[1] Univ Colorado, Dept Phys, Boulder, CO 80309 USA
[2] Univ Colorado, JILA, Boulder, CO 80309 USA
[3] Univ Calif Santa Barbara, Dept Phys, Santa Barbara, CA 93106 USA
[4] Univ Calif Santa Barbara, Kavli Inst Theoret Phys, Santa Barbara, CA 93106 USA