Institut Transdisciplinaire d'Information Quantique (INTRIQ)
Spring 2014 INTRIQ meeting, May 6th and 7th
At the Hotel of the Château Bromont
Organizers:
Professor Richard MacKenzie, Université de Montréal
Professor Louis Salvail, Université de Montréal
90, rue Stanstead, Bromont QC J2L 1K6
Téléphone : 1 800 304 3433 Directions

Meeting program
Tuesday, May 6th
6h30  8h30 Breakfast (Dining room)
8h45  9h00 Registration
9h00  9h10 Opening remarks (Salon A)
9h10  10h10 Frédéric Dupuis, Postdoc, Aarhus University (Salon A)
Bounding the uncertainty of constrained adversaries
10h10  10h30 Coffee break (Salon B)
Nogo Theorems and FluidDynamical or “BackgroundBased” Theories for
Quantum Mechanics
Strong squeezing and robust entanglement in cavity electromechanics
Quantum software and quantumsafe cryptography
Designing photonic crystal ring resonators at the band edge
15h35  16h00 Arne Grimsmo, Student visitor, Université de Sherbrooke (Salon A)
Controlling rate of convergence for open quantum systems using
Wednesday, May 7th
6h30  8h30 Breakfast (Dining room)
8h00  9h00 Check out
9h00  10h00 Andrew Sachrajda, Quantum Physics Group Leader, NRCCNRC (Salon A)
The Three Spin System for Quantum Information Applications
10h00  10h15 Coffee break (Salon B)
10h15  11h00 Michael Hilke, Professor, McGill University
Anderson localization and quantum information channels
11h00  12h00 Poster session (Salon B)
The quest for selfcorrecting quantum memory
Manipulating spin qubits with nitetime Stuckelberg interferometry
Softdecoding quantum measurement devices
Note : Business meeting (all members) from 16h00 to 17h00 (Salon A)
INVITED SPEAKERS
Dr Frédéric Dupuis
Center for the theory of interactive computation  CTIC
Aarhus University
Bounding the uncertainty of constrained adversaries
In many cryptographic protocols, the main ingredient of the security proof involves showing that a dishonest party has a limited amount of information about a particular string or quantum system of interest. This bound on the adversary's information often comes from a physical constraint, such as a limited or noisy quantum memory, which must then be harnessed by the security proof. In this talk, I will present a general technique for making use of this type of constraint in security proofs, and will give concrete applications to cryptography in the bounded storage model and to bounds on randomaccess codes.
For more information, see arXiv:1305.1316.
Dr Andrew Sachrajda
Quantum Physics Group Leader, National Research Council Canada
The Three Spin System for Quantum Information Applications
In this talk I will review our experimental and theoretical results on the three spin system in triple quantum dots. In particular I will focus on two aspects. The first is a systematic study of leakage paths away from targeted three spin qubits. The three spin system is complicated and various leakage paths are triggered under specific pulse conditions. We use the magnetic field dependence to identify two specific leakage mechanisms. The second topic will deal with nonlocal coherent transfer that we have observed in this system. In particular it will be argued that an arbitrary single spin state can be transferred nonlocally in this system via a swap related process.
Professor Michele Mosca
Institute for Quantum Computing
Quantum software and quantumsafe cryptography
Quantum algorithms allow us to solve several important problems with a substantially reduced computational complexity.
For example, Shor’s algorithms will solve integer factorization and finding discrete logarithms in polynomial time, and thus compromise RSA and DiffieHellman based cryptosystems. These systems are used ubiquitously today, and, for example, underpin internet security.
For any problem, the precise point at which an available quantum computer will outperform classical algorithms depends on many factors. One of these factors is the efficiency with which the algorithm is compiled into the available physical quantum operations.
I will discuss the problem of quantum compiling and overview some of our results on this field.
