# Zhiren Wang

Affiliation
CEA Paris-Saclay
Title of Poster
Single electron spin resonance by microwave photon counting
Abstract Regular

Electron spin resonance (ESR) spectroscopy is the method of choice for characterizing paramagnetic impurities in a sample, 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. The sensitivity needed to detect single electron spins has been reached using spin-dependent photoluminescence and transport measurements, as well as scanning-probe techniques. These methods are system-specific or sensitive only in a small detection volume ($<10^4\,\mathrm{nm}^3$), so that practical single spin detection remains an open challenge. Here, we demonstrate single electron spin 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 small-mode-volume, high-quality factor superconducting resonator to enhance their radiative decay rate, with a signal-to-noise ratio of 1 spin/$\sqrt{Hz}$. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters. Spin coherence times up to $3$ ms are measured, limited by the ion radiative lifetime. The method applies to arbitrary paramagnetic species with long enough non-radiative relaxation time, and offers large detection volumes ($\sim 100 \mu \mathrm{m}^3$ in the present experiment); as such, it is likely to find applications in magnetic resonance and quantum computing.

Poster Session
D