Tuning $p$-Wave Interactions in an Ultracold Fermi Gas of Atoms

We have measured a $p$-wave Feshbach resonance in a single-component, ultracold Fermi gas of ${}^{\mathrm{40}}\mathrm{K}$ atoms. We have used this resonance to enhance the normally suppressed $p$-wave collision cross section to values larger than the background $s$-wave cross section between ${}^{\mathrm{40}}\mathrm{K}$ atoms in different spin states. In addition to the modification of two-body elastic processes, the resonance dramatically enhances three-body inelastic collisional loss.

Figure 1

Magnetic-field Feshbach resonances between ${}^{\mathrm{40}}\mathrm{K}$ atoms in the $|9/2,-7/2⟩$ state (a) and between atoms in the $|9/2,-9/2⟩$ and $|9/2,-7/2⟩$ states (b). The $p$-wave and $s$-wave data were taken at temperatures of $3.2\pm 0.7\mu \mathrm{K}$ and $4.4\pm 0.9\mu \mathrm{K}$, respectively (both $T\sim 2T_F$). The lines are based upon our best-fit potassium potentials.

Figure 2

Temperature dependence of the $p$-wave elastic collision cross section. The two temperatures sets are $3.7\pm 0.5\mu \mathrm{K}$ (●) and $2.7\pm 0.3\mu \mathrm{K}$ (△).

Figure 3

Resonant three-body loss for a gas of atoms in the (a) $|9/2,-7/2⟩$ state and (b) $|9/2,-7/2⟩$ and $|9/2,-9/2⟩$ states. The data in (a) were taken at a temperature of $2.4\pm 0.8\mu \mathrm{K}$, while the data in (b) were taken at $1.25\pm 0.10\mu \mathrm{K}$ (●) and $2.8\pm 0.4\mu \mathrm{K}$ (□). The error bars are determined from scatter among repeated loss measurements.

Figure 4

Density dependence of $|9/2,-7/2⟩$ atom loss at $B=198.8\mathrm{G}$. The lines are results of best-fit curves that assume either exclusively two-body loss (dashed line) or exclusively three-body loss (solid line).

Figure 5

Comparison of three-body and two-body loss of $|9/2,-7/2⟩$ atoms across the $p$-wave resonance at a temperature of $2.7\pm 0.7\mu \mathrm{K}$. Data shown are $L_3$ (●) and an experimental upper limit on the value of $L_2$ (solid lines). For comparison to $L_3$, $L_2$ is divided by a typical density of $⟨n⟩=3\times {10}^{12}{\mathrm{c}\mathrm{m}}^{-3}$. The dashed line is the result of a close-coupling calculation of the two-body inelastic atom loss rate.