Towards indistinguishable single photons from spatially separated emitters:A rare-earth ion-based quantum node for future quantum networks

Rare earth ions (REI) in crystals are promising candidates for quantum information processing and networking applications. Among them, Er³⁺ ions are particularly attractive due to their telecom C-band emission, which is compatible with existing fiber optics, as well as their long spin coherence and lifetimes, making them ideal for quantum memory applications.

To date, multi-photon interference remains challenging due to distinct spectral profiles and low photon emission rates.

Here, we discuss experiments aimed at realizing multiple distinct emitters with indistinguishable photons. In order to achieve this, several critical steps have to be take: we first demonstrate that coupling Er³⁺ ions to a silicon nanophotonic cavity enhances the emission rate by up to 143 times. Additionally, at Millikelvin temperatures and under a magnetic field, we achieve lifetime-limited photons. Notably, we show for the first time linear Stark tuning of a single Er³⁺ ion’s emission by up to 50 MHz/V using on-chip electrodes, enabling the frequency matching required for photon indistinguishability.