Fig. 2: Experimental layout.
From: Entanglement-based quantum communication complexity beyond Bell nonlocality
a Conceptual layout of the three-user GYNI protocol. The tripartite GHZ state is distributed among the three users who locally measure their photon based on input bits {xi, xj}. To compute the target function, each user broadcasts a one-bit message using their measured outcome and a local bit, yi. b We create the GHZ state using two polarisation-entangled photon-pair sources and a linear-optics fusion gate. Each source is implemented with an aperiodically poled KTP crystal embedded in a Sagnac loop that is optically pumped bidirectionally using a picosecond mode-locked laser, see Methods for details. Down-converted photons are separated from the pump laser using dichroic mirrors (DM) and interference filters (IF) then fibre coupled into single mode fibres. One photon from each source non-classically interferes on a polarising beamsplitter (PBS) creating the three-photon GHZ state conditioned on measuring the forth photon as a Trigger. Each user performs projective measurements on their qubit using a quarter-wave plate (QWP), half-wave plate (HWP), and PBS. Single photons are detected using superconducting nanowire single-photon detectors (SNSPD) and time-tagged for coincidence measurements within a 1 ns window.
