Fig. 4: Interaction-free, single-pixel quantum imaging result of the ‘NJU’ plate with undetected photons.

The three characters ‘N’, ‘J’, and ‘U’ are measured independently with the single-pixel imaging technique. Note that in our experiment, the micromirror of the SLM is rotated 45° at a mount. The edge of SLM can be vaguely seen at the upper left corner of the image. We rotate the reconstructed images by 45° to obtain the above images. The background noise in the signal-photon counts results in some speckles in the reconstructed images. Because of the structural difference of characters and limited detection area of the fiber-coupled detector, the visual result of character ‘N’ is less prominent than ‘J’ and ‘U’. The length of the scale bar (white colour) in the figure is 500 \({{{\mathrm{\mu m}}}}\).