Les activités de l'INTRIQ

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nov. 11, 2019

At Hotel Château Bromont

Organizers :
     Éva Dupont Ferrier, Université de Sherbrooke
     Dave Touchette, Université de Sherbrooke

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 11th from 9h30 to 10h30

Meeting program

November 11th

10h30 - 10h55  Registration

10h55 - 11h00  Opening remarks (Salon A)

11h00 - 11h45  Pr Frédéric Dupuis, Université de Montréal
                         Purely quantum polar codes 

11h45 - 12h05  Marco David, Student, McGill University
                         QED. The Quest to Formally Verify Mathematics

12h05 - 13h30  Lunch  (Dining room - 4 Canards)

13h30 - 14h15  Dr Louis Gaudreau, National Research Council (NRC) - Ottawa
                         Entanglement distribution via coherent photon-to-spin conversion in semiconductor quantum dot circuits

14h15 - 14h45  Dr Joel Griesmar, Université de Sherbrooke
                         A mesoscopic spectrometer based on the Josephson effect

14h45 - 15h15  Coffee break  (Salon B)

15h15 - 15h45  Dr Stephane Virally, Polytechnique Montréal
                          Quantum optics in the time domain 

15h45 - 16h25  Industry & Startups in quantum technologies
                              Dr Félix Beaudoin, Les Technologies Nanoacademic Inc (www.nanoacademic.com)
                              Dr David  Roy-Guay, SB Quantum (www.sbquantum.com)
                              Pr David Poulin, Microsoft (0pen positions at Microsoft)

16h25 - 17h00  Equity, diversity & inclusion (minutes and photos of the workshop)

17h00 -             Poster session with refreshments (Salon B)

19h30 -             INTRIQ dinner (Knowlton room)


November 12th

  8h30 -  9h00  Pr Anne Broadbent, Université d'Ottawa
                          Quantum encryption with certified deletion

 9h00 - 10h00  Dr Tomas Jochym-O'Connor, IBM - Yorktown Heights, New York
                        Disjointness in stabilizer codes

10h00 - 10h30  Coffee break (Salon B)

10h30 - 11h30 Pr Signe Seidelin, Institut NEEL CNRS/UGA
                        Rare-Earth Doped Crystals for strain-coupled optomechanics

11h30 - 12h00  Dr Erika Janitz, McGill University
                         Cavity-Enhanced Photon Emission from a Single Germanium-Vacancy Center in a Diamond Membrane

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

13h30 - 14h00  Pr Jérôme Bourassa, Cégep de Granby
                         Quantum illumination : exploiting quantum correlations when entanglement is lost

14h00 - 14h30  Dr Thomas Baker, Université de Sherbrooke
                          Modeling superconducting circuits with a tensor network

14h30 - 15h00  Dr Anirban Chowdhury, Université de Sherbrooke
                          Simulating thermal physics on quantum computers

15h00 - 15h30  Questions and answers

15h30 - 15h40  Closing remarks

mai 29, 2019

Colloque scientifique au congrès de l'Acfas, mercredi le 29 mai 2019

L’information quantique : avancées fondamentales et possibilités technologiques

Organisateurs :
     Professeure Anne Broadbent, Université d'Ottawa
     Professeur Stéphane Kéna-Cohen, Polytechnique Montréal

janv. 8, 2019

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 8-10, 2019 at the Hôtel Château Bromont in Bromont, Québec.

Click here

Click here


Institut Transdisciplinaire d'Information Quantique (INTRIQ)

nov. 11, 2014
Posté par : Marc Leclair

Fall 2014 INTRIQ meeting, November 11th and 12th

At the Hotel of the Château Bromont


Professor Nicolas Godbout, École Polytechnique de Montréal
Professor Sébastien Francoeur, École Polytechniquede Montréal

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

(Note : the venue is at the Hôtel, not the Auberge)

Meeting program

Tuesday, November 11th

 6h30 - 8h30   Breakfast (Dining room)

 8h30 - 8h50   Registration  
 8h50 - 9h00   Opening remarks (Salon A)

 9h00 - 9h50  Paola Cappellaro, Professor, Massachusetts Institute of Technology (Salon A)
                         Time-Optimal Control by a Quantum Actuator

