Mediated interactions between Fermi polarons and the role of impurity quantum statistics

Cosetta Baroni; Bo Huang; Isabella Fritsche; Erich Dobler; gregor anich; Emil Kirilov; Rudolf Grimm; Miguel Angel Bastarrachea Magnani; Pietro Massignan; Georg Bruun

doi:10.1038/s41567-023-02248-4

Mediated interactions between Fermi polarons and the role of impurity quantum statistics

Cosetta Baroni, Bo Huang, Isabella Fritsche, Erich Dobler, gregor anich, Emil Kirilov, Rudolf Grimm, Miguel Angel Bastarrachea Magnani, Pietro Massignan , Georg Bruun

Department of Physics and Astronomy - Center for Complex Quantum Systems

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

26 Citations (Scopus)

Abstract

The notion of quasi-particles is essential for understanding the behaviour of complex many-body systems. A prototypical example of a quasi-particle is a polaron, formed by an impurity strongly interacting with a surrounding medium. Fermi polarons, created in a Fermi sea, provide a paradigmatic realization of this concept. Importantly, such quasi-particles interact with each other via the modulation of the medium. However, although quantum simulation experiments with ultracold atoms have substantially improved our understanding of individual polarons, the detection of their interactions has so far remained elusive. Here we report the observation of mediated interactions between Fermi polarons consisting of K impurities embedded in a Fermi sea of Li atoms. Our results confirm two predictions of Landau’s Fermi-liquid theory: the shift in polaron energy due to mediated interactions, which is linear in the concentration of impurities; and its sign inversion with impurity quantum statistics. For weak-to-moderate interactions between the impurities and the medium, our results agree with the static predictions of Fermi-liquid theory. For stronger impurity–medium interactions, we show that the observed behaviour at negative energies can be explained by a more refined many-body treatment including retardation and dressed molecule formation.

Original language	English
Article number	68
Journal	Nature Physics
Volume	20
Issue	1
Pages (from-to)	68-73
Number of pages	6
ISSN	1745-2473
DOIs	https://doi.org/10.1038/s41567-023-02248-4
Publication status	Published - Jan 2024

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title = "Mediated interactions between Fermi polarons and the role of impurity quantum statistics",

abstract = "The notion of quasi-particles is essential for understanding the behaviour of complex many-body systems. A prototypical example of a quasi-particle is a polaron, formed by an impurity strongly interacting with a surrounding medium. Fermi polarons, created in a Fermi sea, provide a paradigmatic realization of this concept. Importantly, such quasi-particles interact with each other via the modulation of the medium. However, although quantum simulation experiments with ultracold atoms have substantially improved our understanding of individual polarons, the detection of their interactions has so far remained elusive. Here we report the observation of mediated interactions between Fermi polarons consisting of K impurities embedded in a Fermi sea of Li atoms. Our results confirm two predictions of Landau{\textquoteright}s Fermi-liquid theory: the shift in polaron energy due to mediated interactions, which is linear in the concentration of impurities; and its sign inversion with impurity quantum statistics. For weak-to-moderate interactions between the impurities and the medium, our results agree with the static predictions of Fermi-liquid theory. For stronger impurity–medium interactions, we show that the observed behaviour at negative energies can be explained by a more refined many-body treatment including retardation and dressed molecule formation.",

author = "Cosetta Baroni and Bo Huang and Isabella Fritsche and Erich Dobler and gregor anich and Emil Kirilov and Rudolf Grimm and {Bastarrachea Magnani}, {Miguel Angel} and Pietro Massignan and Georg Bruun",

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AU - Baroni, Cosetta

AU - Huang, Bo

AU - Fritsche, Isabella

AU - Dobler, Erich

AU - anich, gregor

AU - Kirilov, Emil

AU - Grimm, Rudolf

AU - Bastarrachea Magnani, Miguel Angel

AU - Massignan , Pietro

AU - Bruun, Georg

PY - 2024/1

Y1 - 2024/1

N2 - The notion of quasi-particles is essential for understanding the behaviour of complex many-body systems. A prototypical example of a quasi-particle is a polaron, formed by an impurity strongly interacting with a surrounding medium. Fermi polarons, created in a Fermi sea, provide a paradigmatic realization of this concept. Importantly, such quasi-particles interact with each other via the modulation of the medium. However, although quantum simulation experiments with ultracold atoms have substantially improved our understanding of individual polarons, the detection of their interactions has so far remained elusive. Here we report the observation of mediated interactions between Fermi polarons consisting of K impurities embedded in a Fermi sea of Li atoms. Our results confirm two predictions of Landau’s Fermi-liquid theory: the shift in polaron energy due to mediated interactions, which is linear in the concentration of impurities; and its sign inversion with impurity quantum statistics. For weak-to-moderate interactions between the impurities and the medium, our results agree with the static predictions of Fermi-liquid theory. For stronger impurity–medium interactions, we show that the observed behaviour at negative energies can be explained by a more refined many-body treatment including retardation and dressed molecule formation.

AB - The notion of quasi-particles is essential for understanding the behaviour of complex many-body systems. A prototypical example of a quasi-particle is a polaron, formed by an impurity strongly interacting with a surrounding medium. Fermi polarons, created in a Fermi sea, provide a paradigmatic realization of this concept. Importantly, such quasi-particles interact with each other via the modulation of the medium. However, although quantum simulation experiments with ultracold atoms have substantially improved our understanding of individual polarons, the detection of their interactions has so far remained elusive. Here we report the observation of mediated interactions between Fermi polarons consisting of K impurities embedded in a Fermi sea of Li atoms. Our results confirm two predictions of Landau’s Fermi-liquid theory: the shift in polaron energy due to mediated interactions, which is linear in the concentration of impurities; and its sign inversion with impurity quantum statistics. For weak-to-moderate interactions between the impurities and the medium, our results agree with the static predictions of Fermi-liquid theory. For stronger impurity–medium interactions, we show that the observed behaviour at negative energies can be explained by a more refined many-body treatment including retardation and dressed molecule formation.

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Mediated interactions between Fermi polarons and the role of impurity quantum statistics

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