INDIGO · Developing an inductive spectrometer for electron paramagnetic resonance detection and imaging at the micron scale using superconducting quantum circuits.

Electron paramagnetic resonance (EPR) is a powerful spectroscopy method which allows to identify paramagnetic species and quantify their interactions with their environment. Because of the weak spin-microwave coupling, conventional EPR spectroscopy has a low sensitivity which limits its use to samples of macroscopic size. Recent experiments demonstrated that superconducting quantum circuits have the potential to drastically enhance the spin detection sensitivity down to the detection of ~10 spins within 5 fL. However, these demonstrations have so far been done using well-known model spin systems and in restrictive conditions: very narrow spin and detector linewidths, extremely low microwave losses, and low static magnetic fields. They are thus incompatible with modus operandi that are typical in EPR spectroscopy: probing aqueous or non-crystalline samples, applying strong magnetic fields, or studying species with short coherence lifetimes or spin-spin interactions which require large excitation bandwidth. The restrictive conditions of these proof-of-concepts are however not a prerequisite for achieving high-sensitivity EPR detection. Using recent advances made in the fabrication process and in the design of quantum circuits, I propose to lift these restrictions and build a quantum-circuit based EPR spectrometer able to probe a large scope of spin species and to detect, characterize and image EPR signals in micron-sized samples. We will meet this goal by 1) developing a resilient high-sensitivity spectrometer able to probe spins with short coherence times and characterize spin-spin interactions; 2) implementing imaging techniques with sub-micron resolution; and 3) benchmarking our spectrometer for typical volume-limited applications. Our EPR spectrometer will open interesting research paths in biology chemistry or condensed matter, for instance by allowing to detect EPR signals in single cells, micro-protein crystals or from organic semiconductors.