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.
AI Summary
The paper asks how exciton energies and transition-dipole orientations determine effective spin–orbit interactions of confined light, usually described by fitted polarization Hamiltonians. It starts from a momentum-dependent exciton–photon Tavis–Cummings model in the dipole gauge, applies the rotating-wave approximation, and eliminates excitons through a second-order Schrieffer–Wolff transformation.
The resulting $2\times2$ photonic Hamiltonian has momentum-dependent self-energy, birefringence, TE–TM coupling, and Zeeman-like terms. Analytical expressions connect these coefficients to excitonic detunings and transition dipoles. In this model, the Zeeman-like term requires out-of-plane dipole components. The paper also derives conditions for band crossings and proposes suppressing the leading birefringence contribution by balancing in-plane and out-of-plane oscillator strengths, assuming similar excitonic detunings.
Four illustrative dipole configurations—isotropic in-plane, uniaxial, anisotropic in-plane, and canted—are studied numerically. Comparisons with the uneliminated exciton–photon Hamiltonian assess dispersions and Stokes polarization textures. For a $200$ nm slab with refractive index $2$, the anisotropic and canted examples yield effective-model crossing locations at $k_y\approx\pm7.21$ and $\pm10.55\,\mu\mathrm{m}^{-1}$, respectively. Canted dipoles additionally produce oppositely circularly polarized branches displaced in momentum.
The treatment assumes dispersionless excitons and uses ideal, polarization-degenerate cavity photon modes, setting aside boundary-induced splitting. Agreement is described as qualitative to semiquantitative. The stated crossing conditions are perturbative: higher-order terms may turn them into avoided crossings. Phonon-induced decoherence and associated topological phenomena are left for future work.
Little sign of AI-generated textOverclaimsMissing comparisonStrong assumptions
Error found: Model IV's predicted finite-momentum diabolical points are artifacts of retaining an out-of-plane fourth-order momentum contribution while omitting an in-plane contribution of the same order; neither unexpanded second-order elimination nor the stated original Hamiltonian has the claimed degeneracies.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
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.
The paper asks how exciton energies and transition-dipole orientations determine effective spin–orbit interactions of confined light, usually described by fitted polarization Hamiltonians. It starts from a momentum-dependent exciton–photon Tavis–Cummings model in the dipole gauge, applies the rotating-wave approximation, and eliminates excitons through a second-order Schrieffer–Wolff transformation.
The resulting 2×2 photonic Hamiltonian has momentum-dependent self-energy, birefringence, TE–TM coupling, and Zeeman-like terms. Analytical expressions connect these coefficients to excitonic detunings and transition dipoles. In this model, the Zeeman-like term requires out-of-plane dipole components. The paper also derives conditions for band crossings and proposes suppressing the leading birefringence contribution by balancing in-plane and out-of-plane oscillator strengths, assuming similar excitonic detunings.
Four illustrative dipole configurations—isotropic in-plane, uniaxial, anisotropic in-plane, and canted—are studied numerically. Comparisons with the uneliminated exciton–photon Hamiltonian assess dispersions and Stokes polarization textures. For a 200 nm slab with refractive index 2, the anisotropic and canted examples yield effective-model crossing locations at ky≈±7.21 and ±10.55μm−1, respectively. Canted dipoles additionally produce oppositely circularly polarized branches displaced in momentum.
The treatment assumes dispersionless excitons and uses ideal, polarization-degenerate cavity photon modes, setting aside boundary-induced splitting. Agreement is described as qualitative to semiquantitative. The stated crossing conditions are perturbative: higher-order terms may turn them into avoided crossings. Phonon-induced decoherence and associated topological phenomena are left for future work.
Spin-orbit interactions (SOIs) of light are manifestations of coupling between components of light's angular momentum. They are at play in most basic optical processes, offering opportunities both to understand their fundamental origin and to control light in novel ways. Because SOIs become significant at subwavelength scale, they have largely been explored in the context of inhomogeneous materials exhibiting wavelength-scale structures, and notably metamaterials. Here we demonstrate that spin-orbit interactions can in fact analogously emerge in moving matter through the well-known light-dragging effects. SOIs in moving media are shown to manifest through a Berry phase induced by vorticity, which then leads to a rotation of the wave's polarization. In bringing together electrodynamics of moving media and SOIs of light, our work not only paves the way for the discovery of new fundamental effects but also uncovers novel means to harness SOIs to control light.
