  Most available theories for correlated electron transport are based on the
Hubbard Hamiltonian. In this effective theory, renormalized hopping and
interaction parameters only implicitly incorporate the coupling of correlated
charge carriers to microscopic degrees of freedom. Unfortunately, no
spectroscopy can individually probe such renormalizations, limiting the
applicability of Hubbard models. We show here that the role of each individual
degree of freedom can be made explicit by using a new experimental technique,
which we term 'quantum modulation spectroscopy' and we demonstrate here in the
one-dimensional Mott insulator ET-F2TCNQ. We explore the role on the charge
hopping of two localized molecular modes, which we drive with a mid infrared
optical pulse. Sidebands appear in the modulated optical spectrum, and their
linshape is fitted with a model based on the dynamic Hubbard Hamiltonian. A
striking asymmetry between the renormalization of doublons and holons is
revealed. The concept of quantum modulation spectroscopy can be used to
systematically deconstruct Hubbard Hamiltonians in many materials, exposing the
role of any mode, electronic or magnetic, that can be driven to large amplitude
with a light field.
