Les activités de l'INTRIQ

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mai 11, 2017

When : Thursday, May 11th, 2017

Where : Pavillon Lassonde, Polytechnique Montréal

Organizer : Professor Sébastien Francoeur, Polytechnique Montréal


For registration, click HERE

mai 10, 2017

When : Wednesday, May 10th, 2017

Where : Pavillon Lassonde, Polytechnique Montréal

Organizers : Young INTRIQ researchers in collaboration with the INTRIQ Technological transfer & partnership committee

More information and registration on the event web site at IQID2017

nov. 25, 2016

CONFETI (CONFérence ÉTudiante de l'INTRIQ) is a yearly student conference sponsored by the INTRIQ. It attracts graduate students and post-docs in the fields of physics, mathematics, computer science and engineering working on quantum computing related projects.

Where and when
The conference will take place on January 10-12, 2017 at the Hôtel Château Bromont in Bromont, Québec.

Click here

Click here



Rencontres INTRIQ

avril 28, 2015
Posté par : Marc Leclair

Spring 2015 INTRIQ meeting, April 28th and 29th

Meeting pictures

At the Hotel of the Château Bromont

Professor Aashish Clerk, McGill University
Professor Thomas Szkopek, McGill University

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

(The venue is at the Hôtel, not the Auberge)



  • The INTRIQ Business meeting will be held in the room Les Cantons on April 28th from 9h30 to 10h30

  • A bus shuttle from Berri-UQAM is organised for students in the morning of April 28th and returning on the 29th Bus shuttle Berri-Bromont-Berri


Meeting program

Tuesday, April 28th

10h30 - 11h00 Registration

11h00 - 12h00 Professor Lorenza Viola, Dartmouth College (Salon A)
                            Dissipative quantum state preparation with quasi-local resources (pdf)

12h00 - 13h30  Lunch (Dining room)

13h30 - 15h15 Professor Sankar Das Sarma, University of Maryland (Salon A)
                             Majorana fermions for solid state topological quantum computation

15h15 - 15h45 Coffee break (Salon B)

15h45 - 16h15 Stéphane Virally, Postdoc, Université de Sherbrooke (Salon A)
                             Discrete photon statistics from continuous measurements (pdf)

16h15 - 17h00 Competition : My thesis in 180 seconds
                               - Christian Kraglund Andersen, Doctorate
                               - Pavithran Iyer, Doctorate
                               - Marc-Antoine Lemonde, Doctorate
                               - Zackary Flansberry, Master
                               - Benjamin Levitan, Master
                               - Baptiste Royer Master

17h00 - 19h00 Poster session with refreshments (Salon B)

19h30 -               Diner (Dining room)

Wednesday, April 29th

6h30 - 8h30 Breakfast (Dining room)
8h00 - 8h55 Check out

9h00 - 9h30 Shruti Puri, Postdoc, Université de Sherbrooke (Salon A)
                         High-Fidelity Resonator-Induced Phase Gate with Squeezing (pdf)

9h30 - 10h00 Anja Metelmann, Postdoc, McGill University (Salon A)
                           Nonreciprocal photon transmission and amplification via reservoir engineering

10h00 - 11h00 Coffee break and poster session (Salon B)

11h00 - 12h00 Professor Aephraim M. Steinberg, University of Toronto (Salon A)
                            Two novel applications of entanglement: compressing 3 qubits into 2, and making 1 photon act like

12h00 - 13h30  Lunch (Salon C)

13h30 - 14h15 Professor Gilles Brassard, Université de Montréal (Salon A)
                            Exact Classical Simulation of the GHZ Distribution

14h15 - 14h45 Benjamin Schmidt, Doctorate, McGill University (Salon A)
                             Time-resolved measurement of the electron-phonon scattering rate in a 2DEG

14h45 - 15h15 Guillaume Dauphinais, Doctorate, Université de Sherbrooke (Salon A)
                             An introduction to anyons in the context of quantum information

15h15 - 15h20  Closing remarks and departure



Professor Sankar Das Sarma
University of Maryland
Majorana fermions for solid state topological quantum computation

Professor Aephraim M. Steinberg
University of Toronto

Two novel applications of entanglement: compressing 3 qubits into 2, and making 1 photon act like 100
I will present two recent experiments making use of photon entanglement for two very different tasks.  In one, we show that all the information about an ensemble of N identically prepared qubits (such as one might use in tomography) may be compressed into log(N+1) qubits.  Given a limited-size quantum memory, this would enable one to more efficiently use the initial ensemble to make predictions about future measurements, relative to simply carrying out tomography and storing the resulting classical information.  In the second experiment, we demonstrate a  cold-atom-based optical nonlinearity which weakly entangles a single-photon-level beam with a coherent-state probe.  We observe the phase shift due to single postselected photons, and show that "weak-value amplification" can lead to effective photon numbers much larger than 1, as manifested in measured phase shifts much larger than the single- photon value.