The advent of a quantum computing device that is able to implement large instances of quantum algorithms will be a major milestone in computing history, as it will bring the possibility of designing advanced quantum materials, simulating chemical reactions at the quantum level, improved optimization methods for a wide range of industries, and so on, including many applications yet to be discovered. However, it is critical that a new generation of cryptographic primitives resistant to quantum attacks is deployed before this happens. It is far from clear that this will happen.
I will outline this challenge, and the ongoing work towards meeting the challenge.
Professor Pable Bianucci
Concordia University
Designing photonic crystal ring resonators at the band edge
For Cavity QED applications, it is important to work with optical resonators with few modes, low losses (high quality factor), and small mode volume.
Because of its ease of integration the microring (a waveguide that closes upon itself) is a very popular microcavity. However, it has not been used much for quantum applications because of their relatively large mode volumes and losses.
By incorporating a periodic pattern of holes in a microring, we can alter the dispersion relation in the waveguide and find regions in the slow light regime, where the group index of the propagating light becomes large. By careful design of the ring and hole geometry, we can find resonant modes in the slow light band that should have reduced losses and an increased interaction with matter.
INTRIQ SPEAKERS
Bill Coish
Professor, McGill University
Softdecoding quantum measurement devices
Quantum measurements are commonly performed by thresholding a collection of analog detectoroutput signals to obtain a sequence of singleshot bit values. The intrinsic irreversibility of the mapping from analog to digital signals results in the loss of “soft information” associated with an a posteriori probability that can be assigned to each bit value when a detector is wellcharacterized. In this talk, I will illustrate advantages in retaining soft information for quantum measurements through two 'realworld' examples. These results
show useful and practical advantages for a wide range of current experiments on quantum state tomography, parameter estimation, and qubit readout.
Hichem Eleuch
Visiting professor, McGill University
Strong squeezing and robust entanglement in cavity electromechanics
I will present our recent published work [PRA 89, 013841 (2014)] about the investigation of the squeezing and the optomechanical entanglement in an electromechanical system in which a superconducting charge qubit is coupled to a transmission line microwave resonator and a movable membrane, simulating the mechanical motion. The membrane is capacitively coupled to a second transmission line resonator. We showed that strong squeezing of the microwave field and robust optomechanical entanglement can be achieved in the presence of moderate thermal decoherence of the mechanical mode. The generated entanglement can be controlled by tuning the input drive pump power and the detuning of the drive frequency from the resonator frequency. Merging of optomechanics with electrical circuits opens avenues for an alternative way to explore creation and manipulation of quantum states of microscopic systems.
Arne Grimsmo
Student visitor, Université de Sherbrooke
Director : Alexandre Blais
Controlling rate of convergence for open quantum systems using timedelayed feedback control
We propose a timedelayed feedback control scheme for open quantum systems that can dramatically reduce the time to reach steady state. No measurement is performed in the feedback loop, and we suggest a simple alloptical implementation for a cavity QED system. We demonstrate the potential of the scheme by applying it to a driven and dissipative Dicke model, as recently realized in a quantum gas experiment. The time to reach steady state can then reduced by two orders of magnitude for parameters taken from experiment, making previously inaccessible long time attractors reachable within typical experimental run times.
Michael Hilke
Professor, McGill University
Anderson localization and quantum information channels
Anderson localization was discovered in 1958, and rigorously proven in 1D for the tightbinding model, leading to the statement: "for an uncorrelated disorder of arbitrary strength ALL states are localized in 1D". Here I will present a new derivation of Anderson localization for an arbitrary disorder potential (even in the presence of disorder correlations). Quite surprisingly, it turns out that some states become delocalized at special values of the disorder correlation length. I will then discuss the implications and applications of Anderson localization to quantum information channels and the possibility of new encryption schemes.
