# Gouvernance

### Fall 2018 INTRIQ meeting, November 13 & 14th

Organizer :

Pr Guillaume Gervais, McGill University

**90, rue Stanstead, Bromont QC J2L 1K6****Téléphone : 1 800 304 3433**

**Note : The INTRIQ Business meeting (reserved for members) will be held in room "Salle des cantons" on November 13th from 9h30 to 10h30**

*The final meeting program will be available soon*

*November 13th*

10h30 - 10h55 Registration

10h55 - 11h00 Opening remarks (Salon A)

11h00 - 12h00 Speaker to be annouced (Salon A)

12h00 - 13h30 Lunch (Dining room - 4 Canards)

13h30 - 15h00 Speakers to be annouced (Salon A)

15h00 - 15h30 Coffee break (Salon B)

15h30 - 17h00 Speakers to be annouced (Salon A)

17h00 - Poster session with refreshments (Salon B)

19h30 - INTRIQ dinner (Salon C)

*November 14th*

9h00 - 10h30 Speakers to be annouced (Salon A)

10h30 - 11h00 Coffee break (Salon B)

11h00 - 12h00 Speakers to be annouced (Salon A)

12h00 - 13h30 Lunch (Dining room - 4 Canards)

13h00 - 15h45 Speakers to be annouced (Salon A)

15h45 - 15h50 Closing remarks

*INVITED SPEAKERS*

*Dr. Kartiek Agarwal**Princeton University**Spatio-temporal 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 non-adiabatic 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 spatio-temporal quenches to efficiently prepare the ground states of arbitrary interacting critical theories in one dimension and beyond.

*Dr. Gustave Kalbe**Head of Unit**High Performance Computing & Quantum Technologies**European Commission Subject to be announced*

*Pr Alexander MaloneyMcGill University Subject to be announced*

*Dr. Dominique Laroche**Delft University of Technology* *Probing the building blocks of topological qubits in superconducting InAs nanowires*

Utilizing the exotic properties of non-Abelian quasiparticles, topological qubits offer an approach towards quantum computing where the information is stored non-locally, making this an architecture resilient against most decoherence sources. Majorana bound states (MBS) arising in proximity-induced 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 quasi-particle poisoning. In this talk, I will present a novel experimental platform where proximitized nanowire devices are coupled on-chip 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 4π-periodic 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 nanowire-based 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.

*Pr Johannes Pollanen**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).

*Dr. Avishay Tal**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 NP-complete problems in sub-exponential 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 pseudo-randomness approach initiated by Aaronson [STOC, 2010]. Our core technical result is constructing a distribution over Boolean strings that "look random" to constant-depth circuits of quasi-polynomial size, but can be distinguished from the uniform distribution by very efficient quantum algorithms.

(joint work with Ran Raz)

*INTRIQ SPEAKERS*

*Yves Bérubé-Lauzière**Professor, Université de Sherbrooke**QSciTech NSERC-CREATE Training Program - Bridging the Gap between Quantum Science and Quantum Technologies*

The QSciTech NSERC-CREATE 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 high-tech economic sector of priority. The goal is to train job-ready 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.

*Clément Godfrin**Postdoc, Université de Sherbrooke*Director : Eva Dupont-Ferrier

**Coherent manipulation of single nuclear spin**Advances in experimental techniques offer physicists the opportunity to implement simple systems worth of the "gedanken-experiments" 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 read-out 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 4-level 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 multi-level 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 self-corrected 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)

*Jonathan Gross**Postdoc, Université de Sherbrooke*Director : Alexandre Blais

*Systems illuminated by squeezed wave-packet modes*White-noise theory is incapable of describing photon-counting 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 two-level atom in squeezed vacuum with squeezing bandwidth narrower than the atomic linewidth, a regime inaccessible to previous techniques.

*Yehua Liu**Postdoc, Université de Sherbrooke**Director : David Poulin**Neural Belief-Propagation Decoders for Quantum Error-Correcting Codes*

Belief-propagation (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 low-density parity-check 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 low-overhead error correction in near-term quantum devices.

*Marc-Olivier Proulx**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 super-quantum correlations. In this work, we study the principle of non-trivial 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 super-quantum correlations that are known to be ruled out by the NTCC principle, thus providing an explanation for their impossibility in quantum mechanics.

*Thomas SzkopekProfessor, McGill University*

**Subject to be announced**

*Maxime Tremblay**Master, Université de Sherbrooke*Director : David Poulin

*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.