Abstract
High-fidelity polarization-entangled photons are a powerful resource for quantum communication, distributing entanglement and quantum teleportation. The Bell-CHSH inequality S\leq2S≤2 is violated by bipartite entanglement and only maximally entangled states can achieve S=2\sqrt{2}S=22, the Tsirelson bound. Spontaneous parametric down-conversion sources can produce entangled photons with correlations close to the Tsirelson bound. Sagnac configurations offer intrinsic stability, compact footprint and high collection efficiency, however, there is often a trade off between source brightness and entanglement visibility. Here, we present a Sagnac polarization-entangled source with 2\sqrt{2}-S=(5.65\pm0.57\times10^{-3})22−S=(5.65±0.57×10−3), on-par with the highest SS parameters recorded, while generating and detecting (4660\pm70)pairs/s/mW(4660±70)pairs/s/mW, which is a substantially higher brightness than previously reported for Sagnac sources and around two orders of magnitude brighter than for traditional cone sources with the highest SS parameters. Our source records 0.9953\pm0.00030.9953±0.0003 concurrence and 0.99743\pm0.000140.99743±0.00014 fidelity to an ideal Bell state. By studying systematic errors in Sagnac sources, we identify that the precision of the collection focal point inside the crystal plays the largest role in reducing the SS parameter in our experiment. We provide a pathway that could enable the highest SS parameter recorded with a Sagnac source to-date while maintaining very high brightness.
Highlights
Sagnac configurations offer intrinsic stability, compact footprint and high collection efficiency, there is often a trade off between source brightness and entanglement vi√sibility. 2 2−S =
By studying systematic errors in Sagnac sources, we identify that the precision of the collection focal point inside the crystal plays the largest role in reducing the S parameter in our experiment
We provide a pathway that could enable the highest S parameter recorded with a Sagnac source to-date while maintaining very high brightness
Summary
Polarization-entangled photons have demonstrated striking quantum phenomena such as quantum teleportation [1, 2], multi-photon entanglement [3], long-distance quantum communication [4] and loophole-free Bell tests [5, 6]. Sagnac interferometer sources occupy minimal space and utilize colinear SPDC in periodically poled crystals, meaning no generated photons are rejected [8,9,10,11,12,13,14,15]. They enable very high fidelity Bell state generation as only the propagation directions must be indistinguishable which can be straightforward to implement unlike, for example, spectral indistinguishability. Are the dominant factors limiting our source and we predict that, with feasible improvements, our source could halve the gap to the Tsirelson bound without reducing the high brightness
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
