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Univ. Paris-Saclay

Sujet de stage / Master 2 Internship

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Fort couplage QED à des conducteurs quantiques

Spécialité : PHYSIQUE / Physique de la matière condensée

Contact : ALTIMIRAS Carles,
e-Mail : carles.altimiras@cea.fr,   Tel : +33 1 69 08 72 35
Laboratoire : SPEC/GNE

Stage pouvant se poursuivre en thèse : Oui
Durée du stage : 0-6 mois
Date limite de constitution de dossier : 30/04/2021

Résumé :
Pendant ce stage nous développerons des circuits de détection microondes de haute impédance et grande bande passante à fin de réaliser des expériences d'électrodynamique quantique avec des conducteurs quantiquement coherents.

Sujet détaillé :
Quantum transport investigates the dynamics of electrical circuits displaying a quantum mechanical behavior. This is achievable by patterning circuits in the nm/um scale in clean room environments, and cooling them at T∼15 mK in dilution fridges. A remarkable aspect of such quantum dynamics is that the electrical current fluctuates, even in response to a strictly DC bias. Detecting these quantum fluctuations is highly informative as it conveys information on the granularity of charge, the statistics of the carriers but also on the characteristic transport times such as the electronic scattering time or on interaction effects.

In the last years, our lab has developed several experimental schemes and technics in order to measure efficiently such quantum fluctuations in the few GHz range. In a qualitative level, measuring at this frequency range fdet∼6 GHz gives access to the quantum optical regime hfdet>>kBT, where one needs to provide a quantum description not only for the electrical current flowing through the conductor, but also for the electromagnetic fields exchanged with its detection scheme. This so-called circuit quantum electrodynamics regime is appealing since the corresponding ligh-matter coupling, proportional to the detection impedance, can be engineered and take non-perturbative values unparalleled in other physical systems. In a quantitative level, using this frequency range increases the experimental window: On the one side, performing faster experiments enables probing shorter transport time scales, or equivalently larger interaction energy scales. On the other side, it naturally provides larger detection bandwidths enabling to perform higher resolution experiments tracking subtle interaction effects.

The purpose of this internship is to design, micro-fabricate and test in a cryogenic environment a new generation of radiofrequency impedance matching circuits, in order to increase notably the bandwidth of the detection window. The goal of this project is to obtain a detection bandwidth larger than the thermal bandwidth at 15 mK thus fdet∼1 GHz, with a detection impedance of the order to the resistance quantum RQ=h/e^2∼25.8 k. Such a device would enable in a future PhD project to detect how the sub-Poissonian properties of Fermions being scattered upon a potential barrier might imprint on the properties of the resulting radiated RF field [1, 2].
[1] Beenaker & Schomerus, Phys.Rev.Lett. 93, 096801 (2004)
[2] Hassler & Otten, Phys. Rev. B 92, 195417 (2015)
Techniques utilisées au cours du stage :
Simulation de circuits microondes, nano et micro fabrication, mesures électriques en environnements cryogéniques

Mots clés : Transport quantique, electrodynamique quantique, radiofréquences

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