While most quantum-information applications are de

While most quantum-information applications are decades away, some organizations including several banks in Switzerland are already using the technique of "quantum cryptography" to ensure the secrecy of their communications. Quantum key distribution (QKD) allows two parties (by convention called Alice and Bob) to exchange an encryption key, secure in the knowledge that the key – which codes and decodes the data – has not been read by an eavesdropper (called Eve). This guarantee is possible because the key is transmitted in terms of quantum bits (qubits) of information. If intercepted and read by a third party, such qubits are changed irrevocably, which signals to Alice and Bob that Eve has seen the key and so not to use it.

Commercial QKD systems use photons as qubits because the particles can travel long distances in optical fibres without losing their quantum nature. The difficulty, however, is picking out a qubit photon from the noisy background of random photons that are created when much more intense data signals are sent through a commercial telecommunications fibre. One solution that has been adopted is to use "dark fibre", which does not carry any telecommunications data signal. Unfortunately, leasing or laying dark fibre is very expensive.

Precise timing

What the Toshiba and Cambridge researchers have done is to find a way of filtering out the noise and focussing on the qubit photons.
http://physicsworld.com/cws/article/news/2012...usy-fibres