arXiv subjects

Chung-Hsien Wang

Publications and source records attributed to Chung-Hsien Wang.

4 recordsLinked to original sources

arXiv2026

Generating broadband optical squeezing via Cascaded Micro-Ring Resonators

Broadband squeezed light functioning as a Markovian reservoir can exponentially enhance light-matter interactions, benefiting quantum technologies. However, conventional single-cavity sources face a trade-off between squeezing depth and spectral bandwidth. We propose a scalable scheme for generating broadband squeezed vacuum using a cascade of parametric microring resonators coupled to a common bus waveguide. By analyzing the output, we identify the specific conditions that yield a broad, flat-topped squeezing spectrum, even under realistic intracavity pump attenuation. We demonstrate that this architecture is robust against fabrication imperfections, including inhomogeneous resonator frequencies and component failures. We show that the flat-topped spectrum converges to the Markovian limit significantly faster than a single-cavity Lorentzian profile. An array of as few as $N=5$ coupled resonators with an intrinsic loss ratio of $κ_I/κ= 0.1$ reduces the required bandwidth to a quarter of that needed by a single cavity to achieve same squeezing. This rapid convergence relaxes the low-$Q$ and high-gain constraints of single broadband cavities, distributing the squeezing process across moderately pumped resonators to provide a practical route for engineering squeezed reservoirs on mature integrated photonic platforms.

quant-ph↗

arXiv2024

Light scattering properties beyond weak-field excitation in atomic ensembles

In the study of optical properties of large atomic system, a weak laser driving is often assumed to simplify the system dynamics by linearly coupled equations. Here, we investigate the light scattering properties of atomic ensembles beyond weak-field excitation through the cumulant expansion method. By progressively incorporating higher-order correlations into the steady-state equations, an enhanced accuracy can be achieved in comparison to the exact solutions from solving a full density matrix. Our analysis reveals that, in the regime of weak dipole-dipole interaction (DDI), the first-order expansion yields satisfactory predictions for optical depth, while denser atomic configurations necessitate consideration of higher-order correlations. As the intensity of incident light increases, atom saturation effects become noticeable, giving rise to significant changes in light transparency, energy shift, and decay rate. This saturation phenomenon extends to subradiant atom arrays even under weak driving conditions, leading to substantial deviations from the linear model. Our findings demonstrate the mean-field models as good extensions to linear models as it balances both accuracy and computational complexity. However, the crucial role of higher-order cumulants in large and dense atom systems remains unclear, since it is challenging theoretically owing to the exponentially increasing Hilbert space in such light-matter interacting systems.

quant-ph↗

arXiv2022

Enhanced dark-state sideband cooling in trapped atoms via photon-mediated dipole-dipole interactions

Resolved sideband cooling provides a crucial step in subrecoil cooling the trapped atoms toward their motional ground state, which is essential in atom-based quantum technologies. Here we present an enhanced dark-state sideband cooling in trapped atoms utilizing photon-mediated dipole-dipole interactions among them. By placing the atoms at the magic interparticle distances, we manifest an outperformed cooling behavior in the target atom, which surpasses the limit that a single atom permits. We further investigate various atomic configurations in a multiatom setup with a laser detuning and different light polarization angles, where multiple magic spacings can be identified and a moderate improvement in cooling performance is predicted as the number of atoms increases. Our results provide insights to subrecoil cooling of atoms with collective and light-induced long-range dipole-dipole interactions, and pave the way toward implementing genuine quantum operations in multiple quantum registers.

quant-ph↗

arXiv2022

Superior dark-state cooling via nonreciprocal couplings in trapped atoms

Cooling the trapped atoms toward their motional ground states is key to applications of quantum simulation and quantum computation. By utilizing nonreciprocal couplings between constituent atoms, we present an intriguing dark-state cooling scheme in $Λ$-type three-level structure, which is shown superior than the conventional electromagnetically-induced-transparency cooling in a single atom. The effective nonreciprocal couplings can be facilitated either by an atom-waveguide interface or a free-space photonic quantum link. By tailoring system parameters allowed in dark-state cooling, we identify the parameter regions of better cooling performance with an enhanced cooling rate. We further demonstrate a mapping to the dark-state sideband cooling under asymmetric laser driving fields, which shows a distinct heat transfer and promises an outperforming dark-state sideband cooling assisted by collective spin-exchange interactions.

quant-ph↗