Publications (70)236.52 Total impact
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ABSTRACT: Silicon chips hosting a single donor can be used to store and manipulate one bit of quantum information. However, a central challenge for realizing quantum logic operations is to couple donors to one another in a controllable way. To achieve this, several proposals rely on using nearby quantum dots (QDs) to mediate an interaction. In this work, we demonstrate the coherent coupling of electron spins between a single 31P donor and an enriched 28Si metaloxidesemiconductor fewelectron QD. We show that the electronnuclear spin interaction on the donor can drive coherent rotations between singlet and triplet electron spin states of the QDdonor system. Moreover, we are able to tune electrically the exchange interaction between the QD and donor electrons. The combination of singlenucleusdriven rotations and voltagetunable exchange provides every key element for future allelectrical control of spin qubits, while requiring only a single QD and no additional magnetic field gradients.  [Show abstract] [Hide abstract]
ABSTRACT: Micromagnets are key components for quantum information processing with individual spins, enabling arbitrary rotations and addressability. In this work, characterization of submicrometer sized CoFe ferromagnets is performed with Hall bars electrostatically defined in a twodimensional electron gas. Due to the ballistic nature of electron transport in the cross junction of the Hall bar, anomalies such as the quenched Hall effect appear near zero external magnetic field, thus hindering the sensitivity of the magnetometer to small magnetic fields. However, it is shown that the sensitivity of the diffusive limit can be almost completely restored at low temperatures using a large current density in the Hall bar of about 10 A/m. Overcoming the size limitation of conventional etched Hall bars with electrostatic gating enables the measurement of magnetization curves of 440 nm wide micromagnets with a signaltonoise ratio above 10^3. Furthermore, the inhomogeneity of the stray magnetic field created by the micromagnets is directly measured using the gatevoltagedependent width of the sensitive area of the Hall bar. 
Article: Robust micromagnet design for fast electrical manipulations of single spins in quantum dots
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ABSTRACT: Tailoring spin coupling to electric fields is central to spintronics and spinbased quantum information processing. We present an optimal micromagnet design that produces appropriate stray magnetic fields to mediate fast electrical spin manipulations in nanodevices. We quantify the practical requirements for spatial field inhomogeneity and tolerance for misalignment with spins, and propose a design scheme to improve the spinrotation frequency (to exceed 50MHz in GaAs nanostructures). We then validate our design by experiments in separate devices. Our results will open a route to rapidly control solidstate electron spins with limited lifetimes and to study coherent spin dynamics in solids. 
Conference Paper: Hall magnetometry of micromagnets for singleelectron spin qubits
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ABSTRACT: The coherence time of a singleelectron spin can reach tens of milliseconds when placed in the right environment [1]. The electricdipole interaction between such a single spin and an electric field can be engineered by the inhomogeneous magnetic field of a micromagnet [2]. This effective spinorbit interaction can be used to manipulate the spin through electricdipole spin resonance [2], but also to couple a single spin to the electric field of a microwave cavity in the circuit QED architecture [3]. We selected the material and improved the shape of the micromagnet in order to maximize magnetic field gradients and remanence. We perform Hall magnetometry of those improved micromagnets using Hall bars electrostatically defined in an AlGaAs/GaAs twodimensional electron gas. The gatevoltage dependent width of the Hall bar enables us to map the averaged magnetic field of the micromagnet, which validates simulations of the inhomogeneous magnetic field profile created by the magnet. We can therefore deduce that our micromagnets can produce magnetic field differences over 200 nm of more than 200 mT.\\[4pt] [1] M. Veldhorst et al., Nat. Nano. 1 (2014).\\[0pt] [2] M. PioroLadri\`{e}re et al., Nat. Phys. 4, 2 (2008).\\[0pt] [3] X. Hu, Y. Liu, and F. Nori, Phys. Rev. B 86, 1 (2012).  [Show abstract] [Hide abstract]
ABSTRACT: We demonstrate fast universal electrical spin manipulation with inhomogeneous magnetic fields. With fast Rabi frequency up to 127 MHz, we leave the conventional regime of strong nuclearspin influence and observe a spinflip fidelity > 96%, a distinct chevron Rabi pattern in the spectraltime domain, and spin resonance linewidth limited by the Rabi frequency, not by the dephasing rate. In addition, we establish fast zrotations up to 54 MHz by directly controlling the spin phase. Our findings will significantly facilitate tomography and error correction with electron spins in quantum dots.  [Show abstract] [Hide abstract]
ABSTRACT: In this work, we demonstrate a silicon nanocrystal Field Effect Transistor (ncFET). Its operation is similar to that of a Tunnelling Field Effect Transistor (TFET) with two barriers in series. The tunnelling barriers are fabricated in very thin silicon dioxide and the channel in intrinsic polycrystalline silicon. The absence of doping eliminates the problem of achieving sharp doping profiles at the junctions, which has proven a challenge for largescale integration and, in principle, allows scaling down the atomic level. The demonstrated ncFET features a 104 on/off current ratio at room temperature, a low 30 pA/μm leakage current at a 0.5 V bias, an onstate current on a par with typical allSi TFETs and bipolar operation with high symmetry. Quantum dot transport spectroscopy is used to assess the band structure and energy levels of the silicon island. 
Dataset: PhysRevLett 2014
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ABSTRACT: Tunneling in a quantum coherent structure is not restricted to only nearest neighbors. Hopping between distant sites is possible via the virtual occupation of otherwise avoided intermediate states. Here we report the observation of longrange transitions in the transport through three quantum dots coupled in series. A single electron is delocalized between the left and right quantum dots, while the center one remains always empty. Superpositions are formed, and both charge and spin are exchanged between the outermost dots. The delocalized electron acts as a quantum bus transferring the spin state from one end to the other. Spin selection is enabled by spin correlations. The process is detected via the observation of narrow resonances which are insensitive to Pauli spin blockade. 
Dataset: PhysRevLett 2014

