In today’s quantum optics laboratories, we primarily find two families of quantum states: (1) Discrete variable states characterised by their photon number distributions. In most experiments, these states comprise less than three photons. (2) Continuous variable states. Prominent examples of continuous variable states are single- and two-mode squeezed states. After adding the local oscillator required for detection, these states contains 1012 to 1015 photons. In PhoG, we create quantum states that live in between, with intensities ranging from the few-photon level up to powers in the micro- to milliwatt regime and with the unique feature of photon-number statistics with a reduced variance. Hence they are characterised by typical discrete variable quantities, whereas their brightness is clearly in the regime of continuous variables. Such states are challenging to detect. To tackle this obstacle, we have developed different detection schemes. In particular, the partner UPB has constructed and tested a large photon-number resolving detector. It is based on the established concept of time-multiplexing, which was pioneered by this member of the consortium. Thus, the PhoG project will complement the quantum sources and detectors developed and/or used across the Quantum Flagship, and in general across the Quantum Technologies arena, with the quantum devices operating in a unique performance range.
In terms of societal applications beyond quantum realm, PhoG will contribute to the development of complex, custom designed 3 dimensional waveguide components that can be quickly changed and prototyped. It will advance on a new level use of mid-infrared transmissive, high refractive index non-linear materials. This is in particular important for biological applications, as mid-infrared sources and detectors allow access to the “fingerprint” region where compounds and molecules have distinct spectra allowing them to be identified. Custom light guiding components, spectrographs and lens arrays for the mid-infrared can be developed for minimally invasive portable detectors for precise and rapid clinical diagnosis and identification of diseases. For astronomical applications, integrated high precision, low loss spectrographs for the mid-infrared can be produced, which when used with ground-based telescopes operating with adaptive optics have the potential to identify and characterise Earth-like planets with the possibility to search for those capable of supporting life. Though not explicitly within the scope of the PhoG project, these PhoG-related advances of techniques and expertise of partners contributes to further progress in all these applications.
