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Non-equilibrium quantum dynamics and formation of the Bose polaron


Advancing our understanding of non-equilibrium phenomena in quantum many-body systems remains one of the greatest challenges in physics. Here we report on the experimental observation of a paradigmatic many-body problem, namely the non-equilibrium dynamics of a quantum impurity immersed in a bosonic environment1,2. We use an interferometric technique to prepare coherent superposition states of atoms in a Bose–Einstein condensate with a small impurity-state component, and monitor the evolution of such quantum superpositions into polaronic quasiparticles. These results offer a systematic picture of polaron formation3,4,5,6,7 from weak to strong impurity interactions. They reveal three distinct regimes of evolution with dynamical transitions that provide a link between few-body processes and many-body dynamics. Our measurements reveal universal dynamical behaviour in interacting many-body systems and demonstrate new pathways to study non-equilibrium quantum phenomena.

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Fig. 1: Dynamical regimes of impurity evolution and the experimental method.
Fig. 2: Impurity dynamics at weak interaction strength.
Fig. 3: Impurity dynamics at intermediate interaction strength.
Fig. 4: Impurity dynamics at unitarity.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Code availability

The code that supports the findings of this study is available from the corresponding author upon reasonable request.


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We thank L. A. Peña Ardila for helpful discussions. This work was supported by the Villum Foundation, the Carlsberg Foundation, the Danish Council for Independent Research, the Danish National Research Foundation through the Center of Excellence ‘CCQ’ (grant no. DNRF156) and T.P. acknowledges support through a Niels Bohr Professorship.

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M.G.S., T.G.S., N.B.J. and J.J.A. designed and carried out the experiment. M.G.S. performed the data analysis. K.K.N., A.C.-G., T.P. and G.M.B. provided the theoretical predictions. All authors contributed to writing the manuscript.

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Correspondence to Magnus G. Skou.

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The authors declare no competing interests.

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Peer review information Nature Physics thanks Francesco Scazza and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Skou, M.G., Skov, T.G., Jørgensen, N.B. et al. Non-equilibrium quantum dynamics and formation of the Bose polaron. Nat. Phys. 17, 731–735 (2021).

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