Experimental characterization of quantum dynamics through many-body   interactions
  We report on the implementation of a quantum process tomography (QPT) technique known as direct characterization of quantum dynamics (DCQD) applied on coherent and incoherent single- qubit processes in a system of trapped calcium 40 ions. Using quantum correlations with an ancilla qubit, DCQD reduces exponentially the number of experimental configurations required for standard QPT. With this technique, the system's relaxation times T1 and T2 were measured with a single experimental configuration. We further show the first complete characterization of single-qubit processes using a single generalized measurement realized through multi-body correlations with three ancilla qubits. 
Daniel Nigg, Julio T. Barreiro, Philipp Schindler, Masoud Mohseni,   Thomas Monz, Michael Chwalla, Markus Hennrich and Raine...
quant-ph