We study numerically the spectrum of the non-Hermitian effective Hamiltonian that describes the dipolar interaction of a gas of $N\ensuremath{\gg}1$ atoms with the radiation field. We analyze the interplay between cooperative effects and disorder for both scalar and vectorial radiation fields. We show that for dense gases, the resonance width distribution follows, both in the scalar and vectorial cases, a power law $P(\ensuremath{\Gamma})\ensuremath{\sim}{\ensuremath{\Gamma}}^{\ensuremath{-}4/3}$ that originates from cooperative effects between more than two atoms. This power law is different from the $P(\ensuremath{\Gamma})\ensuremath{\sim}{\ensuremath{\Gamma}}^{\ensuremath{-}1}$ behavior, which has been considered as a signature of Anderson localization of light in random systems. We show that in dilute clouds, the center of the energy distribution is described by Wigner's semicircle law in the scalar and vectorial cases. For dense gases, this law is replaced in the vectorial case by the Laplace distribution. Finally, we show that in the scalar case the degree of resonance overlap increases as a power law of the system size for dilute gases, but decays exponentially with the system size for dense clouds.
Following the methods of Dicke, the authors study the cooperative emission of light which is produced from a periodic linear lattice consisting of N exchange-coupled two-level atoms. The atom-field coupling is assumed to be much smaller than the atom-atom coupling, as in the case of both parity- and spin-forbidden optical transitions in magnetic insulators. Numerical computations show that enhanced radiation may be produced by some highly excited quasi-equilibrium states. Using analytical calculations, the rate of the strongest radiation is shown to be proportional to N 1.5 when the interaction of atomic excitations is absent though the transfer of atomic excitations is operative. The pair correlation between transition dipole moments in the state bearing such a rate is examined, as well as the effect of a non-vanishing propagation vector of light. Finally, the crucial role of rapid non-radiative relaxations is pointed out, in observing these enhanced radiations.
The unique properties of two-dimensional moiré systems have been widely studied from many perspectives. However, relatively little work has investigated how the real-space structure of moiré systems can directly engender novel properties and functionalities. In this Letter, we explore how intriguing cooperative optical effects can emerge from the real-space superlattice formed by moiré excitons. Particularly, we show that the collective moiré exciton states can have either strongly enhanced (superradiant) or suppressed (subradiant) radiative decay rates, depending on their in-plane wave vector. These super- and subradiant states can be efficiently switched by a gate-induced electric field gradient. Moreover, the cooperative transmittance T of the atomically thin moiré system can be switched from
T≈0 (opaque) to
T≈1 (transparent) with
≲ 1% heterostrain or a
1∘ adjustment in the twist angle
θ. These features are robust against nonradiative losses and disorders, making the moiré system a highly versatile platform for cooperative quantum optics with potential applications in, e.g., single photon storage and switching.