Role of time-frequency correlations in two-photon-two-atom resonance energy transfer

Abstract

Since 2004, there exists a long standing discussion on the role that frequency anti-correlation and entanglement, as well as time-ordered excitation pathways, plays in the energy transfer from a two-photon donor to an acceptor comprising two non-interacting two-level particles. In this talk, I will present a general model for describing the joint excitation of two non-interacting two-level particles with photon pairs produced by Spontaneous Parametric Down Conversion (SPDC). We will see that while strong frequency anti-correlation between photons guarantees a large two-photon excitation (TPE) probability, photons bearing a sine cardinal spectral shape (the joint photon spectrum that is naturally produced during the SPDC process) exhibit a ~3.8 times larger TPE signal than photons with a Gaussian spectrum. More importantly, and in stark contrast to previous authors, we will see that suppression of time-ordered excitation pathways does not substantially modify the TPE probability for two-photon states with a Gaussian spectral shape; whereas photons with a sine cardinal spectrum exhibit the strongest TPE signal of all when two-photon excitation pathways are not suppressed. Our results not only help elucidating the role of time-frequency correlations in resonance energy transfer with SPDC photons, but also provide valuable information regarding the optimal source to be used in its experimental verification.