Probing Interactions Between Ultracold Fermions
G. K. Campbell,1
M. M. Boyd,1
J. W. Thomsen,1
M. J. Martin,1
S. Blatt,1
M. D. Swallows,1
T. L. Nicholson,1
T. Fortier,2
C. W. Oates,2
S. A. Diddams,2
N. D. Lemke,2
P. Naidon,3*
P. Julienne,3
Jun Ye,1
A. D. Ludlow1
At
ultracold temperatures, the Pauli exclusion principle suppresses
collisions
between identical
fermions. This has motivated the
development of atomic clocks with fermionic isotopes. However,
by
probing an optical clock transition with thousands of lattice-confined,
ultracold fermionic strontium atoms, we observed density-dependent
collisional frequency shifts. These collision effects were measured
systematically and are supported by a theoretical description
attributing them to inhomogeneities in the probe excitation
process that render the atoms distinguishable. This work also
yields insights for zeroing the clock density shift.
2 Time and Frequency Division, National Institute of Standards and Technology, Boulder, CO 80302, USA.
3 Atomic Physics Division and Joint Quantum Institute, National Institute of Standards and Technology, 100 Bureau Drive Stop 8423, Gaithersburg, MD 20899–8423, USA.
* Present address: ERATO (Exploratory Research for Advanced Technology) Macroscopic Quantum Project, Japan Science and Technology Agency, Tokyo, 113-0033, Japan.
Present address: Time and Frequency Division, National Institute of Standards and Technology, Boulder, CO 80302, USA.
To whom correspondence should be addressed. E-mail: junye{at}jilau1.colorado.edu
