Optical coherent states are classical light fields with high purity, and are essential carriers of information in optical networks. If these states could be controlled in the quantum regime, allowing for their quantum superposition (referred to as a Schrödinger-cat state), then novel quantum-enhanced functions such as coherent-state quantum computing (CSQC)1,2,3,4,5, quantum metrology6,7 and a quantum repeater8,9 could be realized in the networks. Optical cat states are now routinely generated in laboratories. An important next challenge is to use them for implementing the aforementioned functions. Here, we demonstrate a basic CSQC protocol, where a cat state is used as an entanglement resource for teleporting a coherent state with an amplitude gain. We also show how this can be extended to a loss-tolerant quantum relay of multi-ary phase-shift keyed coherent states. These protocols could be useful in both optical and quantum communications.
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Qubit-Programmable Operations on Quantum Light Fields
Scientific Reports Open Access 15 October 2015
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The authors acknowledge helpful discussions with K. Wakui, M. Takeoka, K. Hayasaka, M. Fujiwara, T.C. Ralph, A.P. Lund, K. Tamaki and M. Koashi. This work was partly supported by the Quantum Information Processing Project in the Program for World-Leading Innovation Research and Development on Science and Technology (FIRST) and by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (Ministry of Education, Science, and Technology; no. 2010-0018295).
The authors declare no competing financial interests.
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Neergaard-Nielsen, J., Eto, Y., Lee, CW. et al. Quantum tele-amplification with a continuous-variable superposition state. Nature Photon 7, 439–443 (2013). https://doi.org/10.1038/nphoton.2013.101
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