Manipulating classical triple correlations for optical information processing and metrology

Wave mixing and the intricate optical interactions therein have traditionally been regarded as hallmarks of nonlinear optics. A quintessential example of wave mixing lies in the nonlocal triple correlation between the pump beam and the generated twin photons via spontaneous parametric down-conversion (SPDC). However, the SPDC process typically requires intense laser pumping and suffers from inherently low conversion efficiencies, necessitating single-photon detection. In this work, we establish that analogous triple correlations can be effectively produced using low-power continuous-wave illumination, achieved through a commercially available spatial light modulator (SLM) in a linear optical configuration. Specifically, we show how to spatially manipulate and customize this triple correlation and further investigate the applicability across diverse domains, including pattern recognition, intelligent nonlocal image processing, and sensitivity-enhanced optical metrology. Our findings establish, to our knowledge, a novel framework for classical, linear emulation of quantum and nonlinear optical information processing paradigms rooted in multi-wave mixing.