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Originally published in Science Express on 8 May 2003
Science 13 June 2003:
Vol. 300. no. 5626, pp. 1723 - 1726
DOI: 10.1126/science.1085335
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Reports

Radio-Frequency Spectroscopy of Ultracold Fermions

S. Gupta,1* Z. Hadzibabic,1 M. W. Zwierlein,1 C. A. Stan,1 K. Dieckmann,1 C. H. Schunck,1 E. G. M. van Kempen,2 B. J. Verhaar,2 W. Ketterle1

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This absence is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a three-level system. However, in the strongly interacting regime, these shifts became very small, reflecting the quantum unitarity limit and many-body effects. This insight into an interacting Fermi gas is relevant for the quest to observe superfluidity in this system.

1 Department of Physics, Massachusetts Institute of Technology (MIT)–Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, MIT, Cambridge, MA 02139, USA.
2 Eindhoven University of Technology, Post Office Box 513, 5600 MB Eindhoven, Netherlands.

* To whom correspondence should be addressed. E-mail: deep{at}mit.edu

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