The physics of ghost imaging

Ghost images are obtained by correlating the output of a single-pixel (bucket) photodetector—which collects light that has been transmitted through or reflected from an object—with the output from a high spatial-resolution scanning photodetector or photodetector array whose illumination has not interacted with that object. The term “ghost image” is apt because neither detector’s output alone can yield an image: the bucket detector has no spatial resolution,while the high spatial-resolution detector has not viewed the object. The first ghost imaging experiment relied on the entangled signal and idler outputs from a spontaneous parametric downconverter, and hence the image was interpreted as a quantum phenomenon. Subsequent theory and experiments showed, however, that classical correlations can be used to form ghost images. For example, ghost images can be formedwith pseudothermal light, for which quantum mechanics is not required to characterize its photodetection statistics. This paper presents an overview of the physics of ghost imaging. It clarifies and unites two disparate interpretations of pseudothermal ghost imaging—two-photon interference and classical intensity-fluctuation correlations—that had previously been thought to be This work was supported by the U.S. Army Research Office MURI grant W911NF-05-0197. J. H. Shapiro (B) Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA e-mail: [email protected] R. W. Boyd Institute of Optics and Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, USA e-mail: [email protected] R. W. Boyd Department of Physics, University of Ottawa, Ottawa, ON, K1N 6N5, Canada