Observation of Spin-Spin Fermion-Mediated Interactions between Ultracold Bosons

Hagai Edri, Boaz Raz, Noam Matzliah, Nir Davidson, and Roee Ozeri
Phys. Rev. Lett. 124, 163401 – Published 22 April 2020
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Abstract

Interactions in an ultracold boson-fermion mixture are often manifested by elastic collisions. In a mixture of a condensed Bose gas (BEC) and spin polarized degenerate Fermi gas (DFG), fermions can mediate spin-spin interactions between bosons, leading to an effective long-range magnetic interaction analogous to Ruderman-Kittel-Kasuya-Yosida [Phys. Rev. 96, 99 (1954); Prog. Theor. Phys. 16, 45 (1956); Phys. Rev. 106, 893 (1957)] interaction in solids. We used Ramsey spectroscopy of the hyperfine clock transition in a Rb87 BEC to measure the interaction mediated by a K40 DFG. By controlling the boson density we isolated the effect of mediated interactions from mean-field frequency shifts due to direct collision with fermions. We measured an increase of boson spin-spin interaction by a factor of η=1.45±0.05stat±0.13syst in the presence of the DFG, providing clear evidence of spin-spin fermion mediated interaction. Decoherence in our system was dominated by inhomogeneous boson density shift, which increased significantly in the presence of the DFG, again indicating mediated interactions. We also measured a frequency shift due to boson-fermion interactions in accordance with a scattering length difference of abf2abf1=5.36±0.44stat±1.43systa0 between the clock-transition states, a first measurement beyond the low-energy elastic approximation [R. Côté, A. Dalgarno, H. Wang, and W. C. Stwalley, Phys. Rev. A 57, R4118 (1998); A. Dalgarno and M. Rudge, Proc. R. Soc. A 286, 519 (1965)] in this mixture. This interaction can be tuned with a future use of a boson-fermion Feshbach resonance. Fermion-mediated interactions can potentially give rise to interesting new magnetic phases and extend the Bose-Hubbard model when the atoms are placed in an optical lattice.

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  • Received 14 November 2019
  • Accepted 3 April 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.163401

© 2020 American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & Optical

Authors & Affiliations

Hagai Edri*, Boaz Raz, Noam Matzliah, Nir Davidson, and Roee Ozeri

  • Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel

  • *Corresponding author. hagai.edri@weizmann.ac.il

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Vol. 124, Iss. 16 — 24 April 2020

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