Dataset: PhysRevLett 2014 reduced

Dataset: Supplementary informations
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ABSTRACT: We report measurements of electrical transport through single CdSe/CdS core/shell colloidal quantum dots connected to source and drain contacts. We observe telegraphic switching noise showing few plateaus at room temperature. We model and interpret these results as charge trapping of individual trap states and therefore we resolve individual charge defects in these highquality lowstrain colloidal quantum dots. The few number of observed defects quantitatively validate the passivation method based on thick CdS shells nearly latticematched to CdSe cores first developped to suppress photoluminescence blinking. Finally, we introduce a figure of merit useful to efficiently distinguish telegraphic noise from noise with a Gaussian distribution.  [Show abstract] [Hide abstract]
ABSTRACT: Tunneling in a quantum coherent structure is not restricted to only nearest neighbours. Hopping between distant sites is possible via the virtual occupation of otherwise avoided intermediate states. Here we report the observation of long range transitions in the transport through three quantum dots coupled in series. A single electron is delocalized between the left and right quantum dots while the centre one remains always empty. Superpositions are formed and both charge and spin are exchanged between the outermost dots. Detection of the process is achieved via the observation of narrow resonances, insensitive to the transport Pauli spin blockade.  [Show abstract] [Hide abstract]
ABSTRACT: A quantum computer is a computer composed of quantum bits (qubits) that takes advantage of quantum effects, such as superposition of states and entanglement, to solve certain problems exponentially faster than with the best known algorithms on a classical computer. Gatedefined lateral quantum dots on GaAs/AlGaAs are one of many avenues explored for the implementation of a qubit. When properly fabricated, such a device is able to trap a small number of electrons in a certain region of space. The spin states of these electrons can then be used to implement the logical 0 and 1 of the quantum bit. Given the nanometer scale of these quantum dots, cleanroom facilities offering specialized equipment such as scanning electron microscopes and ebeam evaporators are required for their fabrication. Great care must be taken throughout the fabrication process to maintain cleanliness of the sample surface and to avoid damaging the fragile gates of the structure. This paper presents the detailed fabrication protocol of gatedefined lateral quantum dots from the wafer to a working device. Characterization methods and representative results are also briefly discussed. Although this paper concentrates on double quantum dots, the fabrication process remains the same for single or triple dots or even arrays of quantum dots. Moreover, the protocol can be adapted to fabricate lateral quantum dots on other substrates, such as Si/SiGe.  [Show abstract] [Hide abstract]
ABSTRACT: Spin qubits involving one or two spins have emerged as potential building blocks for quantum information processing applications, resulting in many double quantum dot (DQD) studies. Coherent control of a twoelectron spin qubit close to the singlet/triplet (S/T+) anticrossing through LandauZenerSt\"uckelberg (LZS) oscillations has been studied theoretically and demonstrated experimentally in DQDs. Recent advances with triple quantum dot (TQD) technology have suggested additional advantages, such as their potential for encoding quantum information, that may soon be possible. Towards these goals we demonstrate, for for first time, the coherent manipulation of threeparticle spin states in a TQD where all three spins play a role. 
Dataset: StudenikinnphysLZS sup
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ABSTRACT: Inductively Coupled Plasma (ICP) etching of amorphous silicon (aSi) nanostructures using a continuous C4F8/SF6 plasma over nanotopography in silicon dioxide (SiO2) is investigated. The coil power of the ICP system is used to tune the aSi etch rate from 20 to 125 nm/min. The etch rates of aSi, SiO2 and electroresist are measured depending on the SF6 ratio, platen power and chamber pressure and used to optimize the aSi:SiO2 etch selectivity. The results on nanostructures show that the presence of an insulating etchstop layer affects the passivation ratio required to achieve vertical sidewalls. A low pressure is also necessary in order to etch the silicon nanostructure embedded into the oxide nanotrenches to form a highly conformable aSi nanowire. We argue that both of these behaviors could be explained by surface charging effects. Finally, etching of 20 nm aSi nanowires that cross 15 nm trenches in oxide with vertical sidewalls and a 4.3:1 aSi:SiO2 etch selectivity is demonstrated. This etching process can be used in applications where nanotopography is present such as single electron transistors or multigate transistors.  [Show abstract] [Hide abstract]
