In the presented work we theoretically demonstrate that it is possible to asymmetrically (chirally) couple circularly polarized transitions in an atom by interfacing it with the nanostructure. We find that by making use of a quite simple plasmonic structure made of two asymmetric dipole scatterers, it is possible to achieve a very strong asymmetry in the interaction between the transitions, and this asymmetry leads to the observable atomic spin polarization even under external continuous wave pumping such that the total local field at the atomic position has a linear polarization.
In the presented work we theoretically demonstrate that it is possible to asymmetrically (chirally) couple circularly polarized transitions in an atom by interfacing it with the nanostructure. We find that by making use of a quite simple plasmonic structure made of two asymmetric dipole scatterers, it is possible to achieve a very strong asymmetry in the interaction between the transitions, and this asymmetry leads to the observable atomic spin polarization even under external continuous wave pumping such that the total local field at the atomic position has a linear polarization.
The effect of the dipole polarization on the quantum dipole dipole interaction near an Ag nanosphere (ANS) is investigated. A theoretical formalism in terms of classical Green function is developed for the transfer rate and the potential energy of the dipole dipole interaction (DDI) between two polarized dipoles. It is found that a linear transition dipole can couple to a left circularly polarized transition dipole much stronger than to a right circularly polarized transition dipole. This polarization selectivity exists over a wide frequency range and is robust against the variation of the dipoles' position or the radius of the ANS. In contrast, a right circularly polarized transition dipole, can change sharply from coupling strongly to another right circularly polarized dipole to coupling strongly to a left circularly polarized dipole with varying frequency. However, if the two dipoles are placed in the same radial direction of the sphere, the right circularly polarized transition dipole can only couple to the dipole with the same polarization while not to the left circularly polarized transition dipole. These findings may be used in solid-state quantum-information processing based on the DDI.
Summary form only given. Controlling the interaction of light and matter is the basis for diverse applications ranging from light technology to quantum information processing. Nowadays, many of these applications are based on nanophotonic structures. It turns out that the confinement of light in such nanostructures imposes an inherent link between its local polarization and its propagation direction, also referred to as spin-momentum locking of light [1]. Remarkably, this leads to chiral, i.e., propagation direction-dependent effects in the emission and absorption of light, and elementary processes of light-matter interaction are fundamentally altered. For example, when coupling plasmonic particles or atoms to evanescent fields, the intrinsic mirror symmetry of the particles' emission can be broken. In our group, we observed this effect in the interaction between single rubidium atoms and the evanescent part of a light field that is confined by continuous total internal reflection in a whispering-gallery-mode microresonator [2]. In the following, this allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the structure is controlled by the polarization of the excitation light [3] or by the internal quantum state of the emitter [4], respectively. Moreover, we employed this chiral interaction to demonstrate an integrated optical isolator [5] as well as an integrated optical circulator [6] which operate at the single-photon level and which exhibit low loss. The latter are the first two examples of a new class of nonreciprocal nanophotonic devices which exploit the chiral interaction between single quantum emitters and transversally confined photons.
We investigate the radiative coupling between two two-level atoms with arbitrarily polarized dipoles in the vicinity of a nanofiber. We present a systematic derivation for the master equation, the single- and cross-atom decay coefficients, and the dipole-dipole interaction coefficients for the atoms interacting with the vacuum of the field in the guided and radiation modes of the nanofiber. We study numerically the case where the atomic dipoles are circularly polarized. In this case, the rate of emission depends on the propagation direction, that is, the radiative interaction between the atoms is chiral. We examine the time evolution of the atoms for different initial states. We calculate the fluxes and mean numbers of photons spontaneously emitted into guided modes in the positive and negative directions of the fiber axis. We show that the chiral radiative coupling modifies the collective emission of the atoms. We observe that the modifications strongly depend on the initial state of the atomic system, the radiative transfer direction, the distance between the atoms, and the distance from the atoms to the fiber surface.
We investigate the radiative coupling between two two-level atoms with arbitrarily polarized dipoles in the vicinity of a nanofiber. We present a systematic derivation for the master equation, the single- and cross-atom decay coefficients, and the dipole-dipole interaction coefficients for the atoms interacting with the vacuum of the field in the guided and radiation modes of the nanofiber. We study numerically the case where the atomic dipoles are circularly polarized. In this case, the rate of emission depends on the propagation direction along the fiber axis and, hence, the radiative interaction between the atoms is chiral. We examine the time evolution of the atoms for different initial states. We calculate the fluxes and mean numbers of photons spontaneously emitted into guided modes in the positive and negative directions of the fiber axis. We show that the chiral radiative coupling modifies the collective emission of the atoms. We observe that the modifications strongly depend on the initial state of the atomic system, the radiative transfer direction, the distance between the atoms, and the distance from the atoms to the fiber surface.
Chiral materials possess some unusual properties for which they have attracted tremendous interest in recent research. In this paper, we discuss the interaction of electromagnetic fields with an initially isotropic material, making it anisotropic chiral by inducing magnetoelectric cross coupling. We consider a four-level double Λ -type configuration of an atomic ensemble, which is simultaneously sensitive to relative phase of the applied fields due to its closed-loop nature, providing an extra degree of freedom for controlling the birefringent nature of the medium. We show that the material splits a linearly polarized probe field into left- (LCP) and right-circularly polarized (RCP) components, and their angular divergence can be related to the optical activity of the medium. This leads to efficient modulation of the probe field, which may be helpful in accurate position detection of the transmitted beams and images. Next, we demonstrate that such a medium can be used to couple incident light with surface plasmons (SPs) in two ways: (1) as a prism-like coupler, in either Otto- or Kretschmann-type geometry, where excitation of SPs can be achieved beyond a certain incident angle of the interacting pulse in a plasmonic waveguide placed closed to it; and (2) direct excitation of SPs by a LCP or RCP beam from the chiral medium in a particular slit-type plasmonic waveguide. We find that the coupled modes in the latter case are unidirectional and highly tunable. Further, we show that the birefringent nature of the medium as well as the plasmonic field intensities can be efficiently manipulated with a number of controlling parameters. Our results may find applications in image coding, plasmonic sensors, and bio-photonics.
Unidirectional (chiral) emission of light from a circular dipole emitter into a waveguide is only possible at points of perfect circular polarization (C points), with elliptical polarizations yielding a lower directional contrast. However, there is no need to restrict engineered systems to circular dipoles, and with an appropriate choice of dipole unidirectional emission is possible for any elliptical polarization. Using elliptical dipoles, rather than circular, typically increases the size of the area suitable for chiral interactions (in an exemplary mode by a factor ∼30), while simultaneously increasing coupling efficiencies. We propose illustrative schemes to engineer the necessary elliptical transitions in both atomic systems and quantum dots.