arXiv subjects

Kai Xiang Lee

Publications and source records attributed to Kai Xiang Lee.

3 recordsLinked to original sources

arXiv2026

Toroidal Transitions in Hydrogenic and Alkali Atoms

In addition to electric and magnetic multipoles, the expansion of current density also yields toroidal terms, a lesser-known family of multipoles. A recent proposal, I. Kuprov $\textit{et al.}$, Science Adv. 8 abq6751 (2022), explores the possibility of a direct observation of optical toroidal transitions in hydrogen and alkali atoms in the presence of a large magnetic field that decouples the spin and the angular momentum of the electron. However, the difficulty of observing these transitions against the nearby electric dipole (E1) transitions were underestimated because of extra admixture coming from diamagnetic coupling. Here, we revisit the toroidal coupling in atoms, taking diamagnetic contribution into account, and discuss the technical challenges of observing toroidal coupling in atomic physics. We show that toroidal transition should be searched in transitions with low principal quantum numbers. The remaining strong electric-dipole contribution could be removed using an appropriate differential measurement.

physics.atom-ph↗

arXiv2025

Demonstrating efficient and robust bosonic state reconstruction via optimized excitation counting

Quantum state reconstruction is an essential element in quantum information processing. However, efficient and reliable reconstruction of non-trivial quantum states in the presence of hardware imperfections can be challenging. This task is particularly demanding for high-dimensional states encoded in continuous-variable (CV) systems, where a large number of grid-based measurements are often used to adequately sample relevant regions of phase space. In this work, we introduce an efficient and robust technique of Optimized Reconstruction with Excitation Number Sampling (ORENS) based on the idea of generalized Q-function. We use a standard bosonic circuit quantum electrodynamics (cQED) setup to experimentally demonstrate effective state reconstruction using the theoretically minimum number of measurements. Our investigation highlights that ORENS is naturally free of parasitic system dynamics and resilient to decoherence effects in the hardware, enabling it to outperform the conventional reconstruction techniques in cQED such as Wigner tomography. Finally, ORENS relies only on the ability to accurately measure the excitation number of a given CV state, making it a versatile and accessible tool for a wide range of CV platforms and readily scalable to multimode systems. Thus, our work provides a crucial and valuable primitive for practical quantum information processing using bosonic modes.

quant-ph↗

arXiv2024

Topological Momentum Skyrmions in Mie Scattering Fields

Topological quasiparticles such as skyrmions and merons have recently attracted enormous attentions in the form of diverse optical degrees of freedom. However, these structures have not been explored in the fundamental momentum vectors of optical fields yet. Here, we reveal the universality of forming skyrmion and meron topological textures from the Poynting vector, canonical momentum, and optical spin field, which are generated from multipole Mie scattering fields. Moreover, we analyze the unconditional topological stability of the skyrmionic momentum fields against perturbation and geometric defects. This work reveals the topological properties of multipole scattered field and will spur new phenomena related to optical forces, metamaterial design and unique light-matter interaction.

physics.optics↗