Mechanical tunability of an ultra-narrow spectral feature with uniaxial stress

Rare-earth doped crystals have numerous applications ranging from frequency metrology to quan- tum information processing. To fully benefit from their exceptional coherence properties, the effect of mechanical strain on the energy levels of the dopants - whether it is a resource or perturbation - needs to be considered. We demonstrate that by applying uniaxial stress to a rare-earth doped crystal containing a spectral hole, we can shift the hole by a controlled amount that is larger than the width of the hole. We deduce the sensitivity of Eu3+ ions in an Y2SiO5 matrix as a function of crystal site and the crystalline axis along which the stress is applied.