Les activités de l'INTRIQ

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nov. 9, 2017

At Hotel Château Bromont

Organizers:

Dr. Jérôme Bourassa, Cégep de Granby
Dr. Olivier Landon-Cardinal, McGill University

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

Note : The INTRIQ Business meeting will be held in room "Salle des cantons" on November 9th from 9h30 to 10h30

Registration

Chartered bus Berri-Bromont-Berri (Departure from Berri on Nov. 9th at 9h00 AM)

Carpooling 

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

 

Institut Transdisciplinaire d'Information Quantique (INTRIQ)

sept. 16, 2010
Posté par : Marc Leclair

Meeting de l'INTRIQ (Septembre 2010)


Meeting de l'INTRIQ (16-17 septembre 2010)

Location

 

1 Rue Belvédère Sud
Sherbrooke

 

Program

Thursday, September 16th

LOCATION: Eastside room

  8h30 - 9h15    Registration & breakfast served in conference room
  9h20 - 9 h30   Opening remarks
  9h30 - 10h00  Guillaume Gervais, Non-abelian electronics
10h00 - 10h30  Thomas Szkopek, Weak Localization Studies of Large Area Graphene

10h30 - 11h00   Coffee break
11h00 - 12h00   Hector Bombin, invited speaker, Anyons, twists and topological code

12h00 - 14h15   Lunch (Auguste restaurant)
 
14h15 - 15h15   Ghislain Granger, invited speaker, Coherent spin manipulation in a triple quantum dot
15h15 - 15h45   Coffee break
 
15h45 - 16h15   Louis Salvail, Secure two-party quantum evaluation of unitaries against specious adversaries

16h45 - 19h00   Poster Session with refreshments. Location: Midtown room.

19h30                Dinner (Auguste restaurant)

 
Friday 17th, September 2010
 
8h30 - 9h30       Business meeting in Washington conference room, members only.
 
LOCATION: Eastside room
 
9h30 - 10h30     William A. Coish, invited speaker, Decoherence in ion-trap quantum registers and quantum-enhanced precision measurement
10h30 - 11h00   Coffee break and check-out
 
11h00 - 11h30   Nicolas Godbout, Business Case for Quantum Information   
11h30 - 12h00   Alexandre Blais, Quantum information processing with superconducting qubits
     
12h00 - 14h15   Lunch (Auguste restaurant)
 
14h15 - 15h00   Bertrand Reulet, High frequency third cumulant of current noise : existence of quantum correlations in the zero-point fluctuations of electrons 
15h00 - 15h30   Marcus Da Silva, Efficient characterization of quantum states and processes 
15h30 - 16h00   Coffee break
 
16h00 - 16h30   David Poulin, The physics of quantum error correction 
16h30-17h00     Michael Hilke, Quantum error correction in a charge qubit quantum computer
 
17h00                Closing and departure

 

Invited speakers

Hector Bombin
Perimeter Institute
 
Anyons, twists and topological codes 
Anyon models can be symmetric under some permutations of their topological charges. One can then conceive topological defects that, under monodromy, transform anyons according to a symmetry. 
We study the realization of such defects in the toric code model, showing that a process where defects are braided and fused has the same outcome as if they were Ising anyons. 
These ideas can also be applied to topological subsystem codes, a family of codes where 2-local measurements are enough to keep track of errors. In particular, we get the whole Clifford group of operations via code deformation.
 
William A. Coish
McGill University
 
Decoherence in ion-trap quantum registers and quantum-enhanced precision measurement 
I will discuss work done recently in collaboration with the experimental group of Rainer Blatt in Innsbruck to understand the mechanisms giving rise to decoherence of large quantum registers consisting of up to 14 trapped-ion qubits. 
Unlike many other implementations, the major sources of decoherence in these systems are typically global fluctuations, resulting in poor scaling of the uncertainty in high-precision frequency measurements, 
even when using GHZ-like entanglement in an attempt to enhance precision.  Some advantage of using GHZ states can, however, be recovered provided errors can be "localized"  
and if a finite environment correlation time \tau_c (typically neglected in these systems) is accounted for.  
 

