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Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture

Nature volume 485, pages 615–618 (2012)Cite this article

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Abstract

Ultracold Fermi gases with tunable interactions provide a test bed for exploring the many-body physics of strongly interacting quantum systems1,2,3,4. Over the past decade, experiments have investigated many intriguing phenomena, and precise measurements of ground-state properties have provided benchmarks for the development of theoretical descriptions. Metastable states in Fermi gases with strong repulsive interactions5,6,7,8,9,10,11 represent an exciting area of development. The realization of such systems is challenging, because a strong repulsive interaction in an atomic quantum gas implies the existence of a weakly bound molecular state, which makes the system intrinsically unstable against decay. Here we use radio-frequency spectroscopy to measure the complete excitation spectrum of fermionic 40K impurities resonantly interacting with a Fermi sea of 6Li atoms. In particular, we show that a well-defined quasiparticle exists for strongly repulsive interactions. We measure the energy and the lifetime of this ‘repulsive polaron’9,12,13, and probe its coherence properties by measuring the quasiparticle residue. The results are well described by a theoretical approach that takes into account the finite effective range of the interaction in our system. We find that when the effective range is of the order of the interparticle spacing, there is a substantial increase in the lifetime of the quasiparticles. The existence of such a long-lived, metastable many-body state offers intriguing prospects for the creation of exotic quantum phases in ultracold, repulsively interacting Fermi gases.

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Figure 1: Energy spectrum of an impurity in the Fermi sea.
Figure 2: Spectral response of 40 K impurities in a 6 Li Fermi sea.
Figure 3: Decay rate of the repulsive polaron.
Figure 4: Rabi oscillations and the quasiparticle residue.

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References

  1. Bloch, I., Dalibard, J. & Zwerger, W. Many-body physics with ultracold gases. Rev. Mod. Phys. 80, 885–964 (2008)

    Article  CAS  ADS  Google Scholar 

  2. Giorgini, S., Pitaevskii, L. P. & Stringari, S. Theory of ultracold atomic Fermi gases. Rev. Mod. Phys. 80, 1215–1274 (2008)

    Article  CAS  ADS  Google Scholar 

  3. Radzihovsky, L. & Sheehy, D. E. Imbalanced Feshbach-resonant Fermi gases. Rep. Prog. Phys. 73, 076501 (2010)

    Article  ADS  Google Scholar 

  4. Chevy, F. & Mora, C. Ultra-cold polarized Fermi gases. Rep. Prog. Phys. 73, 112401 (2010)

    Article  ADS  Google Scholar 

  5. Duine, R. A. & MacDonald, A. H. Itinerant ferromagnetism in an ultracold atom Fermi gas. Phys. Rev. Lett. 95, 230403 (2005)

    Article  CAS  ADS  Google Scholar 

  6. LeBlanc, L. J., Thywissen, J. H., Burkov, A. A. & Paramekanti, A. Repulsive Fermi gas in a harmonic trap: ferromagnetism and spin textures. Phys. Rev. A 80, 013607 (2009)

    Article  ADS  Google Scholar 

  7. Conduit, G. J., Green, A. G. & Simons, B. D. Inhomogeneous phase formation on the border of itinerant ferromagnetism. Phys. Rev. Lett. 103, 207201 (2009)

    Article  CAS  ADS  Google Scholar 

  8. Jo, G.-B. et al. Itinerant ferromagnetism in a Fermi gas of ultracold atoms. Science 325, 1521–1524 (2009)

    Article  CAS  ADS  Google Scholar 

  9. Pilati, S., Bertaina, G., Giorgini, S. & Troyer, M. Itinerant ferromagnetism of a repulsive atomic Fermi gas: a quantum Monte Carlo study. Phys. Rev. Lett. 105, 030405 (2010)

    Article  CAS  ADS  Google Scholar 

  10. Chang, S.-Y., Randeria, M. & Trivedi, N. Ferromagnetism in the upper branch of the Feshbach resonance and the hard-sphere Fermi gas. Proc. Natl Acad. Sci. USA 108, 51–54 (2011)

    Article  CAS  ADS  Google Scholar 

  11. Sanner, C. et al. Correlations and pair formation in a repulsively interacting Fermi gas. Preprint at 〈http://arxiv.org/abs/1108.2017〉 (2012)

  12. Massignan, P. & Bruun, G. M. Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases. Eur. Phys. J. D 65, 83–89 (2011)

    Article  CAS  ADS  Google Scholar 

  13. Schmidt, R. & Enss, T. Excitation spectra and rf response near the polaron-to-molecule transition from the functional renormalization group. Phys. Rev. A 83, 063620 (2011)

    Article  ADS  Google Scholar 

  14. Landau, L. D. The theory of a Fermi liquid. Sov. Phys. JETP 3, 920–925 (1957)

    CAS  MathSciNet  MATH  Google Scholar 

  15. Lobo, C., Recati, A., Giorgini, S. & Stringari, S. Normal state of a polarized Fermi gas at unitarity. Phys. Rev. Lett. 97, 200403 (2006)

    Article  CAS  ADS  Google Scholar 

  16. Schirotzek, A., Wu, C.-H., Sommer, A. & Zwierlein, M. W. Observation of Fermi polarons in a tunable Fermi liquid of ultracold atoms. Phys. Rev. Lett. 102, 230402 (2009)

    Article  ADS  Google Scholar 

  17. Navon, N., Nascimbène, S., Chevy, F. & Salomon, C. The equation of state of a low-temperature Fermi gas with tunable interactions. Science 328, 729–732 (2010)