Professor Lorenza Viola
Dartmouth College

Dissipative quantum state preparation with quasi-local resources
Techniques for quantum reservoir and dissipation engineering are playing an increasingly important role in controlling open quantum systems. Implications range from dissipative quantum state preparation and quantum computation, to non-equilibrium quantum phases of matter and quantum thermodynamics. In this talk, I will describe progress toward developing a general control-theoretic framework for the analysis and synthesis of quasi-local open-system dynamics that admits a desired quantum state as its unique asymptotically stable state, with focus on continuous-time Markovian dynamics and entangled target states. In particular, after reviewing existing necessary and sufficient conditions for quasi-local stabilization of a pure state, I will discuss the additional challenges that the stabilization problem entails for a general mixed target state, and present recent rigorous results for a natural class of quasi-local frustration-free Lindblad dynamics.



Professor Gilles Brassard
Université de Montréal
Exact Classical Simulation of the GHZ Distribution
John Bell has shown that the correlations entailed by quantum mechanics cannot be reproduced by aclassical process involving non-communicating parties. But can they be simulated with the help of bounded communication? This problem has been studied for more than two decades and it is now well understood in the case of bipartite entanglement. However, the issue was still widely open for multipartite entanglement, even for the simplest case, which is the tripartite Greenberger-Horne-Zeilinger (GHZ) state. We give an exact simulation of arbitrary independent von Neumann measurements on general n-partite GHZ states. Our protocol requires O(n^2) bits of expected communication between the parties, and O(n log n) expected time is sufficient to carry it out in parallel. Furthermore, we need only an expectation of O(n) independent unbiased random bits, with no need for the generation of continuous real random variables nor prior shared random variables. In the case of equatorial measurements, we improve on the prior art with a protocol that needs only O(n log n) bits of communication and O(log^2 n) parallel time. At the cost of a slight increase in the number of bits communicated, these tasks can be accomplished with a constant expected number of rounds.

Guillaume Dauphinais
Doctorate, Université de Sherbrooke
Director: David Poulin
An introduction to anyons in the context of quantum information
In this talk, I will briefly present various concepts of the algebraic theory of anyons. The focus will be put on the use of anyons in the context of quantum information, namely on the various ways to encode quantum information in such systems and how braiding operations can be used to apply gates. Simple analytical models giving rise to anyonic quasiparticles will be presented to concretely illustrate the concepts introduced in the algebraic theory of anyons. If time permits, I will also briefly discuss error corretion and fault-tolerance in the context of quantum memories built with systems of non-abelian anyons.

Anja Metelmann
Postdoc, McGill University
Director: Aashish Clerk
Nonreciprocal photon transmission and amplification via reservoir engineering
The general desire to break reciprocity in engineered photonic structures has garnered an immense amount of recent interest. For example nonreciprocal microwave-frequency devices are crucial to efforts at quantum-information processing with superconducting circuits. We discuss a general method for constructing nonreciprocal, cavity-based photonic devices, based on matching a given coherent interaction with its corresponding dissipative counterpart; it generalizes the basic structure used in the theory of cascaded quantum systems. In contrast to interference-based schemes, our approach allows directional behavior over a wide bandwidth. We show how it can be used to devise isolators and directional, quantum-limited amplifiers; of particular interest is a directional phase-sensitive amplifier which is not limited by any fundamental gain-bandwidth constraint. Our approach is particularly well-suited to implementations using superconducting microwave circuits.

