The paper, titled “High Extraction Efficiency Source of Photon Pairs Based on a Quantum Dot Embedded in a Broadband Micropillar Cavity” demonstrates device producing photon pairs with world-class efficiency that does not compromise on bandwidth.

Sources of entangled photons are a key enabler of quantum technology. In particular quantum communication is reliant on the ability to distribute quantum correlations encoded on photons between multiple parties. The current workhorse for these protocols are photons produced from spontaneous parametric down conversion or attenuated laser sources. Both suffer from low single photon probabilities that can limit the scaling and bit rate in quantum networks. The optimal source would be an on-demand pair of entangled photons that can be produced at fast rates.

The exciton-biexciton cascade in QDs has the potential to provide an on-demand source of entangled photon-pairs. The optical transitions are fast (>GHz) and photons can be collected with highly efficient integrated photonic structures. The challenge is ensuring the collection efficiency for both the exciton and the biexciton remains high. This necessitates the use of broad band photonic modes that can efficiently couple to the two spectrally separate transitions (~nm).

This paper demonstrates using a broadband (low Q-factor) pillar microcavity that pairs with an efficiency of ~70% can be collected. The high performance was enabled by micropillar cavity design that features strong suppression of emissions into non-cavity modes, which with further optimizations can be reach values >80%. What makes this device exceptional is the outstanding performance combined with an extremely low fabrication complexity. This greatly increases potential device yield and provides a near term route to highly efficient entangled photon pair sources.

Read the full paper here: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.033601