Witnessing entangled two-photon absorption via quantum interferometry

Recent investigations have suggested that the use of non-classical states of light, such as entangled photon pairs, may open new and exciting avenues in experimental two-photon absorption spectroscopy. Despite several experimental studies of entangled two-photon absorption (eTPA), there is still a heated debate on whether eTPA has truly been observed. This interesting debate has arisen mainly because it has recently been argued that single-photon-loss mechanisms, such as scattering or hot-band absorption, may mimic the expected entangled-photon linear absorption behavior. In this work, we focus on transmission measurements of eTPA and explore three different two-photon quantum interferometers in the context of assessing eTPA. We demonstrate that the so-called N00N-state configuration is the only one among those considered insensitive to linear (single-photon) losses. Remarkably, our results show that N00N states may become a potentially powerful tool for quantum spectroscopy, placing them as a strong candidate for the certification of eTPA in an arbitrary sample.

Automated summary

Recent investigations have shown the potential of using non-classical states of light in experimental two-photon absorption spectroscopy. However, there is still a debate on whether entangled two-photon absorption has truly been observed, as single-photon-loss mechanisms may mimic this behavior. In this study, transmission measurements of entangled two-photon absorption were conducted, and it was found that the N00N-state configuration is insensitive to linear (single-photon) losses, making it a strong candidate for the certification of this phenomenon in any sample.