Seminars

The seminar with Sara DUCCI is postponed to a later date.

Generation and manipulation of quantum states of light with AlGaAs chips

The development of miniaturized devices for the generation and manipulation of entangled states of light is one of the key issues on the way towards a broad diffusion of quantum information technologies. Different platforms are currently under study and, among them, semiconductors present a strong case for integrability; in this context, AlGaAs is particularly attractive to monolithically integrate active and passive components thanks to its compliance with electrical injection and to manipulate quantum photonic states via its large electro-optic effect. In this seminar, I will review our main results on the generation of quantum states of light with AlGaAs devices operating at room temperature and telecom wavelength and I will present our recent work on the generation and manipulation of high dimensional quantum frequency states of light opening promising perspectives for quantum simulations and computing.

Sara Ducci is professor at Université de Paris and member of the Laboratory « Matériaux et Phénomènes Quantiques ». She received her PhD in Physics at the University of Florence (Italy) in 2000, with a work on pattern formation in nonlinear optical systems. After a postdoctoral position at Laboratoire Kastler Brossel and a position as temporary assistant professor at Ecole Normale Supérieure de Cachan, she joined the University Paris Diderot in 2002. Her research focuses on the development of semiconductor sources of quantum states of light operating at room temperature and telecom wavelengths; the work ranges from device development to fundamental quantum optics and applications in quantum information. She has been awarded the Louis Ancel Prize of the French Physical Society in 2016 and she is honorary member of the Institut Universitaire de France.

External visitors should be register beforehand via e-mail at com@c2n.upsaclay.fr

Seminars

The Colloquium with Claudia Felser is postponed to a later date.

Seminars

Abstract: Would you appreciate a tool capable of providing stoichiometry of freshly deposited thin films in just a few minutes?
In a context of growing competition, reducing the cycle time for materials is becoming crucial and requires rapid feedback for process optimization. For such fast feedback purposes, a plasma profiling time-of-flight mass spectrometry (PP-TOFMS) instrument (HORIBA Scientific, France) is now commercially available.
PP-TOFMS is a sputtering-based elemental depth profiling technique combining a pulsed radio-frequency argon plasma source (generating a glow discharge) for sample sputtering and ionization with an orthogonal time-of-flight mass spectrometer. PP-TOFMS produces, in a few minutes, nm-scale depth resolved profiles of all elements (including light ones) of the periodic table, over a wide dynamic range (from 100% down to ppm). A simple ratio of the number of ions detected from a given layer provides a calibration free semi-quantification.
Various data obtained with an instrument installed in the clean room of the CEA-LETI will be presented. We will illustrate how useful PP-TOFMS analysis turned out to be for materials designed for applications like power electronics (III-nitrides), phase change memories (GeSbTe) or magnetic sensors (FeCoB).
A comparison with ToF-SIMS will demonstrate the performance of PP-TOFMS in determining composition, detecting contamination, and measuring doping level.

Bio: Agnès Tempez is PP-TOFMS product manager since 2011 and an application scientist in the Nanoscopy AFM Raman team at HORIBA, France. She holds a Ph.D. in Analytical Chemistry from the University of Houston, Texas. She worked as a research scientist at Ionwerks Inc. (Houston) to develop time of flight mass spectrometry instrumentation for materials characterization and MALDI/ion mobility coupling for complex biological samples.

External visitors should be register beforehand via e-mail at com@c2n.upsaclay.fr

Seminars

Spin current generation and magnetization reversal are core technologies to realize not only for a non-volatile memory but also for neuromorphic and probabilistic bit computing [1-3]. Spin-orbit interaction (SOI) becomes a key to efficiently generate spin current by spin Hall effect and an interface effect [4,5], and intensive studies have been conducted in various heavy metals (Pt, W and Ta). However, most studies are based on polycrystal or amorphous structures. High quality heterointerface would be necessary for precise control of spin-orbit-related phenomenon in a metal system.

We focus on epitaxial films for efficient control of spin current and magnetization [6-10]. We also focus on a heterointerface on polycrystal heavy metals as well as oxidation and nitridation of light metal Cu to realize large Rashba SOI [11-15]. We epitaxially grow Pt and a-Ta by employing sputtering method on MgO and Al₂O₃ substrates as shown in Fig. 1 for a-Ta case. We first reveal the spin relaxation mechanism by measuring magnetoconductance at cryogenic temperature. Induced weak antilocalization reveals that D’yakonov-Perel’ spin relaxation mechanism due to Rashba/ Dresselhaus SOIs is dominated in epitaxial Pt and Ta films [6-8]. This becomes contrast to polycrystal film where the impurity scattering governs the spin relaxation. We then investigated the spin-orbit torque and magnetization reversal with ferromagnetic layers [9,10,14,15]. Spin torque efficiency in a-Ta / CoFeB is enhanced from that of amorphous Ta (Fig. 2). Both epitaxial Pt and a-Ta enable the zero-field magnetization switching. I will also discuss about the spin current generation in W/Pt interface and Cu nitride structures for efficient spin orbit torque.

