Terahertz quantum optics in the time-domain: from field correlation measurements on vacuum field fluctuations in free space towards cavity electro-optics

Abstract

The ground state of electromagnetic radiation is characterised by a fluctuating electromagnetic field even in a vacuum. We measure its correlation function as a function of time and space using the electro-optic effect. We determine the spectral content and the amplitude of this state and find excellent agreement with the second quatisation theory.