We theoretically investigate the spectral property of a biphoton state from multiplexed thermal atomic ensembles. This biphoton state originates from the cascade emissions, which can be generated by two weak pump fields under four-wave mixing condition. Under this condition, a signal photon from the upper transition, chosen in a telecommunication bandwidth, can be generated along with a correlated idler photon from the lower infrared transition. We can spectrally shape the biphoton state by multiplexing the atomic ensembles with frequency-shifted emissions, where the entropy of entanglement can be analyzed via Schmidt decompositions. We find that this spectral entanglement increases when more vapor cells are multiplexed with correlated or anti-correlated signal and idler fields. The eigenvalues in Schmidt bases approach degenerate under this multiplexing scheme, and corresponding Schmidt numbers can be larger than the number of the multiplexed vapor cells, showing the enlarged entropy of entanglement and excess correlated modes in continuous frequency spaces. We also investigate the lowest entropy of entanglement allowed in the multiplexing scheme, which is preferential for generating a pure single photon source. This shows the potentiality to spectrally shape the biphoton source, where high-capacity spectral modes can be applied in long-distance quantum communication and multimode quantum information processing.
Single-Image Entanglement Verification with Spatially Encoded Measurement Contexts
University of Ottawa（渥太华大学）；National Research Council of Canada（加拿大国家研究委员会）；Sorbonne Université（索邦大学）；CNRS, Institut des NanoSciences de Paris, INSP（法国国家科学研究中心，巴黎纳米科学研究所）；School of Physics & Astronomy, University of Glasgow（格拉斯哥大学物理与天文学学院）；Institute for Quantum Studies, Chapman University（查普曼大学量子研究所）
