Measurement based quantum computing in optical fibres
Alex Clark
University of Bristol, United Kingdom
Abstract: Single photons make excellent qubits due to extremely low intrinsic decoherence, and ease of manipulation at the single qubit level. The difficulty for quantum computing has been in realising the interactions between single photons that are required for two-qubit logic gates. The breakthrough proposed in 2001 by Knill Laflamme and Milburn used single photon measurements to non-deterministically induce the required interactions. Although scalable in principle, the non-deterministic gates made the resource overhead in this scheme tremendous. This overhead was dramatically decreased by Nielsen, and Browne and Rudolph, who applied the ideas of measurement based quantum computing. Optical quantum computing is now a promising approach to realising a scalable architecture.
In parallel with these theoretical developments, there have been a number of demonstrations of two qubit logic gates, and even the generation and manipulation of small optical cluster states. Further progress is currently limited by the lack of bright single and entangled pair photon sources. We demonstrate a solution based on photonic crystal fibres: four wave mixing produces a correlated pair of photons at widely spaced wavelengths (583nm and 900nm). We demonstrate a bright source of heralded single photons, exhibiting a non-classical interference visibility of 95% for independent sources; and a bright entangled pair source, with 89% fidelity with a maximally entangled state [1]. Finally we demonstrate an all-fibre implementation of an entangling logic gate that can be used to build up multi-photon cluster states. Combined, these components represent an essential toolkit for exploring measurement based quantum computing with single photons.
[1] Fulconis, Alibart, O’Brien, Wadsworth, Rarity, submitted to Nature Physics