9h50 - 10h20 Coffee break (Salon B)

10h20 -11h10 Mete Atature, Professor, Cavendish Laboratory, University of Cambridge (Salon A)
                          Quantum Optics with Solid-State Spins and Photons
11h10 -11h35 Félix Beaudoin, Student, McGill University (Salon A)
                          Pure dephasing from nuclear-spin and charge noise in semiconductor qubits
11h35 -12h00 Louis Gaudreau, Research Fellow, ICFO-Institute of Photonics Sciences, Barcelone (Salon A)
                          Nanophotonics using novel hybrid graphene devices
12h00 - 13h30 Lunch (Dining room)
13h30 - 14h15 Alexandre Blais, Professor, Université de Sherbrooke (Salon A)
                           Introduction to superconducting qubits
14h15 - 15h15 John M. Martinis, Professor, University of California - Santa Barbara(Salon A)
                           Superconducting qubits poised for fault-tolerant quantum computation

15h15 - 15h45 Coffee break (Salon B)

15h45 - 16h15 Nicolas Didier, Postdoc, Université de Sherbrooke (Salon A)
                           Qubit readout with squeezed light in circuit quantum electrodynamics
16h15 - 17h00 Ph.D. competition : My thesis research in 180 seconds
                          Julien Camirand Lemyre, Université de Sherbrooke
                              A single spin Ferrari
                          Benjamin D'Anjou, McGill University
                             Optimal processing of realistic qubit readouts: the juice is worth the squeeze
                          Guillaume Dauphinais, Université de Sherbrooke
                             Error Correction and Fault Tolerance for Systems of Non Abelian Anyons
                          Gabriel Éthier-Majcher, École Polytechnique
                             Quantum computing with isoelectronic centers
                          Pavithran Iyer, Université de Sherbrooke
                             Transversal gates
                          Dany Lachance Quirion, Université de Sherbrooke
                             A single spin takes the bus
                          Kevin Lalumière, Université de Sherbrooke
                             Observation of strong interaction between artificial atoms in a 1 dimensional vacuum
                         Sophie Rochette, Université de Sherbrooke
                             They were building a quantum computer... without knowing it
                         David Roy-Guay, Université de Sherbrooke
                             A single spin compass
17h00 - 18h30 Poster session with refreshments (Salon B)
                            Group A : 17h00 - 17h45
                            Group B : 17h45 - 18h30
19h00 -           Dinner  (Dining room)

Wednesday, November 12th

 6h30 - 8h30   Breakfast (Dining room)
 8h00 - 9h00   Check out

 9h00 - 9h45   David Poulin, Professor, Université de Sherbrooke (Salon A)
                          A quantum algorithm primer
 9h45 - 10h45 Joseph Emerson, Professor, University of Waterloo (Salon A)
                          Negative Quasi-Probability, Contextuality and the Power of Quantum Computation

10h45 - 11h15 Coffee break (Salon B)

11h15 - 12h00  Open discussions (Salon B)

12h00 - 13h30  Lunch (Dining room)
13h30 - 14h20  Anne Broadbent, Professor, University of Ottawa (Salon A)
erifying quantum mechanics in the regime of high computational  complexity
14h20 - 14h45 Philippe Lamontagne, Student, Université de Montréal (Salon A)
                            One bit cut-and-choose is universal
14h45 - 15h15
Louis Vervoort, Postdoc, Université de Montréal (Salon A)

                            Analogies between quantum mechanics and fluid mechanics
15h15 - 15h20  Closing remarks and departure

