ESR spectroscopy of a single Er3+ ion in CAW04 using fluorescence signal

Electron spin resonance (ESR) spectroscopy is the method of choice for characterizing paramagnetic impurities and their immediate nuclear environment, with applications ranging from chemistry to quantum computing. Here, we report a new method for the detection of single electron spins at millikelvin temperatures based on a microwave photon counter.

We study the coherence of individual spins thanks to classical ESR sequences. We measure the T2* (ranging from 5 to 300us) of several ions with a Ramsey sequence. The T2 is also measured via an echo sequence and reach ~2*T1 for all ions. Finally, we applied dynamical decoupling sequence through which we measured the presence of surrounding tungsten nuclear spins.