Generation of a single-cycle acoustic pulse: a scalable solution for transport in single-electron circuits

The synthesis of single-cycle, compressed optical and microwave pulses sparked novel areas of fundamental research. In the field of acoustics, however, such a generation has not been introduced yet. For numerous applications, the large spatial extent of surface acoustic waves (SAW) causes unwanted perturbations and limits the accuracy of physical manipulations. Particularly, this restriction applies to SAW-driven quantum experiments with single flying electrons, where extra modulation renders the exact position of the transported electron ambiguous and leads to undesired spin mixing. Here, we address this challenge by demonstrating single-shot chirp synthesis of a strongly compressed acoustic pulse. Employing this solitary SAW pulse to transport a single electron between distant quantum dots with an efficiency exceeding 99%, we show that chirp synthesis is competitive with regular transduction approaches. Performing a time-resolved investigation of the SAW-driven sending process, we outline the potential of the chirped SAW pulse to synchronize single-electron transport from many quantum-dot sources. By superimposing multiple pulses, we further point out the capability of chirp synthesis to generate arbitrary acoustic waveforms tailorable to a variety of (opto)nanomechanical applications. Our results shift the paradigm of compressed pulses to the field of acoustic phonons and pave the way for a SAW-driven platform of single-electron transport that is precise, synchronized, and scalable.Comment: To be published in Physical Review

Superconducting routing platform for large-scale integration of quantum technologies

To reach large-scale quantum computing, three-dimensional integration of scalable qubit arrays and their control electronics in multi-chip assemblies is promising. Within these assemblies, the use of superconducting interconnections, as routing layers, offers interesting perspective in terms of (1) thermal management to protect the qubits from control electronics self-heating, (2) passive device performance with significant increase of quality factors and (3) density rise of low and high frequency signals thanks to minimal dispersion. We report on the fabrication, using 200 mm silicon wafer technologies, of a multi-layer routing platform designed for the hybridization of spin qubit and control electronics chips. A routing level couples the qubits and the control circuits through one layer of Al0.995Cu0.005 and superconducting layers of TiN, Nb or NbN, connected between them by W-based vias. Wafer-level parametric tests at 300 K validate the yield of these technologies and low temperature electrical measurements in cryostat are used to extract the superconducting properties of the routing layers. Preliminary low temperature radio-frequency characterizations of superconducting passive elements, embedded in these routing levels, are presented

Transport cohérent à longue distance de spin électroniques intriqués

Quantum computing is a field of growing interest, especially in Grenoble with an exceptional concentration of both research and industrials groups implicated in this field. The global aim is to develop a new kind of nano-processors, based on quantum properties. Its building brick is a two-level quantum system, in our case the spin of electrons trapped in a quantum dot.In this quest for a large-scale architecture, networked quantum computers offer a natural path towards scalability. Indeed, separating the computational task among quantum core units interconnected via a coherent quantum mediator would greatly simplify the addressability challenges. These quantum links should be able to coherently couple arbitrary nodes on fast timescales, in order to share entanglement across the whole quantum circuit. In semiconductor quantum circuits, nearest neighbor entanglement has already been demonstrated, and several schemes exist to realize long-range coupling. Among them, a possible implementation of this quantum mediator would be to prepare an entangled state and shuttle individual electron spins across the structure, provided that this transport preserves the entanglement.In this work, we demonstrate the fast and coherent transport of electron spin qubits across a 6.5 μm long channel, in a GaAs/AlGaAs laterally defined nanostructure. Using the moving potential induced by a propagating surface acoustic wave, we send sequentially two electron spins initially prepared in a spin singlet state. During its displacement, each spin experiences a coherent rotation due to spin-orbit interaction, over timescales shorter than any decoherence process. By varying the electron separation time and the external magnetic field, we observe quantum interferences which prove the coherent nature of both the initial spin state and the transfer procedure.We show that this experiment is analogous to a Bell measurement, allowing us to quantify the entanglement between the two electron spins when they are separated, and proving this fast and long-range qubit displacement is an efficient procedure to share entanglement across future large-scale structures.L’informatique quantique est un domaine d’intérêt croissant, notamment à Grenoble avec une concentration exceptionnelle de chercheurs et groupes industriels impliqués dans ce domaine. L’objectif global est de développer un nouveau type de nano-processeur, basé sur des propriétés quantiques. Son bloc élémentaire est un système quantique à deux niveaux (le qubit), dans notre cas le spin d'électrons piégés dans une boîte quantique.Dans la quête d’une architecture à large échelle, un ordinateur quantique en réseau offre un chemin naturel vers l’évolutivité. En effet, séparer le calcul dans des cœurs quantiques interconnectés par des médiateurs quantiques cohérents simplifierai grandement les contraintes d’adressabilité. Ces liens quantiques devraient offrir une connexion rapide et cohérente entre des cœurs arbitraires, permettant de créer un état intriqué utilisant tout le circuit quantique. Dans les circuits quantiques à base de semiconducteurs, l’intrication entre plus proches voisins a déjà été démontrée, et plusieurs méthodes ont été proposées pour réaliser un couplage à distance. Parmi elles, une implémentation possible de ce médiateur quantique consiste à préparer un état intriqué et transférer individuellement des spins électroniques à travers la structure, à condition que ce transfert préserve l’intrication.Dans cette thèse, nous démontrons le transfert rapide et cohérent de qubits de spin électronique à travers un long canal de 6.5 μm, dans une hétérostructure GaAs/AlGaAs. En utilisant le potentiel se propageant avec par une onde acoustique de surface, nous transférons séquentiellement deux spins électroniques formant initialement un état singulet. Durant le déplacement, chaque spin subit une rotation cohérente due à l’interaction spin-orbite, sur une durée plus courte que tout processus de décohérence. En variant le temps de séparation des électrons et le champ magnétique appliqué, nous observons des interférences quantiques qui prouvent la nature cohérente de l’état initial et de la procédure de transfert.Nous montrons que cette expérience est analogue à une mesure de Bell, et nous permet de quantifier l’intrication entre les deux spins électroniques lorsqu’ils sont séparés, démontrant que ce déplacement rapide et à longue portée est une procédure efficace pour propager une intrication quantique au sein des futures structures à large échelle

