Probing topological edge states in a molecular synthetic dimension

TL;DR

This paper demonstrates the use of ultracold polar molecules to encode a synthetic topological lattice, enabling the study of edge states and topological properties with long coherence times and site-resolved readout.

Contribution

It encodes a 1D synthetic lattice in molecular rotational states to investigate topological edge states in the SSH model, showcasing long coherence and site-resolved dynamics.

Findings

Achieved long coherence times (~500 times the tunnelling period) in synthetic lattice.

Performed site-resolved spectroscopy and dynamics to probe topological edge states.

Demonstrated the ability to test effects of perturbations on topologically protected states.

Abstract

Engineering synthetic dimensions, where the physics of additional spatial dimensions is simulated within the internal states of a quantum system, allows the realisation of phenomena not otherwise accessible in experiments. Ultracold ground-state polar molecules are an ideal platform to encode synthetic dimensions, offering access to large Hilbert spaces of long-lived internal states associated with the rotational and hyperfine degrees of freedom, that can be coupled together with microwave fields to simulate tunnelling. Here, to benchmark the advantages of ultracold molecules, we encode a 1D synthetic lattice in the rotational states of ultracold RbCs molecules and use it to investigate the well-known Su-Schrieffer-Heeger (SSH) model, a minimal model displaying topological properties. To probe the system, we perform spectroscopy using an auxiliary rotational state and study the time dynamics after deterministic state preparation. We demonstrate long coherence times, typically ~500 times the lattice tunnelling period, even for a synthetic lattice using 8 rotational states. Observations of dynamics at long times with full site-resolved readout of the synthetic dimension allow us to test the effects of chiral and non-chiral perturbations on the topologically protected edge states. Our work lays the foundation for further quantum simulations using the rich internal structure of molecules, including dipolar string phases in interacting samples of molecules, and adiabatic state preparation of many-body Hamiltonians.