Microwave fluorescence detection of spin echoes

TL;DR

This paper demonstrates microwave fluorescence detection of spin echoes in electron spins, enabling sensitive EPR spectroscopy with improved signal-to-noise ratio using fluorescence-detected echoes in erbium ions.

Contribution

It introduces a novel fluorescence detection method for spin echoes, allowing measurement of spin coherence and coupling effects with enhanced sensitivity.

Findings

Detection of spin echoes via microwave fluorescence in erbium ions

Measurement of erbium spin coherence time

Comparison shows fluorescence detection has higher SNR than inductive methods

Abstract

Counting the microwave photons emitted by an ensemble of electron spins when they relax radiatively has recently been proposed as a sensitive method for electron paramagnetic resonance (EPR) spectroscopy, enabled by the development of operational Single Microwave Photon Detectors (SMPD) at millikelvin temperature. Here, we report the detection of spin echoes in the spin fluorescence signal. The echo manifests itself as a coherent modulation of the number of photons spontaneously emitted after a $\pi/2_X - \tau - \pi_Y - \tau - \pi/2_\Phi $ sequence, dependent on the relative phase $\Phi$. We demonstrate experimentally this detection method using an ensemble of $\mathrm{Er}^{3+}$ ion spins in a scheelite crystal of $\mathrm{CaWO}_4$. We use fluorescence-detected echoes to measure the erbium spin coherence time, as well as the echo envelope modulation due to the coupling to the $^{183}\mathrm{W}$ nuclear spins surrounding each ion. We finally compare the signal-to-noise ratio of inductively-detected and fluorescence-detected echoes, and show that it is larger with the fluorescence method.