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Observation of chiral edge transport in a rapidly rotating quantum gas

Nature Physics (2024)Cite this article

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Abstract

The frictionless directional propagation of particles at the boundary of topological materials is a striking transport phenomenon. These chiral edge modes lie at the heart of the integer and fractional quantum Hall effects, and their robustness against noise and disorder reflects the quantization of Hall conductivity in these systems. Despite their importance, the controllable injection of edge modes, and direct imaging of their propagation, structure and dynamics, remains challenging. Here we demonstrate the distillation of chiral edge modes in a rapidly rotating bosonic superfluid confined by an optical boundary. By tuning the wall sharpness, we reveal the smooth crossover between soft wall behaviour in which the propagation speed is proportional to wall steepness and the hard wall regime that exhibits chiral free particles. From the skipping motion of atoms along the boundary we infer the energy gap between the ground and first excited edge bands, and reveal its evolution from the bulk Landau level splitting for a soft boundary to the hard wall limit. Finally, we demonstrate the robustness of edge propagation against disorder by projecting an optical obstacle that is static in the rotating frame.

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Fig. 1: Controllable injection of chiral edge modes.
Fig. 2: Density profiles of the bulk and edge modes.
Fig. 3: Variation in edge mode speed with wall steepness.
Fig. 4: Frequency of skipping orbits at the boundary.
Fig. 5: Robustness of edge modes against disorder.

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Data availability

All data files are available from the corresponding author upon request. Accompanying data, including data for Figs. 1–5 and Extended Data Figs. 1 and 2 are available via Zenodo at https://doi.org/10.5281/zenodo.12724216 (ref. 55).

Code availability

The simulation and analysis code is available from the corresponding author upon reasonable request.

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Acknowledgements

We thank V. Crépel, P. Patel, C. Wilson and Z. Yan for early contributions to the experiment. This work was supported by the NSF through the Center for Ultracold Atoms and grant number PHY-2012110, the ARO through grant number W911NF-23-1-0382 and by DURIP grant number W911NF-23-1-0326. M.Z. acknowledges funding from the Vannevar Bush Faculty Fellowship (ONR number N00014-19-1-2631). R.J.F. acknowledges funding from the AFOSR Young Investigator Program (grant number FA9550-22-1-0066).

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Authors and Affiliations

  1. MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA

    Ruixiao Yao, Sungjae Chi, Biswaroop Mukherjee, Airlia Shaffer, Martin Zwierlein & Richard J. Fletcher

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Contributions

R.Y., S.C., B.M., A.S. and R.J.F. performed the measurements. R.Y. and S.C. analysed the data. B.M. and R.Y. contributed the Gross–Pitaevskii numerical simulations. R.Y., S.C., R.J.F. and M.Z. developed the theoretical description. R.J.F. and M.Z. supervised the project. All authors contributed to interpretation of the results and preparation of the manuscript.

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Correspondence to Richard J. Fletcher.

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Nature Physics thanks Luca Asteria for his contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Analysis of the boundary potential.

(a,d) Images of the projected optical boundary. The white boxes indicate the approximate azimuthal range explored by the atoms as they pass through the saddle minimum, and hence the edge mode speed is maximum. (b,e) The measured radial intensity I(r), averaged over the indicated range of azimuthal angles. The green line shows a fitted error function. (c,f) The black curve is the inferred intensity profile at the atoms, obtained by de-convolution of the green curve in (b,e). The orange line is a piecewise linear fit to the black curve, whose slope provides the effective steepness of the boundary potential.

Extended Data Fig. 2 Evolution of the condensate density obtained from a Gross-Pitaevskii simulation.

We perform a numerical simulation of the condensate evolution based on time-evolution of the Gross-Pitaevskii equation under an identical protocol to the experiment. Panels show the condensate density (a) before rotation; (b) when Ω = 0.85ω; (c) once Ω = ω, approximately corresponding to the time at which the condensate encounters the edge potential; (d) after 5ms of edge mode propagation.

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Yao, R., Chi, S., Mukherjee, B. et al. Observation of chiral edge transport in a rapidly rotating quantum gas. Nat. Phys. (2024). https://doi.org/10.1038/s41567-024-02617-7

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