document: Operations that do not disturb partially known quantum states Consider a situation in which a quantum system is secretly prepared in a state chosen from the known set of states . We present a principle that gives a definite distinction between the operations that preserve the states of the system and those that disturb the states . The principle is derived by alternately applying a fundamental property of classical signals and a fundamental property of quantum ones . The principle can be cast into a simple form by using a decomposition of the relevant Hilbert space , which is uniquely determined by the set of possible states . The decomposition implies the classification of the degrees of freedom of the system into three parts depending on how they store the information on the initially chosen state : one storing it classically , one storing it nonclassically , and the other one storing no information . Then the principle states that the nonclassical part is inaccessible and the classical part is read-only if we are to preserve the state of the system . From this principle , many types of no-cloning , no-broadcasting , and no-imprinting conditions can easily be derived in general forms including mixed states . It also gives a unified view on how various schemes of quantum cryptography work . The principle helps one to derive optimum amount of resources -LRB- bits , qubits , and ebits -RRB- required in data compression or in quantum teleportation of mixed-state ensembles
doc_bio_tags: O O O O O B I I I O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B O B O O B O O O O O O O B I O O O
extractive_keyphrases: partially known quantum states quantum system classical signals hilbert space degrees of freedom nonclassical part quantum cryptography bits qubits ebits quantum teleportation
abstractive_keyphrases: secretly prepared quantum state mixed-state ensembles