Ghislain Granger
Institute for Microstructural Sciences
National Research Council Canada

Coherent spin manipulation in a triple quantum dot 
"Spin qubits have been of considerable interest thanks to their realization in semiconductor quantum dots.
The electron spin resonance of a single electron spin in a quantum dot driven by microwaves is the simplest example of a qubit in such a system. 
Double quantum dots allow the use of the singlet-triplet qubit, based on the exchange energy between the spin singlet and the spin triplet. 
No microwaves are needed, but a magnetic field gradient between the dots originating from either the hyperfine interaction with the nuclei of the host material or a micromagnet is required [1, 2].
In a series triple quantum dot [3], it is possible to operate a qubit that uses the exchange interaction only [4]. If a double dot is put in a parallel magnetic field,
an interesting qubit forms when the detuning pulse goes slowly enough through an avoided-crossing from the hyperfine interaction between the singlet and the lower energy spin split triplet.
As this process is repeated backwards, interference is revealed in the form of Landau-Zener-Stükelberg oscillations [5].
In this talk, we introduce the triple dot design that we use at NRC-IMS and tune the gate voltages to reach the fundamental resonance condition relevant for quantum computation with spin qubits.
The way singlet-triplet qubits in double quantum dots have been operated involves the spin to charge conversion of the spin blockade signal. 
In our triple dot, we show that transport occurs at six quadruple points, and that spin blockade occurs for all the quadruple points at both bias polarities, making the triple dot a “spinsulator.” 
Spin blockade is also observed in charge detection in the presence of a pulse going from one charge configuration to another and back, where the last step is spin blockaded. 
Using this method, but with small pulses going from the triple dot lowest energy doublet to the lowest energy quadruplet, we resolve the Landau-Zener-Stükelberg oscillations as a function of detuning and pulse time. 
This triple dot approach constitutes a step forward towards scalability.
[1] R. Hanson et al., Rev. of Mod. Phys. 79, 1217 (2007).
[2] M. Pioro-Ladrière et al., Nat. Phys. 4, 776 (2008).
[3] L. Gaudreau et al., Appl. Phys. Lett. 95, 193101 (2009).
[4] E. A. Laird et al., arXiv:1005.0273 (unpublished).
[5] J. R. Petta et al., Science 327, 669 (2010).
 

Bertrand Reulet
Université de Sherbrooke.

High frequency third cumulant of current noise : existence of quantum correlations in the zero-point fluctuations of electrons 
We have measured the high frequency third cumulant of voltage quantum fluctuations  across a tunnel junction in the high frequency regime  hf » eV » kT. 
This quantity is obtained by correlating the fluctuations of the high frequency noise power with the low frequency part of the fluctuating voltage .
In this regime, the high frequency voltage/current fluctuations are due to zero point motion of electrons. We obtain that the third cumulant of current fluctuations is simply given by e^2I, independent of f.
Despite its classical look, this result expresses that the fluctuations of the square of the high frequency current due to vacuum fluctuations are correlated with the low frequency fluctuating current. 
We discuss how this result raises the problem of how to calculate high order correlators in quantum mechanics for a given experimental setup.
 
 
Speakers
Michael Hilke
McGill University
 
Quantum error correction in a charge qubit quantum computer 
We evaluate  the performance of the 5 qubit quantum error correction code for a charge qubit quantum computer. We show that the fidelity approaches one when the error correction frequency is increased.
 

Guillaume Gervais
McGill University

Non-abelian Electronics
It is well-established that as the size of transistor and devices is reduced towards the nanoscale new quantum effects emerge that are for the most part a nuisance from the point-of-view engineering. 
Here, we shall discuss the richness of the quantum physics that is likely to exist in extremely pure semiconductor-based  devices, and in particular the link between quantum statistics, fractional quantum Hall liquids and topological quantum computation will be discussed. 
Experiments that are underway and designed to uncover this physics will be  presented.


