Near Infrared Quantum Ghost Imaging of Living and Unperturbed Plants

Quantum ghost imaging (QGI) at near-infrared (NIR) wavelengths offers a powerful non-invasive technique for studying biological processes essentially in the dark. QGI with non-degenerate entangled photon pairs has the distinct advantage that the sample can be probed in the near infrared (where vibrational absorption provides contrast), with imaging done in the visible (where we have better imaging technologies). QGI exploits the quantum properties of entangled photon pairs for image formation. As entangled photon pairs are created at nearly the exact same place and at nearly the exact same time, the physical properties of one photon, such as its propagation direction, are directly linked to the corresponding physical property of the other photon. As such, measuring the trajectory taken by one of the photons reveals the path taken by the other photon. Similarly, measuring the spatial position where one photon was generated in a nonlinear optical crystal leads to knowing where its pair was generated. Quantum ghost imaging exploits these quantum correlations to form images of objects from photons that have never interacted with the sample being imaged. Coincidence detection between the pairs suppresses many sources of background (stray light, detector dark counts), enabling imaging with exceedingly low illumination powers. Using a photo-cathode based single photon counting imaging sensor, NCam, we demonstrated nondegenerate QGI with unprecedented sensitivity and contrast, obtaining images of living plants with less than 1% light transmission. As the photon flux on the plant is well below ambient moonlight, QGI was able to capture plant processes usually associated with nocturnal behavior, such as stomatal closing.