Quantum Process Tomography of Light-Matter Interactions with a Polarization-entangled Biphoton Probe

Quantum-light spectroscopy can yield higher spatio-temporal resolution and information inaccessible using its classical counterpart. Most current research on quantum-light spectroscopy uses entangled photon pairs (EPPs) as an analog for classical light. In contrast, our approach is to use quantum process tomography to treat the light-matter interaction fully quantum mechanically. By characterizing the density matrix of an entangled biphoton state in the polarization basis before and after interaction with a sample, we can measure the quantum mechanical operator associated with the light-matter interaction. With this technique we probe whether the correlated triplet-triplet pair intermediate in the singlet fission of TIPS-tetracene is an entangled state.