Tuning spin-orbit coupling is essential in controlling both spin and charge in confined semiconductor nanostructures, yet it is rarely a truly controllable parameter. Here, we show control over the spin-orbit Hamiltonian in quantum dots and the resulting quantum states by tailoring the confinement potential with atomic-scale precision. Using scanning tunnelling microscopy and spectroscopy, we pattern individual Cs ions into designer quantum dot structures on the surface of indium antimonide, in which electrons from a two-dimensional electron gas are confined with chosen in-plane electric-field gradients. We then quantify the atomic level structure, both spatially resolving the orbital character of the electronic states and their magnetic-field evolution. We demonstrate that the level structure, including the induced zero-field splitting, can be tailored by the designed geometry of the local electric fields. These effects can be described using a Hamiltonian that allows consistent treatment of the confinement-induced spin-orbit coupling beyond the conventional Bychkov-Rashba description. This Hamiltonian is derived from a multiband k.p model and takes the energy dependence of the relevant physical parameters into account. Such precise control of spin-orbit coupling in semiconductor quantum dots is relevant to quantum and spintronic technologies.
Coupling between quantum emitters and modes of light is foundational to studies of quantum systems. Coherent interactions between matter and light have greatly advanced the development of quantum technologies. When an ensemble of atoms interacts with light that is confined within a cavity---a resonator for photons---light also mediates atom-atom interactions, leading to collective phenomena that cannot be extrapolated from microscopic behaviors. Understanding how interactions among quantum particles lead to macroscopic phenomena, such as phase transitions and breaking of symmetries, remains a challenge in modern physics. In this dissertation, I present results addressing this challenge in the context of mesoscopic arrays of optical-tweezer-trapped atoms interfaced with a high-finesse optical cavity. In particular, the physics we investigate arises from the collective scattering of light. Utilizing the ability to place atoms with nanometer-scale precision, we engineer superradiant and subradiant states, where control over interference of the emission from multiple atoms leads to collectively enhanced or suppressed amounts of scattered light. Building on this work, we investigate the emergence of optomechanical self-organization, mediated by superradiance in the cavity electromagnetic field. By coupling atoms to the same cavity mode, the atoms exert forces on one another through the exchange of photons, leading them to autonomously order themselves spatially. We characterize mesoscopic fluctuations and their effect on symmetry-breaking dynamics associated with self-organization. Finally, we extend this framework to theoretically investigate how the phase of the atom-cavity coupling can be altered to generate higher symmetries. Our analysis reveals first-order phase transitions and instabilities induced by non-reciprocal forces. Altogether, this work establishes a path towards realizing mesoscopic systems of complex phases of matter in cavity quantum electrodynamics with unprecedented programmability.
When in a quantum optical system the coupling between matter and cavity mode becomes comparable to the bare excitation frequency, we enter a non-perturbative coupling regime, as perturbation theory fails describing the system’s dynamics. While recent advances in Cavity Quantum Electrodynamics allowed to achieve very high values of the coupling strength, thanks to the resonators properties optimization and the employment of solid-state devices, an ever growing interest has been shown about the possibility of significantly modify materials’ properties. It has been demonstrated that the chemical structure of molecules strongly coupled to a photon mode can be altered, which opens the possibility to manipulate and control chemical reactions. The aim of this thesis is to explore non-perturbative regimes on several quantum systems, and to investigate the effects of the coupling upon their properties, such as internal degrees of freedom or electronic states structure. I first developed a novel theory to determine the polariton spectrum of a dipolar ensamble in which a Ising-like dipole-dipole interaction in the 2 non-perturbative regime is considered. A further important focus is the investigation of the saturation effects due to the inclusion of the inter-dipole interaction, and the interplay between the latter and light-matter coupling strength. I also explored specifically the influence of the coupling on the rotational degrees of freedom of an ensemble of two-dimensional freely rotating dipoles, all coupled to a single cavity mode, finding that they are driven by the collective light-matter coupling to undergo a crossover between an isotropic and an aligned phase. I then investigated the case of cavity-embedded doped quantum wells, demonstrating that not only it is possible to couple a discrete cavity mode and bound-to-continuum transitions, but also that a novel bound exciton state appears, induced by the coupling strength. This results shows how light–matter coupling can be used to tune both optical and electronic properties of semiconductor heterostructures beyond those permitted by mere crystal properties. Finally, I explored the physics of an array of THz metamaterial resonators coupled to cyclotron resonances of a two-dimensional electron gas, developing a multiple-mode theory that takes in account the interaction between multiple photon modes mediated by the electrons. My results show that this cross-interaction, due to the strong two-dimensional geometry of the optically active medium, leads to the hybridization of different uncoupled photon modes, and manifests as a visible change of the distribution of the coupled electromagnetic field.