Note : Business meeting (all members) from 15h30 to 16h30 (Salon A)
Cavendish Laboratory, University of Cambridge
Quantum Optics with Solid-State Spins and Photons
Spins confined in solids, such as quantum dots and atomic impurities provide interesting and rich physical systems. Their inherently mesoscopic nature leads to a multitude of interesting interaction mechanisms of confined spins with the solid state environment of spins, charges, vibrations and light. Implementing a high level of control on these constituents and their interactions with each other creates exciting opportunities for realizing stationary and flying qubits within the context of  spin-based quantum information science. I will provide a snapshot of the progress and challenges for optically interconnected spins, as well as first steps towards hybrid distributed quantum networks.
University of Ottawa
Verifying quantum mechanics in the regime of high computational complexity
Quantum computers promise to revolutionize the way we communicate and calculate, giving us access to unprecedented computational power. Experimental implementations of quantum computers are in their infancy, but already we are faced with the following conundrum: if quantum computers are indeed exponentially more powerful than their classical counterparts, how can we devise an experiment to verify quantum computations, in the regime of high computational complexity?
Because an experimenter cannot, in general, predict the outcome of a large-scale quantum computation, such experiment would appear to be in violation with the scientific method of "predict-and-verify". A well-known result in theoretical computer science is that an interactive verification process is much more powerful than a static one. Applying this idea to the verification of quantum mechanics, we devise an interactive experiment that can verify the accuracy of quantum devices even in the case that the outcome of the computation cannot be efficiently predicted.
Massachusetts Institute of Technology
Time-Optimal Control by a Quantum Actuator
Fast and high fidelity control of quantum systems is a key ingredient for quantum computation and sensing devices. The critical task is to reliably control a quantum system, while staving off decoherence,  by keeping it isolated from any external influence. These requirements pose a contradiction: fast control implies a strong coupling to an external controlling system, but this entails an undesired interaction with the environment, leading to decoherence.
A strategy to overcome these issues is to use a hybrid system where a quantum actuator interfaces the quantum system of interest to the classical controller, thus allowing fast operations while preserving the system isolation and coherence. This indirect control is particularly appropriate for nuclear spin qubits, which only couple weakly to external fields, but often show strong interactions with nearby electronic spins. In this talk I will describe a strategy to achieve time-optimal indirect control of a nuclear spin qubit by an electronic spin quantum actuator. In particular, I will consider the specific case of the NV center in diamond with applications to both control and sensing.
Université of Waterloo
Negative Quasi-Probability, Contextuality and the Power of Quantum Computation
Quantum computers promise dramatic advantages over their classical counterparts, but identifying the source of the power in quantum computing has remained elusive. I will describe a remarkable equivalence between two very old notions of non-classicity, namely the appearance of negative quasi-probability in a Wigner function and the onset of contextuality in hidden variable models of quantum mechanics, and show that these non-classical features are necessary for achieving universal quantum computation via ‘magic state’ distillation, which is the leading model for experimentally realizing a fault-tolerant quantum computer. In addition to clarifying  conceptual issues about the power of quantum computation, these connections advance the resource framework for quantum computation, which has a number of practical applications, such as characterizing the efficiency and trade-offs between distinct theoretical and experimental schemes for achieving robust quantum computation, and putting bounds on the overhead cost for the classical simulation of quantum algorithms.
Dr Louis Gaudreau, Research Fellow
ICFO-Institute of Photonics Sciences, Barcelone
Nanophotonics using novel hybrid graphene devices
