About the Authors
Center for Theoretical Biology and School of Physics, Peking University, Beijing, China
IBM T. J. Watson Research Center, Yorktown Heights, New York, United States of America
The State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing, China
The authors have declared that no competing interests exist.
Conceived and designed the experiments: QO YT. Performed the experiments: LJ YT. Analyzed the data: LJ QO YT. Wrote the paper: LJ QO YT.