Long optical and electron spin coherence times for erbium ions in silicon

Spins in silicon that are accessible via a telecom-compatible optical transition are a versatile platform for quantum information processing that can leverage the well-established silicon nanofabrication industry. Key to these applications are long coherence times on the optical and spin transitions to provide a robust system for interfacing photonic and spin qubits. Here, we report telecom-compatible Er³⁺ sites with long optical and electron spin coherence times, measured within a nuclear spin-free silicon crystal (<0.01 % ²⁹Si) using optical detection. We investigate two sites and find 0.1 GHz optical inhomogeneous linewidths and homogeneous linewidths below 70 kHz for both sites. We measure the electron spin coherence time of both sites using optically detected magnetic resonance and observe Hahn echo decay constants of 0.8 ms and 1.2 ms at ~ 11 mT. These optical and spin properties of Er³⁺:Si are an important milestone towards using optically accessible spins in silicon for a broad range of quantum information processing applications.