Ancilla-assisted quantum process tomography.

  title={Ancilla-assisted quantum process tomography.},
  author={Joseph Altepeter and David Branning and Evan Jeffrey and Tzu-Chieh Wei and Paul G. Kwiat and Rob Thew and Jeremy Lloyd O'Brien and Michael A. Nielsen and A. G. White},
  journal={Physical review letters},
  volume={90 19},
Complete and precise characterization of a quantum dynamical process can be achieved via the method of quantum process tomography. Using a source of correlated photons, we have implemented several methods, each investigating a wide range of processes, e.g., unitary, decohering, and polarizing. One of these methods, ancilla-assisted process tomography (AAPT), makes use of an additional "ancilla system," and we have theoretically determined the conditions when AAPT is possible. Surprisingly… 

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