Olivier LandonCardinal
Postdoc, Caltech
The quest for selfcorrecting quantum memory
A selfcorrecting quantum memory is a physical system whose quantum state can be preserved over a long period of time without the need for any external intervention. The most promising candidates are topological quantum systems which would protect information encoded in their degenerate groundspace while interacting with a thermal environment. Many models have been suggested but several approaches have been shown to fail due to nogo results of increasingly general scope. In this presentation, I will explain the desiderata for selfcorrection, review the recent advances and nogo results, and describe the current endeavours to define a selfcorrecting system in 2D and 3D.
Paul RaymondRobichaud
Student, Université de Montréal
Director : Gilles Brassard
Parallel Lives
We propose a new set of axioms for quantum mechanics in ﬁnitedimensional Hilbert space. Our system is easily proven to be both local and realistic, notwithstanding Bell’s theorem. Our axioms and interpretation are built upon the density matrix formalism, and on the Everett picture of quantum mechanics. It inherits the conceptual problems of Everett’s picture, except for problems related to nonlocality. While other similar approaches already exist, the main advantage of our formalism is its simplicity and its familiarity, for quantum information theory and quantum computing. The formalism can also be used by researchers in quantum information theory, irrespective of whether or not they agree with the underlying metaphysical concepts.
Hugo Ribeiro
Postdoc, McGill University
Directors : Bill Coish & Aashish Clerk
Manipulating spin qubits with nitetime Stuckelberg interferometry
LandauZenerStuckelbergMajorana (LZSM) physics has been exploited to coherently manipulate twoelectron spin states in a GaAs double quantum dot system at an anticrossing between a singlet S and a triplet T+ resulting from the hyperne interaction with nuclear spins of the host material [1,2]. However, the fluctuations of the nuclear spin bath result in spin dephasing within T*2~10 20 ns. As a consequence, the sweep through the anticrossing would have to be performed on a timescale comparable to T*2 to achieve LZSM oscillations with 100% visibility. Moreover, the ST+ anticrossing is located near the (1; 1)(2; 0) interdot charge transition, where (nl; nr) denotes the number of electrons in the left and right quantum dot. As a result, the singlet state involved in the dynamics is a superpostion of (1; 1) and (2; 0) charge states which renders the qubit susceptible to charge noise.
In this talk, I will show how to overcome limitations set by both nuclear spins and charge environment by using a tailored pulse with a detuning dependent level velocity [3], for which a correct interpretation of experimental data is only possible when nitetime eects are taken into account [4].
[1] J. R. Petta, H. Lu, and A. C. Gossard, Science 327, 669 (2010)
[2] H. Ribeiro, J. R. Petta, and G. Burkard, Phys. Rev. B 82, 115445 (2010)
[3] H. Ribeiro, G. Burkard, J. R. Petta, H. Lu, and A. C. Gossard, Phys. Rev. Lett. 110, 086804 (2013)
[4] H. Ribeiro, J. R. Petta, G. Burkard, Phys. Rev. B 87, 235318 (2013)
Louis Vervoort
Postdoc, Université de Montréal
Director : Richard MacKenzie
Nogo Theorems and FluidDynamical or “BackgroundBased” Theories for Quantum Mechanics
Recently experiments by Couder et al. (PRL 2006, 2010, 2012) have shown that fluid systems can exhibit striking quantum behavior. Brady et al. and Sbitnev have claimed that under some assumptions the Schroedinger equation can be derived from the NavierStokes equation, and shown how this can explain the Couder experiments. If fluid dynamical theories would indeed be able to reproduce QM, and thus locally explain / complete QM, they should bypass various nogo theorems, such as Bell’s theorem and the KochenSpecker theorem. Here we show how they can do so. In some detail, we have investigated the simplest and most general mathematical models that allow to describe a Bell experiment in which the 2 particles and the 2 analyzers interact with a background medium or field (e.g. a fluid, the physical vacuum,…).
