Single electron-spin-resonance detection by microwave photon counting

TL;DR

This paper demonstrates a novel method for single-electron spin detection using microwave photon counting at cryogenic temperatures, enabling detection in larger volumes and with potential applications in quantum technologies.

Contribution

The authors introduce a new technique for single-electron spin resonance detection via spin fluorescence and microwave photon counting, expanding detection volume and applicability.

Findings

Detected individual erbium ions with a signal-to-noise ratio of 1.9 in one second

Measured spin coherence times up to 3 ms, limited by radiative lifetime

Proved single-emitter origin through fluorescence anti-bunching

Abstract

Electron spin resonance (ESR) spectroscopy is the method of choice for characterizing paramagnetic impurities, with applications ranging from chemistry to quantum computing, but it gives access only to ensemble-averaged quantities due to its limited signal-to-noise ratio. Single-electron-spin sensitivity has however been reached using spin-dependent photoluminescence, transport measurements, and scanning-probe techniques. These methods are system-specific or sensitive only in a small detection volume, so that practical single spin detection remains an open challenge. Here, we demonstrate single electron magnetic resonance by spin fluorescence detection, using a microwave photon counter at cryogenic temperatures. We detect individual paramagnetic erbium ions in a scheelite crystal coupled to a high-quality factor planar superconducting resonator to enhance their radiative decay rate, with a signal-to-noise ratio of 1.9 in one second integration time. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters. Coherence times up to 3 ms are measured, limited by the spin radiative lifetime. The method has the potential to apply to arbitrary paramagnetic species with long enough non-radiative relaxation time, and allows single-spin detection in a volume as large as the resonator magnetic mode volume ( 10 um^3 in the present experiment), orders of magnitude larger than other single-spin detection techniques. As such, it may find applications in magnetic resonance and quantum computing.