Shruti Puri
Postdoc, Université de Sherbrooke
Director: Alexandre Blais
High-Fidelity Resonator-Induced Phase Gate with Squeezing
With the recent developments in superconducting parametric amplifiers, it is now possible to generate squeezed microwave fields and to couple this radiation to a  resonator. Here we propose to use a squeezing to increase the fidelity of two-qubit gates in circuit QED. We focus on the resonator-induced phase gate where a drive, off-resonant with both the qubit and the resonator,  leads to a controlled-phase gate. This gate has the advantage of working with fixed frequency qubits that have longer coherence times than their frequency-tunable counterparts. The gate fidelity is limited by  ''which-path information'' due to photons leaking from the resonator. We show that there exists an optimal squeezing angle and strength to erase which-path information. Analytic estimate of the gate fidelity is compared to numerical simulations. With realistic parameters, we find that it is possible to achieve a two-qubit controlled-Z gate of average fidelity >99.9 % within ~ 200 ns.

Benjamin Schmidt
Doctorate, McGill University
Director: Guillaume Gervais
Time-resolved measurement of the electron-phonon scattering rate in a 2DEG
A number of groups have studied the electron-phonon coupling in GaAs/AlGaAs two-dimensional electron gases; however existing estimates of the electron-phonon scattering rate have been calculated by combining measurements of DC power dissipation with a simple model of the 2DEG specific heat at zero magnetic field. We have measured the scattering rate directly, using a time-resolved technique, in an ultra-high mobility Corbino sample below 100 mK. By combining these results with standard DC power dissipation measurements, we can infer the heat capacity of the 2DEG. We propose to use this technique to study exotic phases in the fractional quantum Hall regime, including the possibly non-Abelian 5/2.

Stéphane Virally
Postdoc, Université de Sherbrooke
Director: Bertrand Reulet
Discrete photon statistics from continuous measurements
In a recent paper [J.-C. Forgues et al., PRL 114, 130403 (2015)], a two-photon squeezed state was observed in the shot noise of a tunnel junction. Squeezed states are associated with the generation of photon pairs (in this case, microwave photons).There are no good photon detectors in the microwave regime to directly detect these pairs.
However, we show that it is possible to extract discrete photon statistics from the cumulants of the continuous distribution of measured voltages at the output of an electrical circuit. Since we want to measure very small signals, we use a parametric amplifier as the quantum-limited first stage in the amplification chain, keeping the number of noise photons in the low single digits. We can thus reconstruct photon statistics for signals with less than one photon on average. We apply this technique to an attenuated coherent state (sine wave) and to the case of the squeezed state generated by a tunnel junction. We also place limits on the expected behavior of classical signals.



Félix Beaudoin
Doctorate, McGill University
Director: Bill Coish
Microscopic models for charge-noise-induced dephasing of solid-state qubits

Several experiments have shown qubit coherence decay of the form exp[-(t/T2)^alpha] due to environmental charge-noise fluctuations. We present a microscopic description for temperature dependences of the parameters T2 and alpha. Our description is appropriate to qubits in semiconductors interacting with spurious two-level charge fluctuators coupled to a thermal bath. We find distinct power-law dependences of T2 and alpha on temperature depending on the nature of the interaction of the fluctuators with the associated bath. We consider fluctuator dynamics induced by first- and second-order tunneling with a continuum of delocalized electron states. We also study one- and two-phonon processes for fluctuators in either GaAs or Si. These results can be used to identify dominant charge-dephasing mechanisms and suppress them.

Salil Bedkihal
Postdoc, McGill University
Director: Bill Coish
Magnetotransport in Aharonov-Bohm interferometers: Numerically exact path integrals The linear conductance of two terminal Aharonov-Bohm  interferometer is an even function of magnetic flux, as dictated by Onsager-Casimir symmetry. Away from linear response this symmetry is broken when many body - interactions are in effect. In this work we study quantum dynamics of various models of double-dot Aharonov-Bohm interferometer with genuine many body interactions using numerically exact influence functional path integral  method (INFPI).
In model-I we consider spinless two level double dot interferometer with interdot Coulomb interaction. In model-II interferometer is interacting with a dissipative environment that may be driven out of equilibrium. In both these models depending on vertical and horizontal mirror symmetries of setup, nonlinear transport coefficients obey certain symmetry relations. Numerically exact results are compared to phenomenological methods.

