Generation and distribution of high-dimensional frequency-entangled   qudits
  We demonstrate a novel scheme to generate frequency-entangled qudits with dimension number higher than 10 and to distribute them over optical fibers of 15 km in total length. This scheme combines the technique of spectral engineering of biphotons generated by spontaneous parametric down-conversion and the technique of spectrally resolved Hong-Ou-Mandel interference. We characterized the comb-like spectral correlation structures of the qudits by time of arrival measurement and correlated spectral intensity measurement. The generation and distribution of the distinct entangled frequency modes may be useful for quantum cryptography, quantum metrology, quantum remote synchronization, as well as fundamental test of stronger violation of local realism. 
Rui-Bo Jin, Ryosuke Shimizu, Mikio Fujiwara, Masahiro Takeoka, Ryota   Wakabayashi, Taro Yamashita, Shigehito Miki, Hirotaka...
quant-ph