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. 2019 May 1;8:41. doi: 10.1038/s41377-019-0153-y

Fig. 2. Characterization of biphoton polarization-entangled states.

Fig. 2

a and b are twofold coincidences as a function of the idler polarizer angle when the signal polarizer angle was kept at 0° (red) and 45° (black), respectively. The error bar was obtained from the square root of the experimental data. c and d give the real (Re) and imaginary (Im) parts of the ideal density matrix and the measured density matrix of the biphoton entangled state from frequency channels ±5, respectively. The fidelity was 0.95 ± 0.01, confirming that the generated biphoton quantum state was high quality and very close to the ideal maximally entangled states