Single spin magnetic resonance by microwave fluorescence detection

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. The sensitivity needed to detect single electron spins has been reached so far using spin-dependent photoluminescence, transport measurements, or 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 spin resonance by spin fluorescence detection [1], using a microwave photon counter at cryogenic temperatures based on a superconducting transmon qubit [2]. 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 [3], with a signal-to-noise ratio of 1.5 in one second integration time. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters [4]. Coherence times up to 3ms 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 ([X]); as such, it may find applications in magnetic resonance and quantum computing.

[1] E. Albertinale et al., Nature 600, 434 (2021)
[2] R. Lescanne et al., Phys. Rev. X 10, 021038 (2020)
[3] A. Bienfait et al., Nature 531, 74 (2016)
[4] Z. Wang et al., in preparation (2022)