Prof. Makoto Kohda received his Master’s degree in engineering in 2002 and Ph.D degree in engineering in 2005 from Tohoku University, Sendai, Japan. After his PhD degree, he was an assistant professor (2005- 2010) and is an associate professor from 2010 at Department of Materials Science in Tohoku University. His current research interests are spin orbit interaction in semiconductor heterostructure and epitaxial metal films for efficient spin generation/manipulation and towards spin-orbitronics.

External visitors should be register beforehand via e-mail at com@c2n.upsaclay.fr

Seminars

One promising approach for beyond CMOS is the so-called MESO transistor proposed by Intel (for MagnetoElectric-Spin-Orbit), a spin-based non-volatile device in which magnetic information is written by a magnetoelectric element and read out by a spin-orbit element through the inverse spin Hall effect (ISHE) or the inverse Edelstein effect (IEE). The IEE occurs in systems with broken inversion symmetry such as two-dimensional electron gases (2DEG) displaying Rashba spin-orbit coupling and results in more efficient conversion than the ISHE.

In this talk, I will show that the 2DEG that forms at the interface of SrTiO3 (STO) with LaAlO3 or reactive metals such as Al may be exploited to interconvert spin and charge currents with very high efficiencies. By applying a gate voltage, we tune the position of the Fermi level in the complex multi-orbital structure of STO, which results in a strong variation of the conversion amplitude with sign changes. This can be related to the band structure through ARPES experiment and tight-binding calculations. Importantly, a finite spin to charge conversion effect persists at room temperature. In a second part, I will present gate-controlled, all-electrical spin current generation and detection in planar nanodevices free from ferromagnets and only based on a STO 2DEG.

Finally, I will propose a new approach to achieve a non-volatile control of spin-charge interconversion with Rashba 2DEGs based on ferroelectricity rather than ferromagnetism, that may pave the way to an entirely new family of ultralow power spintronics devices.

 Manuel Bibes is a CNRS Research Director at the CNRS/Thales laboratory in Palaiseau, France. After a double PhD degree in France and Spain with a thesis on manganite interfaces (ICMAB Barcelona, 2001) he became a CNRS Researcher in 2003. Bibes has pioneered research lines on multiferroics, ferroelectric tunnel junctions and explored novel routes for the electrical control of magnetism and spin transport in oxide architectures. Bibes is the recipient of the 2013 EU40 Materials Prize of the E-MRS, the 2017 Descartes-Huygens prize, the 2017 Friedrich-Wilhelm Bessel award of the Humboldt Foundation and the laureate of two ERC grants.

Figure caption : Conversion of a spin current injected in the 2DEG at the LaAlO₃/SrTiO₃ interface into a charge current.

External visitors should be register beforehand via e-mail at com@c2n.upsaclay.fr

Seminars

In this presentation, I will give a general introduction to the field of quantum computing.

Quantum computing emerges from the idea that one could exploit the most subtle concepts of quantum mechanics, such as quantum superposition and entanglement, to provide an extraordinary speed-up of computational power.

Recently, these concepts have started to emerge in the laboratories, with the first quantum computing machines being developed using various platforms: superconducting quantum bits, trapped ions, photons, Rydberg atoms, etc.

I will explain the basic working principles of a quantum computer, its figures of merits, and the main scientific and technological challenges that the various approaches are facing to develop a scalable technology.

Pascale Senellart is a senior CNRS researcher at Center for Nanoscience and Nanotechnology. Her team develops building blocks for the optical quantum computer based on semiconductor devices. She is co-founder of the start-up company Quandela. Within University Paris Saclay, she is in charge of coordinating Quantum  Sciences and Technologies.

External visitors should be register beforehand

Seminars

On this a broad topic, I have picked three sets of questions to which I will bring some elements of answer:
How does a wind turbine work? Why do they look the way they do? Can they really extract energy although the blades occupy so little space? Why are they white? Many elements of answer to these questions may be obtained based on simple considerations from aerodynamics. A brief review of their history will be given, emphasizing the timescales of the research and development involved, and the factors that led to the success of the 'Danish concept'.
How much can we forecast wind? It often rains when I plan a picnic: have weather forecasts ever improved? On what timescale is it possible to make forecasts - can anything be said beyond a week? This will be an opportunity to discuss some of the research activities at the Laboratoire de Météorologie Dynamique. One aim is to explore methods providing information (necessarily probabilistic) for renewable energies on timescales from 2 weeks to a season.
Is it worth developing wind energy? What are the motivations? Can it provide a non-negligible part of our electricity supply? Is it really urgent? Some key numbers regarding climate change, green house gas emissions and renewable energies will be recalled, drawing on reports from the IPCC and from the IEA (Intergovernmental Panel on Climate Change, and International Energy Agency, respectively). This last part may be followed by a small debate if time allows.

Riwal Plougonven is Professor at Ecole Polytechnique since 2012, in the Mechanics Department. Since 2016 he is deputy director of the Laboratoire de Météorologie Dynamique. His research has evolved into two main domains: the study of dynamical processes in the upper-troposphere and lower-stratosphere using balloon observations, and the forecasting of the atmospheric state for the energy applications.

External visitors should be register beforehand