In the last decade there have been many scientific efforts to explore the extraordinary properties of graphene for electronics, optics, quantum information, and material applications.  Since its discovery in 2004, this new zero band gap semiconductor, consisting of a single atomic layer of carbon atoms arranged in a hexagonal lattice, continues to exhibit surprising characteristics, including carrier mobilities in the order of 105 cm2/Vs at room temperature, ultra-fast optical response time and broad spectral bandwidth. In this talk, I will discuss recent experiments in the emerging field of graphene nano-photonics using hybrid devices. First, we will look at the near-field interaction between dipole emitters and graphene. Through lifetime measurements of emitters placed in close proximity of a graphene flake, we observe that due to the two-dimensionality and gapless character of graphene, the nonradiative coupling at distances below 30 nm is greatly enhanced, leading to a modification of the decay rate of the emitters, reaching up to 90 times their decay rate in vacuum and > 90% energy transfer efficiency. I will show how this nonradiative energy transfer process, often regarded as a loss channel for an optical emitter towards the electron bath of graphene, can be read-out by detecting corresponding currents with picosecond time resolution. More precisely, we electrically detect for the first time the spin of nitrogen vacancy centers (NVC) in diamond and control the nonradiative energy transfer to graphene by electron spin resonance. Secondly, I will present a novel optomechanical system comprised of NVC’s in diamond coupled to graphene nanoresonators. In these devices the emitters transduce the mechanical movement of the resonator into optical fields in both the frequency and time domains leading to the optical readout of the resonator.
University of California - Santa Barbara
Superconducting qubits poised for fault-tolerant quantum computation
Superconducting quantum computing is now at an important crossroad, where “proof of concept” experiments involving small numbers of qubits can be transitioned to more challenging and systematic approaches that could actually lead to building a quantum computer.  Our optimism is based on two recent developments: a new hardware architecture for error detection based on “surface codes”, and recent improvements in the coherence of superconducting qubits.  I will explain how the surface code is a major advance for quantum computing, as it allows one to use qubits with realistic fidelities, and has a connection architecture that is compatible with integrated circuit technology.  We have also recently demonstrated a universal set of logic gates in a superconducting Xmon qubit that achieves single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up to 99.4%. This places Josephson quantum computing at the fault-tolerant threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbor coupling. Using this device we have further demonstrated generation of the five-qubit Greenberger-Horne-Zeilinger (GHZ) state using the complete circuit and full set of gates, giving a state fidelity of 82% and a Bell state (2 qubit) fidelity of 99.5%.  These results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.
Université de Sherbrooke
Introduction to superconducting qubits
There have been significant developments in the field of superconducting qubits since the first observation, almost 15 years ago, of coherent oscillations in a superconducting electrical circuit. In this talk, I will introduce the most elementary superconducting qubit and explain how it can be strongly coupled to light.
Félix Beaudoin
Student, McGill University
Director: Bill Coish
Pure dephasing from nuclear-spin and charge noise in semiconductor qubits
One of the most challenging obstacles in the realization of solid-state quantum computing devices is the destruction of quantum superpositions through decoherence. In this talk, I will present basic principles
useful in understanding pure dephasing. I will then apply these concepts in two contexts: (i) the dephasing of a spin qubit due to coupling to nuclear spins in a magnetic-field gradient, and (ii) the dephasing of a qubit due to charge noise from two-level fluctuators. In the first scenario, I will explain how nuclear spins in a magnetic-field gradient can be the dominant source of dephasing for a semiconductor spin qubit. In the second scenario, I will explain how the temperature dependence of the coherence time of a qubit afflicted by charge noise can help in identifying physical mechanisms causing the dynamics of environmental charge fluctuators.
Postdoc, McGill University - Université de Sherbrooke
Directors: Aashish Clerk and Alexandre Blais
Qubit readout with squeezed light in circuit quantum electrodynamics
The usual qubit readout scheme in the dispersive regime of circuit quantum electrodynamics is based on the distinguishability between the two coherent states of the microwave resonator associated to the qubit states. We show how to improve the measurement fidelity using squeezed light and present a possible experimental implementation.

