title: Experimental optimal single qubit purification in an NMR quantum information processor.
abstract: High quality single qubits are the building blocks in quantum information processing. But they are vulnerable to environmental noise. To overcome noise, purification techniques, which generate qubits with higher purities from qubits with lower purities, have been proposed. Purifications have attracted much interest and been widely studied. However, the full experimental demonstration of an optimal single qubit purification protocol proposed by Cirac, Ekert and Macchiavello [Phys. Rev. Lett. 82, 4344 (1999), the CEM protocol] more than one and half decades ago, still remains an experimental challenge, as it requires more complicated networks and a higher level of precision controls. In this work, we design an experiment scheme that realizes the CEM protocol with explicit symmetrization of the wave functions. The purification scheme was successfully implemented in a nuclear magnetic resonance quantum information processor. The experiment fully demonstrated the purification protocol, and showed that it is an effective way of protecting qubits against errors and decoherence.
authors.affiliation: 1] State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China [2] The Innovative Center of Quantum Matter, Beijing 100084, China [3] Tsinghua National Laboratory of Information Science and Technology, Beijing 100084, China.
authors.forename: Shi-Yao
authors.initials: SY
authors.lastname: Hou
authors.affiliation: 1] State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China [2] Institute of Signal Processing Transmission, Nanjing University of Posts and Telecommunications, Nanjing, 210003, China.
authors.forename: Yu-Bo
authors.initials: YB
authors.lastname: Sheng
authors.affiliation: 1] State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China [2] The Innovative Center of Quantum Matter, Beijing 100084, China [3] Tsinghua National Laboratory of Information Science and Technology, Beijing 100084, China.
authors.forename: Guan-Ru
authors.initials: GR
authors.lastname: Feng
authors.affiliation: 1] State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China [2] The Innovative Center of Quantum Matter, Beijing 100084, China [3] Tsinghua National Laboratory of Information Science and Technology, Beijing 100084, China.
authors.forename: Gui-Lu
authors.initials: GL
authors.lastname: Long