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Quantum time reflection and refraction of ultracold atoms

Nature Photonics volume 18, pages 68–73 (2024)Cite this article

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Abstract

Time reflection and refraction are temporal analogies of the spatial boundary effects derived from Fermat’s principle. They occur when classical waves strike a time boundary where an abrupt change in the properties of the medium is introduced. The main features of time-reflected and time-refracted waves are the shift in frequency and conservation of momentum, which offer a new degree of freedom for steering extreme waves and controlling the phases of matter. The concept was originally proposed for manipulating optical waves more than five decades ago. However, due to the extreme challenges in the ultrafast engineering of optical materials, the experimental realization of the time boundary effects remains elusive. Here we introduce a time boundary into a momentum lattice of ultracold atoms and simultaneously demonstrate time reflection and refraction experimentally. Through launching a Gaussian-superposed state into the Su–Schrieffer–Heeger atomic chain, we observe the time-reflected and time-refracted waves when the input state strikes a time boundary. Furthermore, we detect a transition from time reflection/refraction to localization with increasing strength of disorder and show that the time boundary effects are robust against considerable disorder. Our work opens a new avenue for the future exploration of time boundaries and spatiotemporal lattices, as well as their interplay with non-Hermiticity and many-body interactions.

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Fig. 1: Schematic of time reflection and refraction.
Fig. 2: Experimental observation of time reflection and refraction.
Fig. 3: Varying time boundary.
Fig. 4: Robustness of the time boundary effect.

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Data availability

All the data supporting the findings of this study are available within this Article and its Supplementary Information. Any additional information can be obtained from the corresponding authors on reasonable request. Source data are provided with this paper.

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Acknowledgements

We acknowledge funding support from the National Key Research and Development Program of China under grant no. 2022YFA1404203; the National Natural Science Foundation of China under grant nos. U21A20437, 12074337, and 12174339; Zhejiang Provincial Natural Science Foundation of China under grant nos. LR21A040002 and LR23A040003; Zhejiang Provincial Plan for Science and Technology grant no. 2020C01019; the Fundamental Research Funds for the Central Universities under grant no. 2021FZZX001-02; the Excellent Youth Science Foundation Project (Overseas); and China Postdoctoral Science Foundation under grant no. 2023M733122.

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Author notes

  1. These authors contributed equally: Zhaoli Dong, Hang Li, Tuo Wan.

Authors and Affiliations

  1. School of Physics, Interdisciplinary Center of Quantum Information, State Key Laboratory of Modern Optical Instrumentation, Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou, China

    Zhaoli Dong, Hang Li, Tuo Wan, Qian Liang, Zhaoju Yang & Bo Yan

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  1. Zhaoli Dong
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Contributions

Z.Y. and B.Y. conceived and designed the experiments. Z.D., H.L. and Q.L. performed the experiments. T.W. and H.L. conducted the theoretical modelling and simulations. Z.Y. and B.Y. supervised this project and wrote the paper, with input from all authors.

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Correspondence to Zhaoju Yang or Bo Yan.

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Nature Photonics thanks Peter Hannaford and the other, anonymous, reviewer(s) for their contribution to the peer review of this paper.

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Supplementary Information

Supplementary Figs. 1–8 and Sections I–VII.

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Numerical data used to generate Fig. 1c.

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Experimental data used to generate Fig. 2b,c.

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Experimental data used to generate Fig. 3b.

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Experimental data used to generate Fig. 4b.

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Dong, Z., Li, H., Wan, T. et al. Quantum time reflection and refraction of ultracold atoms. Nat. Photon. 18, 68–73 (2024). https://doi.org/10.1038/s41566-023-01290-1

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