  The development of key devices and systems in quantum information technology,
such as entangled particle sources, quantum gates and quantum cryptographic
systems, requires a reliable and well-established method for characterizing how
well the devices or systems work. We report our recent work on experimental
characterization of pulsed entangled photonic states and photonic quantum
channels, using the methods of state and process tomography. By using state
tomography, we could reliably evaluate the states generated from a two-photon
source under development and develop a highly entangled pulsed photon source.
We are also devoted to characterization of single-qubit and two-qubit photonic
quantum channels. Characterization of typical single-qubit decoherence channels
has been demonstrated using process tomography. Characterization of two-qubit
channels, such as classically correlated channels and quantum mechanically
correlated channels is under investigation. These characterization techniques
for quantum states and quantum processes will be useful for developing photonic
quantum devices and for improving their performances.
