Homogeneous broadening of the S to P transition in InGaAs/GaAs quantum dots measured by infrared absorption imaging with nanoscale resolution

Absorption of single InGaAs self-assembled quantum dots is spatially resolved in resonance with the S to P polaron transitions around λ = 25 μm wavelength. We show that the spatial resolution down to 50 nm (λ/500) combined with the analysis of the absorption nanoscopy images provides a measurement of the homogeneous broadening at room temperature. The 2.5 ± 1 meV measured S-P homogeneous broadening supports the calculated value accounting for acoustic phonon-induced decoherence.