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Title: Quantum rangefinding
Author: Frick, Stefan
ISNI:       0000 0004 7961 6341
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2019
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Rangefinding has many applications in navigation, civil engineer, construction, military, surveillance and security. Most commonly rangefinders estimate the distance to an object by measuring the time of flight of light for the journey to and returning from the target. Conventional techniques use lasers as the light source of choice in state of the art rangefinding systems. Lasers are nowadays cheap to manufacture and can produce amounts of optical powers excessive of the typically required microwatts, yet, the particular state of light they are producing makes them also easy to detect. Spontaneous parametric down-conversion is a quantum process, happening in non-linear crystals, that allows for one photon of shorter wavelength to be destroyed while at the same time a photon pair of longer wavelength is created. If the non-linear crystal is engineered carefully, one photon of such a pair will be in a quantum state of light much closer to background radiation than other light sources, and especially much closer than the quantum state produced by lasers. Such a photon-pair source can be utilised for rangefinding by keeping the first photon of the pair locally as a timing reference, while using the second photon to illuminate the target. The delay between the first and the second photon, after its return from the target, can then be used to estimate the time of flight to the target and back, effectively determining the distance. The principle of measuring distance via the time of flight of light is common to classical rangefinding and the rangefinding system presented here. However, the state of light of one photon, produced in the down-conversion process, provides efficient camouflaging against background light and therefore makes the detection of the rangefinding signal impossible.
Supervisor: Rarity, John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available