On a possible “crystallized” state of exciton matter

E. A. Gazazyan, A. D. Gazazyan, V. O. Chaltykyan

We study the possibility to store and retrieve quantum information with use of “dark” and ”bright” polaritons in solids with excitonic resonances. In a crystal with Λ-type impurity atoms the upper level lying in the excitonic band of the crystal forms a Fano-type resonant state via configuration interaction with the continuum of crystal’s excitonic band. Polariton states are introduced in case of transitions through excitonic resonance and the properties of these states are studied. We also investigate propagation of dark polariton and show that its shape and quantum state are preserved during propagation. Limiting cases of adiabatic and non-adiabatic turning-on the fields are analyzed in detail.

Christo I. Ivanov, H. Barentzen, Marvin D. Girardeau

Monique Combescot

Marina Litinskaya, Roman V. Krems

Ultracold polar molecules trapped on an optical lattice is a many-body system that, under appropriate conditions, may support collective excitations reminiscent of excitons in solid state crystals. Here, we discuss the rotational excitations of molecules on an optical lattice leading to rotational Frenkel excitons. Apart from solid hydrogen, there is no other natural system that exhibits rotational excitons. The rotational excitons have unique properties that can be exploited for tuning non-linear exciton interactions and exciton-impurity scattering by applying an external electric field. We show that this can be used to explore the competing role of the dynamical and kinematic exciton-exciton interactions in excitonic energy transfer and to study quantum localization in a dynamically tunable disordered potential. The rotational excitons can also be used as a basis for quantum simulation of condensed matter models that cannot be realized with ultracold atoms. As an example, we discuss the possibility of engineering the Holstein model with polar molecules on an optical lattice.

P. Stenius, Ataç İmamoğlu

Summary form only given.Recent experiments show signatures of exciton Bose-Einstein condensation in semiconductors. Thus a device that creates a coherent population of excitons while being pumped by a thermal source may be possible. Such an exciton matter laser could consist of a quantum well, possibly embedded in an optical microcavity. In it hot excitons slightly below the bandgap are created by a thermal distribution of free electrons and holes (generated by electrical injection or optical pumping). The excitons interact with (LA) phonons. At low densities excitons are bosonic, and their scattering is affected by statistical enhancement into states with large occupation. Under certain conditions the excitons can condense into a single state, with statistics similar to a coherent state. Light emitted by radiative recombination has the coherence properties of the condensate and is similar to laser light. However, the electronic population in the device does not need to be inverted. We consider 1S heavy-hole excitons in a two-dimensional harmonic trap, realized by a quantum well where interface roughness inevitably localizes low-energy excitons, or by strain fields in lattice mismatched structures. We treat the lowest two trap levels quantum mechanically, and the higher lying states act as a reservoir. Our model is valid at low density, where phase space filling and collisions are negligible. While simplistic, the model displays the main features of an exciton matter laser. Our model is described by the master equation.

Tokio Ohta