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Quantum rifling and some quantum goodies from hybrid structures

Mardi 26 mars 2019 13:30 - Duree : 1 heure
Lieu : Salle « Remy Lemaire » (K223) de l’Institut Néel – au n°25 de la rue des martyrs, Grenoble.

Orateur : Daniel SZOMBATI (University of Queensland)

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Resumé/Abstract :

Quantum mechanics postulates that a measurement forces the wave-function of a qubit to collapse to one of its two eigenstates. The result of the measurement can then be recorded as a discrete outcome designating the particular eigenstate the qubit collapsed to. I will show that this well-accustomed picture of quantum measurement breaks down when the qubit is strongly driven during measurement. More specifically, when the evolution speed exceeds a threshold defined by the characteristic measurement time, the measurement outcome does not contain any information about the initial state of the qubit and thus the measurement does not generate any back-action. We call this phenomenon quantum rifling, as the fast spinning of the Bloch vector protects it from being deflected into either of its two eigenstates. We study this phenomenon with two superconducting qubits coupled to one to the same detector and demonstrate that the quantum rifling allows us to measure either one of the qubi ts on demand while protecting the state of another one from the measurement back-action. If time permits it, I will also cover the results of my PhD from TU Delft, where I have been studying the Josephson effect in semiconducting InSb nanowires. These nanowires bare exotic electronic properties, such as large g-factor and spin-orbit interaction, leading to peculiar behaviour of the Josephson supercurrent. Specifically, the switching current exhibits non-monotonic behaviour with increasing magnetic field, due to the orbital interference of many modes in the wire[1]. For certain magnetic field values, we observe supercurrent flowing at zero phase difference, otherwise known as a Josephson-phi0 junction[2]. Such phi0-junctions can serve as smoking gun signatures of Majorana fermions.

[1] Zuo, K., Mourik, V., Szombati, D.B., Nijholt, B., Van Woerkom, D.J., Geresdi, A., Chen, J., Ostroukh, V.P., Akhmerov, A.R., Plissard, S.R. and Car, D., 2017. Supercurrent interference in few-mode nanowire Josephson junctions. Physical review letters, 119(18), p.187704.

[2] Szombati, D.B., Nadj-Perge, S., Car, D., Plissard, S.R., Bakkers, E.P.A.M. and Kouwenhoven, L.P., 2016. Josephson phi0-junction in nanowire quantum dots. Nature Physics, 12(6), p.568.

Contact : equipe-seminaires-nano@fondation-nanosciences.fr

Discipline évènement : (Physique)
Entité organisatrice : (Fondation Nanosciences)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire Nanoélectronique Quantique)
Site de l'évènement : Polygone scientifique

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