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 contained 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 potential for systems exploiting quantum physics. Problems associated with the small energy of millimetre wave photons can be overcome by combining homodyne interferometers with parametric amplifiers. Decoherence is less than in the optical band, as waves interact less with materials per unit length. These systems can be used to develop Continuous Variable (CV) novel sensors that use quantum mechanically squeezed sources of millimetre wave radiation, using existing electronic technology. This would offer a supremacy over existing classical systems, enabling more secure communications, lower transmit-power radars and quantum imaging. Experimentation using techniques such as quantum state tomography can provide new insights into the fundamental nature of entanglement and the clockwork universe in a largely uncharted spectral band.
The objective of this area of research is to bring the science of quantum optics into the millimetre wave band. Potential novel sources of entangled photons to enable this require materials or devices with nonlinear responses to electromagnetic radiation. Phase matching, by the tuning of refractive indices, can increase the efficiencies of entangled photon creation. Diodes, surface acoustic wave devices, dielectrics or magnetic materials are potential sources.
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