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Optical Realization of Universal Quantum Cloning |
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2005-08-14 |
| Optical Realization of Universal Quantum Cloning |
Guo Guangcan et al
School of Science, USTC
A deterministic and perfect quantum cloner for arbitrary quantum states is forbidden by the quantum no-cloning theorem. But, beyond the no-cloning theorem, the universal symmetric quantum cloning machine was first addressed by Bužek and Hillery. This kind of cloning machine works on any unknown quantum state and produces identical approximate copies equally well (original state also changed). In our experiment, we realized the 1??2 qubit Bužek-Hillery cloning machine (which has been optimized and generalized) with linear optical devices. This method relies on the representation of several qubits by a single photon, i. e. qubits are represented by different freedom degrees of a single photon, such as polarization and location. In the experiment we cloned the polarization qubit to one location qubit and the result showed that the fidelities between the two output qubits and the original qubit are both 5/6 (which proved to be the optimal fidelity of 1??2 qubit universal cloner) for arbitrary input pure states. In the future, quantum cloning may be used to improve the performance of some quantum computation, and may be helpful in understanding the quantum information theory, processing quantum information and eavesdropping versus quantum cryptography. Now we can improve the performance of the measurements on observables by performing measurements on clones of the original quantum system.
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