Letter

Nature 464, 1170-1173 (22 April 2010) | doi:10.1038/nature08988; Received 18 November 2009; Accepted 10 March 2010; Published online 31 March 2010

Atom-chip-based generation of entanglement for quantum metrology

Max F. Riedel1,2, Pascal Böhi1,2, Yun Li3,4, Theodor W. Hänsch1,2, Alice Sinatra3 & Philipp Treutlein1,2,5

  1. Fakultät für Physik, Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
  2. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
  3. Laboratoire Kastler Brossel, ENS, 24 rue Lhomond, F-75005 Paris, France
  4. State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China
  5. Departement Physik, Universität Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland

Correspondence to: Alice Sinatra3Philipp Treutlein1,2,5 Correspondence and requests for materials should be addressed to P.T. (Email: philipp.treutlein@unibas.ch) and A.S. (Email: alice.sinatra@lkb.ens.fr).

Atom chips provide a versatile quantum laboratory for experiments with ultracold atomic gases1. They have been used in diverse experiments involving low-dimensional quantum gases2, cavity quantum electrodynamics3, atom–surface interactions4, 5, and chip-based atomic clocks6 and interferometers7, 8. However, a severe limitation of atom chips is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far. Such techniques enable chip-based studies of entangled many-body systems and are a key prerequisite for atom chip applications in quantum simulations9, quantum information processing10 and quantum metrology11. Here we report the experimental generation of multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential12. We use this technique to generate spin-squeezed states of a two-component Bose–Einstein condensate13; such states are a useful resource for quantum metrology. The observed reduction in spin noise of -3.7±0.4dB, combined with the spin coherence, implies four-partite entanglement between the condensate atoms14; this could be used to improve an interferometric measurement by -2.5±0.6dB over the standard quantum limit15. Our data show good agreement with a dynamical multi-mode simulation16 and allow us to reconstruct the Wigner function17 of the spin-squeezed condensate. The techniques reported here could be directly applied to chip-based atomic clocks, currently under development18.

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