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Experimental quantum key distribution without monitoring signal disturbance


Quantum key distribution (QKD) is a method of realizing private communication securely against an adversary with unlimited power. The QKD protocols proposed and demonstrated over the past 30 years relied on the monitoring of signal disturbance to set an upper limit to the amount of leaked information. Here, we report an experimental realization of the recently proposed round-robin differential-phase-shift protocol. We used a receiver set-up in which photons are randomly routed to one of four interferometers with different delays so that the phase difference is measured uniformly over all pair combinations among five pulses comprising the quantum signal. The amount of leak can be bounded from this randomness alone, and a secure key was extracted even when a finite communication time and the threshold nature of photon detectors were taken into account. This demonstrates the first QKD experiment without signal disturbance monitoring, thus opening up a new direction towards secure communication.

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Figure 1: Experimental set-up for RRDPS QKD.
Figure 2
Figure 3: Experimental results.
Figure 4: Results of finite-key security analysis.


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The authors thank Y. Yamamoto, T. Yamada and M. Oguma for discussions. This work was funded in part by the ImPACT Program of the Council for Science, Technology and Innovation (Cabinet Office, Government of Japan) and the Photon Frontier Network Program (MEXT).

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Authors and Affiliations



H.T. designed and constructed the experimental set-up and performed the QKD experiments. T.S. and M.K. designed the detailed procedure for secure key generation. H.T., T.S. and K.T. undertook the data analysis. M.K. led the project. All authors discussed the results and wrote the paper.

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Correspondence to Hiroki Takesue or Toshihiko Sasaki.

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The authors declare no competing financial interests.

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Takesue, H., Sasaki, T., Tamaki, K. et al. Experimental quantum key distribution without monitoring signal disturbance. Nature Photon 9, 827–831 (2015).

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