Quantum Cryptography Over 24 km of Underground Optical Fibers

Richard Hughes, G. G. Luther, George L. Morgan +2 more

Richard Hughes, G. G. Luther, George L. Morgan +1 more

Richard Hughes, W. T. Buttler, Paul G. Kwiat +5 more

The secure distribution of the secret random bit sequences known as `key' material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is an emerging technology for secure key distribution with single-photon transmissions: Heisenburg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal single-photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single- photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. In our optical fiber experiment we have performed quantum key distribution over 24-km of underground optical fiber using single-photon interference states, demonstrating that secure, real-time key generation over `open' multi-km node-to-node optical fiber communications links is possible.

Richard Hughes, Buttler, William T., Kwiat, Paul G. +5 more

The secure distribution of the secret random bit sequences known as {open_quotes}key{close_quotes} material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is an emerging technology for secure key distribution with single-photon transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal single-photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. In our optical fiber experiment we have performed quantum key distribution over 24-km of underground optical fiber using single-photon interference states, demonstrating that secure, real-time key generation over {open_quotes}open{close_quotes} multi-km node-to-node optical fiber communications links is possible. We have also constructed a quantum key distribution system for free-space, line-of-sight transmission using single-photon polarization states, which is currently undergoing laboratory testing. 7 figs.

Paul D. Townsend

Qi-Chao Sun, Yang-Fan Jiang, Ya-Li Mao +12 more

Realizing long-distance entanglement swapping with independent sources in the real-world condition is important for both future quantum networks and fundamental study of quantum theory. Currently, entanglement swapping over a few tens of kilometers of underground optical fiber has been achieved. However, future applications demand entanglement swapping over longer distances in more complicated environments. We exploit two independent 1-GHz-clock sequential time-bin entangled photon-pair sources; develop several automatic stability controls; and successfully implement a field test of entanglement swapping over an optical fiber link of more than 100 km, including coiled, underground, and suspended optical fibers. Our result verifies the feasibility of such technologies for long-distance quantum networks and for many interesting quantum information experiments.