POSTER SESSION
Abeer Barasheed
Student, McGill University
Director : Jack Sankey
Toward Stronger Optomechanical Coupling Photonic Crystals and Microcavities
In the modern field of optomechanics, we have learned to use radiation forces to gain a new level of control over the motion of solid mechanical elements. A possible route to maximize the impact of each photon is to use mechanical elements that are both lightweight and highly reflective. These attributes are typically at odds with one another, but it should be possible to achieve both using a photonic crystal reflector, which consists of an appropriate array of holes punched into a thin dielectric slab. Whereas a 100 nm thick slab of silicon nitride might reflect ~ 20% of incident light, a photonic crystal reflector of the same thickness might weigh half as much and reflect > 99% of incident light. We will discuss progress toward fabricating photonic crystals that are both highly reflective (> 99% at the design wavelength) and sufficiently lightweight / mechanically compliant to be strongly influenced by radiation pressure from lowpower lasers. Specifically, we will discuss our fabrication process for 100 nm thick silicon nitride and 200 nm thick silicon freestanding membranes and their simulated optical performance.
Another route to maximize the impact of each photon is to reduce the cavity mode volume. To this end we report progress toward fabricating ultrasmooth concave substrates for highfinesse fiberbased microcavities using a CO2 laser ablation technique. We can now produce a concave surface of curvature ~ 30 microns with a roughness < 0.2 nm positioned within a micron of the core of a cleaved optical fiber end. Another route to reduced cavity (and mechanical!) mode volume is to fabricate point defects in photonic crystals that are capable of simultaneously colocalizing an optical and mechanical mode within a volume comparable to their wavelengths; in such a system, the periodic dielectric constant and the periodic mass density of the surrounding crystal act as Bragg mirrors to confine optical waves, and acoustic waves respectively. To achieve strong confinement, the mechanical and optical frequencies of interest have to be located within both the phononic and the photonic band gaps of the crystal. Here we will discuss preliminary simulations of wavelengthscale defects in such crystals.
Félix Beaudoin
Student, McGill University
Director : Bill Coish
Microscopic models for charge dephasing in semiconductor qubits
Charge noise is a ubiquitous source of dephasing in solidstate qubits. In typical models seeking to explain this decoherence mechanism, the charge qubit is dipolecoupled to twolevel charge fluctuators distributed in the host material, at interfaces or in oxide layers. Here, we consider various microscopic mechanisms causing fluctuations in the environmental twolevel systems, and study the charge qubit’s coherence roperties in each scenario. In light of recent experimental results reported with semiconductor qubits, we identify which noise mechanism reasonably dominates, and make testable predictions for future experiments.
Simon Bernard
Student, McGill University
Director : Jack Sankey
Toward Stronger Optomechanical Coupling: Photonic Crystals and Micro Cavities
In the modern field of optomechanics, we have learned to use radiation forces to gain a new level of control over the motion of solid mechanical elements. A possible route to maximize the impact of each photon is to use mechanical elements that are both lightweight and highly reflective. These attributes are typically at odds with one another, but it should be possible to achieve both using a photonic crystal reflector, which consists of an appropriate array of holes punched into a thin dielectric slab. Whereas a 100 nm thick slab of silicon nitride might reflect ~ 20% of incident light, a photonic crystal reflector of the same thickness might weigh half as much and reflect > 99% of incident light. We will discuss progress toward fabricating photonic crystals that are both highly reflective (> 99% at the design wavelength) and sufficiently lightweight / mechanically compliant to be strongly influenced by radiation pressure from lowpower lasers. Specifically, we will discuss our fabrication process for 100 nm thick silicon nitride and 200 nm thick silicon freestanding membranes and their simulated optical performance.
