Paper appeared in Scientific Reports

03.08.2017

Our paper on "A novel single-crystal & single-pass source for polarisation- and colour-entangled photon pairs" appeared in Scientific Reports.

We demonstrate a new generation mechanism for polarisation- and colour-entangled photon pairs. In our approach we tailor the phase-matching of a periodically poled KTP crystal such that two downconversion processes take place simultaneously. Relying on this effect, our source emits entangled bipartite photon states, emerging intrinsically from a single, unidirectionally pumped crystal with uniform poling period. Its property of being maximally compact and luminous at the same time makes our source unique compared to existing photon-entanglement sources and is therefore of high practical significance in quantum information experiments.

 

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Possible configurations allowing for intrinsic entanglement of photons generated by CDDC in ppKTP. The blue and red lines represent the short- and longwave photons respectively (each coming in both polarisations H and V); the green line represents the wavelength of the pump laser. The dashed purple line and corresponding inset graph highlight our specific experimental setup with λ p0 = 532.3 nm, λ B  = 904.3 nm and λ R  = 1293.9 nm. With increasing crystal periodicity Λ the wavelengths λ B and λ R are approaching each other which gives rise to the opportunity of creating entangled photon pairs with similar bandwidths and group velocities, as depicted by the right inset graph over the light blue dashed line. The calculations were performed assuming a crystal temperature of T = 50 °C. However, the actual temperature required for accurate matching of horizontal and vertical wavelength may vary due to imperfection of the used dispersion equations.