ABSTRACT: Spin qubits based on interacting spins in double quantum dots have been demonstrated successfully. Readout of the qubit state involves a conversion of spin to charge information, which is universally achieved by taking advantage of a spin blockade phenomenon resulting from Pauli's exclusion principle. The archetypal spin blockade transport signature in double quantum dots takes the form of a rectified current. At present, more complex spin qubit circuits including triple quantum dots are being developed. Here we show, both experimentally and theoretically, that in a linear triple quantum dot circuit the spin blockade becomes bipolar with current strongly suppressed in both bias directions and also that a new quantum coherent mechanism becomes relevant. In this mechanism, charge is transferred nonintuitively via coherent states from one end of the linear triple dot circuit to the other, without involving the centre site. Our results have implications for future complex nanospintronic circuits.  [Show abstract] [Hide abstract]
ABSTRACT: We report on the Overhauser shift (OHS) of electric dipole spin resonance peaks in the reverse direction to that previously reported. Measuring electric dipole spin resonance in a double quantum dot, we observe two resonance peaks reflecting a Zeeman energy difference between the two quantum dots, and find that the dependence of the peak position on microwave power is different for each dot. The perturbation theory for hybridizing the flipflop and photonassisted tunneling mechanisms is discussed and is found to successfully explain the power dependence. This theory can also consistently explain the OHS in both directions, explaining the experimental results previously reported. Our results reveal the bidirectionality of OHSs and this is expected to play an important part in the development of effective nuclear spin squeezing techniques.  [Show abstract] [Hide abstract]
ABSTRACT: Nitrogenvacancy (NV) centers in diamond are a promising candidate as a solid state qubit memory for quantum information as they possess very long coherence times even at room temperature. Furthermore, NV centers are very sensitive to their electromagnetic environment and are addressable in the GHz frequency range. Here we review our progress towards the detection of single NV centers for the implementation of fast on demand coupling between NV centers and GHz electromagnetic fields. Precisely, we present efforts towards mapping NV centers with a cathodoluminescence setup. Developing such capability is important for patterning local onequbit gates for the application of high amplitude electromagnetic fields as a tuning parameter. 
Conference Paper: Pairwise control of exchange interaction between individual spins in a triple quantum dot
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ABSTRACT: The original spin qubit proposal [1] suggested a linear array of spins for quantum computations and the exchange interaction for 2 qubit operations. An essential component of the proposal was the ability to control pairwise the exchange interaction between neighbouring pairs of spins. In this work we experimentally demonstrate such a pairwise control of the exchange interaction between three spins localized in a triple quantum dot (TQD) device. The TQD potential was formed using electrostatic lateral splitgate technology on a GaAs/GaAlAs heterostructure with a highmobility twodimensional electron gas [2]. We employ fast pulsing technique based on the LandauZenerStuckelberg (LZS) approach for creating and manipulating coherent superpositions of three spin quantum states [3]. We show that we are able to maintain coherence when increasing the exchange coupling of one spin with another while simultaneously decreasing its coupling with the third.[4pt] [1] D. Loss, and D.P. DiVincenzo, Phys. Rev. A57, 120126 (1998).[0pt] [2] L. Gaudreau , et al., Appl. Phys. Lett. v.95, 193101 (2009). [0pt] [3] J.R. Petta, H. Lu, and A.C. Gossard, Science v.327, 669672 (2010).
Publication Stats
1k  Citations  
236.52  Total Impact Points  
Top Journals
Institutions

20032014

Université de Sherbrooke
 Department of Physics
Шербрук, Quebec, Canada


20072011

Japan Science and Technology Agency (JST)
Edo, Tōkyō, Japan


20012006

National Research Council Canada
 Institute for Microstructural Sciences (IMS)
Ottawa, Ontario, Canada
