In typical organic based microcavities, large values of Rabi splitting are accompanied by any amount of structural disorder. We present a microscopic approach which treats on equal footing the strong light-matter coupling and the disorder scattering which breaks translational symmetry. Through direct numerical diagonalization in a long, but finite, disordered one-dimensional microcavity, the nature of the eigenstates is elucidated and compared to that of the plane-wave-like cavity polaritons of a perfect system. It is shown that delocalized states with well defined wave vectors or strongly localized states may occur, depending on their energy. In particular, at energies close to the excitonic resonance as well as at the bottom of the polariton branches, the states are definitely not plane-wave-like.

Giant atoms are attracting interest as an emerging paradigm in the quantum optics of engineered waveguides. At variance with the well-known artificial giant atoms for microwave photonics, here we propose the archetype of a giant atom working in the optical regime by considering a pair of interacting Rydberg atoms coupled to a photonic crystal waveguide (PCW) and also driven by a coherent field. Giant-atom effects are observed as a phase-dependent decay of the double Rydberg excitation during the initial evolution stage while a nontrivial internal entanglement is exhibited at later times. Such an entanglement onset occurs in the presence of intrinsic atomic decay toward nonguided vacuum modes and is accompanied by antibunching in the emitted photons. Our predictions should be observable in current Rydberg-PCW experiments and may open the way toward giant-atom optical photonics for quantum information processing.

We study the collective dynamics of a clean Floquet system of cold atoms, numerically simulating two realistic setups based on a regular chain of interacting Rydberg atoms driven by laser fields. In both cases, the population evolution and its Fourier spectrum display clear signatures of a discrete time crystal (DTC), exhibiting the appearance of a robust subharmonic oscillation which persists on a timescale increasing with the chain size, within a certain range of control parameters. We also characterize how the DTC stability is affected by dissipative processes, typically present in this atomic system even though the Rydberg state is very long lived.

Two interacting Rydberg atoms coupled to a waveguide may realize a giant-atom platform that exhibits controllable (phase-dependent) chirality through which the direction of nonreciprocally scattered photons can be switched on demand, e.g., by the geometrical tuning of an external driving field. In our platform, at variance with traditional setups, the chirality arises from a simple optical implementation of the local phase difference between two coupling points of the Rydberg giant atom. When employing two (or more) driving fields, this platform can also be used as a frequency converter with its strongly asymmetric efficiency being significantly enhanced via the chiral couplings. Our Rydberg giant-atom platform is well suited for chiral quantum optics applications and further offers direct scalability for reaching tunable frequency conversion in the optical domain.

We theoretically consider a hybrid heterostructure made of an inorganic quantum well in close proximity with an organic material overlayer whereby the latter is used to funnel excitation energy to the former in order to exploit the optical nonlinearities of the two-dimensional Wannier excitons. On the one hand, the diffusion length of Frenkel excitons in the organic medium is assumed to be comparable or larger than the corresponding absorption length. On the other hand, the nonradiative energy transfer from the organic to the inorganic subsytem can be very efficient when the Frenkel exciton energy is significantly higher than the band gap of the inorganic semiconductor. We show in this regime that the resonant optical pumping of the Frenkel excitons can lead to an efficient indirect pumping of the Wannier excitons (or electron-hole plasma) in the inorganic quantum well turning on the corresponding nonlinearities.

The renormalization of the electron $g$ factor by the confining potential in semiconductor nanostructures is considered. A new effective $\mathbf{k}·\mathbf{p}$ Hamiltonian for the electronic states in III–V semiconductor nanostructures in the presence of an external magnetic field is introduced. The mesoscopic spin-orbit (Rashba type) and Zeeman interactions are taken into account on an equal footing. It is then solved analytically for the electron effective $g$ factor in symmetric quantum wells ($g_{\mathrm{QW}}^{*}$). Comparison with different spin quantum beat measurements in GaAs and InGaAs structures demonstrates the accuracy and utility of the theory. The quantum size effects in $g_{\mathrm{QW}}^{*}$ are easily understood and its anisotropy $\Delta g_{\mathrm{QW}}^{*}$ (i.e., the difference between the in-plane and perpendicular configurations) is shown to be given by a mesoscopic spin-orbit effect having the same origin as the Rashba one. DOI: http://dx.doi.org/10.1103/PhysRevB.86.195302 ©2012 American Physical Society