Entangled photon pair sources

Engineering bright sources

The team actively investigates designs and concepts for the generation of entangled photon pairs, and evaluates if these designs are suitable for implementation into portable instruments, such as SPEQS. 

The photon pairs are typically generated via the SPDC process where an individual pump photon within an appropriate non-linear material is sometimes split into a pair of lower energy photons, while obeying energy and momentum conservation. 

We have published results on new designs as well as on optimization criteria.

In 2018, the team published two papers describing in detail a novel arrangement of crystals to enable bright polarization-entangled photon pairs. The novelty stemmed from the use of two non-linear crystals with parallel-aligned axes and was called Parallel Aligned Crystals Entanglement Source (PACES). The results were  published in Optics Express and Applied Physics Letters, and featured also in CQT's Highlights. The major result of PACES is that it reduces the effects of spatial walk-off allowing easier photon pair collection, but also could allow very bright, high quality entangled photon pairs to be generated. In fact, the brightness of over 100,000 detected pairs per second per mW of pump power, has only been observed by specially engineered crystals in the past, and not in the conventional, single-domain crystals used in PACES.

The team also works on optimization work, exploring the interplay of walk-off with beam sizes. The results are available in a paper called "Thick-crystal regime in photon pair sources" from the journal Optica. This paper was also featured on CQT's Highlights page.

Fig. 1. The experimental setup for collecting the emitted photon pairs.

Fig. 2. The collection efficiency and brightness observed for different pump and collection beam parameters.