Quantum Sensors

Quantum sensors and their applications referred to here are those that are exploit superposition and entanglement, phenomena that have no classical counterpart. The opportunity is that these phenomena may revolutionise sensing. 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 in this band is less than that in the optical band, as waves interact less with materials per unit length. Built from existing technology, these systems can be used in Continuous Variable (CV) novel sensors for the phase detection of quantum mechanically squeezed sources of millimetre wave radiation. This would enable the Heisenberg limit of detection to be approached, offering quantum 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 exploit quantum optics in the millimetre wave band, to enable capabilities that are not possible in the optical or infrared 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.

The strategy is the quantum analysis of sensors to reveal the easiest mechanism to exploit effects that lead to quantum supremacy, this being the status of the quantum sensor, surpassing its classical counterpart by a significant margin.