Thomas Szkopek
McGill University

Weak Localization Studies of Large Area Graphene 
Graphene is a 2D material of potential interest to implementing quantum information processing in the solid state. Large area graphene can be produced by epitaxial growth techniques on SiC and transition metals. 
We report magneto-transport experiments on large area graphene. Weak-localization has been observed and fit to the theory of McCann et al. to extract electron scattering rates. 
Preliminary work on the effect of molecular adsorbates on graphene conduction is presented, as is ongoing work to modify the electronic properties of graphene via exposure to atomic hydrogen.


Louis Salvail
Université de Montréal

Secure Two-Party Quantum Evaluation of Unitaries Against Specious Adversaries
We describe how any two-party quantum computation, specified by a unitary which simultaneously acts on the registers of both parties, can be privately implemented against a quantum version of classical semi-honest adversaries that we call specious. Our construction requires two ideal functionalities to garantee privacy: a private SWAP between registers held by the two parties and a classical private AND-box equivalent to oblivious transfer. If the unitary to be evaluated is in the Clifford group then only one call to SWAP is required for privacy.  On the other hand, any unitary not in the Clifford group requires one call to an AND-box per R-gate in the circuit. Since SWAP is itself in the Clifford group, this functionality is universal for the private evaluation of any unitary in that group. 
SWAP can be built from a classical bit commitment scheme or an AND-box but an AND-box cannot be constructed from SWAP. It follows that unitaries in the Clifford group are to some extent the easy ones. We also show that SWAP cannot be implemented privately in the bare model.

Alexandre Blais
Université de Sherbrooke

Quantum information processing with superconducting qubits


David Poulin
Université de Sherbrooke

The physics of quantum error correction 
I will review some recent work in my group, illustrating the many connections between quantum error correction and statistical physics. 
 

Richard MacKenzie
Université de Montréal

Optimizing adiabaticity in quantum mechanics
I will describe a recent effort to address the following question: Given a quantum mechanical system with a Hamiltonian depending on a number of time-dependent parameters, 
what evolution between given initial and final Hamiltonians (with fixed total time of evolution) maximizes the extent to which the evolution is adiabatic? 
A variational approach will be used to derive a criterion for maximization. The criterion is rather difficult to use; however, it will be illustrated in some simple toy models.
 
POSTER SESSION
 

Jamie Gardner
Student, McGill university
Director: Aashish Clerk

Damping of a mechanical oscillator coupled to a double quantum dot 
Dynamical interactions between a conducting cantilever and a quantum confined electronic system depend on both classical and quantum effects, but can often be understood using straightforward semiclassical reasoning.  The case of cantilever damping via coupling to a single quantum dot (QD) system is analyzed using linear response theory, and the results are subsequently derived using simpler heuristic arguments.  Double QD (DQD) damping is more complex and exhibits divergent behavior in the negative-bias, zero-frequency limit.  Comparison to the single QD case helps establish the cause of this phenomenon, which in some cases could dominate experimental results.
 

Carolyn Young
Student, McGill university
Director: Aashish Clerk

Heisenberg Backaction in Quantum Point Contact Qubit Detectors
 

Benjamin Schmidt
Student, McGill university
Director: Guillaume Gervais

Non-Abelian Electronics 
An ideal candidate system for practical quantum computation should be easy to manipulate, yet, paradoxically, robust against decoherence, which is in a sense manipulation by the environment. 
Two dimensional particles known as non-Abelian anyons are of particular interest, since their set of degenerate ground states are topologically protected - they can only be manipulated by looping particles around each other, which is extremely unlikely to happen spontaneously. Numerical studies strongly suggest that the 5/2 fractional quantum hall state has non-Abelian quasiparticle excitations, but experimental results are still difficult to interpret.
We will discuss the fractional quantum hall effect and non-Abelian statistics with a focus on experimental progress towards understanding the 5/2   state.
 

