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.

Figures (4)

• Figure 1: Concept for the generation and detection of hyper-entangled photons: Polarization entangled bi-photons are generated by a pair of crossed type-0 nonlinear crystals, where each crystal acts as an OPA for one polarization (generating the $\Phi^{\pm}$ states) via SPDC over a broad bandwidth (limited by phase matching). Phase and polarization manipulations allow complete manipulation of the polarization Bell-state and selection of the detection basis. Another identical pair of crossed crystals detects the quantum state of the light by further amplification or annihilation of the bi-photons from the first pair, depending on the relative phase between the pair and the pump in each polarization (forming a dual-polarization SU1,1 interferometer).
• Figure 2: Experimental layout
• Figure 3: Raw Camera Images; $A-C$ show $HH+VV, HH-VV, HV+VH$ accordingly.
• Figure 4: Simulated and experimental results: $A-C$ show the measured spectra of $HH+VV,HH-VV,HV+VH$ accordingly; $D-F$ depict the simulated spectra of $HH+VV,HH-VV,HV+VH$ accordingly.