Fig. 1. Schematics of experiment setups. (a) SPDC photon pairs generation and collection. Pump spectrum is controlled using a pair of diffraction gratings (DGs) in a 4 f optical configuration. (b) Single-fiber spectrometer with counter-propagating signal and idler and coincidence detection by SNSPDs D1 and D2. (c) DCM spectrometer providing high resolution JSI measurements. A, rectangular aperture; L1, f = 20 cm lens; L2, f = 40 cm lens; L3, f = 10 cm lens; LPF, long-pass filter; PBS, polarization beam splitter.
Fig. 2. 3D plot showing the UPDC procedure in the two-pump-photon subspace that realizes unity-efficiency conversion from the |0, 0, 2> input state, shown as the blue dot, to the |2, 2, 0> final state, shown as the red dot, in a single Grover iteration. The UPDC procedure’s initial state, prepared by passing the input state through a type-II phase-matched χ (2) crystal for an interaction time, is shown by the purple dot that is obtained by evolution around the red circle from the blue dot. Sign flip on the marked state (|0, 0, 2>) transforms the initial state to a new state, which is indicated by the green dot. Rotation toward the marked state by passing this new state through a type-II phase-matched χ (2) crystal for an interaction time designed according to interaction strength of the crystal leads to the desired output state |2, 2, 0>.