Professor David Poulin

Université de Sherbrooke
A quantum algorithm primer
Like the title says, I'll present some of the early quantum algorithms which lead to Shor's algorithm.
Philippe Lamontagne
Student, Université de Montréal
Director : Louis Salvial
One bit cut-and-choose is universal
Proving the security of quantum cryptographic protocols is a challenging task for cryptographers. They are constantly on the lookout for new tools general enough to be used in a variety of proofs. In this perspective, we propose a new proof technique that bounds the adversary's probability of acomplishing a simple task: to
force a certain measurement result on the honest party's quantum register. We show that to succeed at this task, the adversary essentially needs as much entanglement as the uncertainty of the honest party's measurement.
We provide two applications for our technique: a secure protocol for bit commitment based on black-box access to the cryptographic primitive one out of two cut and choose, and secure protocol for bit commitment in the bounded storage model with the novelty that memory bound is applied to the party that sends qubits.


Dr Louis Vervoort
Postdoc, Université de Montréal
Director: Richard MacKenzie
Analogies between quantum mechanics and fluid mechanics
Recently experiments by a group in Paris have shown that fluid systems (oil droplets floating on vibrating oil films) can strikingly mimic quantum phenomena, such as double-slit interference, quantization of angular momentum, Zeeman splitting etc. Madelung had already shown in 1926 that the Schrödinger equation (SE) can be interpreted as a fluid-mechanical equation. Since the Paris experiments put Madelung’s result in a new perspective, I will show here under which conditions the SE can be derived from the Navier-Stokes equation, and discuss the potential of interpreting the whole of QM as a fluid-dynamical theory. In such a theory a particle is a singularity in a fluid-like medium (a field, the ether, the physical vacuum,…). I will show that Bell’s and Kochen-Specker’s theorems can_not preclude such a local theory to exist. If this vast program could be brought to a good end, would it be bad news for quantum computation & QIT ? Not necessarily.
Félix Beaudoin
Student, McGill University
Director: Bill Coish
Microscopic models for charge-noise-induced dephasing of solid-state qubits
We study the pure dephasing properties of a qubit undergoing charge-noise induced pure dephasing based on a microscopic description of independent two-level charge fluctuators. Such models naturally give rise to a Lorentzian noise spectrum. Yet, we show that the qubit coherence factor is well approximated by a compressed exponential, characterized by a decay time T2 and a stretching parameter alpha. We then evaluate the temperature dependence of T2 and alpha for various fluctuator-bath interactions. We first consider tunneling and cotunneling with an electron reservoir. We then consider interactions with a phonon bath through the direct, two-phonon sum, and Raman processes. We show that different interactions lead to distinct combined behaviors for the decay time and the stretching parameter. This provides a tool to experimentally identify physical mechanisms at the root of charge fluctuations.
Salil Bedkihal
Postdoc, McGill University
Director: Bill Coish
Flux dependent effects in double-dot Aharonov-Bohm interferometer
We study steady state characteristics and the transient behavior of the non-equilibrium double-dot Aharonov-Bohm interferometer using analytical tools and numerically exact influence functional path integrals. Our simple set-up includes two degenerate dots that are coupled to two biased metallic leads at the same strength. A magnetic field pierces the interferometer perpendicularly. As we tune degenerate dots away from the symmetric point we observe four non-trivial magnetic flux control effects: (i) flux dependency of occupation of the dots, (ii) magnetic flux induced occupation difference between the dots, at degeneracy , (iii) the effect of phase localization of dot coherence only hold at the symmetric point, while in general both real and imaginary parts of the coherence are non-zero, and (iv) coherent evolution survives even when the dephasing strength, introduced via Buttiker dephasing probe, is large and comparable to the dot energies and bias voltage. In fact finite elastic dephsing can actually introduce new types of coherent oscillations in the system dynamics. These four phenomena take place when dot energies are gated, to be positioned away from the symmetric point , demonstrating delicate control over occupations of each of the dots.
Keyan Bennaceur
Postdoc, Université de Sherbrooke - McGill University
Directors: Bertrand Reulet and Guillaume Gervais
Electronic Fabry-Pérot interferometer in the fractional quantum Hall regime
The Quantum Hall effect is the quantum version of the Hall effect where electrons in 2 dimensions have quantized energy, as a result, the Hall resistance is quantized as  R_(H)=h/e^2.  In a 2D electron gas (2DEG) with high electron mobility, electron interactions lead to the Fractional quantum Hall effect: interacting electrons binding with magnetic field flux create quasiparticles carrying fractional charges and obeying peculiar statistics. Albeit a nobel prize for FQHE was given in 1998, some states are still not understood.  In particular in the 5/2 state which remain one of the most exciting problem in 2DEG physics, quasiparticles have been predicted to obey non-abelian statistics, leading to quantum states  topologicaly protected from decoherence. This makes it a good candidate for quantum computer. But experimental confirmation is missing due to the fragility of this state, which requires an ultra-high mobility.
It is possible to control the path of quasiparticles in a 2DEG and build the equivalent of an optical beam splitter with capacitive gates.  This opens the possibility to build an electronic interferometer equivalent of an optical Fabry-Pérot interferometer (FPI). It enables to probe the charge and statistics of quasiparticles and answer the open question about the 5/2 states.
Device fabrication often results in a decrease of mobility, killing the fragile fractional quantum Hall states. We have developed and patented a new technique using another substrate on which to perform the fabrication of a FPI and flip it onto the 2DEG to avoid this problem and conserve our devices pristine.