Simon Bernard
Master, McGill University
Director: Jack Sankey
Toward Stronger Optomechanical Coupling: High-reflectivity Photonic Crystal Membranes
A central goal in the field of optomechanics is to use the forces exerted by laser light as a new means of control over the motion of micro-electromechanical system (MEMS). Radiation forces can be used to tune a solid object's mechanical frequency or dissipation, laser cool its motion to the quantum mechanical ground state, or levitate it. To maximize the impact of each photon, it is desirable to create MEMS that are highly reflective, lightweight, and mechanically compliant. These requirements can be simultaneously met by fabricating a 2D photonic crystal (i.e. an appropriately-spaced lattice of holes) into a thin (~ 50 - 100 nm) free-standing dielectric membrane. The process flow for fabrication as well as the measurement and simulation of the photonic crystal's transmission will be reported.

Benjamin D'Anjou
Student, McGill University
Director: Bill Coish
Soft decoding of a qubit readout apparatus
Qubit readout is commonly performed by thresholding a collection of analog detector signals to obtain a sequence of single-shot bit values. The intrinsic irreversibility of the mapping from analog to digital signals discards soft information associated with an "a posteriori" confidence that can be assigned to each bit value when a detector is well characterized. Accounting for soft information, we show significant improvements in enhanced state detection with the quantum repetition code as well as quantum state or parameter estimation. These advantages persist in spite of non-Gaussian features of realistic readout models, experimentally relevant small numbers of qubits, and finite encoding errors. These results show useful and achievable advantages for a wide range of current experiments on quantum state tomography, parameter estimation, and qubit readout.

Mark Dimock
Master, McGill University
Director: Lilian Childress
Toward cavity assisted processes with NV centers

 Nicolas Didier
Postdoc, Université de Sherbrooke
Director : Alexandre Blais
In collaboration with : Jérôme Bourassa, Professor at Cégep de Granby
Fast quantum non-demolition readout from longitudinal qubit-oscillator interaction
We show how to realize high-fidelity quantum non-demolition qubit readout using longitudinal qubit-oscillator interaction. This is realized by modulating the longitudinal coupling at the cavity frequency. The qubit-oscillator interaction then acts as a qubit-state dependent drive on the cavity, a situation that is fundamentally different from the standard dispersive case. Single-mode squeezing can be exploited to exponentially increase the signal-to-noise ratio of this readout protocol. We present an implementation of this idea in circuit quantum electrodynamics and a possible multi- qubit architecture.

 Zackary Flansberry
Master, McGill University
Director: Lilian Childress
NV Centres to Study the Magnetization Dynamics of STT Devices
In spite of its tremendous potential for the development of a new generation of random access memory, the Spin-Transfer Torque (STT) effect continues to be difficult to use efficiently; in particular, the writing of prototypical memory bits requires current densities that are still well above the theoretical expectations. In order to gain fundamental insight onto the origins of this discrepancy (among others), we use NV centres as atomic-scale probes to study the local magnetization dynamics of STT-driven devices using the Spin Hall Effect. By virtue of a ground state manifold that exhibits the Zeeman splitting, this defect centre in the crystal structure of diamond can resolve magnetic excitations of the gigahertz domain on spatial scales below 10 nanometers by using versatile and easily accessible optical methods.
This presentation shall overview the design and fabrication of the studied magnetic nanocircuits onto diamond substrates previously embedded with NV centres; it will also discuss ferromagnetic resonance experiments performed on those devices, the response of the defect centres to such resonant excitations as well as the applicability of this system to other magnetic configurations.

Julia Hildmann
Postdoc, McGill University
Director: Bill Coish & Aashish Clerk
Optimal dynamical decoupling from colored noise with finite-bandwidth pulses

Patrick Hofer
Doctorate, McGill University
Director: Aashish Clerk
Squeezed light from a tunnel junction
We theoretically investigate the creation of squeezed light by a tunnel junction biased with a time dependent voltage as observed recently [Gasse et al. PRL 111, 136601 (2013)]. We find that the 3db limit can be reached by biasing the tunnel junction with a train of Lorentzian voltage pulses. A comparable amount of squeezing can be obtained by a biharmonic voltage bias. We discuss the squeezing as resulting from a noisy force on the photonic mode provided by the tunneling electrons and point out the limitations of this scheme due to the accompanying heating effects.

