Structured-Pump-Enabled Quantum Pattern Recognition

We report a new scheme of ghost imaging by using a spatially structured pump in the Fourier domain of spontaneous parametric down-conversion for quantum-correlation-based pattern recognition. We exploit the mathematical feature of Laguerre-Gaussian mode’s Fourier transform to describe the pump-modulated formation of a ghost image. Of particular interest is the experimental demonstration of a quantum equivalence of a Vander Lugt filter, based on which the nonlocal spiral phase contrast for vortex mapping and quantum-correlation-based human face recognition are implemented successfully. The photons used for probing a test object, scanning the database, and producing a correlation signal can belong to three different light beams, which suggests some security applications where low-light-level illumination and covert operation are desired.

Figure 1

Schematic illustration of the experimental setup. See Supplemental Material [40] for full details.

Figure 2

Experimental results for nonlocal vortex mapping. First column: Vortices displayed by the SLM. Second and third columns: Ghost images created by summing 20 frames and 100 frames, respectively. Fourth column: Bright spots revealing the dark cores of each vortex after nonlocal mapping with 20 frames. The gray-scale bar is in units of photons/pixel.

Figure 3

Experimental results for human face recognition. The test photographs (left axis) are binarized in phase and imparted to the UV light; they are then Fourier transformed to participating SPDC. For each test photograph, the five reference photographs (right axis) are scanned by loading them sequentially in the SLM. Correlation signals for $5\times 5$ combinations are recorded by summing 20 frames with the ICCD camera. The top-left inset suggests the potential in covert imaging: The photons for probing the sample face, scanning the face database, and producing the correlation signal belong to three different light beams.