Coherent and incoherent dipole-dipole interactions between atoms

Katharina Brechtelsbauer

I. I. Khvalchenko

Vyacheslav Shatokhin, Mattia Walschaers, Frank Schlawin +1 more

One of the most pertinent problems in the debate on non-trivial quantum effects in biology concerns natural photosynthesis. Since sunlight is composed of thermal photons, it was argued to be unable to induce quantum coherence in matter, and that quantum mechanics is therefore irrelevant for the dynamical processes following photoabsorption. Our present analysis of a toy 'molecular aggregate'—composed of two dipole–dipole interacting two-level atoms treated as an open quantum system—however shows that incoherent excitations indeed can trigger persistent, coherent dynamics in both the site and the exciton bases: we demonstrate that collective decay processes induced by the dipole–dipole interactions create coherent intermolecular transport—regardless of the coherence properties of the incoming radiation. Our analysis shows that the steady state coherence is mediated by the population imbalance between the molecules and, therefore, increases with the energy difference between the two-level atoms. Our results establish the importance of collective decay processes in the study of ultrafast photophysics, and especially their potential role to generate stationary coherence in incoherently driven quantum transport.

P. Anantha Lakshmi, Ashok Vudayagiri, Shaik Liyakhath Ahmed

Eugene K. Bashkirov, Michail S. Mastyugin

In this paper, we have investigated the entanglement between two dipole coupled two-level atoms. The model, in which only one atom is trapped in an lossless cavity and interacts with single-mode thermal field, and the other one can be spatially moved freely outside the cavity has been carried out. We have considered the effect of the atomic coherence on the entanglement behavior. We have shown that a thermal field might cause high entanglement between the atoms both for coherent and incoherent initial atomic states only for small values of the cavity mean photon number. In the considered model the atoms would get entangled even when both atoms are initially in the excited state. We have also derived that the degree of entanglement is weakly dependent on the strength of dipole-dipole interaction for coherent initial states.

Thomas F. Gallagher, P. Pillet