Mode-locked Bloch oscillations in a ring cavity
  We present a new technique for stabilizing and monitoring Bloch oscillations of ultracold atoms in an optical lattice under the action of a constant external force. In the proposed scheme, the atoms also interact with a unidirectionally pumped optical ring cavity whose one arm is collinear with the optical lattice. For weak collective coupling, Bloch oscillations dominate over the collective atomic recoil lasing instability and develop a synchronized regime in which the atoms periodically exchange momentum with the cavity field. 
M. Samoylova, N. Piovella, D. Hunter, G.R.M. Robb, R. Bachelard, and   Ph.W. Courteille
cond-mat.quant-gas