Another route to maximize the impact of each photon is to reduce the cavity mode volume. To this end we report progress toward fabricating ultrasmooth concave substrates for highfinesse fiberbased microcavities using a CO2 laser ablation technique. We can now produce a concave surface of curvature ~ 30 microns with a roughness < 0.2 nm positioned within a micron of the core of a cleaved optical fiber end. Another route to reduced cavity (and mechanical!) mode volume is to fabricate point defects in photonic crystals that are capable of simultaneously colocalizing an optical and mechanical mode within a volume comparable to their wavelengths; in such a system, the periodic dielectric constant and the periodic mass density of the surrounding crystal act as Bragg mirrors to confine optical waves, and acoustic waves respectively. To achieve strong confinement, the mechanical and optical frequencies of interest have to be located within both the phononic and the photonic bang gaps of the crystal. Here we will discuss preliminary simulations of wavelengthscale defects in such crystals.
Julien CamirandLemyre
Student, Université de Sherbrooke
Director : Michel PioroLadrière
Integration of Nanomagnets for single spin manipulation in double quantum dot
Micromagnets have been proven useful to manipulate spin qubits in semiconductor quantum dots. However, in the previous architectures, the micromagnet were not optimally integrated to the quantum dots architecture, hence limiting the magnetic field amplitude and the gradients it produces. In this poster, I will present how to modify the fabrication of the magnet to optimize the magnetic field gradients. I will show how the strong magnetic field gradients can be use for readout and manipulation of a single spin in a double quantum dot.
Christopher Chamberland
Student, McGill University
Directors : Aashish Clerk and Bill Coish
Adiabatic quantum state transfer in the presence of cavity shot noise
Many areas of physics rely upon adiabatic state transfer protocols, allowing a quantum state to be moved between different physical systems for storage and retrieval or state manipulation. However, these state transfer protocols suffer from dephasing and dissipation. This work goes beyond standard opensystems treatment of quantum dissipation allowing us to consider nonMarkovian environments. After developing the general theoretical tools, we apply our methods to adiabatic state transfer between qubits in a driven cavity. We explicitly consider dephasing effects due to unavoidable photon shot noise. Also, we find an interesting analogy between the problems of adiabatic state transfer and dynamical decoupling for state preservation. These results will be useful to ongoing experiments in circuit QED systems.
Benjamin D'Anjou
Student, McGill University
Director : Bill Coish
Optimal postprocessing for a generic singleshot qubit readout
We analyze three different postprocessing methods applied to a singleshot qubit readout: the averagesignal (boxcar filter), peaksignal, and maximumlikelihood methods. In contrast to previous work, we account for a stochastic turnon time t_i associated with the leading edge of a pulse signaling one of the qubit states. This model is relevant to spinqubit readouts based on spintocharge conversion and would be generically reached in the limit of large signaltonoise ratio r for several other physical systems, including fluorescencebased readouts of iontrap qubits and nitrogenvacancy center spins. We find that the peaksignal method outperforms the boxcar filter significantly when t_i is stochastic, but is only marginally better for deterministic t_i. We generalize the theoretically optimal maximumlikelihood method to stochastic t_i and show numerically that a stochastic turnon time t_i will always result in a larger singleshot error rate. Based on this observation, we propose a general strategy to improve the quality of singleshot readouts by forcing t_i to be deterministic.
Guillaume Dauphinais
Student, Université de Sherbrooke
Director : David Poulin
Error correction with Ising anyons living on a torus
System presenting nonabelian exchange statitics are promising candidates to serve as building blocks for a quantum computer. Ising anyons are an exemple of such nonabelian particles. When living in a torus, this system possesses a 3degenerate ground state. In this poster, we study the effect of noise on this system and an error correction code is presented.
Nicolas Delfosse
Postdoc, Université de Sherbrooke
Director : David Poulin
A family of quantum LDPC codes based on Cayley graphs
We study a construction of quantum error correcting codes based on Cayley graphs proposed by MacKay, Mitchison and Shokrollahi. We provide a lower bound on the minimum distance of these quantum codes based on Cayley graphs.
This is based on joint work with Alain Couvreur and Gilles Zémor and on joint work with Zhentao Li and Thomassé.
