Heralded amplification of nonlocality via entanglement swapping for long-distance device-independent quantum key distribution
○Yoshiaki Tsujimoto（NICT）・Chenglong You（LSU）・Kentaro Wakui・Mikio Fujiwara・Kazuhiro Hayasaka・Shigehito Miki・Hirotaka Terai・Masahide Sasaki（NICT）・Jonathan P. Dowling（LSU）・Masahiro Takeoka（NICT）
||To realize the practical implementation of device-independent quantum key distribution~(DIQKD), the main difficulty is that its security relies on the detection-loophole-free violation of the Clauser-Horne-Shimony-Holt~(CHSH) inequality, i.e. the CHSH value $S>2$.
One of the simplest methods to circumvent the loss in the transmission
channel, which creates the detection loophole, is to utilize the entanglement swapping relay~(ESR).
Here, we propose
an improved version of the heralded nonlocality amplifier protocol based on the ESR, and numerically show that our scheme is much more robust against the transmission loss than the previously developed protocol.
In experiment, we observe that the obtained probability distribution is in excellent agreement with those expected by the numerical simulation with experimental parameters which are precisely characterized in a separate measurement.
Moreover, after the transmission of 10~dB loss,
the nonlocality of the heralded state just before detection is estimated to be $S=2.104>2$, which indicates that our final state possesses strong nonlocality even with various experimental imperfections.
Our result clarifies an important benchmark of the ESR protocol, and paves the way towards the long-distance realization of the loophole-free CHSH-violation as well as DIQKD.
||量子通信 / 量子暗号 / パラメトリック下方変換 / 量子もつれ光子対 / ベルの不等式 / / /
||Quantum communication / Quantum cryptography / Spontaneous parametric-down conversion / entangled photon pair / Bell inequality / / /
||Print edition: ISSN 0913-5685 Online edition: ISSN 2432-6380