Samuel Boutin
Student, Université de Sherbrooke
Director: Alexandre Blais
Nonlinear corrections to standard quantum parametric amplifier theory
Josephson Parametric Amplifiers (JPA) have allowed to greatly improve the readout fidelity of superconducting qubits. A good understanding of current designs is necessary in order to create a new generation of amplifiers with larger gain, bandwidth and dynamic range. In this work, we go beyond the standard "stiff-pump" approximation and look both numerically and analytically at the impact of usually neglected nonlinear corrections on the properties of the JPA.
Julien Camirand Lemyre
Student, Université de Sherbrooke
Director: Michel Pioro-Ladrière
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/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.
Guillaume Dauphinais
Student, Université de Sherbrooke
Director: David Poulin
Fault-Tolerant Quantum Memory Using Non-Abelian Anyons
Non-Abelian anyons are of great interest in the field of quantum information, as these exotic particles present numerous interesting feautures for the construction of a quantum computer. One of the main feature is that the states encoded with these anyons are topologically protected, i.e. local perturbations on the system does not change their state. However, some noise processes can still corrupt the encoded information. It was recently shown that there exists error correction codes for a system containing Ising anyons subjected to a physically reasonnable noise model. In this work, we present an algorithm based on the idea of cellular automaton and renornalization, first proposed by Gacs, for a fault-tolerant quantum memory using Ising anyons. Such ideas where previously used to create a fault-tolerant quantum memory in the context of the toric code, but has never been studied in the context of non-Abelian anyons.
Nicolas Delfosse
Postdoc, Université de Sherbrooke
Director: David Poulin
Wigner function negativity and contextuality in quantum computation
We describe a universal scheme of quantum computation based on rebits (states with real density matrices). For this scheme, we establish contextuality and Wigner function negativity as computational resources.
Gabriel Éthier-Majcher
Student, Polytechnique
Director: Sébastien Francoeur
Light-hole charged excitons for qubit manipulation
Jean-Charles Forgues
Student, Université de Sherbrooke
Director: Bertrand Reulet
Experimental Bell-like Inequality Violations By Electronic Shot Noise
Bell inequalities are an ideal tool when attempting to demonstrate the existence of entanglement in a physical process. This test criterion was initially devised to prove the validity of quantum theory with regard to spins but can also be extended to continuous variable systems such as the electro-magnetic field. Here, we show that the EM field radiating from a tunnel junction can also violate Bell-like inequalities, thereby demonstrating the presence of entanglement in noise.
Pavithran Iyer
Student, Université de Sherbrooke
Director: David Poulin
Transversal Gates and the Clifford hierarchy
The components of a quantum computer are very sensitive to noise. What is worse is that if a single qubit is noisy, this can corrupt all the qubits in the computation if we are not careful in selecting what quantum gates we use. There is a class of gates known as Transversal gates, which have nice properties in the sense that they do not propagate errors. However, not all unitary operations on an encoded state can be expressed in terms of Transversal gates. On the other hand, the limitations of Transversal gates in terms of the unitary operations they can implement, was an open question until the discovery of Robert Konig and Sergey Bravyi in 2013. Their result finely interrelates the spatial dimensionality of the lattice defining a stabilizer code to the type of unitary operations that can be carried out transversally on that code. I will review these results and mention some possibilities for how one can extend their result to the case of a general LDPC code.
Refs: Bravyi, Sergey, and Robert König. "Classification of topologically protected gates for local stabilizer codes." Physical review letters 110.17 (2013): 170503.
Erika Janitz
Student, McGill University
Director: Lilian Childress
Toward Cavity Assisted Processes with NV Centers
