Time-Bin Encoded Four-Qubit GHZ State: Generation and Characterization

We report initial results from the experimental generation and characterization of a four-qubit time-bin entangled GHZ-state. Two high-fidelity time-bin entangled photon pairs are produced via spontaneous parametric down-conversion. The signal photons from each source interfere at an optical switch, which transmits photons in the 'early' time bins and reflects those in the 'late' time bins, while the idler photons are directly sent to the detection system. By post-selecting coincidence events at all four output modes, a four-qubit GHZ state is heralded.