What is Possible Without Disturbing Partially Known Quantum States?
Abstract
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 readonly if we are to preserve the state of the system. From this principle, many types of nocloning, nobroadcasting, and noimprinting 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 to derive optimum amount of resources (bits, qubits, and ebits) required in data compression or in quantum teleportation of mixedstate ensembles.
 Publication:

arXiv eprints
 Pub Date:
 January 2001
 arXiv:
 arXiv:quantph/0101144
 Bibcode:
 2001quant.ph..1144K
 Keywords:

 Quantum Physics
 EPrint:
 24 pages, no fogure