Thursday
4
July
11h

#### Séminaire Temps & Fréquence (SYRTE)

# Ultracold atoms carrying orbital angular momentum: Quantum sensing and topology

Veronica Ahufinger – Departament de Física, Universitat Autònoma de Barcelona

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Pushing the limits of sensing technologies is one of the main challenges in modern physics, opening the door to high-precision measurements of fundamental constants as well as applications in many different areas of science. On the other hand, since the observation of the quantum Hall effect in two-dimensional electron gases and the discovery of its relation with topology, the study of systems with non-trivial topological properties has become a central topic in condensed matter physics. In this talk, we will show that ultracold atoms carrying orbital angular momentum (OAM) constitute a novel platform to explore both scenarios.
In particular, we propose a quantum sensing device to measure with high sensitivity non-linear interactions, scalar magnetic fields and rotations [1]. It consists in an imbalanced superposition of OAM modes of a Bose–Einstein condensate (BEC) in a ring trap with opposite winding numbers, for which a minimal atomic density line appears. A weak two-body interaction between the atoms of the BEC leads to a rotation of the minimal atomic density line whose angular frequency is directly related to the strength of such interactions. We derive an analytical model relating the angular frequency of the minimal density line rotation to the strength of the non-linear atom-atom interactions and the difference between the populations of the counter-propagating modes. Additionally, we propose a full experimental protocol based on direct fluorescence imaging of the BEC that allows measuring all the quantities involved in the analytical model and use the system for sensing purposes.
In the context of topology, we study the single-particle properties of a system formed by ultracold atoms loaded into the manifold of l=1 OAM states of an optical lattice with a diamond chain geometry [2,3]. Through a series of successive basis rotations, we show that the OAM degree of freedom induces phases in some tunneling amplitudes of the tight-binding model that are equivalent to a net pi flux through the plaquettes and give rise to a topologically non-trivial band structure and protected edge states. In addition, we demonstrate that quantum interferences between the different tunneling processes involved in the dynamics may lead to Aharanov-Bohm caging in the system. All these analytical results are confirmed by exact diagonalization numerical calculations.
[1] G. Pelegrí, J. Mompart and V. Ahufinger, Quantum sensing using imbalanced counter-rotating Bose-Einstein condensate modes. New Journal of Phys. 20, 103001 (2018).
[2] G. Pelegrí, A. M. Marques, R. G. Dias, A. J. Daley, V. Ahufinger and J. Mompart, Topological edge states with ultracold atoms carrying orbital angular momentum in a diamond chain. Phys. Rev. A 99, 023612 (2019).
[3] G. Pelegrí, A. M. Marques, R. G. Dias, A. J. Daley, J. Mompart and V. Ahufinger, Topological edge states and Aharanov-Bohm caging with ultracold atoms carrying orbital angular momentum. Phys. Rev. A 99, 023613 (2019).