Pavithran Iyer
Doctorate, Université de Sherbrooke
Director: David Poulin
Metrics to measure the strength of noise on quantum information
Every error correcting code can only protect quantum information against noise upto a certain threshold. It is very important to know this threshold, for any given error correcting code and a quantum channel. A considerable amount of work has been done to derive numerical estimates of the threshold of various error correcting codes, however, often over quantum channels where the noise is limited to the set of Pauli errors. On the other hand, this restriction to Pauli errors is an over-simplification of a realistic noise model. In a real experimental scenario, noise affecting a quantum system is never as simple as a Pauli error. There is an intrinsic difficulty with a noise model which is not Pauli — there is no general method to say than a channel is more noisy than the other. In this work, we are trying to characterize the strength of a generic noise model by some metrics and observing how the strength of noise changes after error correction.

Erika Janitz
Doctorate, McGill University
Director: Lilian Childress
Toward Cavity Assisted Processes with NV Centers

Benjamin Levitan
Master, McGill University
Director: Aashish Clerk
Dispersive qubit measurement using an integrated on-chip parametric amplifier

Tina Müller
Postdoc, McGill University
Director: Jack Sankey
Enhanced optomechanical levitation of minimally supported dielectrics

Hugo Ribeiro
Postdoc McGill University
Director: Bill Coish
Coherent mechanically-mediated state transfer between a superconducting qubit and a cavity

Alessandro Ricottone
Doctorate, McGill University
Director: Bill Coish
Dynamic Nuclear Polarization and Nuclear Spin Superradiance in 1D systems
The hyperfine coupling between an electron and many nuclei spin 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 strong coherence between the nuclei could lead to the observation of nuclear superradiance, a phase in which the spin flip rate is drastically enhanced. We propose a new device for the observation of this collective phase.

Anne-Marie Roy
Master, Université de Sherbrooke
Director: Michel Pioro-Ladrière

Tunable radiofrequency charge sensor
Manipulating the spin of single electrons in quantum dots is a promising avenue for quantum information processing. As the readout of the spins is performed via spin-to-charge conversion, establishing a charge sensing technique that is fast and highly sensitive is crucial. For this reason, radio-frequency quantum point contact charge sensors have become widespread. Here we present a tunable quantum point contact charge sensor using a cryogenic variable capacitor, tunable from 2 to 12 pF. We obtain optimal impedance matching for different quantum dot devices over a frequency range from 125 to 210 MHz. The flexibility of our setup allows the integration of radio-frequency charge sensors to a variety of nanostructures.

Baptiste Royer
Master, Université de Sherbrooke
Director: Alexandre Blais
Lattice waveguide QED : many-body interactions by dissipation
In waveguide QED, superconducting qubits acting as artificial atoms are coupled to a 1D superconducting transmission line playing the role of common bath for the qubits. By controlling their effective separation, it is possible to engineer various types of dissipation-induced interactions between the qubits. We consider the situation where multiple superconducting qubits are coupled to a lattice of superconducting transmission lines. Depending on the choice of lattice, the qubits exhibit a rich variety of interactions. We present a Markovian master equation framework to describe these systems, and discuss results obtained for simple lattices.

Maximilian Ruf
Master, McGill University
Director: Jack Sankey
Toward cavity assisted processes with NV centers

Jean Olivier Simoneau
Master, 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 quantum-limited 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.

Jean-René Souquet
Postdoc, McGill University
Director: Aashish Clerk
Photon-assisted tunnelling with nonclassical light

Vahid Tayari
Postdoc, McGill University
Director: Thomas Szkopek
Two-Dimensional Magnetotransport in a Black Phosphorus Naked Quantum Well
Black phosphorus (bP) is the second known elemental allotrope with a layered crystal structure that can be mechanically exfoliated down to atomic layer thickness. We have fabricated bP naked quantum wells in a back-gated field effect transistor geometry with bP thicknesses ranging from 6±1 nm to 47±1 nm. Using an encapsulating polymer superstrate, we have suppressed bP oxidation and have observed field effect mobilities up to 600 cm2/Vs and on/off current ratios exceeding 105. Importantly, Shubnikov-de Haas (SdH) oscillations observed in magnetotransport measurements up to 35 T reveal the presence of a 2-D hole gas with Schrodinger fermion character in an accumulation layer at the bP/oxide interface. Our work demonstrates that 2-D electronic structure and 2-D atomic structure are independent. 2-D carrier confinement can be achieved in layered semiconducting materials without necessarily approaching atomic layer thickness, advantageous for materials that become increasingly reactive in the few-layer limit such as bP.

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