Researchers from the Centre for Quantum Photonics, have published their findings on this natural phenomena. They report on a silicon photonic chip which integrates resonant-enhanced sources, filters, and reconfigurable optics to generate a path-entangled two-qubit state--the smallest non-trivial cluster state--and to coherently analyse its entanglement on-chip.

The team led by PhD Students Joshua Silverstone and Raffaelle Santagati, show that two ring-resonator-based spontaneous four-wave mixing (SFWM) sources can be made highly indistinguishable, despite their well-documented nonlinear dynamics, and they show the first evidence that their frequency correlations are small, as predicted.

Using quantum state tomography, and the strict Bell-CHSH inequality violation to quantify the entanglement present in the device, and use that entanglement as an indicator of device performance. Finding a 91+/-1% overlap with a maximally entangled state, and a Bell-CHSH violation of 2.69+/-0.03, demonstrating a very high level of entanglement.

Their quantum photonic device is the most functionally complex ever: it integrates components which will be invaluable for building devices and systems to harness quantum entanglement on the large scale.

If you would like to read more about their work you can find the full article on the arXiv website.