The current position：Research < Quantum Correlated Imaging
Quantum imaging, or more specified, ghost
imaging (GI) is a special indirect imaging method, which takes advantage of the
second, even higher order correlation of the light field to reconstruct the
image of a non-contact object. Unlike the ordinary imaging which registers the
spatial intensity profile of the illumination light field goes through the
object by an array-detector, GI divide the light into two: one pass the object
to be registered by a bucket detector with no spatial resolution, while the
other recorded by an array without touching the object, and the correlation of
corresponding records of the two leads to a reconstructed image. Due to this
‘spooky’ property that from none of the two parts alone can one gets the image,
until the correlation is conducted, GI has been named ‘ghost’.
The original idea of GI was brought out in a research on the behavior of entangled parametric down conversion photon pairs under local measurement in 1988. When GI got its first realization in 1995, early researchers naturally took entanglement as necessary. Meanwhile, ever since 2002, theoretical analysis show that pseudo-thermal light and thermal light, which are not entangled and being considered as ‘classical’ light, can also fulfill the GI task. Experimental verifications have been done. Then the community is divided on the nature of GI: some believe even ‘classical’ light has non-local quantum correlation inside, and GI is a full-quantum phenomenon, while some think classical intensity correlation can do the work. The argument is still going on. Therefore, like the EPR paradox, GI becomes another test bed for quantum optics theories, especially the non-local correlation of light field. GI and its descendant topics, e.g., ghost interference, quantum erasing, and quantum illumination, are among the frontiers of the quantum information and quantum optics field.
The application research of GI owes a lot to the concept of computational GI and the compressive sensing (CS) algorithm. If one can know in advance, or even modulate the intensity profile of the no-touching light field, GI facility can be reduced into a single bucket detector. This is the very reason it has been called single-pixel camera. This idea has significant meaning for imaging tasks under extreme conditions, in which large array camera of high performance and capacity is rare. The CS algorithm can break the Nyquist sampling limit for objects with sparsity, which can get high fidelity results within much fewer samples, thus makes GI more plausible. As a typical emerging interdisciplinary subject, the combination of GI and other high technologies in optics and imaging, e.g., LIDAR, hyper-spectroscopy, ultra-narrow band filtering, super-resolution imaging, bring about numerous opportunities. The study on GI, either fundamental or applicant, is both unfading and unfolding.