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Published Online May 8, 2003
Science DOI: 10.1126/science.1085335

Reports

Submitted on April 4, 2003
Accepted on April 25, 2003

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. Ketterle 1

1 Department of Physics, MIT-Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, MIT, Cambridge, MA 02139, USA.
2 Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

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

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 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.


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