Towards a source of photon pairs with spatial-polarization–frequency hybrid entanglement based on birefringent few-mode fibers

Abstract: 

Optical fiber-based sources of photon pairs with hybrid entanglement across multiple degrees of freedom (DOFs) are essential for a wide range of quantum technologies, while remaining compatible with existing communication networks [1]. In this talk, I will present a new scheme for the generation of photon pairs with hybrid entanglement in the spatial-polarization-frequency DOFs using a birefringent few-mode fiber [2]. This entanglement is realized by spectrally overlapping two pairs of signal-idler bands generated in a single intermodal-vectorial four-wave-mixing process involving four distinct modes. Using the phase-matching conditions, I will show that the pairs of bands become spectrally indistinguishable when the group refractive indices of the signal and idler modes intersect at the pump wavelength. The theoretical predictions are confirmed through experimental observations corroborated by numerical simulations. Finally, I will discuss how the two-photon state associated with the overlapping bands can be engineered into a maximally entangled Bell state. 

[1] K. Garay-Palmett, D. B. Kim, Y. Zhang, F. A. Domínguez-Serna, Vi. O. Lorenz, and A. B. U’Ren, “Fiber-based photon-pair generation: tutorial,” Journal of the Optical Society of America B 40, 469 (2023). 
[2] A. Gawlik, M. Bernaś, K. Żołnacz, and K. Tarnowski, “Spectrally indistinguishable intermodal-vectorial four-wave-mixing in birefringent few-mode fibers for spatial-polarization-frequency hybrid-entangled photon-pairs generation,” arXiv:2412.09214, http://arxiv.org/abs/2412.09214 (2024).