We generate correlated photon pairs at 839 nm and 1392 nm from a single-mode photonic crystal fiber pumped in the normal dispersion regime. This compact, bright, tunable, single-mode source of pair-photons will have wide application in quantum communications.

We develop a theoretical analysis of four-wave mixing used to generate photon pairs useful for quantum information processing. The analysis applies to a single mode microstructured fibre pumped by an ultra-short coherent pulse in the normal dispersion region. Given the values of the optical propagation constant inside the fibre, we can estimate the created number of photon pairs per pulse, their central wavelength and their respective bandwidth. We use the experimental results from a picosecond source of correlated photon pairs using a micro-structured fibre to validate the model. The fibre is pumped in the normal dispersion regime at 708 nm and phase matching is satisfied for widely spaced parametric wavelengths of 586 nm and 894 nm. We measure the number of photons per pulse using a loss-independent coincidence scheme and compare the results with the theoretical expectation. We show a good agreement between the theoretical expectations and the experimental results for various fibre lengths and pump powers.

We demonstrate two key components for optical quantum information processing: a bright source of heralded single photons; and a bright source of entangled photon pairs. A pair of pump photons produces a correlated pair of photons at widely spaced wavelengths (583 nm and 900 nm), via a χ (3) four-wave mixing process. We demonstrate a non-classical interference between heralded photons from independent sources with a visibility of 95%, and an entangled photon pair source, with a fidelity of 89% with a Bell state.Single photons are ideal for quantum technologies, including quantum communication [1] and quantum metrology [2], due to intrinsically low decoherence and easy one-qubit rotations. However, realising two-qubit logic gates for quantum computation requires a massive optical nonlinearity. Measurement-induced nonlinearies can be realised using only single photon sources and detectors, and linear optical networks [3]. Much progress has been made on each of these components, however, progress on linear optical networks is currently limited by the lack of bright single and pair photon sources. Here we describe 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. These sources provide an essential toolkit for photonic quantum information processing.Since the original proposal [3] there have been a number of important theoretical improvements [4,5,6] and experimental proof-of-principal demonstrations [7,8,9,10,11,12], which combined make optical quantum computing promising. Experiments have typically relied on producing photons via spontaneous parametric downconversion, and detecting them with silicon avalanche photodetectors (Si APDs) with intrinsic quantum efficiencies of ∼ 70% and no number resolution. However, the practical limit of standard downconversion is five [11,13] or six [14] photons. Tremendous progress has been made in the development of triggered, high efficiency single photon sources [15,16,17,18] (SPSs) and high efficiency, number resolving single photon detectors [19,20], however, these technolgies will not be commonplace in single photon quantum optics labs for some time. Therefore, in order to make further progress in testing single photon optical circuits for generation of large entangled cluster states, error correcting protocols, and measurement of fault tolerant thresholds, there is an urgent practical need for a bright SPS at the visible wavelengths where Si APDs are efficient.The development of microstructured and photonic crystal fibres [22] (PCFs) enables the engineering of profoundly different optical properties to conventional optical fibres, opening the way for a range of new technologies. PCFs with very small solid cores ( Fig. 1(a)) can have zero dispersion wavele...

In this paper, we demonstrate a source of photon pairs based on four-wave-mixing in photonic crystal fibres. Careful engineering of the phase matching conditions in the fibres enables us to create photon pairs at 597 nm and 860 nm in an intrinsically factorable state showing no spectral correlations. This allows for heralding one photon in a pure state and hence renders narrow band filtering obsolete. The source is narrow band, bright and achieves an overall detection efficiency of up to 21% per photon. For the first time, a Hong-Ou-Mandel interference with unfiltered photons from separate fibre sources is presented.

We demonstrate a picosecond source of correlated photon pairs using a micro-structured fibre with zero dispersion around 715 nm wavelength. The fibre is pumped in the normal dispersion regime at ~708 nm and phase matching is satisfied for widely spaced parametric wavelengths. Here we generate up to 10;7 photon pairs per second in the fibre at wavelengths of 587 nm and 897 nm, while on collecting this light in single-mode-fibre-coupled Silicon avalanche diode photon counting detectors, we detect ~3.2x10;5 coincidences per second at pump power 0.5 mW.