Abstract: The rapidly advancing field of quantum materials demands increasingly precise methods for characterizing and controlling entanglement. While early progress was made in quantum optics, extending these approaches to complex many-body systems in quantum materials remains a major challenge. In this talk, I will introduce the entanglement witness framework for characterizing the bounds of entanglement depth using solid-state spectroscopies. In the first half of the talk, I will begin with the detection of spin entanglement in quantum magnets through the quantum metrology and spin quantum Fisher information (QFI). These metrics can be accessed via inelastic neutron scattering and resonant inelastic x-ray scattering (RIXS). Importantly, RIXS provides a route to extend such probes far out of equilibrium, enabling the control of entanglement with light. In the second half of the talk, I will move beyond entanglement among distinguishable local modes to explore entanglement in systems of indistinguishable fermions. I will present a generalized framework for multi-particle entanglement among electrons, based on the cumulant reduced density matrix and the nonlinear response characteristics of RIXS.