How state preparation can affect a quantum experiment: Quantum process tomography for open systems
Abstract
We study the effects of the preparation of input states in a quantum tomography experiment. We show that maps arising from a quantum process tomography experiment (called process maps) differ from the wellknown dynamical maps. The difference between the two is due to the preparation procedure that is necessary for any quantum experiment. We study two preparation procedures: stochastic preparation and preparation by measurements. The stochastic preparation procedure yields process maps that are linear, while the preparations using von Neumann measurements lead to nonlinear processes and can only be consistently described by a bilinear process map. A process tomography recipe is derived for preparation by measurement for qubits. The difference between the two methods is analyzed in terms of a quantum process tomography experiment. A verification protocol is proposed to differentiate between linear processes and bilinear processes. We also emphasize that the preparation procedure will have a nontrivial effect for any quantum experiment in which the system of interest interacts with its environment.
 Publication:

Physical Review A
 Pub Date:
 October 2007
 DOI:
 10.1103/PhysRevA.76.042113
 arXiv:
 arXiv:0706.0394
 Bibcode:
 2007PhRvA..76d2113K
 Keywords:

 03.65.Ta;
 03.65.Yz;
 03.67.Mn;
 Foundations of quantum mechanics;
 measurement theory;
 Decoherence;
 open systems;
 quantum statistical methods;
 Entanglement production characterization and manipulation;
 Quantum Physics
 EPrint:
 13 pages, no figures, submitted to Phys. Rev. A