From Bits to Qubits: Quantum Information Processing using Quantum Optics

24 November 2011

On 16 November Professor Sir Peter Knight, President of the Institute of Physics, explained the limitations of Bits and how Qubits have the potential to greatly increase processing speed and communication.

From Bits to Qubits

The first quantum algorithms were created by Peter Short and were capable of rapidly factorising large numbers. This in turn could break keys in encrypted communications. 

Quantum communication can allow the sending and reception of secure information with the ability to see if the communication has been intercepted. 

This is because the uncertainty principle states that ’a quantum system cannot be measured without disturbing it’. Qubits of light having one of two polarizations, eg vertically and horizontally can be used to represent, 1 or 0. 

A key is sent using a string of randomly polarized photons. The receiver randomly detects the information using two analysers. The sender then states the correct analyser settings and this allows the receiver to pick out the key from the results. 

Arthur Ekert proposed a system using entangled pairs of photons where any detection by an eavesdropper would destroy the correlation. Experiments have now been conducted over distances approaching 150 km and 1 megabits/second has been achieved over 50 km, enough for video conferencing. 

Different systems used for the quantum processor were discussed, correlated spin states of hydrogen nuclei, NMR, trapped atoms and atom chips. Nature could well have got here before us as experiments indicate that entanglement has a role in fast information exchange during photosynthesis. 

Quantum coherence seems to have a role with bird navigation and could improve the efficiency solar energy devices. A fascinating talk around the topic including new developments.

The IOP booklet ‘The Age of the Qubit’ by Nina Hall extends the above information, as did Professor Sir Peter Knight's talk.