Generation and Detection of Hyperentangled Bell States at an Ultra-High Flux

Abstract

We demonstrate both the generation and detection of an ultra-high flux of polarization Bell states using broadband hyper-entangled bi-photons that are quantum-correlated in both polarization and time-energy. Bell states of polarization embody the most basic form of two-state entanglement, and are a key component of quantum protocols of communication and sensing. High-speed generation, processing and detection of polarization Bell-states is therefore critical for quantum technology. However, all current protocols that employ polarization entangled photons are inherently slow, primarily due to the photo-detectors (Photomultiplier tubes, avalanche photo-diodes, etc.) that can handle only $10^{6-7}$ photons/s, whereas sources may easily produce $10^{10-13}$ photons/s or more (if properly designed). We fully alleviate this detection bottleneck by resorting to physical detection of the bi-photons with nonlinear interferometry. We harness a generalized, dual polarization SU1,1 interferometer to generate, manipulate \textit{and measure} all the triplet Bell-states at a flux of $\sim\!5\times10^{11}$ photons/s, enhancing the speed of quantum processing by >5 orders of magnitude compared to standard methods.