Violences conjugales, analyse du lien violent à l’épreuve du confinement

International audienceAim: The aim of this article is to present the preliminary results of a multidisciplinary research project, which focuses on the potential effects of lock-down on intra-family and domestic violence. More specifically, it is a question of considering the effects of confinement on the precipitation of the violent marital bond, in order to consider the difficulties and levers identified by the perpetrators as well as the victims to get out of the violent circularity.Method: Questionnaires were widely distributed on social networks. Some are intended for perpetrators, others for victims. All question the evolution of the marital bond in the test of lock-down and the way in which the subject positions himself in the couple relationship. Interview grids have also been developed. Perpetrators and victims of domestic violence were therefore able to be met in the context of semi-structured interviews aimed at evaluating the impact of confinement on the dynamics of the violent bond between the two partners.Results: The first trends indicate a magnifying effect on the effects of influence in the couple, increasing the expression of violence, whether pre-existing to the lock-down, or revealed by them. The hold in the relationship and the attempt to master the other are, it would seem, to be read from the angle of a counterbalancing of the experience of passivity linked to the fact of feeling “locked in”, subject to constraints. imposed spaces. The resources to get out of this violent circle and the process of constraint, do not seem to be able to be mobilized, as if lock-down removed any possibility of seizing the levers likely to stop the violent process.Objectif: L’objectif de cet article est de présenter les résultats préliminaires d’un projet de recherche pluridisciplinaire qui s’intéresse aux effets potentiels du confinement sur les violences intrafamiliales et conjugales. Plus spécifiquement, il s’agit d’envisager les effets de l’enfermement sur la précipitation du lien conjugal violent, afin d’envisager les difficultés et leviers identifiés par les auteur/autrices comme les victimes pour sortir de la circularité violente.Méthode: Des questionnaires ont été diffusés à large échelle sur les réseaux sociaux. Certains sont à destination des auteurs/autrices, d’autres à destination des victimes. Tous questionnent l’évolution du lien conjugal à l’épreuve du confinement et la manière dont le sujet se positionne dans la relation de couple. Des grilles d’entretien ont également été élaborées. Des auteurs et des victimes de violences conjugales ont donc pu être rencontrés dans le cadre d’entretiens semi-directifs visant à évaluer le retentissement de l’enfermement sur la dynamique du lien violent entre les deux partenaires.Résultats: Les premières tendances indiquent un effet de loupe sur les effets d’emprise dans le couple, accroissant l’expression des violences, qu’elles soient préexistantes aux confinements, ou bien révélées par ceux-ci. L’emprise dans la relation et la tentative de maîtrise de l’autre sont, semblerait-il, à lire sous l’angle d’un contre-balancement du vécu de passivité lié au fait de se sentir « enfermé », assujetti à des contraintes spatiales imposées. Les ressources pour sortir de ce cercle violent et du processus de contrainte ne semblent pas pouvoir être mobilisées, comme si l’enfermement supprimait toute possibilité de se saisir des leviers susceptibles d’enrayer le processus violent

Coherent control of individual electron spins in a two-dimensional quantum dot array

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Enhanced Spin Coherence while Displacing Electron in a Two-Dimensional Array of Quantum Dots

International audienceThe ability to shuttle coherently individual electron spins in arrays of quantum dots is a key procedure for the development of scalable quantum information platforms. It allows the use of sparsely populated electron spin arrays, envisioned to efficiently tackle the one-and two-qubit gate challenges. When the electrons are displaced in an array, they are exposed to site-dependent environment interactions such as hyperfine coupling with substrate nuclear spins. Here, we demonstrate that the electron multidirectional displacement in a 3 × 3 array of tunnel-coupled quantum dots enhances the spin-coherence time via the motional narrowing phenomenon. More specifically, up to ten charge configurations are explored by the electrons to study the impact of the displacement on spin dynamics. An increase of the coherence time by a factor up to 10 is observed in the case of fast and repetitive displacement. A simple model quantitatively captures the physical mechanism underlying this enhancement of the spin-coherence time induced by displacement. The implications on spin-coherence properties during the electron displacement are discussed in the context of large-scale quantum circuits

Distant spin entanglement via fast and coherent electron shuttling

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Controlled quantum dot array segmentation via highly tunable interdot tunnel coupling

International audienceRecent demonstrations using electron spins stored in quantum dot array as qubits are promising for developing a scalable quantum computing platform. An ongoing effort is, therefore, aiming at the precise control of the quantum dot parameters in larger and larger arrays which represents a complex challenge. Partitioning of the system with the help of the inter-dot tunnel barriers can lead to a simplification for tuning and offers a protection against unwanted charge displacement. In a triple quantum dot system, we demonstrate a nanosecond control of the inter-dot tunnel rate permitting to reach the two extreme regimes, large GHz tunnel coupling, and sub-Hz isolation between adjacent dots. We use this development to isolate a subpart of the array in a metastable configuration while performing charge displacement and readout in the rest of the system. The degree of control over tunnel coupling achieved in a unit cell should motivate future protocol development for tuning, manipulation, and readout including this capability