Photon-pair generated by spontaneous parametric down-conversion (SPDC) entangled in the degree of freedom of orbital angular momentum(OAM).1958aniUhnCi vfeor syigtyol oofn ShccieeTn cde anAn annual-ring type quasi-phase-matching crystal for generation of narrow-band high-dimensional entanglment1111Yi-Lin Hua , Zong-Quan Zhou , Chuan-Feng Li , and Guang-Can Guo1. Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, 230026IntroductionConclusionsThis entanglement is naturally wide-band, hard to be applied in quantummemories and other tasks of quantum information. We notice that narrow -band entanglement can be realized by optical filtering, but the high-order modes will decrease dramatically because of phase mismatching.Design of quasi-phase matching(QPM) grating can eliminate the phase mismatching. The dimensionality of the entanglement can be greatlyenhanced and the quality of entanglement can be improved effectively =2p0 =p0 =1/2p0Narrow band dilemmaDesigns of QPM crystalEffect of design Diagram of the cross-section views of two special designs of the quasi-phase-matching grating. We only display right half part the QPM grating. The structures are circularly symmetric as shown by the circular structures on both sides so the rectangles in the middle are cylinders as a matter of fact. Only a few orders of modes are shown in the designs, but actually the designs can support quite wide range of modes.(a) Accurate design of QPM crystal(b)Approximate design of QPM crystalThe relative brightness of the 5-lowest-order of modes and its relationship with temperature.(a),(b)and (c) under different parameters(a) The spiral bandwidths of the narrow-band state with and without accurate compensation of the phase mismatching(b) The fidelities of the narrow-band state with and without accurate compensation of the phase mismatchingWe notice that narrow-band high-dimension OAM entanglement has different phase matching condition compared to the wide-band situation, which will decreasing the high order modes components, for the first time.We propose a technology of design an annual-ring type quasi-phase-matching crystal which will enhance the dimension of narrow-band entanglement and improve the quality of the entanglement Adetunmise C. Dada et al,Nature Physics, 2011, 7(9): 677-680.Zong-Quan Zhou et al,PRL 115, 070502(2015)Analytical calculation Temperature tuningWide band distributionTwo methods of calculation for different crystal length, quite similarGeometrical calculationCalculationProposalContactYi-Lin Huahuayilinmail.ustc.edu.cn Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, Miles Padgett et al,New J. Phys. 17 (2015)Kiyoshi Kato et al,Applied optics, 2002, 41(24): 5040-5044.Filippo M. Miatto et al,PRA. 83, 033816 (2011)al,Our focus(a)Geometrical calculation of phase mismatching(b)Analytical calculation of phase mismatching(c)Diagram of LG mode propagationDesign of QPM grating enhances dimension and improves the quality of entanglementNarrow band by optical filtering, problem of phase mismatching,high orders of modes decrease sharplyHigh-dimension entanglement(a)(b)Quantum number lDimension of entanglement=, cp0 =2, cp0=, ncp0 =2, ncp0=, cp0 =2, cp0=, ncp0 =2, ncp0=, cp0 =2, cp0=, ncp0 =2, ncp0=, cp0 =2, cp0=, ncp0 =2, ncp0WeightFidelity2. Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, CAS, Hefei, 230026