We present a theoretical investigation of spin-orbit photonics within a fixed mirror cavity system containing a Bose-Einstein condensate (BEC), in which the Bogoliubov excitation modes of the condensate are treated as effective mechanical oscillators. By embedding the condensate in a single-mode optical cavity, we explore the emergence and modulation of the photonic spin Hall effect (PSHE) through the spin-dependent transverse shifts of a weak probe field. The optical response —encoded in the real and imaginary components of the output field susceptibility— is systematically analyzed as a function of the condensate-cavity coupling strength, revealing a controllable enhancement or suppression of the spin-orbit interaction. Our model captures how the interplay between collective BEC excitations and cavity photon dynamics induces nontrivial modifications in spin-dependent light propagation. Notably, we uncover that the Bogoliubov mode coupling acts as a tunable channel for mediating spin angular momentum transfer within the cavity, offering a novel route for engineering compact, quantum-coherent spin-orbit photonic devices.
Quantum light-matter interactions, described by the theory of quantum electrodynamics (QED), have motivated numerous scientific discoveries and technological developments over the past few decades. Considerable effort has been made to develop different QED platforms, e.g., free space, waveguides, cavities, and photonic crystals, for engineering quantum light-matter interactions. This thesis explores a new frontier, deep microscopic QED, which leverages the deep microscopic response of materials to reveal new topological, quantum, and thermal photonic phenomena with applications to quantum sensing and information processing. In the first part of this thesis, we investigate unique topological photonic effects arising in the deep microscopic QED regime. Previous efforts focused on topological photonic phases and edge states arising from artificial spatial structures of materials (e.g., photonic crystals or metamaterials). One fundamental question is whether topological photonic states can also arise from the intrinsic response of many-body systems and do not rely on materials' macroscopic structures. Here, we first discuss a new topological electromagnetic phase - ‘optical N-phase’ arising in two-dimensional (2D) viscous hydrodynamic electrons in graphene, which originates from the microscopic response of 2D materials and does not rely on materials' macroscopic structures. We then introduce the associated edge states, optical N-plasmons, which are topologically protected ultra-subwavelength edge magneto-plasmons. We further show how these topological plasmons can be harnessed to design chiral radio-frequency nonreciprocal circuit components, topological hydrodynamic circulators, that interface quantum and classical hardware.In the second part of this thesis, we focus on collective atom-photon interactions in the deep microscopic QED regime. In atom interactions with photonic environments, there exist two non-unitary processes -- pure dephasing and spontaneous emission. Despite considerable interest in collective effects in spontaneous emission since the 1950s, one long-standing problem is whether collective effects in pure dephasing can arise in atom-photon interactions. This question is particularly important in the quantum information era since pure dephasing is the main obstacle in current quantum information technologies. Here, we first introduce a new collective quantum phenomenon, ‘nanophotonic superdephasing,’ occurring in atom/spin ensembles in nanoscale photonic environments. This nanophotonic superdephasing phenomenon originates from low-frequency photonic environment correlations, and leads to collectively accelerated disentanglement without photon emission, in stark contrast to conventional collective spontaneous emission/superradiance effects. We further reveal the effects of nanophotonic environment mediated correlated dynamics on quantum computing and sensing. We demonstrate that correlations of nanoscale EM environments in spin qubit quantum computing devices can induce correlated errors and limit quantum gate fidelity. Meanwhile, based on nanophotonic collective dephasing, we also propose a multiqubit quantum sensing protocol that exploits spatially correlated noise near materials to enable order parameter symmetry characterization of materials beyond single-qubit methods.In the final part, we explore thermal photonic phenomena in the deep microscopic regime. Conventional techniques in engineering near-field radiative heat transfer typically rely on phonons, plasmons, and electromagnetic modes in structured materials. Here, we reveal a new approach to enhance near-field thermal radiation: leveraging intrinsic quantum coherence in superconducting materials. We reveal the quantum fingerprint of superconductivity in thermal photonics, ‘superconducting coherence peak’ in near-field thermal radiation, which originates from quantum coherence of Bogoliubov quasiparticles, with potential applications in thermal engineering in superconducting circuits.Overall, the thesis establishes a deep microscopic QED platform for new quantum, topological, and thermal photonic phenomena in many-body systems, with applications in quantum sensors and devices.