Experimentally obtaining the Likeness of Two Unknown Quantum States on   an NMR Quantum Information Processor
  Recently quantum states discrimination has been frequently studied. In this paper we study them from the other way round, the likeness of two quantum states. The fidelity is used to describe the likeness of two quantum states. Then we presented a scheme to obtain the fidelity of two unknown qubits directly from the integral area of the spectra of the assistant qubit(spin) on an NMR Quantum Information Processor. Finally we demonstrated the scheme on a three-qubit quantum information processor. The experimental data are consistent with the theoretical expectation with an average error of 0.05, which confirms the scheme. 
Fei Xue, Jiangfeng Du, Xianyi Zhou, Rongdian Han, Jihui Wu