Coherent control of Er in Si

Rare-earth ions in solid-state hosts exhibit low homogeneous broadening and long spin coherence at cryogenic temperatures, thus making them a promising candidate for optical-spin interfaces to achieve long-distance spin-spin coupling. Here, we present the electron spin properties of Er ensembles in Si accessed via resonant photoluminescence excitation. Samples were positioned directly on top of dedicatedly fabricated superconducting single photon detectors and resonantly excited using fiber optics. We investigated Si samples with different O doping levels and Er densities between 10¹⁶ cm^-3 to 10¹⁸ cm^-3 implanted using ion beam. The samples with an Er doping level of 10¹⁸ cm^-3 showed an inhomogeneous linewidth of less than 400 MHz and an upper bound of 350 kHz on the homogeneous broadening.

The lower Er concentration samples of 10¹⁶ cm^-3 showed inhomogeneous broadening of less than 100 MHz. Using bichromatic excitation, we were able to polarize the spin states and extract a site that is present in the high and low oxygen concentration samples. The measured lifetime of the electron spin in the optical ground state was as long as 30 seconds at a magnetic field of 60 mT and a temperature of 20 mK. By introducing a wire antenna, we observed Rabi oscillations of over 1 MHz. These narrow optical linewidths and long spin lifetimes show that Er in Si is a promising candidate for future quantum information processing applications.