Gabriel ÉthierMajcher
Student : École Polytechnique
Director : Sébastien Francoeur
Complete quantum control of exciton qubits bound to isoelectronic centers
JeanCharles Forgues
Student : Université de Sherbrooke
Director : Bertrand Reulet
Hidden Signal in Electronic Noise: Photon Pair Emission
In electronic systems, the desired signal is often accompanied by fluctuations around an average value. These fluctuations, often called noise, can reveal hidden information if studied carefully. This poster summarises how driving a linear component, a tunnel junction, at a frequency f0 can lead to photon pair emissions at frequencies f' and f0f', which would normally be hidden in the noise. The pairs are more readily observed in the quantum regime, kBT<<hf0, which is why the experiment is performed at f0=11.6 GHz, T=20 mK.
Julia Hildmann
Postdoc, McGill University
Directors: Bill Coish and Aashish Clerk
Quantum limit for nuclear spin polarization in semiconductor quantum dots
One of main sources of decoherence for spin qubits confined in semiconductor quantum dots comes from hyperfine interaction of the electron spin with the nuclear spins. By polarizing the nuclear spins to 100% it is possible to extend coherence times. A recent experiment by E. A. Chekhovich et al. [Phys. Rev. Lett. 104, 066804 (2010)] has demonstrated that high nuclear spin polarization can be achieved in selfassembled quantum dots by exploiting an optically forbidden transition between a heavy hole and a trion state. However, a fully polarized state is not obtained as expected from a classical rate equation. We theoretically investigate this problem with the help of a quantum master equation and we demonstrate that a fully polarized state cannot be reached due to formation of a nuclear dark state. We also show that the maximal degree of polarization depends on the form of the electron envelope wave function inside of the quantum dot.
Pavithran Iyer
Student, Université de Sherbrooke
Director : David Poulin
Quantum Lowdensity Paritycheck codes
Lowdensity Paritycheck (LDPC) codes are one of the most widely used type of classical codes in communication devices, for error correction purposes. They were discovered by Robert Gallager in 1962 and have been shown to posses all of the desirable features expected from a good error correcting code. I will describe Gallager's construction of LDPC codes and discuss its properties. The LDPC formalism can be extended to the setting of quantum codes too. However, until recently, a prescription for constructing a quantum LDPC code, with given parameters, was not known. I will describe one construction of quantum LDPC codes, which was proposed by J.P.Tillich in 2009. These codes were given the name: Hypergraph product codes. I studied the properties of these codes, as part of a project for a course. I am working on finding an expression for the weight distribution of hypergraph product codes. I will discuss the properties of hyper graph product codes and outline some of the attempts I made to determine its weight distribution.
Sources:
Classical LDPC codes: “Lowdensity paritycheck codes”, Robert Gallager, IRE Transactions on Information Theory, Vol 8, No 1, pp 2128, 1962
Hyper graph product codes: “ Quantum LDPC codes with positive rate and minimum distance proportional to n^{1/2} ”, JeanPierre Tillich and Gilles Zemor, arXiv:0903.0566v2
Saeed Khan
Student, McGill University
Directors : Aashish Clerk
Large gain quantumlimited qubit state measurement using a twomode nonlinear cavity
A single nonlinear cavity dispersively coupled to a qubit functions as a large gain detector near a bifurcation, but also has an unavoidable large backaction that prevents QND measurement at weak couplings. We show theoretically that a modified setup involving two cavities, one linear and one nonlinear, and a dispersively coupled qubit, allows for a far more optimal measurement. In particular, operating near a point of bifurcation, one is able to both achieve a large gain as well as a near quantumlimited backaction. The increased system flexibility also enables faster measurement rates and smaller shot noise dephasing than is possible with single nonlinear cavity setups. We present analytic results for the gain and noise of the twocavity detector and a heuristic understanding of the physics, thus presenting a complete description of this new way of performing weak qubit state measurements. e setup we describe can easily be realised in experiments with superconducting circuits involving Josephson junctions, with particular application to onchip integration of qubits and nearquantumlimited amplifiers.
