In quantum information theory, a quantum channel is a communication channel that can transmit quantum information, as well as classical information. An example of quantum information is the general dynamics of a qubit. An example of classical information is a text document transmitted over the Internet. Terminologically, quantum channels are completely positive (CP) trace-preserv. Memoryless quantum channelWe will assume for the moment that all state spaces of the systems considered, classical or quantum, are finite. For a purely quantum system, the time evolution, at certain time t, is given by where and H is the and t is the time. This gives a CPTP map in the Schrödinger picture and is therefore a channel. T. Experimentally, a simple implementation of a quantum channel is (or free-space for that matter) transmission of single. Single photons can be transmitted up to 100 km in standard fiber optics before losses dom. Before giving the definition of channel capacity, the preliminary notion of the norm of complete boundedness, or cb-norm of a channel needs to be discussed. When considering the capacity of a channel, we need to co.
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