Pulsed Electron Spin Resonance of an Organic Microcrystal by Dispersive Readout

TL;DR

This paper presents a cryogenic ESR system using a superconducting microresonator to detect and analyze small organic spin samples with high sensitivity, enabling potential quantum information and surface chemistry applications.

Contribution

It introduces a high-sensitivity ESR testbed with a Niobium Nitride microresonator capable of coupling to tiny spin samples at cryogenic temperatures, demonstrating high cooperativity and dispersive readout.

Findings

Achieved high-cooperativity coupling ($C \\approx 19$) at 65 mK.

Detected spin-lattice decoherence via dispersive frequency shifts.

Successfully coupled to $10^{12}$ spins in a pico-litre volume.

Abstract

We establish a testbed system for the development of high-sensitivity Electron Spin Resonance (ESR) techniques for small samples at cryogenic temperatures. Our system consists of a Niobium Nitride thin-film planar superconducting microresonator designed to have a concentrated mode volume to couple to a small amount of paramagnetic material, and to be resilient to magnetic fields of up to 400 mT. At 65 mK we measure high-cooperativity coupling ($C \approx 19$) to an organic radical microcrystal containing $10^{12}$ spins in a pico-litre volume. We detect the spin-lattice decoherence rate via the dispersive frequency shift of the resonator. Techniques such as these could be suitable for applications in quantum information as well as for pulsed ESR interrogation of very few spins and could provide insights into the surface chemistry of, for example, the material defects in superconducting quantum processors.