Figure 2. The schematic diagram and set-up of experimental demonstration.

(a) The K₄ graph. (b) The quantum circuit for implementing CTQW on the K₄ graph. This can also be used to implement CTQW on the K₄ graph without self-loops, up to a global phase factor . H and X represent the Hadamard and Pauli-X gate, respectively. is a phase gate. (c) The experimental set-up for a reconfigurable two-qubit photonics quantum processor, consisting of a polarization-entangled photon source using paired type-I BiBO crystal in the sandwich configuration and displaced Sagnac interferometers. See further details in Methods.