Ultracold Ground-State $^{87}$Rb$_2$ Formation using Nanosecond-Timescale Frequency-chirped Light

We present results on ultracold molecule formation using frequency-chirped pulses. The chirps, either positive or negative, sweep 1 GHz in 100 ns through a photoassociation resonance located below the $D_2$ line in $^{87}$Rb. The intensity pulses are Gaussian with a full width at half-maximum (FWHM) of 40 ns. We use resonantly-enhanced multi-photon ionization to directly detect ground-state $^{87}$Rb$_2$ formed through photoassociation by linearly frequency-chirped pulses and subsequent spontaneous decay. In particular, we measure the rates of formation ($R$) and photodestruction ($\Gamma_{\mathrm{PD}}$) for positive and negative frequency-chirped pulses, as well as for unchirped pulses. We find that unchirped pulses yield higher values of both $R$ and $\Gamma_{\mathrm{PD}}$ than those of positively-chirped pulses, whose values in turn are greater than those of negatively-chirped pulses. Our results are an important step towards coherent control of ultracold ground-state molecule formation. This work is supported by DOE.