Kinetic Inductance Detectors, a promising technology for precision astronomy

RETROSPECTIVE. In order to observe the cosmos and its infinitely distant phenomena, each additional photon captured may be indispensable. The new generation of kinetic inductance detectors, currently being developed at the APC laboratory, is therefore a promising technology for developing ultra-precise astronomical instruments. This result, published last year, provides an update on the progress of this project.

How to observe what is barely visible? This issue is at the core of astronomy and instrumental astrophysics. In those fields, any tiny or faint source of light (and its variation) originating from infinitely far astrophysical phenomena, could tell us more about our Universe. Therefore, every photon counts.

But not only is it essential to catch as much light as possible (using very big telescope mirrors), it is also important to look at how photons are recorded by the detector. The most efficient detector should ideally be able to gather all available information for each and every single captured photon. One promising device could actually achieve this exploit: the Kinetic Inductance Detector (KID).

KID technology offers several advantages:  it is fast, has extremely low noise, is simple to build and can be easily implemented in large arrays. This is why KIDs are developed for numerous applications, ranging from the far-infrared to X-rays astronomy. This is also why the APC laboratory is also involved in the development of KIDS, as part of a project supported by the LabEx UnivEarthS.

Two kinds of detectors are currently on the work: the first one, detecting photons in the microwave range, is built to measure polarization of the Cosmic Microwave Background, and a second one, in the near-infrared and optical bands, to detect faint galaxies. But how does a KID work?

KID is essentially a superconducting resonator on a circuit chip. When the superconducting material absorbs a photon, this shifts the resonating frequency of the circuit. If we are able to measure this frequency shift, we can not only rapidly detect a single-photon event, but also measure the energy of the inciding photon on the chip.

Superconductors mean extremely low temperature. For the new kind of KIDs in the near-infrared and optical bands that the APC and GEPI labs are developing, aluminium and gold were the chosen materials. This Al/Au KID needs to be cooled down to temperature below 1K in order for the superconducting properties of aluminium and gold to occur. The cryostat used at the APC laboratory for the KIDs testing and characterization can actually reach 50mK.

References :

Hu, Jie, Maria Salatino, Alessandro Traini, Christine Chaumont, Faouzi Boussaha, Christophe Goupil, et Michel Piat. “Proximity-Coupled Al/Au Bilayer Kinetic Inductance Detectors”. Journal of Low Temperature Physics 199, no 1: 355‑61.

The LabEx UnivEarthS contributed to this research by funding the Valorization project NGKIDs (V3).