ALP Seminar: Making and Probing Coupled 2D Quantum Field Simulator

Coherent and controllable coupling of multiple many-body quantum systems result in rich emergent behaviour with numerous applications, e.g., Josephson junction created by a weak link between two macroscopic wavefunctions. An intriguing extension of this is a bilayer junction of two-dimensional (2D) systems, which also gives us an extremely useful control parameter, the inter-well coupling, for probing non-equilibrium dynamics.

In this talk, I will introduce our experiments to create and probe highly controllable bilayer 2D systems of ultracold atoms. The bilayer trap is generated by the multiple-RF dressing technique developed in our group which gives precision control of the trap geometry, free from the controllability limitation imposed by the diffraction limit for the case of optical trapping. We probe the phase fluctuation of the bilayer system in symmetric and antisymmetric modes by using matter-wave interferometry and spatial noise correlation measurements, obtaining information on second-order correlation functions for a complete understanding of the coupled systems [1]. Using this tool, we investigate the Berezinskii-Kosterlitz-Thouless (BKT) phase of the bilayer in the presence of variable inter-layer coupling and identify a coupling-induced superfluid phase. Furthermore, dynamical control of the trap geometry allows the preparation of unique non-equilibrium initial state by quenching the bilayer. As an example, we perform coherent splitting of a single 2D system into two copies, which serves as clean and repeatable superfluid-to-normal quench. We probe universal relaxation dynamics using matter-wave interferometry and interpret the two-step decoherence dynamics using real-time renormalization-group theory [2].

[1] S. Sunami et al., Phys. Rev. Lett. 128, 250402 (2022)

[2] S. Sunami et al., Science 382, 443 (2023).