As two forms of the quantum entanglement control (QEC), the quantum entanglement swapping and preservation are demonstrated in a three-qubit nuclear magnetic resonance (NMR) quantum computer. The pseudopure state is prepared to represent the entangled states through macroscopic signals. Through controlling the interactions between the system and its environment, we can preserve an initial entangled state for a longer time. Experimental results show an agreement between theory and experiment.
The influence of the disturbance caused by the imperfection of the engineering coupling constants in the perfect state transfer is calculated. The results show that the fidelity for the perfect state transfer is seriously affected by the errors occurring near the input and output spins. Such results are helpful for the realization of the perfect state transfer in the case where there exist errors in experiments.
We present a complete multiple round quantum dense coding scheme for improving the source ca-pacity of that introduced recently by Zhang et al. The receiver resorts to two qubits for storing the four local unitary operations in each round.
LI ChunYan1,2,LI XiHan1,2,DENG FuGuo1,2,3,ZHOU Ping1,2 & ZHOU HongYu1,2,3 1 Key Laboratory of Beam Technology and Material Modification of Ministry of Education,Beijing Normal University,Beijing 100875,China
Dense coding using superpositions of Bell-states is proposed. The generalized Grover's algorithm is used to prepare the initial entangled states, and the reverse process of the quantum algorithm is used to determine the entangled state in the decoding measurement. Compared with the previous schemes, the superpositions of two Bell-states are exploited. Our scheme is demonstrated using a nuclear magnetic resonance (NMR)quantum computer. The corresponding manipulations are obtained. Experimental results show a good agreement between theory and experiment. We also generalize the scheme to transmit eight messages by introducing an additional two-state system.
ZHANG Jingfu, XIE Jingyi, DENG Zhiwei & LU Zhiheng Key Laboratory for Quantum Information and Measurements, Department of Physics, Tsinghua University, Beijing 100084, China
