Collective Effects in Casimir-Polder Forces

Selective mode excitations and spontaneous emission engineering in quantum emitter-photonic structure coupled systems

We study the excitation conditions of the supported field modes, as well as the spontaneous decay property of a two-level quantum emitter coupled to photonic structures containing topological insulators (TIs) and left-handed materials. Within the proper field quantization scheme, the spontaneous decay rates of dipoles with different polarizations are expressed in forms of the Green's functions. We find that in the proposed structure, the variation in the topological magnetoelectric polarizability (TMP) has a deterministic effect on the excitation of different field modes. As the result, the spontaneous decay property of the quantum emitter can be engineered. For a dipole placed in different spatial regions, the spontaneous decay feature indicates a dominant contribution from the waveguide modes, the surface plasmon modes or the free vacuum modes. Moreover, a special kind of the surface plasmon modes displaying asymmetric density of states at the interfaces, becomes legal in the presence of nontrivial TIs. These phenomena manifest the feasibility in controlling dipole emissions via manipulations of the topological magnetoelectric (TME) effect. Our results have potential applications in quantum technologies relied on the accurate control over light-matter interactions.

Nonadditive Enhancement of Nonequilibrium Atom-Surface Interactions

The motion-induced drag force acting on a particle moving parallel to an arrangement of N objects is analyzed. Particular focus is placed on the nonequilibrium statistics of the interaction and on the interplay between the system's geometry and the different dissipative processes occurring in realistic setups. We show that the drag force can exhibit a markedly nonadditive enhancement with respect to the corresponding additive approximation. The specific case of a planar cavity-a relevant configuration for many experiments-is calculated, showing an enhancement of about one order of magnitude. This and similar configurations are of significant potential interest for future measurements that aim to detect the drag force.

Interaction of atomic systems with quantum vacuum beyond electric dipole approximation

The photonic environment can significantly influence emission properties and interactions among atomic systems. In such scenarios, frequently the electric dipole approximation is assumed that is justified as long as the spatial extent of the atomic system is negligible compared to the spatial variations of the field. While this holds true for many canonical systems, it ceases to be applicable for more contemporary nanophotonic structures. To go beyond the electric dipole approximation, we propose and develop in this article an analytical framework to describe the impact of the photonic environment on emission and interaction properties of atomic systems beyond the electric dipole approximation. Particularly, we retain explicitly magnetic dipolar and electric quadrupolar contributions to the light-matter interactions. We exploit a field quantization scheme based on electromagnetic Green’s tensors, suited for dispersive materials. We obtain expressions for spontaneous emission rate, Lamb shift, multipole-multipole shift and superradiance rate, all being modified with dispersive environment. The considered influence could be substantial for suitably tailored nanostructured photonic environments, as demonstrated exemplarily.

Non-Markovian Collective Emission from Macroscopically Separated Emitters

We study the collective radiative decay of a system of two two-level emitters coupled to a one-dimensional waveguide in a regime where their separation is comparable to the coherence length of a spontaneously emitted photon. The electromagnetic field propagating in the cavity-like geometry formed by the emitters exerts a retarded backaction on the system leading to strongly non-Markovian dynamics. The collective spontaneous emission rate of the emitters exhibits an enhancement or inhibition beyond the usual Dicke superradiance and subradiance due to self-consistent coherent time-delayed feedback.

Interaction and Entanglement of a Pair of Quantum Emitters near a Nanoparticle: Analysis beyond Electric-Dipole Approximation

In this paper, we study the collective effects which appear as a pair of quantum emitters is positioned in close vicinity to a plasmonic nanoparticle. These effects include multipole–multipole interaction and collective decay, the strengths and rates of which are modified by the presence of the nanoparticle. As a result, entanglement is generated between the quantum emitters, which survives in the stationary state. To evaluate these effects, we exploit the Green’s tensor-based quantization scheme in the Markovian limit, taking into account the corrections from light–matter coupling channels higher than the electric dipole. We find these higher-order channels to significantly influence the collective rates and degree of entanglement, and in particular, to qualitatively influence their spatial profiles. Our findings indicate that, apart from quantitatively modifying the results, the higher-order interaction channels may introduce asymmetry into the spatial distribution of the collective response.

Enhancement of long-distance Casimir-Polder interaction between an excited atom and a cavity made of metamaterials

Within the framework of macroscopic quantum electrodynamics, we investigate both the radiation force and the potential of Casimir-Polder type acting on an excited cold two-level atom in a cavity made of left-handed materials and topological insulators. As the time-reversal symmetry is broken on the surface of the topological insulators, the spontaneous emission of the atom placed near the focus point(s) exhibits anisotropic properties. While the potential wells are normally shallow for topological trivial dielectric, they may be amplified in the presence of topological magnetoelectric effect. We find that when there exists only one focus point in the cavity, it is possible to boost the forces or the potential wells by up to one order of magnitude. Meanwhile, the lifetime of the atom could be prolonged owing to the focus effect of the left-handed materials, where the emitted photons can trace back to the atom and reabsorbed by itself. Our results indicate the possibility in forming long-lived potential wells, which may have potential applications in trapping and guiding cold atoms far away from the surface.

Superradiant diamond color center arrays coupled to concave plasmonic nanoresonators

Superradiantly enhanced emission of SiV diamond color centers was achieved via numerically optimized concave plasmonic nanoresonators. Advantages of different numbers of SiV color centers, diamond-silver (bare) and diamond-silver-diamond (coated) core-shell nanoresonator types, spherical and ellipsoidal geometries were compared. Indistinguishable superradiance is reached via four color centers, which is accompanied by line-width narrowing except in a coated ellipsoidal nanoresonator that outperforms its bare counterpart in superradiance. Seeding of both spherical and bare ellipsoidal nano-resonators with six color centers results in larger fluorescence enhancement and better overridden superradiance thresholds simultaneously. Both phenomena are the best optimized in a six color centers seeded ellipsoidal bare nanoresonator according to the pronounced bad-cavity characteristics.