Kevin Lalumière
Student, Université de Sherbrooke
Director : Alexandre Blais
Waveguide QED with an ensemble of inhomogeneous atoms
Superconducting qubits are promising candidates for quantum information processing because of their relatively long coherence time combined with short operation time scales. Moreover, several of these qubits can be made to interact at long distance by coupling them to the standing waves of the electromagnetic field in a transmission line resonator. This setup is referred to as circuit QED setup because of its close analogy to cavity QED where single photons can be store for long times in a high quality cavity. In this work, we study the consequences of letting qubits interact via electromagnetic waves free to travel in a open onedimentional transmission line. We show how interaction between the qubits mediated by this open environment can be revealed in the reflection and transmission experiments. These theoretical predictions are compared to experimental results from the ETH Zurich group.
MarcAntoine Lemonde
Student, McGill University
Director: Aashish Clerk
Nonlinear interactions effects in a strongly driven optomechanical cavity
Anja Metelmann
Postdoc, McGill University
Director : Aashish Clerk
Quantumlimited amplification via reservoir engineering
We describe a new kind of phasepreserving quantum amplifier which utilizes dissipative interactions in a parametricallycoupled threemode bosonic system.
The use of dissipative interactions provides a fundamental advantage over standard cavitybased parametric amplifiers: large photon number gains are possible
with quantumlimited added noise, with no limitation on the gainbandwidth product.
We show that the scheme is simple enough to be implemented both in optomechanical systems and in superconducting microwave circuits.
Pericles Philippopoulos
Student, McGill University
Director : Bill Coish
Hyperfine Interactions for Hole Spins in Quantum Dots
Due to the anisotropic nature of the hyperfine coupling for hole spins in semiconductor quantum dots, these systems may show significantly longer coherence times than electron spins given the correct quantumdot geometry and magnetic field orientation. This advantage of hole spins relies on the hyperfine tensor takingon an Isinglike form. This Isinglike form of the hyperfine coupling has been recently called into question with experiments [1] that have been interpreted to indicate a strong hybridization of plike and dlike components in the valence band of IIIV semiconductors. However, this interpretation relies on two assumptions: (1) That spinorbit coupling is weak in these systems compared to the anisotropic crystal field, and (2) that higherangularmomentum (flike, glike, ...) contributions are negligible. Assumption (1) may break down in light of the fact that the spinorbit energy is even larger than the principle gap in InAs, and assumption (2) is difficult to justify in any crystal that breaks pure rotational symmetry. Using a generalization of the grouptheoretic analysis in [1], we show here that relaxing either of these assumptions can restore the Isinglike nature of the hyperfine tensor, albeit for a particular choice of coupling constants. Future work will address the issue of a generic limit in which the Isinglike hyperfine coupling could be robust for hole spins.
[1] E. A. Chekhovich et al. Elementsensitive measurement of the hole nuclear spin interaction in quantum dots. Nature Physics, 9, 7478, 2012
Edouard Pinsolle
Postdoc, Université de Sherbrooke
Director : Bertrand Reulet
Investigate interactions using noise in metallic diffusive wires
Every electronic component exhibits current fluctuations at its terminals called current noise. Those fluctuations are a manifestation of the electrons behaviour at a microscopic range. In the canonical example of a tunnel junction the current noise come partly from the discreetness of the electric charge and is found to be Poissonian due to the independence of the electrons. We present a study of metallic wires in which electrons are no more independent. In this case the electronelectron interaction or electronphonon interaction modifies the current fluctuations and are then accessible by measuring the current noise at the sample terminals. In particular one can easily access the electronphonon interaction by the measurement of noise fluctuation in presence of AC bias which is of great interest in more complicated materials such as High Tc Superconductors.
