Coherent control of rare-earth ions in photonic cavities

Rare-earth ions, particularly Erbium (Er³⁺), are highly attractive for quantum communication because their optical transitions lie in the telecommunications C-band (around 1.54 μm). This allows quantum states to be transmitted over optical fibers with minimal attenuation.

However, rare-earth ions in bulk crystals typically suffer from weak light-matter interaction due to their shielded, forbidden 4f-4f transitions. To overcome this, we embed them into nanophotonic cavities. These cavities confine light to small volumes, enhancing the electric field and significantly increasing the transition rate via the Purcell effect.

The challenge lies in preserving coherence inside these nanostructures. The proximity to etched surfaces and interfaces introduces strain, surface charge noise, and defects, which accelerate decoherence. We use coherent control techniques, such as dynamical decoupling pulse sequences, to refocus the spin and optical coherence.

Our recent simulations demonstrate that optimized cavity design and phase-modulated spin echo sequences can achieve strong coupling while maintaining optical coherence times long enough for scalable quantum memory applications.