Excitons and cavity polaritons for cold-atoms in an optical lattice

Hashem Zoubi, Helmut Ritsch

Hashem Zoubi

王嫣 WANG Yan, 郑任菲 ZHENG Ren-fei, 张衡 Zhang Heng +1 more

Hashem Zoubi, Helmut Ritsch

We study the effect of defects in the Mott insulator phase of ultracold atoms in an optical lattice on the dynamics of resonant electronic excitations. These excitations can be described analogous to Frenkel excitons in solids and form polaritons, when coupled to an optical resonator. Defects, which are empty sites in a singly occupied Mott insulator state or singly occupied sites for a filling factor two, change the exciton dynamics. We show that vacancies behave like hard sphere scatterers, while singly occupied sites in a doubly filled region generate either attractive or repulsive interaction potentials. We suggest cavity polaritons as tools which detect such defects and show how the scattering can be controlled by changing the exciton–photon detuning. In the case of aspherical individual lattice sites, we calculate the effective scattering potential as a function of the cavity photon polarization direction which exhibits a crossover from a repulsive into an attractive potential and should give a clearly observable signal.

Hashem Zoubi, Helmut Ritsch

Hashem Zoubi, Helmut Ritsch

We study the resonant electronic excitation dynamics for ultracold atoms trapped in a deep optical lattice prepared in a Mott-insulator state. Excitons in these artificial crystals are similar to Frenkel excitons in noble atom or molecular crystals. They appear when the atomic excited state linewidth is smaller than the exciton bandwidth generated by dipole-dipole coupling. When the atoms are placed within a cavity the electronic excitations and the quantized cavity mode get coupled. In the collective strong coupling regime excitations form two branches of cavity polaritons with Rabi splitting larger than the atomic and the cavity linewidth. To demonstrate their properties we calculate the transmission, reflection, and absorption spectra for an incident weak probe field, which show resonances at the polariton frequencies.