• Photonics Research
  • Vol. 9, Issue 10, 10001998 (2021)
Yi-Chen Liu1、†, Dong-Jie Guo1、†, Ran Yang1, Chang-Wei Sun1, Jia-Chen Duan1, Yan-Xiao Gong1、2、*, Zhenda Xie1、3、*, and Shi-Ning Zhu1
Author Affiliations
  • 1National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
  • 2e-mail: gongyanxiao@nju.edu.cn
  • 3e-mail: xiezhenda@nju.edu.cn
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    Scheme of the counterpropagating polarization-entangled photon source. (a) Phase-matching diagram of the BSPDC; (b) polarization entanglement generation from the BSPDC with bidirectional pump light.
    Fig. 1. Scheme of the counterpropagating polarization-entangled photon source. (a) Phase-matching diagram of the BSPDC; (b) polarization entanglement generation from the BSPDC with bidirectional pump light.
    Experimental setup. HWP, half-wave plate; QWP, quarter-wave plate; PBS, polarization beam splitter; DM, dichroic mirror; PC, polarization controller; LPF, long-pass filter; BPF, bandpass filter; FPF, Fabry–Perot filter; P, prism; SNSPD, superconducting nanowire single-photon detector; C.C., coincidence counts.
    Fig. 2. Experimental setup. HWP, half-wave plate; QWP, quarter-wave plate; PBS, polarization beam splitter; DM, dichroic mirror; PC, polarization controller; LPF, long-pass filter; BPF, bandpass filter; FPF, Fabry–Perot filter; P, prism; SNSPD, superconducting nanowire single-photon detector; C.C., coincidence counts.
    SHG measurement. SHG output power as a function of FL wavelength. The red curve is a sinc2-function fit.
    Fig. 3. SHG measurement. SHG output power as a function of FL wavelength. The red curve is a sinc2-function fit.
    BSPDC measurements. (a) Measurement of BSPDC spectrum. Black and red dots correspond to signal and idler photon spectra, respectively. The curve is fitted to sinc2 functions in solid curves. Inset, transmission spectrum of the FPF for spectral cleaning. (b) Quantum interference measurement with HOM interferometer. The HOM dip is fitted to a triangle function.
    Fig. 4. BSPDC measurements. (a) Measurement of BSPDC spectrum. Black and red dots correspond to signal and idler photon spectra, respectively. The curve is fitted to sinc2 functions in solid curves. Inset, transmission spectrum of the FPF for spectral cleaning. (b) Quantum interference measurement with HOM interferometer. The HOM dip is fitted to a triangle function.
    Entanglement correlation measurement. Coincidence counts are recorded as a function of HWP1 angle for changing the linear polarization projection measurement on one photon with the other photon projected to four states: H (blue), V (pink), D (red), and A (black), respectively. The curves are fitted with sine and cosine functions.
    Fig. 5. Entanglement correlation measurement. Coincidence counts are recorded as a function of HWP1 angle for changing the linear polarization projection measurement on one photon with the other photon projected to four states: H (blue), V (pink), D (red), and A (black), respectively. The curves are fitted with sine and cosine functions.
    (a) Real and (b) imaginary parts of the reconstructed density matrix for the produced polarization entanglement state.
    Fig. 6. (a) Real and (b) imaginary parts of the reconstructed density matrix for the produced polarization entanglement state.
    Phase stability test. Coincidence counts for |DD⟩ (black square dots) and |DA⟩ (red dots) projection measurements. The inset is a zoom-in for |DD⟩ measurement in 6 min.
    Fig. 7. Phase stability test. Coincidence counts for |DD (black square dots) and |DA (red dots) projection measurements. The inset is a zoom-in for |DD measurement in 6 min.
    Characterization of the two Fabry–Perot resonators. (a) AFM image of FPC before and after coating; (b) Fabry–Perot resonator test setup. TSL, tunable semiconductor laser; PC, polarization controller; TC, temperature controller; FPC, Fabry–Perot cavity; FBS, fiber beam splitter; PD, photodetector. (c) FPC transmission intensity as a function of wavelength detuning from the center transmission peak. The upper inset shows the zoom-in of one transmission peak of 7.8 pm linewidth, and the lower inset is the measured temperature-wavelength relationship. (d) Transmission measurements for the FPF, with 6.17 nm FSR and 132 pm linewidth for the transmission peak.
    Fig. 8. Characterization of the two Fabry–Perot resonators. (a) AFM image of FPC before and after coating; (b) Fabry–Perot resonator test setup. TSL, tunable semiconductor laser; PC, polarization controller; TC, temperature controller; FPC, Fabry–Perot cavity; FBS, fiber beam splitter; PD, photodetector. (c) FPC transmission intensity as a function of wavelength detuning from the center transmission peak. The upper inset shows the zoom-in of one transmission peak of 7.8 pm linewidth, and the lower inset is the measured temperature-wavelength relationship. (d) Transmission measurements for the FPF, with 6.17 nm FSR and 132 pm linewidth for the transmission peak.
    Polarization-Entangled Photon SourceMethodWavelength (nm)BandwidthBrightness [Hz/(mW · MHz)]Fidelity
    Fedrizzi et.al. [38]Sagnac interferometer810137 GHz0.59799.78%
    Kuzucu et al. [39]Sagnac interferometer780.773.8 GHz4.2298.85%
    Sansoni et al. [40]Two periodically poled waveguides1554260 GHz38.797.3%
    Herrmann et al. [41]Biperiodic poling waveguide1551/157185 GHz797.5%
    Sun et al. [42]Dual-periodic poling waveguide1489.9/1335270 GHz4294.5%
    Bao et al. [43]Cavity and postselection7809.6 MHz694%
    Tian et al. [44]Cavity and postselection79515 MHz395.2%
    This workCounter propagating1553.57.1 GHz3.495.7%
    Table 1. List of Narrowband Polarization-Entangled Photon Sources