The detection and characterization of paramagnetic species by electron-spin resonance (ESR) spectroscopy has numerous applications in chemistry, biology, and materials science [1]. Most ESR spectrometers rely on the inductive detection of the small microwave signals emitted by the spins during their Larmor precession into a microwave resonator in which they are embedded. Using the tools offered by circuit Quantum Electrodynamics (QED), namely high quality factor superconducting micro-resonators and Josephson parametric amplifiers that operate at the quantum limit when cooled at 20mK [2], we investigate magnetic resonance in a new regime where the quantum nature of the microwave field plays a role. In particular, the spin detection sensitivity is strongly enhanced [3,4] and spin relaxation is governed by spontaneous emission through the cavity [5]. In this talk we will consider applications of this new regime to ultra-high-sensitivity nuclear spin detection [6] and electron spin hyperpolarization.

- [1] A. Schweiger and G. Jeschke, Principles of Pulse Electron Magnetic Resonance (Oxford University Press, 2001)

- [2] X. Zhou et al., Physical Review B 89, 214517 (2014).

- [3] A. Bienfait et al., Nature Nanotechnology 11(3), 253-257 (2016)

- [4] S. Probst et al., to appear in APL (2017)

- [5] A. Bienfait et al., Nature 531, 74 (2016)

- [6] S. Probst et al., in preparation