Building a quantum information processing technology requires precise control over highly isolated quantum elements and a means to join them into a scalable network. The nitrogen vacancy (NV) center in diamond and its associated spin degrees of freedom have been proposed as quantum bits [1], but it remains an outstanding challenge to translate a few-qubit system into a scalable quantum network. We propose a method for developing a coherent quantum interface between NV centers and photons confined to a micro-cavity, enabling photon-mediated interactions between distant spins. Building on technology developed in atomic physics, our approach uses a microscopic optical cavity formed by mirrors deposited on the tips of optical fibers [2]. A diamond membrane containing NV defects can be positioned between the mirrors, with the cavity length tuned into resonance with the desired optical transition. Using state-of-the-art mirror coatings it should be possible to bring the fraction of coherent emission to nearly 100%, with built in fiber coupling for high collection efficiency. Here, we present progress in fabricating such cavities and diamond membranes, and in building our preliminary cavity setup.
[1] P. Maurer, G. Kucsko, C. Latta, L. Jiang, N. Yao, S. Bennett, F. Pastawski, D. Hunger, N. Chisholm, M. Markham, D. Twitchen, J. Cirac, and M. Lukin, Room-temperature quantum bit memory exceeding one second, Science 336, 1283 (2012).
[2] D. Hunger, T. Steinmetz, Y. Colombe, C. Deutsch, T.W. Hänsch, and J. Reichel, A fiber Fabry-Perot cavity with high finesse, New Journal of Physics 12, 065038 (2011).
Dany Lachance-Quirion
Student, Université de Sherbrooke
Director: Michel Pioro-Ladrière
Marc-Antoine Lemonde
Student, McGill University
Director: Aashish Clerk
Photon antibunching for squeezed states
Photon antibunching is a quantum phenomenon observed in strongly nonlinear systems where photon blockade prevents to measure two photons at the same time. Conversely, I show how to obtain antibunching with Gaussian states, without the need for explicitly nonlinear dynamics. To do this, I present the intensity correlation function of displaced squeezed thermal states and show that, for a specific range of squeezing and displacement, intensity correlations present classically forbidden behaviors such as antibunching. Based on the intensity correlation, these results then give a sufficient condition for a field to be non-Gaussian. I illustrate how to exploit this physics using a degenerate parametric amplifier, a generic system where squeezing is well controlled. I finally shed light on the so-called unconventional photon blockade effect predicted in a driven two-cavity setup with surprisingly weak Kerr nonlinearities, stressing that it is a particular realisation of this mechanism.
Benjamin Levitan
Student, McGill University
Director: Aashish Clerk
Electromagnetic Squeezing and Amplification Using a Parametrically Driven Mechanical Resonator
Anja Metelmann
Postdoc, McGill University
Director: Aashish Clerk
Tina Muller
Postdoc, McGill University
Director: Jack Sankey
Edouard Pinsolle
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 electron-phonon regime and a diffusion regime and extracted the associated relaxation times and there dependence on temperature.
Hugo Ribeiro
Postdoc, McGill University
Directors: Bill Coish and Aash Clerk
Sophie Rochette
Student, Université de Sherbrooke
Director: Michel Pioro-Ladrière
Fast spin manipulation in Si DQD using micro-magnets: The first chapter
Silicon is a promising candidate for the implementation of long coherence time spin quits in quantum dots. Recently, T2* measured in a purified silicon quantum dot has shown orders of magnitude improvement compared to GaAs/AlGaAs devices (120 μs[1] versus 94 ns[2]). However, the implementation of fast spin manipulation remains challenging.
Our goal is to implement fast spin rotation using micro-magnets in a metal-oxydesemiconductor type double quantum dot (DQD) in silicon. We present here preliminary results showing the feasibility of our scheme. First, we obtained a lithographic double quantum dot, and we were able to deplete it completely, demonstrating the isolation of a single electron. We also observed Pauli spin blockade, a prerequisite for spin readout. Finally, we included a micro-magnet on a device without observing a damaging impact on the number of defects, and numerical simulations suggest really fast spin rotation of the order of 30 ns.
Anne-Marie Roy
Student, Université de Sherbrooke
Director: Michel Pioro-Ladrière
Radio frequency charge sensing in lateral quantum dots
In gallium arsenide double quantum dots, charge sensing is performed via a quantum point contact (QPC) located near the dots. The number and position of electrons in the dot affect conductance in the QPC. Conductance changes are usually measured with DC signal but this technique requires a long integration time, leading to experiments that last months.  The solution is to combine the QPC with a resonant circuit in order use radio frequency signal instead. Higher frequency lead to reduction of the noise and smaller integration time.
Baptiste Royer
Student, Université de Sherbrooke
Director: Alexandre Blais
David Roy-Guay
Student, Uni
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