A Principle Behind No-cloning and No-imprinting Theorems

摘要

Consider a situation in which a quantum system is secretly prepared in a state chosen from the known set of n states. We present a principle that gives a definite distinction between the operations that preserve the marginal states of the system and those that do not. Many types of no-cloning and no-imprinting conditions for mixed states and entangled states can easily be derived from this principle. The principle also gives a unified view on how various schemes of quantum cryptography work.