Quantum applications referred to here are those applications that are dependent on the preservation of quantum information. In the millimetre wave band this is an undeveloped area of technology as:
1) The natural (digital) information contain in packets of energy hf has an energy far smaller than the thermal quanta of energy kT, meaning this signal is swamped (or hidden) when processing using sensors operating at ambient temperature.
2) Quantum information in the form of entangled states has the potential for novel forms of digital processing, however entanglement can easily be lost through decoherence.
The above indicates a great potential for systems exploiting quantum physics. Problems of associated with the small energy of millimetre wave photons and decoherence can be overcome by using novel homodyne interferometers. Development of these systems can then be used to explore powerful novel sensing capabilities, to explore secure communications, covert radar and imaging, and to provide new insights into fundamental nature of entanglement in a relatively unchartered spectral band.
The objective of this area of research therefore is to bring the science of quantum optics into the millimetre wave band, to explore new opportunities. Potential non-linear sources would comprise novel (meta, synthetic or natural) materials with non-linear susceptibilities (electrical or magnetic) and phase matching properties.