Probabilistic unitary quantum channels

Probabilistic unitary maps and probabilistic unitary quantum channels are introduced, many quantum information applications, including (unambiguous) teleportation, can be described as probabilistic unitary quantum channels. Some properties of probabilistic unitary maps and probabilistic unitary quantum channels are derived. The property of a probabilistic unitary quantum channel ensures certain simple form for the measurements involved in realizing the probabilistic unitary quantum channel. The relation between a probabilistic unitary quantum channel and a uniformly entangled state is established. The combined operation of a noisy quantum channel and the error correction operation is a probabilistic unitary channel, from this point of view the condition for the errors to be correctable is easily derived. The condition for the errors caused by a noisy channel to be correctable with any nonzero probability is also obtained. Dense coding with a partially entangled state can also be viewed as a probabilistic unitary quantum channel when all messages are required to be transmitted with equal probability of success, the maximal achievable probability of success is derived and the optimum protocol is also obtained.