Fig. 1
A general proposal of the experimental QNG witness. a Multi-photon light is collected and brought to a balanced multichannel detector, where coincidences R n , Rn+1 are compared to the QNG threshold. b The detector in our experiment consists of ten silicon single-photon avalanche diodes (SPAD) and a balanced array of polarizing beam splitters (PBS) and half-wave plates (HWP) to control the splitting ratio. The half-wave plates can be adjusted to split the light equally to any number of selected channels, so there is no need to physically add or remove SPADs