    Article  CAS  ADS  Google Scholar 

  18. Nascimbène, S. et al. Fermi-liquid behavior of the normal phase of a strongly interacting gas of cold atoms. Phys. Rev. Lett. 106, 215303 (2011)

    Article  ADS  Google Scholar 

  19. Pekker, D. et al. Competition between pairing and ferromagnetic instabilities in ultracold Fermi gases near Feshbach resonances. Phys. Rev. Lett. 106, 050402 (2011)

    Article  ADS  Google Scholar 

  20. Chin, C., Grimm, R., Julienne, P. S. & Tiesinga, E. Feshbach resonances in ultracold gases. Rev. Mod. Phys. 82, 1225–1286 (2010)

    Article  CAS  ADS  Google Scholar 

  21. Naik, D. et al. Feshbach resonances in the 6Li-40K Fermi-Fermi mixture: elastic versus inelastic interactions. Eur. Phys. J. D 65, 55–65 (2011)

    Article  CAS  ADS  Google Scholar 

  22. Petrov, D. S. Three-boson problem near a narrow Feshbach resonance. Phys. Rev. Lett. 93, 143201 (2004)

    Article  CAS  ADS  Google Scholar 

  23. Punk, M., Dumitrescu, P. T. & Zwerger, W. Polaron-to-molecule transition in a strongly imbalanced Fermi gas. Phys. Rev. A 80, 053605 (2009)

    Article  ADS  Google Scholar 

  24. Combescot, R., Recati, A., Lobo, C. & Chevy, F. Normal state of highly polarized Fermi gases: simple many-body approaches. Phys. Rev. Lett. 98, 180402 (2007)

    Article  CAS  ADS  Google Scholar 

  25. Sadeghzadeh, K., Bruun, G. M., Lobo, C., Massignan, P. & Recati, A. Metastability in spin-polarized Fermi gases and quasiparticle decays. N. J. Phys. 13, 055011 (2011)

    Article  Google Scholar 

  26. Nascimbène, S. et al. Collective oscillations of an imbalanced Fermi gas: axial compression modes and polaron effective mass. Phys. Rev. Lett. 103, 170402 (2009)

    Article  ADS  Google Scholar 

  27. Prokof’ev, N. & Svistunov, B. Fermi-polaron problem: diagrammatic Monte Carlo method for divergent sign-alternating series. Phys. Rev. B 77, 020408 (2008)

    Article  ADS  Google Scholar 

  28. Chin, C. et al. Observation of the pairing gap in a strongly interacting Fermi gas. Science 305, 1128–1130 (2004)

    Article  CAS  ADS  Google Scholar 

  29. Shin, Y., Schunck, C. H., Schirotzek, A. & Ketterle, W. Tomographic rf spectroscopy of a trapped Fermi gas at unitarity. Phys. Rev. Lett. 99, 090403 (2007)

    Article  CAS  ADS  Google Scholar 

  30. Stewart, J. T., Gaebler, J. P. & Jin, D. S. Using photoemission spectroscopy to probe a strongly interacting Fermi gas. Nature 454, 744–747 (2008)

    Article  CAS  ADS  Google Scholar 

  31. Spiegelhalder, F. M. et al. All-optical production of a degenerate mixture of 6Li and 40K and creation of heteronuclear molecules. Phys. Rev. A 81, 043637 (2010)

    Article  ADS  Google Scholar 

  32. Trenkwalder, A. et al. Hydrodynamic expansion of a strongly interacting Fermi-Fermi mixture. Phys. Rev. Lett. 106, 115304 (2011)

    Article  CAS  ADS  Google Scholar 

  33. Gezerlis, A., Gandolfi, S., Schmidt, K. E. & Carlson, J. Heavy-light fermion mixtures at unitarity. Phys. Rev. Lett. 103, 060403 (2009)

    Article  ADS  Google Scholar 

  34. Kasevich, M. & Chu, S. Laser-cooling below a photon recoil with three-level atoms. Phys. Rev. Lett. 69, 1741–1744 (1992)

    Article  CAS  Google Scholar 

Download references

Acknowledgements

We thank A. Sidorov for contributions in the early stage of the experiments, and T. Enss, S. Giorgini, W. Ketterle, J. Levinsen, C. Lobo, D. Petrov, A. Recati, R. Schmidt, J. Song, C. Trefzger, P. Zoller, W. Zwerger, M. Zwierlein and, in particular, M. Baranov for many discussions. We acknowledge support from the Austrian Science Fund FWF through the SFB FoQuS. M.Z. is supported by the Lise Meitner programme of the FWF. P.M. is indebted to M. Lewenstein for support through the ERC Advanced Grant QUAGATUA.

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Authors and Affiliations

  1. Institut für Quantenoptik und Quanteninformation, Österreichische Akademie der Wissenschaften, 6020 Innsbruck, Austria ,

    C. Kohstall, M. Zaccanti, M. Jag, A. Trenkwalder, F. Schreck & R. Grimm

  2. Institut für Experimentalphysik und Zentrum für Quantenphysik, Universität Innsbruck, Innsbruck, 6020, Austria

    C. Kohstall, M. Jag & R. Grimm

  3. Institut de Ciències Fotòniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain ,

    P. Massignan

  4. Department of Physics and Astronomy, University of Aarhus, Aarhus C, 8000, Denmark

    G. M. Bruun

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Contributions

C.K., M.Z., M.J., A.T., F.S. and R.G. did the experimental work and P.M. and G.M.B. did the theoretical work.

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Correspondence to M. Zaccanti.

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Kohstall, C., Zaccanti, M., Jag, M. et al. Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture. Nature 485, 615–618 (2012). https://doi.org/10.1038/nature11065

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