Entangled photon spectroscopy of molecules

Abstract

In this talk, I will discuss the growing field of entangled-photon spectroscopy as related to mol. systems. An entangled state is represented by a wavefunction, describing a group of particles, which cannot be factored into sep. states of individual particles. For photons, these correlations lead to non-classical light-matter interactions, potentially creating new opportunities for spectroscopic techniques. For example, second-order processes with two entangled photons, such as two-photon absorption or sum frequency generation, occur at a linear rate with a cross section that should be close to that of one-photon classical processes. However, early results in the field have produced conflicting measurements as to its magnitude. I will discuss the role of excited state dephasing and time-ordering for entangled photon interactions. I will also briefly remark on other interesting prospects of entangled photons, such as their ability to break the temporal-spectral Fourier transform limit. For instance, few-femtosecond spectroscopy is predicted to be possible with entangled light sources of MHz linewidths. Given the entangled photons quantum correlations, this property may lead to interesting opportunities in directing quantum coupled quantum states, although the techniques are still at an early stage.