Michael Jag

University of Innsbruck, Innsbruck, Tyrol, Austria

Are you Michael Jag?

Claim your profile

Publications (4)46.33 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate a mixture of ultracold fermionic K40 atoms and weakly bound Li6K40 dimers on the repulsive side of a heteronuclear atomic Feshbach resonance. By radio-frequency spectroscopy we demonstrate that the normally repulsive atom-dimer interaction is turned into a strong attraction. The phenomenon can be understood as a three-body effect in which two heavy K40 fermions exchange the light Li6 atom, leading to attraction in odd partial-wave channels (mainly p wave). Our observations show that mass imbalance in a fermionic system can profoundly change the character of interactions as compared to the well-established mass-balanced case.
    Physical Review Letters 02/2014; 112(7):075302. · 7.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: There is a growing interest in repulsively interacting Fermi gas mixtures, which could enable investigations of correlated quantum systems. As repulsive interactions in Fermi gases near a Feshbach resonance arise from the presence of a loosely bound molecular state, they are always associated with decay into bosonic molecules [1]. The interplay between repulsion and decay has made the realization and understanding of repulsive Fermi systems challenging [2,3]. We investigate the dynamics of a strongly interacting ^40K-^6Li Fermi-Fermi mixture on the repulsive side of an interspecies Feshbach resonance. For this purpose, we employ magnetic field ramps, RF spectroscopy, in-situ and time-of-flight imaging. Close to the resonance, we observe a static behavior of the K atomic population, redistribution of the Li density away from the K cloud and an absence of the interaction-induced shifts in the dissociation RF spectra in the strongly interacting repulsive regime. In spite of a strong initial atom loss, our results suggest that repulsive interactions are crucial for the dynamics of our system.[4pt][1] D. Pekker, et al., Phys. Rev. Lett. 106, 050402 (2011).[0pt][2] G. Jo, et al., Science 325, 5947 (2009).[0pt][3] C. Sanner et al., arXiv:1108.2017
    06/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultracold Fermi gases with tunable interactions represent a unique test bed to explore the many-body physics of strongly interacting quantum systems. In the past decade, experiments have mainly focused on the ground-state properties but metastable states in Fermi gases with strong repulsive interactions represent an exciting new frontier in the field. Here, we exploit 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. For this ``repulsive polaron'' we measure its energy and its lifetime against decay. We also 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 a non-zero range of the order of the interparticle spacing results in a substantial lifetime increase. This major benefit for the stability of the repulsive branch opens up new perspectives for investigating novel phenomena in metastable, repulsively interacting fermion systems.
    06/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ultracold Fermi gases with tunable interactions provide a test bed for exploring the many-body physics of strongly interacting quantum systems. 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 interactions 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 (40)K impurities resonantly interacting with a Fermi sea of (6)Li 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', 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.
    Nature 05/2012; 485(7400):615-8. · 38.60 Impact Factor