Quantum Directions

                         Ramon Muñoz-Tapia
                  Univ. Autonoma de Barcelona-IFAE


  Imagine that Bob went into an intergalactic journey. Because of a
classical computer failure, he is completely lost in space. At the
earth base, Alice still shares a one way quantum channel with
Bob. In the absence of a common reference frame, the only way to
indicate Bob the direction to go  back home is to send a physical
object pointing into that direction. In the quantum realm these
objects are spin systems. I review the optimal protocols for
encoding and decoding this analogical information. I will also present 
other related problems in the general framework of of quantum state
estimation.