In-flight manipulation of single electrons
le mardi 21 mai 2019 à 14h00
Séminaire nano-électronique quantique
Personne à contacter : Robert Whitney ()
Lieu : Salle Rémy Lemaire K223, Institut Néel
Résumé :
Over the past decade, an important effort has been made in the field of low-dimensional electronic conductors towards single-electron electronics with the goal of gaining coherent control over single flying electrons in solid-state devices [1]. In this talk I will present our recent advances towards the realization of electronic flying-qubit architectures using ultrashort charge pulses (Levitons) as well as surface acoustic wave (SAW) driven single electrons.
In the first part of the talk I will present time-resolved measurements of ultrashort single-electron charge pulses injected into a quasi-one-dimensional quantum conductor. We show that the velocity of such a single-electron pulse is found to be much faster than the Fermi velocity due to the presence of strong electron-electron interactions and can be tuned over more than an order of magnitude by electrostatic confinement. In addition, our set-up allows us to tune our system continuously from a clean one-channel Tomonaga-Luttinger liquid to a multi-channel Fermi liquid [2]. Our results are in quantitative agreement with a parameter-free theory and demonstrate a powerful new probe for directly investigating real-time dynamics of fractionalisation phenomena in low-dimensional conductors.
In the second part of the talk, I will concentrate on SAW-assisted single-electron transport. I will present our recent results on highly-efficient electron routing in a beam-splitter configuration. For this we connect four quantum dots via two 22 μm long quantum rails that are coupled by a tunnel barrier along a 2 µm long interaction region. Changing the energy detuning in the interaction region we can partition the electrons on-demand into two paths with electron transport efficiencies of 99.7 % [3].
Our results demonstrate the potential of these two approaches for the implementation of an electronic solid-state flying qubit having high relevance in fundamental research and quantum information technology.
[1] C. Bäuerle et al., Rep. Prog. Phys. 81, 056503 (2018)
[2] G. Roussely, E. Arrighi et al., Nature Comm. 9, 2811 (2018)
[3] S. Takada, H. Edlbauer et al., arXiv:1903.00684v1
Superfluidity in the inner crust of neutron stars
le vendredi 24 mai 2019 à 11h00
Colloque CPTGA
Personne à contacter : Julia Meyer ()
Lieu : Amphithéâtre, maison des Magistères
Résumé : After a general introduction to neutron stars, I will focus on the
special role of their inner crust. This region is characterized by the
coexistence of a Coulomb lattice of neutron-rich nuclei ("clusters")
in a uniform background of ultrarelativistic degenerate electrons and a
gas of unbound neutrons. The unbound neutrons are supposed to be
superfluid, which gives rise to remarkable phenomena, such as the
famous "glitches" (sudden increases of the neutron star's rotation
frequency) and changes in the star's cooling behaviour. However,
making reliable predictions for the superfluid critical temperature
remains a challenging problem for nuclear many-body theory, mostly
because of medium-polarisation effects. Another important unsolved
problem is the "entrainment" between the neutron gas and the clusters
in the crust, since it determines the density of superfluid neutrons.
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
