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Direct observation of second-order atom tunnelling

Nature volume 448, pages 1029–1032 (2007)Cite this article

Abstract

Tunnelling of material particles through a classically impenetrable barrier constitutes one of the hallmark effects of quantum physics. When interactions between the particles compete with their mobility through a tunnel junction, intriguing dynamical behaviour can arise because the particles do not tunnel independently. In single-electron or Bloch transistors, for example, the tunnelling of an electron or Cooper pair can be enabled or suppressed by the presence of a second charge carrier due to Coulomb blockade1,2. Here we report direct, time-resolved observations of the correlated tunnelling of two interacting ultracold atoms through a barrier in a double-well potential. For the regime in which the interactions between the atoms are weak and tunnel coupling dominates, individual atoms can tunnel independently, similar to the case of a normal Josephson junction. However, when strong repulsive interactions are present, two atoms located on one side of the barrier cannot separate3, but are observed to tunnel together as a pair in a second-order co-tunnelling process. By recording both the atom position and phase coherence over time, we fully characterize the tunnelling process for a single atom as well as the correlated dynamics of a pair of atoms for weak and strong interactions. In addition, we identify a conditional tunnelling regime in which a single atom can only tunnel in the presence of a second particle, acting as a single atom switch. Such second-order tunnelling events, which are the dominating dynamical effect in the strongly interacting regime, have not been previously observed with ultracold atoms. Similar second-order processes form the basis of superexchange interactions between atoms on neighbouring lattice sites of a periodic potential, a central component of proposals for realizing quantum magnetism4,5,6,7.

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Figure 1: Schematics of double-well generation, loading and detection sequences.
Figure 2: Tunnelling dynamics.
Figure 3: Tunnelling frequencies versus short-lattice depth (barrier height).
Figure 4: Conditional tunnelling.

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Acknowledgements

We thank A. M. Rey and B. Paredes for discussions. We acknowledge funding through the DFG and the European Union (MC-EXT QUASICOMBS). R.S. acknowledges support by the EU QUDEDIS programme as well as SJCKMS and the Kempe I and II foundations.

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Authors and Affiliations

  1. Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Germany

    S. Fölling, S. Trotzky, P. Cheinet, M. Feld, A. Widera, T. Müller & I. Bloch

  2. Department of Physics, Umeå University, 90187 Umeå, Sweden

    R. Saers

  3. Institut für Angewandte Physik, Universität Bonn, 53115 Bonn, Germany

    A. Widera

  4. Institute of Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland,

    T. Müller

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Correspondence to I. Bloch.

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Fölling, S., Trotzky, S., Cheinet, P. et al. Direct observation of second-order atom tunnelling. Nature 448, 1029–1032 (2007). https://doi.org/10.1038/nature06112

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