“Asynchronous” Quantum Cryptography

The MIT Technology Review has reported a breakthrough in quantum cryptography from Anthony Laing of the University of Bristol, and several colleagues. While quantum cryptography promises to furnish unbreakable key exchange protocols for example, there are many practical problems to be solved before such systems can be considered industrial grade. The main drawback is that quantum cryptography

can only be used over point-to-point connections and not through networks where data has to be routed. That's because the routing process destroys the quantum properties of the photons used to secure messages.

The relevant properties of the photons are maintaining perfect alignment so that polarisation measurements at the receiver can be done accurately. But unfortunately network or satellite routing is not very alignment-friendly.

Laing and his colleagues have devised a way to circumvent the alignment problem by encoding an additional dimension in the qubits that is independent of space. In physics jargon the qubits are “reference frame independent”, making their encoded information far more robust to transmission. This reminded me of asynchronous data communication where timing information is sent as part of the data so that the sender and receiver do not need to maintain common clocking information.

Full paper here (4 pages).

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