Quantum optical inference: unraveling “which pathway?” information

Quantum systems are remarkably sensitive to changes in their environment. This renders them extraordinary probes for sensing applications. In contrast to classical probes, they undergo transitions upon coupling that encode trajectory dependent quantum information in their statistics. Decoding this information requires a new set of inference methodologies, such as the one we introduce here.

Entangled photon pairs have inspired a myriad of quantum-enhanced metrology platforms, which outperform their classical counterparts. However, the role of photon exchange-phase and degree of distinguishability have not yet been utilized in quantum-enhanced applications. We show that when a two-photon wave-function is coupled to matter, it is encoded with “which pathway?” information even at a low degree of entanglement. An interferometric exchange-phase-cycling protocol is developed, revealing phase-sensitive information for each interaction history individually. Moreover, we find that quantum-light multimode interferometry introduces a new set of time variables that enable time-resolved signals, unbound by uncertainty to the inverse bandwidth of the wave-packet. We illustrate our findings on an exciton model-system and discuss future applications. 

Zoom link: https://us02web.zoom.us/j/9305767498?pwd=enFmcVg1UStqbEExbWUzSGhhdXNWdz…