Quantum-enhanced THz spectroscopy and imaging

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Quantum mechanics promises to be the driving force underneath the next technological revolution, and quantum cryptography, providing a commercial solution for the ultimate security, may well be considered the harbinger of this change. With this proposal, we aim at showing how quantum mechanics can allow to overcome the limits faced in the detection of long wavelength radiation, specifically at terahertz frequencies.Terahertz is a portion of the electromagnetic spectrum that is both extremely hard to access to, and incredibly important from a technological standpoint. It is indeed a key player in security (explosives, drugs, and hazard-free concealed weapons detection), telecommunications (increased data-rate of short distance wireless communication), monitoring and quality control (spectroscopy). Despite its high potential, the lack of efficient sources and detectors prevents a widespread commercial application of terahertz time-domain spectroscopy and imaging. Yet, a number of high-tech companies are investing into terahertz technology and recent market studies hint for a 40%/year increase in the turnover associated to this technology.It is therefore vital to identify now strategies for overcoming the limitations of the current terahertz detectors. This proposal aims at developing such a strategy exploiting the unique properties of quantum, entangled states of light. Entangled photons, separated in space but sharing a common wavefunction, can be generated by commercial nonlinear crystals and boost unusual properties not accessible by classical means. Two of these properties, namely the ability to acquire twice the phase of a classical state upon propagation and the reduced amplitude noise below the classical shot-noise limit, offer a mean for increasing the sensitivity of terahertz time-domain detectors, that operate indeed as a differential phase sensor. Combining such an improvement with recent concepts of super-resolved imaging will also result in an increased resolution of long wavelength mapping.Combining for the first time concepts of quantum optics, recognised as a main pillar for our future technology, and of terahertz photonics, boosting a number of underdeveloped application potential, this proposal is in line with the research strategy set by the UK research councils, and promise to deliver impact on a number of different disciplines, such as biology and material science, as well as on the quality control and security inspection activities.