Farzad Qassemi
Postdoc, Université de Sherbrooke
Director : Alexandre Blais
Nonclassical microwave radiation generated by electron transport in a tunnel junction
Electrons coupled to a bath of photons in a tunnel junction form an interesting platform for manybody quantum phenomena. Recently, squeezing of radiated electromagnetic field due to electron shot noise has been observed [G. Gasse et al PRL 111, 136601 (2013)]. To investigate the relation between photonic and electronic correlation functions, we develop an inputoutput theory for electronphoton system in a tunnel junction. We show the effect of electronic transport on the equation of motion for the photon fields giving rise to nonclassical effects. In particular, we demonstrate that by modulating the bias voltage across the tunnel junction we can squeeze the radiated light.
Christoph Reinhardt
Student, McGill University
Director : Jack Sankey
Laser Controlled Micromechanical Systems
We report on the progress toward a cavity optomechanical setup in which a partiallyreflective, flexible membrane is positioned near the center of an optical cavity in an ultrahigh vacuum (UHV) environment. The presentation will cover the design and building process of the UHV setup as well as the fabrication of lightweight, highquality silicon nitride "trampoline" resonators (~100 nm thickness) which will serve as the mechanical element. The ultimate goal of the apparatus is to optically trap the mechanical element in a regime where optical forces begin to dominate over material stresses. In this regime both the mechanical frequency and mechanical ringdown time should increase as a function of trap strength, hopefully approaching the highquality limits of an opticallylevitated object. The reduction in force noise associated with this transition should in principle enable subzeptonewton force detection, potentially enabling nanoscale magnetic resonance imaging (NMRI) at the single nucleus limit (<10 nm these days) or the sensing of quantum superposition forces from a variety of qubit technologies.
David RoyGuay
Student, Université de Sherbrooke
Director : Michel PioroLadrière
NitrogenVacancy centers for magnetic field mapping of micromagnets
Jean Olivier Simoneau
Student, Université de Sherbrooke
Director : Bertrand Reulet
Shot Noise Measurements Using a Josephson Parametric Amplifier
We present a novel use of the Josephson Parametric Amplifier (ParAmp) for electric noise measurements. The ParAmp is based on a standard LC oscillator with its Inductor replaced by a Superconducting Quantum Interference Device (SQUID), making it nonlinear. It is theoretically a quantum limited component that is widely used in qubit measurements. We hereby present the device and its usefulness for shot noise measurements as well as preliminary results.
JeanRené Souquet
Postdoct, McGill University
Director : Aashish Clerk
PhotonAssisted Tunneling with nonclassical light
Motivated by recent experiments where superconducting microwave circuits have been coupled to electrons in semiconductor nanostructures, we consider theoretically the general problem of a mesoscopic conductor (such as a quantum point contact) driven by quantum states of a microwave field in a cavity. We show that even in the simplest case of a coherent state, there are significant corrections to the dc current over the completely classical treatment used in standard photonassisted tunnelling theory. The case of a squeezed microwave field leads to even more striking deviations. Our calculations incorporate both the use of quantumoptics phasespace methods, and also a general Keldysh formalism that allows a more complete description.
Philippe StJean
Student : École Polytechnique
Director : Sébastien Francoeur
Modeling the recombination dynamics of excitons bound to isoelectronic centers in GaAs
Karl Thibault
Student, Université de SherbrookeDirector : Bertrand Reulet
Currentcurrent correlations in time domain for a tunnel junction in the quantum regime
This poster presents measurements of the current fluctuations emitted by a tunnel junction with a very wide bandwidth, from 0.5 to 12 GHz, down to very low temperature T=35mK. This measurement allowed us to perform the spectroscopy (i.e., measure the frequency dependence) of thermal noise (no dc bias, variable temperature), shot noise (low temperature, variable dc voltage bias) and photonassisted noise (ac bias). Thanks to the very wide bandwidth of our measurement, we can deduce the currentcurrent correlator in time domain. We observe the thermal decay of this correlator as well as its oscillations with a period h/eV, a direct consequence of the effect of the Pauli principle in quantum transport.