Experimental demonstration of an efficient quantum phase-covariant cloning and its possible applications to simulating eavesdropping in quantum cryptography

摘要

We describe a nuclear magnetic resonance (NMR) experiment which implements anefficient one-to-two qubit phase-covariant cloning machine(QPCCM). In theexperiment we have achieved remarkably high fidelities of cloning, 0.848 and0.844 respectively for the original and the blank qubit. This experimentalvalue is close to the optimal theoretical value of 0.854. We have alsodemonstrated how to use our phase-covariant cloning machine for quantumsimulations of bit by bit eavesdropping in the four-state quantum keydistribution protocol.