Physics Research Seminar: Mehedi Hasan (University of Cambridge, UK)

Welcome to join us for a research seminar by Dr. Mehedi Hasan from Cambridge University, UK!

Host: Sebastiano Peotta/Quantum Dynamics group

Title: Geometric Frustration in Optical Triangular and Kagome Lattices

Abstract: 

In this talk, I will focus on one common theme in two different quantum simulated systems – triangular and Kagome optical lattices, with ultracold K(39) atoms. Firstly, I will discuss our experiment on quantum simulation of the geometric frustration of bosons in a triangular optical lattice where geometric frustration arises due to the existence of two non-equivalent points 𝑲 and 𝑲′ in the Brillouin zone that are not connected via a reciprocal lattice vector. We populate the 𝑲 and 𝑲′ points by creating a negative absolute temperature state where the entropy of a closed system reduces as the internal energy increases, and this leads to the peculiar situation where atoms in a band dominantly occupy the highest energy states of the band [1]. This geometric frustration leads to strikingly different critical interaction strengths for the bosonic superfluid to Mott insulator transition for a frustrated lattice, compared to the unfrustrated lattice. I will furthermore show, for both the frustrated and Unfrustrated lattices, how coherence emerges dynamically, and how we experimentally reveal the order of phase transition in the frustrated lattice. Finally, I discuss our results on Kagome optical lattice where atoms in the flat band are predicted to occupy selective point(s) in the Brillouin zone [2]. Moreover, I will give a brief overview on implementing a quantum gas microscope, in our experiment, for single-site-resolved imaging. 

References: 

[1] S. Braun, J.P. Ronzheimer, M. Schreiber, S.S. Hodgman, T. Rom, I. Bloch, and U. Schneider. Science 339, 52 (2013). 

[2] A. Julku, G.M. Bruun, and P. Törmä, Phys. Rev. Lett. 127, 170404 (2021).