Controlling the Rotational and Hyperfine State of Ultracold   $^{87}$Rb$^{133}$Cs Molecules
  We demonstrate coherent control of both the rotational and hyperfine state of ultracold, chemically stable $^{87}$Rb$^{133}$Cs molecules with external microwave fields. We create a sample of ~2000 molecules in the lowest hyperfine level of the rovibronic ground state N = 0. We measure the transition frequencies to 8 different hyperfine levels of the N = 1 state at two magnetic fields ~23 G apart. We determine accurate values of rotational and hyperfine coupling constants that agree well with previous calculations. We observe Rabi oscillations on each transition, allowing complete population transfer to a selected hyperfine level of N = 1. Subsequent application of a second microwave pulse allows transfer of molecules back to a different hyperfine level of N = 0. 
Philip D. Gregory, Jesus Aldegunde, Jeremy M. Hutson, and Simon L.   Cornish
cond-mat.quant-gas physics.atom-ph quant-ph