Quantum Ghost Imaging

Learn about applications for the not-so-spooky ghosts of quantum computing
Marks & Clerk

With Halloween approaching, we are looking at a niche quantum area with a topical name for this time of year. However, despite the spooky name, quantum ghost imaging is an imaging technology that has widespread commercial applications.

Quantum ghost imaging uses the principle of quantum entanglement which is was the subject of one of the earlier posts on quantum computing. If two photons are entangled in a certain property, for example, polarization, then measurement of the polarization of one of the photons affects the polarization of the other photon. In 2017, entanglement was demonstrated over a distance of more than 1200 km.

In quantum ghost imaging, entangled pairs of photons are generated, one photon of a pair of photons is sent through an object to be imaged and the other photon of the pair is sent to a detector. Due to the entanglement, a property of the photons measured at the detector is influenced by the photons passing through the object. The detector therefore obtains information about the object by measuring photons that have not passed through the object, a “ghost image”.

Ghost imaging has the potential to allow the imaging of an object with very low levels of light.

This ability to create a ghost image has received considerable interest for defense based applications. The US army has been publicly active in this field of research for well over a decade. There are also reports that China is developing a spy satellite using quantum ghost imaging to spot stealth bombers and other objects that are challenging for traditional radar. In addition to the defense applications above, quantum ghost imaging is also a potential medical imaging technique due to its potential increase in accuracy at low levels of radiation.

The current state of play in quantum ghost imaging is that there is active research into how to prepare suitable entangled states, protocols and detectors. However, there is an overlap in the technology being developed specifically for quantum ghost imaging and that being developed for other quantum technologies such as quantum cryptography and computing. Therefore, when applying for protection for quantum ghost imaging hardware and techniques, it is also important to consider whether these hardware and techniques have applications outside of quantum imaging.

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