September 13, 2013
In this edition of the ARL Fellows Corner, Dr. Howard E. Brandt discusses quantum copiers--the theory, what they are, and how they can be used.
According to the no-cloning theorem of quantum information theory, arbitrary quantum states cannot be cloned because of the linearity of quantum mechanics . The security of quantum key distribution in quantum cryptography depends on this physical fact. The implication is that one cannot produce an exact copy of an arbitrary qubit. This does not mean however that an approximate copy cannot be made. The function of one type of quantum copier is to produce an approximate copy of a qubit that is as close to being an exact copy as possible, and with the original qubit changed as little as possible in the process. A variety of quantum copiers have been considered in the literature on quantum information processing....read more