Probing quantum Hall conductors with low and high frequency noise
le mardi 30 avril 2019 à 14h00
Séminaire nano-électronique quantique
Personne à contacter : Robert Whitney ()
Lieu : Salle Rémy Lemaire K223, Institut Néel
Résumé :
In my seminar, I will discuss measurements of low and high frequency noise in quantum Hall conductors and how they can probe the elementary excitations propagating along the edge channels in the integer and fractional cases.
I will first present how low frequency noise measurements can be used to extract the electronic states propagating along the edge channels of the integer quantum Hall regime. Combining two-electron Hong-Ou-Mandel interferometry [1] with signal processing techniques, we have implemented a quantum tomography protocol [2,3] able of extracting from any electrical current the generated electron and hole wavefunctions as well as their emission probabilities
In the second part of my presentation, I will discuss the measurement of high frequency noise [4] generated by the random transfer of fractional excitations through a potential barrier biased with a dc voltage Vdc. At high frequencies (few GHz), the emitted noise can be interpreted as the generation of microwave photons in a coaxial measurement line weakly coupled to the sample. We observe that photons are only emitted when their frequency is smaller than the frequency threshold fJ=qVdc/h called the Josephson frequency [5,6] in analogy with the Josephson relation in superconductors. This threshold provides a direct determination of the fractional charge q.
[1] E. Bocquillon et al. Science 339, 1054 (2013)
[2] C. Grenier et al. NJP 13, 093007 (2011)
[3] T. Jullien et al. Nature 514, 603 (2014)
[4] R. Bisognin et al., Nature Communications 10, 1708 (2019).
[5] C. de C. Chamon, D. E. Freed, and X. G. Wen, Phys. Rev. B, 51, 2363 (1995).
[6] M. Kapfer et al., Science 363, 846 (2019).
Analytical Large Deviation and Uncertainly Relation
le vendredi 17 mai 2019 à 11h00
Séminaire théorie
Personne à contacter :
Lieu : Amphithéâtre, maison des Magistères
Résumé : In this talk, I will talk about the theory of large deviations. After a general introduction, I will present some recent developments on the large deviations associated with a Markov process and on applications for thermodynamic uncertainty relations.
From billiards for light to mesoscopic optic
le mardi 28 mai 2019 à 14h00
Séminaire nano-électronique quantique
Personne à contacter : Robert Whitney ()
Lieu : Salle Rémy Lemaire K223, Institut Néel
Résumé : The investigation of the propagation of light in mesoscopic, i.e. often micrometer-scale, systems is a rich subject providing insights ranging from quantum chaos in open systems to new schemes for realizing microlasers. The concept of quantum-classical, here wave-ray, correspondence, proves to be as useful as for electronic mesoscopic systems such as quantum dots. Whereas there the electrons are confined by means of gate voltages, the confinement of light in optical microresonators is due to total internal reflection, leading to billiards for light. There are, however, semiclassical deviations from the naive ray-picture expectation in the reflection and refraction of light at dielectric interfaces yielding for example to deviations from Snell's law. We illustrate these effects and discuss their impact on the far-field emission characteristics of optical microcavities.
The propagation of electromagnetic waves in three-dimensional optical microcavities requires to pay attention to the evolution of the light's polarization as a new degree of freedom. In systems like dielectric Möbius-strips or cone-shaped microtube cavities, the polarization state of resonant whispering gallery-type modes may differ strongly from the reference case of homogeneous cylinders. Whereas we find that the polarization of the electromagnetic field follows the wall orientation in thin Möbius strips, thereby reflecting the accumulated geometric phase, we observe that the electromagnetic field ignores the Möbius topology when the strip thickness is increased. Breaking of symmetries further influences the morphology of resonances and can induce a transition from linear to elliptical polarization that is both of theoretical interest from the point of view of spin-orbit interaction of light and their interpretation in terms of Berry phases, and relevant for potential applications.
Laboratoire de Physique et Modélisation des Milieux Condensés
