We introduce a condition for memoryless quantum channels which, when satisfied guarantees the multiplicativity of the maximal l p -norm with p a fixed integer. By applying the condition to qubit channels, it can be shown that it is not a necessary condition, although some known results for qubits can be recovered. When applied to the Werner-Holevo channel, which is known to violate multiplicativity when p is large relative to the dimension d, the condition suggests that multiplicativity holds when d≥ 2p-1. This conjecture is proved explicitly for p=2,3,4. Finally, a new class of channels is considered which generalizes the depolarizing channel to maps which are combinations of the identity channel and a noisy one whose image is an arbitrary density matrix. It is shown that these channels are multiplicative for p=2.
|Titolo:||Conditions for multiplicativity of maximal lp-norms of channels for integer p|
|Data di pubblicazione:||2005|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1063/1.1862094|
|Appare nelle tipologie:||1.1 Articolo in rivista|