Blackbody radiation shift of the 27Al+ 1S0 → 3P0 transition

The differential polarizability, due to near-infrared light at 1126 nm, of the ²⁷Al+ ¹S₀ → ³P₀ transition is measured to be Δα = 4πε₀ × (1.6 ± 0.5) × 10^-31 m³, where Δα = α_P - α_S is the difference between the excited and ground state polarizabilities. This measurement is combined with experimental oscillator strengths to extrapolate the differential static polarizability of the clock transition as Δα(0) = 4πε₀×(1.5-0.5)×10^-31 m³. The resulting room temperature blackbody shift of Δυ/υ = -8(3)×10^-18 is the lowest known shift of all atomic transitions under consideration for optical frequency standards. A method is presented to estimate the differential static polarizability of an optical transition, from a differential light shift measurement.