Optical sensing makes use of continuously variable quantum systems such as different degrees of freedom of the electromagnetic field, vibrational modes of solids, and Bose–Einstein condensates.
[4][14] With new technological advancements, individual quantum systems can be used as measurement devices, utilizing entanglement, superposition, interference and squeezing to enhance sensitivity and surpass performance of classical strategies.
APDs, in the form of 2-D and even 3-D stacked arrays, can be used as a direct replacement for conventional sensors based on silicon diodes.
[6][17][18][19] The United States judges quantum sensing to be the most mature of quantum technologies for military use, theoretically replacing GPS in areas without coverage or possibly acting with ISR capabilities or detecting submarine or subterranean structures or vehicles, as well as nuclear material.
[21] Injecting squeezed light into interferometers allows for higher sensitivity to weak signals that would be unable to be classically detected.
[22] Gravitational wave detectors, such as LIGO, utilize squeezed light to measure signals below the standard quantum limit.
[23] Squeezed light has also been used to detect signals below the standard quantum limit in plasmonic sensors and atomic force microscopy.
[25][26] The diminishing projection noise has direct applications in communication protocols and nano-Nuclear Magnetic Resonance.