2023-01-25 - Florian Schreck - University of Amsterdam

Title: Continuous Bose-Einstein condensation and superradiant clocks

Host: Peter van der Straten


Ultracold quantum gases are excellent platforms for quantum simulation and sensing. So far these gases have been produced using time-sequential cooling stages and after creation they unfortunately decay through unavoidable loss processes. This limits what can be done with them. For example it becomes impossible to extract a continuous-wave atom laser, which has promising applications for precision measurement through atom interferometry [1]. I will present how we achieve continuous Bose-Einstein condensation and create condensates (BECs) that persist in a steady-state for as long as we desire. Atom loss is compensated by feeding fresh atoms from a continuously replenished thermal source into the BEC by Bose-stimulated gain [2]. Our experiment is the matter wave analog of a cw optical laser with fully reflective cavity mirrors. The only step missing to create a continuous-wave atom laser beam is the addition of a coherent atom outcoupling mechanism. In addition this BEC may give us access to interesting driven-dissipative quantum phenomena over unprecedented timescales. The techniques we developed to achieve the continuous source of thermal atoms are also nicely suited to tackle another challenge: the creation of a continuously operating superradiant clock [3,4,5,6]. These clocks promise to become more rugged and/or more short-term stable than traditional optical clocks, thereby opening new application areas. In the second part of my talk I will present how we are developing two types of superradiant clocks within the European Quantum Flagship consortium iqClock [4,5,6].

    [1] N. P. Robins, P. A. Altin, J. E. Debs, and J. D. Close, Atom lasers: Production, properties and prospects for precision inertial measurement, Physics Reports 529, 265 (2013).
    [2] C.-C. Chen, R. González Escudero, J. Minář, B. Pasquiou, S. Bennetts, and F. Schreck, Continuous Bose-Einstein condensation, Nature 606, 683 (2022).
    [3] M. A. Norcia, New tools for precision measurement and quantum science with narrow linewidth optical transitions, PhD thesis, JILA, University of Colorado, Boulder, USA (2018).
    [4] J. Chen, Active Optical Clock, Chinese Science Bulletin 54, 348 (2009).
    [5] D. Meiser, J. Ye, D. R. Carlson, M. J. Holland, Prospects for a Millihertz-Linewidth Laser, PRL 102, 163601 (2009).
    [6] H. Liu, S. B. Jäger, X. Yu, S. Touzard, A. Shankar, M. J. Holland, and T. L. Nicholson, Rugged mHz-Linewidth Superradiant Laser Driven by a Hot Atomic Beam, PRL 125, 253602 (2020).

2023-01-11 - Philipp Raßmann - Forschungszentrum Jülich

Title: Density functional Bogoliubov-de Gennes calculations for a topological superconductor

Host: Zeila Zanolli

The possibility to combine topological electronic band structures and superconductivity (SC) opens new pathways towards engineering exotic quantum matter. Proximity-induced SC in the topological surface state of topological insulators (TIs) offers the possibility to realize a chiral 𝑝-wave superconductor. This is an exotic state of matter which supports non-Abelian anyons and is of great interest for Majorana-based quantum computing applications. Material-specific insights into the microscopic details of such SC/TI interfaces are of great interest and an indispensable ingredient in the challenging materials optimization problem. Here we first introduce the recent Bogoliubov de-Gennes (BdG) extension to the all electron full potential relativistic Korringa-Kohn-Rostoker (KKR) Green function code juKKR [1,2]. This KKR-BdG method allows a description of inhomogeneous superconductors on the basis of density functional theory. We apply this method to the 𝑠 -wave superconductor Nb and study its (110) surface [1]. We then turn to the investigation of the proximity effect in Nb/TI interfaces and discuss the induced superconductivity in the topological surface state of this SC/TI heterostructure [3].

This work was supported by the ML4Q Cluster of Excellence (EXC 2004/1 – 390534769) and by the Bavarian Ministry of Economic Affairs, Regional Development and Energy within Bavaria’s High-Tech Agenda Project “Bausteine für das Quantencomputing auf Basis topologischer Materialien mit experimentellen und theoretischen Ansätzen” (grant allocation no. 07 02/686 58/1/21 1/22 2/23).

[1] Philipp Rüßmann and Stefan Blügel, Phys. Rev. B 105, 125143 (2022)
[2] The juKKR code package, https://jukkr.fz-juelich.de
[3] Philipp Rüßmann and Stefan Blügel, arXiv:2208.14289 (2022)

2022-11-02 - Mark Golden - Amsterdam University

Title: Momentum dependent scaling exponents of cuprate strange-metal self energies: ARPES meets semi-holography

Host: Collective

ARPES enables the precise experimental determination of the electronic self-energy as we present here from the strange metal single-layer cuprate (Pb,Bi)_2Sr_(2−x)La_xCuO_(6+δ) overa wide range in w- and T for k along the nodal direction. Constant energy cuts through the spectral function (MDCs) show a non-Lorentzian lineshape as k increases away from kF: the nodal self-energy is k dependent. These experimental data provide a new test for aspiring theories.

The self energy extracted from experiment is captured remarkably well by a power law that smoothly evolves with hole doping with – crucially – a k-dependent scaling exponent. In fact, this description emerges naturally from AdS/CFT-based semi-holography, putting a spotlight on holographic methods for the quantitative modelling of strongly interacting quantum materials like the cuprate strange metals [1].

[1] S. Smit et al., arxiv.org/pdf/2112.06576.

Scroll to Top