connect to external experimental devices the inverse frame transformation back to the lab frame is required. In this work, we show that in the lab frame the system is best described by an entangled state known as the dressed coherent state. We discuss how this results in further qubit evolution depending on both the amplitude and phase of the cavity field. In addition, we show how standard dispersive qubit readout is quantum nondemolition (QND) only in the limit of infinite measurement time, as the formation of a dressed coherent state in the qubitcavity system results in an effective qubit rotation. A protocol to correct for this, and improve qubit initialization, is also introduced.
Master, Université de Sherbrooke
Director: Bertrand Reulet
Cryogenic nanobolometer as a noise detector
Building a good quantum computer working with many qubits requieres a good understanding of the electronic noise. To understand fundamental concepts of the electronic transport, we need the right tools. A cryogenic nanobolometer is an exemple of tools able to detect electron noise without bandpass limitation. The goals of this project are to build a such device, caracterize it in a cryogenic system and optimize its use.
Doctorate, Université de Sherbrooke
Director: David Poulin
Learning the noise rate of a quantum channel
Noise is intrinsic to a quantum computation process. The theory of quantum error correction was developed to show that it is in fact possible to perform meaningful quantum computation in the presence of noise. However, it assumes a simplistic picture, where the noise on a quantum system can be modelled as the action of Pauli matrices. In such a case, the effect of the noise process on the quantum system can be encapsulated into a quantity often called the noise rate, whose value can help determine if an error correction procedure can save the computation result from the effect of noise.
An experimental scenerio is far from the simplistic picture of Pauli noise, one can imagine amplitude damping, leakage errors or even small rotations which cannot be captured by Pauli matrices. In this case, it is useful to provide a notion of a noise strength which can directly relate to the usefulness of an error correction procedure. Here, we try to come up with a measure of a noise strength for a noise process on a single qubit system. To do this, we apply machine learning techniques with a large database of quantum channels and we aim to arrive at a metric for the channel that can best describe the logical error on the quantum computation.
Doctorate, McGill University
Director: Bill Coish
Hyperfine Interactions for Hole Spins
Due to the anisotropic nature of the hyperfine coupling for hole spins in semiconductor quantum dots, these systems may show significantly longer coherence times than electron spins given the correct quantumdot geometry and magnetic field orientation. This advantage of hole spins relies on the hyperfine tensor takingon an Isinglike form. This form of the hyperfine coupling has been recently called into question with experiments [1] that have been interpreted to indicate a strong hybridization of plike and dlike components in the valence band of IIIV semiconductors. However, this interpretation relies on two assumptions: (1) That spinorbit coupling is weak in these systems compared to the anisotropic crystal field, and (2) that higherangularmomentum contributions are negligible. Assumption (1) may break down in light of the fact that the spinorbit energy is even larger than the principal gap in InAs, and assumption (2) is difficult to justify in any crystal that breaks pure rotational symmetry. Using a generalization of the grouptheoretic analysis in , we show here that relaxing either of these assumptions can restore the Isinglike nature of the hyperfine tensor, albeit for a particular choice of coupling constants. We propose a way in which to test for these dlike components using optical selection rules. Finally, we use density functional theory (D.F.T.) to estimate hyperfine couplings. In contrast to other works, we include offdiagonal elements of the spindensity operator.
Postdoc, Université de Sherbrooke
Director: Bertrand Reulet
The Noise Thermal Impedance
We have developed a technique to probe heat relaxation times of the electron gaz. We applied it to study a metallic wire as a test. From those measurements we were able to separate two regimes where the heat relaxation is due to different phenomenons. We distinguished between an electronphonon regime and a diffusion regime and extracted the associated relaxation times and there dependence on temperature.
Postdoc, Université d'Ottawa
Director: Anne Broadbent
Topological Invariants for Abelian Reduced Spaces of Multiparticle Quantum States
We present a mathematical framework to study geometry and topology of quotients for multiparticle quantum systems. In particular, we are interested in geometrical and topological properties of abelian symplectic reduced spaces of pure multipartite states, as complex projective spaces, which are acted upon in a Hamiltonian fashion by maximal tori of the semisimple compact Local Unitary Lie groups. We discuss that the existing geometrical methods equip us with a powerful set of tools to compute topological invariants for these reduced spaces. More precisely, given the components in the moment (Kirwan) polytope for multiqubits, we utilize a recursive wallcrossing formula for the Poincar\'e polynomials and Euler characteristics of abelian symplectic quotients and as some examples we elaborate the procedure for quantum systems with two and three qubits in their pure states and propose an algorithm for a general rqubits.
Doctorate, Université de Sherbrooke
Directors: Denis Morris, Michel PioroLadrière
Vectorial magnetometry with NV centers
Doctorate, Université de Sherbrooke
Director: Bertrand Reulet
Photon statistics of shot noise measured using a Josephson parametric amplifier
Quantum measurements are very sensitive to external noise sources. Such measurements require careful amplification chain design so as not to overwhelm the signal with extraneous noise. A quantumlimited amplifier, like the Josephson parametric amplifier (paramp), is thus an ideal candidate for this purpose. We used a paramp to investigate the quantum noise of a tunnel junction. This measurement scheme allowed us to improve upon previous observations of shot noise by an order of magnitude in terms of noise temperature. With this setup, we have measured the second and fourth cumulants of current fluctuations generated by the tunnel junction within a 40 MHz bandwidth around 6 GHz. From theses measurements, we deduce the variance of the photon number fluctuations for various bias schemes of the junction. In particular, we investigate the regime where the junction emits pairs of photons.
Doctorate, McGill University
Director: Bill Coish
Magnetotransport in topological Kondo insulators