Distinguishability and "which pathway" information in multidimensional interferometric spectroscopy with a single entangled photon-pair

TL;DR

This paper demonstrates how interferometric spectroscopy with entangled photons can encode pathway information and distinguish microscopic interaction histories, even with low entanglement, enabling new quantum metrology techniques.

Contribution

It introduces an exchange-phase-cycling protocol that leverages photon distinguishability and phase information for pathway discrimination in quantum spectroscopy.

Findings

Pathway information is encoded even at low entanglement levels.

The protocol enables phase-sensitive discrimination of interaction histories.

Time-delay variables are unbound by wave-packet bandwidth constraints.

Abstract

Correlated photons inspire abundance of metrology-related platforms, which benefit from quantum (anti-) correlations and outperform their classical-light counterparts. While such demonstrations mainly focus on entanglement, the role of photon exchange-phase and degree of distinguishability have not been widely utilized in quantum-enhanced applications. Using an interferometric setup we show that even at low degree entanglement, when a two-photon wave-function is coupled to matter, it is encoded with a reliable "which pathway?" information. An interferometric exchange-phase-cycling protocol is developed, which enables phase-sensitive discrimination between microscopic interaction histories (pathways). We find that quantum-light interferometry facilitates utterly different set of time-delay variables, which are unbound by uncertainty to the inverse bandwidth of the wave-packet. We illustrate our findings on an exciton model-system, and demonstrate how to probe intraband dephasing in time-domain without temporal resolution at the detection. The exotic scaling of multiphoton coincidence with respect to the applied intensity is discussed.