Frequency-bin entanglement-based quantum key distribution

Entanglement is an essential ingredient in many quantum communication protocols. In particular, entanglement can be exploited in quantum key distribution (QKD) to generate two correlated random bit strings whose randomness is guaranteed by the non-local property of quantum mechanics. While QKD protocols based on polarization and time-bin entanglement have been experimentally realized, secure key distribution based on frequency-bin entangled photon sources have not yet been demonstrated. We experimentally implement the BBM92 protocol using a frequency-bin encoded entangled state, generated by an integrated source of photon pairs in a silicon photonic chip. We execute a passive basis selection scheme and simultaneously record sixteen projective measurements over two mutually unbiased basis sets. An adaptive rotation of the measurement base is introduced to compensate the random relative phase fluctuation b e tween t h e t w o 1 5 -GHz-spaced frequency bins in a fiber l o op. S t able t r ansmission o ver a 2 6 k m fi be r sp oo l is de mo nstrated wi th a se cr et ke y ra te ≥ 4.5 bit/s.