The optimum conditions for observing superradiance and subradiance effects in an ensemble of two-level atoms, placed in a waveguide cladding with a metamaterial with near-zero refractive index, are discussed.
We describe collective spontaneous emission of N two-level atoms placed within a photonic band-gap material. When the atomic resonance frequency lies at the band edge, superradiant emission remains localized in the vicinity of the atoms. This leads to a steady state with spontaneously broken symmetry in which the atomic system acquires a macroscopic polarization. The superradiant decay rate is proportional to N2/3 and N2 for isotropic and anisotropic 3D band gaps, respectively. The corresponding peak intensity of superradiance is proportional to N5/3 and N3, respectively.
We analytically and numerically study collective emission from an ensemble of atoms in the weak-excitation regime with the initial condition of uniform excitation of the ensemble. We show that under certain conditions, subradiance at the later stages of the collective decay does not necessarily need to be accompanied by early-time superradiance. We analyze the conditions where such subradiance-only decay occurs for ordered and disordered ensembles in one-, two-, and three-dimensional spatial configurations.
We demonstrate a plasmonic route to control the collective spontaneous emission of two-level quantum emitters. Superradiance and subradiance effects are observed over distances comparable to the operating wavelength inside plasmonic nanochannels. These plasmonic waveguides can provide an effective epsilon-near-zero operation in their cut-off frequency and Fabry-Pérot resonances at higher frequencies. The related plasmonic resonant modes are found to efficiently enhance the constructive (superradiance) or destructive (subradiance) interference between different quantum emitters located inside the waveguides. By increasing the number of emitters located in the elongated plasmonic channel, the superradiance effect is enhanced at the epsilon-near-zero operation, leading to a strong coherent increase in the collective spontaneous emission rate. In addition, the separation distance between neighboring emitters and their emission wavelengths can be changed to dynamically control the collective emission properties of the plasmonic system. It is envisioned that the dynamic modification between quantum superradiant and subradiant modes will find applications in quantum entanglement of qubits, low-threshold nanolasers and efficient sensors.