Generation of spin-motion entanglement in a trapped ion using   long-wavelength radiation
  Applying a magnetic field gradient to a trapped ion allows long-wavelength microwave radiation to produce a mechanical force on the ion's motion when internal transitions are driven. We demonstrate such a coupling using a single trapped \Yb{171}~ion, and use it to produce entanglement between the spin and motional state, an essential step towards using such a field gradient to implement multi-qubit operations. 
K. Lake, S. Weidt, J. Randall, E. Standing, S. C. Webster, W. K.   Hensinger
quant-ph