Research ArticleAPPLIED PHYSICS

Quantum interference of topological states of light

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Science Advances  14 Sep 2018:
Vol. 4, no. 9, eaat3187
DOI: 10.1126/sciadv.aat3187
  • Fig. 1 Photonic boundary-state beamsplitter.

    (A) Illustrative representation of a waveguide array implementing stationary topologically boundary states (red shaded regions) that propagate at the edges of the device. We used this device to confirm that the boundary state is preserved during the propagation inside the array. (B) Illustrative representation of a waveguide array implementing a TBS that interferes two topologically boundary states. (C) Photonic supermodes (eigenvectors) of the arrays at the start and end of the both devices. (D and E) Band structure (eigenenergies) along the length of the arrays (A and B). The topological bands (B and D) are highlighted in red, and the bulk bands (A, C, and E) are shaded in blue.

  • Fig. 2 Characterization of the stationary boundary-state device and the TBS.

    We characterized the output of the chip using laser light and a CCD camera. (A) The normalized output intensity distribution of the stationary boundary state. (B and C) The normalized output intensity distribution of the TBS with injection into the left and right inputs, respectively.

  • Fig. 3 Experimental setup for interfering topological boundary states.

    (A) Setup to characterize the indistinguishability of the photon pairs generated from a SPDC source. The photons are interfered in a 50:50 beamsplitter via PMF. The output of the beamsplitter is pigtailed with single-mode fiber (SMF) connected to single-photon avalanche photodiodes (APDs). We measured coincidence counts between the two detectors with a timing card. CW, continuous wave; BiBO, bismuth triborate. (B) To perform the indistinguishability measurements of single photon topologically protected states, we replaced the pigtailed beamsplitter in (A) with the TBS device. We used PMF, multimode fibers (MMFs), and free-space lenses to couple photons to the device.

  • Fig. 4 Measurements of indistinguishability.

    (A) HOM interference of single photons using a commercially available fiber pigtailed 50:50 beamsplitter with a visibility of 94.5 ± 0.5%. (B) HOM interference on the TBS with a visibility of 93.1 ± 2.8%. The error bars shown are based on Poissonian statistics.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Experimental setup
    • Section S2. SPDC source
    • Section S3. HOM dip
    • Fig. S1. Ray tracing simulation of the coupling setup.

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