Solid-state optimal phase-covariant quantum cloning machine

Here, we report an experimental realization of optimal phase-covariant quantum cloning machine with a single electron spin in solid state system at room temperature. The involved three states of two logic qubits are encoded physically in three levels of a single electron spin with two Zeeman sub-levels at a nitrogen-vacancy defect center in diamond. The preparation of input state and the phase-covariant quantum cloning transformation is controlled by two independent microwave fields. The average experimental fidelity reaches 85.2% which is very close to theoretical optimal fidelity 85.4% and is beyond the bound 83.3% of universal cloning. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624595]