Probing Pair-Correlated Fermionic Atoms through Correlations in Atom Shot Noise

Pair-correlated fermionic atoms are created through dissociation of weakly bound molecules near a magnetic-field Feshbach resonance. We show that correlations between atoms in different spin states can be detected using the atom shot noise in absorption images. Furthermore, using time-of-flight imaging we have observed atom pair correlations in momentum space.

Figure 1

Atom shot noise in a time-of-flight (TOF) absorption image. (a) One spin state of a weakly interacting, two-component, degenerate Fermi gas with $2.3\times {10}^5$ atoms per spin state is imaged after 19.2 ms of expansion. (b) The noise on the absorption image was extracted using a filter with an effective bin size of $15.5\mu \mathrm{m}$. (c) The noise at the cloud center (●) is dominated by atom shot noise, while the noise at the edge of the image (○) shows the photon shot noise. The noise in $\mathrm{OD}$ decreases when averaged over a larger bin size. The predicted dependence for atom and photon shot noise is shown by the solid and dashed lines, respectively.

Figure 2

Pair-correlated atoms. We plot the measured noise correlation as a function of a relative angle of rotation between absorption images of atoms in the two spin states (inset), averaged over 11 image pairs. The effective bin size is $10.3\mu \mathrm{m}$. Spatial pair correlations ${\tilde{\mathcal{G}}}_{\alpha \beta }(0)$ can clearly be seen when molecules are dissociated after expansion and then the atoms are immediately imaged [(a) and ● in (b)]. The correlation signal disappears when the molecules are dissociated during an early stage of expansion [○ in (b)]. By changing the low-pass filter to correspond to larger effective bin sizes, we measure a correlation signal as large as $75\%$ (b). However, the signal-to-noise ratio in detecting the correlation is maximized for a lower effective bin size (c).

Figure 3

(a) Atoms with equal but opposite momenta are found on opposite sides of the atom cloud in TOF expansion. (b) This atom absorption image was taken after rf photodissociation of weakly bound molecules using an rf detuning of $\Delta {\nu }_{\mathrm{rf}}=1.3\mathrm{MHz}$. The pair-correlated atoms compose an expanding spherical shell, containing approximately $1.3\times {10}^5$ atoms per spin state, which appears as a ring around a small cloud of residual atoms and molecules in the 2D absorption image.

Figure 4

Atom pair correlations in momentum space. (a) The averaged correlation signal for 102 image pairs shows a peak for atoms with equal but opposite momenta. The effective bin size is $15.5\mu \mathrm{m}$. (b) For large effective bins, we observe a correlation signal as high as 30%. The signal-to-noise ratio is on the order of 10.