We show the directional excitation of Bloch surface waves controlled by the optical magnetic field, thus demonstrating the first magnetic spin-orbit interaction of light. Because it solely relies on the helicity of the optical magnetic field, this magnetic effect appears to be nonnegligible even with a non-resonant dielectric scatterer (electric dipole) used as a Bloch surface wave coupler. Magnetic spin-locking opens new degrees of freedom in the manipulation and detection of light.
We show the directional excitation of Bloch surface waves controlled by the optical magnetic field, thus demonstrating the first magnetic spin-orbit interaction of light. Because it solely relies on the helicity of the optical magnetic field, this magnetic effect appears to be nonnegligible even with a non-resonant dielectric scatterer (electric dipole) used as a Bloch surface wave coupler. Magnetic spin-locking opens new degrees of freedom in the manipulation and detection of light.
Light-matter interactions are often considered driven by the electric optical field alone, ignoring the magnetic component of light. However, this magnetic component plays a key role in many optical processes, such as chiral light-matter interactions, ultrasensitive detection, enhancement of Raman optical activity, photon-avalanching, or forbidden photochemistry, which makes the manipulation of magnetic processes extremely important. For instance, it was demonstrated in Eu3+ ions that magnetic emission could be manipulated by tuning the local magnetic quantum environment surrounding magnetic dipoles by means of dielectric or plasmonic nanostructures [1], [2]. Along the same line, it is also possible to manipulate the electric and magnetic excitation of these ions by controlling the electric and magnetic fields distribution of the excitation light [3].
Optical spin-orbit interactions (SOI), demonstrated experimentally in optical cavities, enable the polarization degrees of freedom of light to be described and controlled as an effective pseudospin, providing a foundation for spintronic-like control of light and the development of next-generation optical technologies. However, prior works describe this emergent effect using phenomenological models that fail to uncover its microscopic quantum origins, and as a result, a rigorous connection between material electronic structure and the optical SOI remains elusive. In this work, we address this fundamental challenge by developing a microscopic quantum theory starting from the non-relativistic quantum electrodynamical (QED) description of light-matter interactions. We show that this effect arises from virtual interactions between confined photons and material excitations. Crucially, our theoretical framework provides microscopic material-design principles for tuning the distinct components of optical SOI, which include the optical birefringence, photonic self-energies, TE-TM splitting, and optical Zeeman splitting, enabling precise engineering of effective magnetic fields, diabolical points, and pseudospin textures. We anticipate that the predictive capability of our microscopic theory will enable systematic screening and design of material systems for photonic spintronics and optical technologies.
By utilizing strong optical resonant interactions in arrays of atoms with electric dipole transitions, we show how to synthesize collective optical responses that correspond to those formed by arrays of magnetic dipoles and other multipoles. Optically active magnetism with the strength comparable with that of electric dipole transitions is achieved in collective excitation eigenmodes of the array. By controlling the atomic level shifts, an array of spectrally overlapping, crossed electric and magnetic dipoles can be excited, providing a physical realization of a nearly reflectionless quantum Huygens' surface with the full 2π phase control of the transmitted light that allows for extreme wavefront engineering even at a single photon level. We illustrate this by creating a superposition of two different orbital angular momentum states of light from an ordinary input state that has no orbital angular momentum.
Engineering the local density of states with nanophotonic structures is a powerful tool to control light-matter interactions via the Purcell effect. At optical frequencies, control over the electric field density of states is typically used to couple to and manipulate electric dipole transitions. However, it is also possible to engineer the magnetic density of states to control magnetic dipole transitions. In this work, we experimentally demonstrate the optical magnetic Purcell effect using a single rare earth ion coupled to a nanophotonic cavity. We engineer a new single photon emitter, Er3+ in MgO, where the electric dipole decay rate is strongly suppressed by the cubic site symmetry, giving rise to a nearly pure magnetic dipole optical transition. This allows the unambiguous determination of a magnetic Purcell factor Pm=1040±30. We further extend this technique to realize a magnetic dipole spin-photon interface, performing optical spin initialization and readout of a single Er3+ electron spin. This work demonstrates the fundamental equivalence of electric and magnetic density of states engineering, and provides a new tool for controlling light-matter interactions for a broader class of emitters.
Tremendous advances in the study of magnetic light-matter interactions have recently been achieved using man-made nanostructures that exhibit and exploit an optical magnetic response. However, naturally occurring emitters can also exhibit magnetic resonances in the form of optical-frequency magnetic-dipole transitions. Here we quantify the magnetic nature of light emission using energy- and momentum-resolved spectroscopy, and leverage a pair of spectrally close electric- and magnetic-dipole transitions in trivalent europium to probe vacuum fluctuations in the electric and magnetic fields at the nanometre scale. These results reveal a new tool for nano-optics: an atomic-size quantum emitter that interacts with the magnetic component of light. Light-matter interactions are generally dominated by electric fields and electric-dipole transitions. This study, however, quantifies magnetic contributions to light emission and so exploits the strong natural magnetic-dipole transitions in lanthanide ions to measure optical-frequency magnetic fields.
Using the sensitivity of atomic transitions on the polarizations of pump fields in multi-Zeeman-sublevel atomic systems, we show the polarization-direction-dependent anisotropic susceptibility of atoms that yields the strong coupling between the spin and the transverse momentum of light, i.e., spin–orbit interaction (SOI). Moreover, we also show that the spin-Hall effect of light can be obtained due to SOI. It can be controlled via the orientation of the anisotropy and frequency of light, and substantially enhanced up to several micrometers, which could be easily observed in experiment.