Leonhard Benno Salwey
S
tudent, Université de Montréal
Directors: Gilles Brassard & Alain Tapp

Classification of multi-partite entanglement in terms of permutation symmetries 
We will present a general concept to unveil the structure of multi-partite entanglement. Two states are said to bear different kinds of entanglement if they cannot be obtained from each other with finite probability by means of local manipulation i.e. local operations and classical communication(LOCC). 
We will derive a framework to discriminate inequivalent entanglement properties, using permutations on the tensor space of multiple, identical quantum states. We can identify states of inequivalent entanglement classes via their distinct permutational symmetries. To be specific we will discuss a few classes of 3-qutrit and 4-qubit systems.
 
 
David Roy-Guay
Student, Université de Sherbrooke
Directors: Michel Pioro-Ladrière & Denis Morris
 
Spin manipulation of NV centers in diamond
 

Maxime Boissonneault
S
tudent, Université de Sherbrooke
Director: Alexandre Blais

Fourth order dispersive regime of circuit QED with a transmon and a CJBA
 

Julien Camirand Lemyre
Student, Université de Sherbrooke
Director: Michel Pioro-Ladrière

Ultra-fast single-spin rotations based on the exchange interaction
Arbitrary qubit rotations are needed to build a universal quantum computer. These rotations have to be performed on a time scale much shorter than the decoherence time of the qubit to achieve high fidelity operations. A new scheme using the exchange interaction between two spins in a double quantum dot could be used to reach this regime [1]. 
Micromagnets along with nuclear spins polarization will be designed in order to produce the necessary magnetic field gradients for this scheme.
[1] W. A. Coish and D. Loss, Phys. Rev. B 75, 161302(R) (2007).
 

Félix Beaudoin
Student, Université de Sherbrooke
Director: Alexandre Blais

Spectroscopy of a superconducting qubit ultra-strongly coupled to an electromagnetic resonator
The dipole interaction between an artificial atom and a resonator field is described by the Rabi Hamiltonian. When the coupling constant g is much smaller than the qubit and cavity frequencies, this Hamiltonian can be approximated by the (simpler) Jaynes-Cummings form, where counter-rotating terms can be neglected. Here we investigate the opposite regime, where g is so strong this approximation is broken. In that case, spontaneous generation of photons in the ground state is predicted. The effect of these photons on the  qubit's absorption spectrum will be presented.
 

Guillaume Duclos-Cianci
Sstudent, Université de Sherbrooke
Director: David Poulin

"Decoders for Topological Quantum Codes."
 

Olivier Landon-Cardinal
Student, Université de Sherbrooke
Director: David Poulin

Efficient Direct Tomography for Matrix Product States
Matrix product states (MPS) are a variational class of states that can be specified by a small number of parameters. Their importance in quantum many-body physics and quantum information science stems from the fact that they seem to capture the low energy physics of a wide range of one-dimensional systems. We adress the following question: given a state, is it possible to efficiently perform quantum state tomography in order to extract its MPS representation ?
We describe a method for reconstructing these states from a small number of efficiently-implementable measurements. Our method is exponentially faster than standard tomography, and can be used to certify that the unknown state is an MPS. The basic idea is to use local unitary operations to disentangle parts of the system, giving direct access to the MPS representation. Put another way, MPS correspond to the outputs of a family of efficient quantum circuits and the method identifies the gates of a circuit that outputs the unknown state.
 

Jonathan Guillemette
Student, McGill University
Director: Thomas Szkopek

Weak Localization in Graphene on SiC and Graphene Grown on Copper 
We measure weak localization in the magnetoconductance  for samples of graphene on SiC as well as graphene samples that were grown by CVD on copper and transferred to oxide substrates. We fit the magnetoconductance curves to McCann's theory and extract scattering times.
 

Eliot Bolduc
Student, Polytechnique de Montréal
Director: Nicolas Godbout &Suzanne Lacroix

Detection electronics for single photon counting and gating
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