Kinetic Inductance Detectors couple an excellent sensitivity to the ability of directly absorbing radiation starting already from the microwave/far infrared bands. Because of this, their use is not limited to astronomy alone, but can span a much broader range of applications. The GIS KID has already been involved in many developments that go beyond astronomical instruments. Among them we can list:
- Passive imaging applications: this is the most straightforward transfer of KID technology. While semiconductor based detectors are ideally suited for higher frequencies, and have the advantage of not requiring cryogenic systems, they are completely blind in the millimeter/submillimeter range. Yet, millimeter waves are ubiquitous, as all bodies at room temperature emit strongly in this range. Furthermore, and due to their large wavelength, millimeter waves can travel through obstacles such as sheets of wood or plastics. A KID based camera could for example be used for passive imaging of passengers at an airport, or for medical applications, by monitoring the skin temperature. - Active imaging applications: in this case, KIDs are used as detectors in a system including an active THz source. THz imaging and spectroscopy has been an active field of research in recent years, and can have multiple applications, for example for cultural heritage conservation (non-invasive testing of paintings), product and defect inspection in industry, or chemical analysis techniques. Coupling a THz source to highly sensitive KID detectors can help to achieve high resolution and high signal-to-noise images. - Materials studies: the study of superconducting resonators can give an insight on the properties of classical superconductors as well as more exotic ones (highly disordered, multilayers, etc). Testing new materials, and determining parameters such as their kinetic inductance fraction, quasiparticle lifetime, and noise, allows us to find the best candidates for different applications, and to investigate new physics. - Quantum information: quantum Qubits and KIDs have many aspects in common, in terms of fabrication techniques, sources of noise or of "bursts" in the signal, readout systems and more. A first example is the use of high kinetic inductance materials in a KID to increase responsivity and in a Qubit to introduce a non-linearity. Another example is the study of phonon propagation in a substrate after a Cosmic Ray impact, which is crucial in determining data loss in KIDs and to understand the origin of decoherence in a Qubit. These similarities can be used to the advantage of both communities, allowing for technological transfers in both directions. - Neutrino detection, nuclear plant monitoring: About 1022 antineutrinos are emitted per second from a typical nuclear reactor, unattenuated and spread in all directions. The isotope fuel composition during operations varies: 235U is consumed and 239Pu is produced. Different antineutrino spectra are emitted by these two producs, so measuring the antineutrino rate gives insight on the composition of the core. Coherent neutrino scattering low-temperature detectors based on KIDs might provide real-time quantitative information about core power and isotopic composition while the reactor is online. It could consist in a portable system to report the reactor status independently of operator declarations (control agencies). It could also be a continuous, non-intrusive, remote, unattended monitoring integrated in the nuclear plant system. - Teaching: KIDs are an excellent "case study" for students in courses of quantum physics and superconductivity. They can show the onset of superconductivity, test the theory of Mattis-Bardeen, extract the properties of a material, monitor the flux of Cosmic Rays, and more. All this can be achieved in a compact cryostat and with the possibility for students to follow all the steps of an experiment, from detector assembly to data taking, in a reasonable amount of time. For this reason, a practical work, "TP KID", has been developed, and is proposed to the students of the Université Grenoble Alpes "Quantum Matter" course on a yearly basis.