Experimental characterization of cluster states using fibre sources

Spontaneous four wave mixing (FWM) in photonic crystal fibre (PCF) is a promising approach to improved sources of photon pairs for quantum information applications. When pumped by a bright pulsed laser, the χ³ nonlinearity of silica can produce correlated photons between a signal and idler wavelength equally spaced above and below the pump in frequency [1]. In PCF, the microstructure surrounding the silica core can be chosen to engineer the dispersion of the fibre, which allows control of the phase-matched signal and idler wavelengths, and even over the degree of spectral correlation between signal and idler - in particular, avoiding all spectral correlation can result in heralded photons in an intrinsically pure quantum state, without the usual need for lossy filtering [2]. Other advantages of PCF include a high brightness with moderate pump power due to the small guided mode area and long interaction length, and good coupling efficiency to single mode fibre for detection because the photons are generated in a similar mode shape.