arXiv subjects

Ruijuan Liu

Publications and source records attributed to Ruijuan Liu.

5 recordsLinked to original sources

arXiv2026

Stability of the Timoshenko Beam Equation with One Weakly Degenerate Local Kelvin-Voigt Damping

We consider the Timoshenko beam equation with locally distributed Kelvin-Voigt damping, which affects either the shear stress or the bending moment. The damping coefficient exhibits a singularity, causing its derivative to be discontinuous. By using the frequency domain method and multiplier technique, we prove that the associated semigroup is polynomial stability. Specifically, regardless of whether the local Kelvin-Voigt damping acts on the shear stress or the bending moment, the system decays polynomially with rate $t^{-\frac{1}{2}}$.

math.OC↗

arXiv2025

Ferromagnetic Traps for Quasi-Continuous Operation of Optical Nanofiber Interfaces

A soft ferromagnetic plate uniformizes Tesla-level fields generated by attached permanent magnets, producing a smooth and electronically tunable surface field on the opposite side. By arranging $n$ precisely fabricated rectangular plates, a nearly ideal magnetic quadrupole field with a substantial gradient can be created at center. This robust and rapidly tunable field configuration is well suited for two-dimensional magneto-optical trapping (2D-MOT) and magnetic guiding of cold atoms. By aligning an optical nanofiber (ONF) along the zero-field line of a planar 2D-MOT in a 2-plate assembly, we demonstrate quasi-continuous, field-free operation of the quantum optical interface without switching off the magnetic field. Transient transmission spectroscopy with nanosecond laser pulses is performed on the $^{87}$Rb D2 line at a measurement repetition rate as high as 250 kHz. The observed line broadening, while not yet fully understood, is partially attributed to residual magnetic fields in the $n=2$ assembly. Through additional measurements and simulations, we verify that these residual fields can be fully eliminated in an $n=4$ assembly, resulting in an ultra-straight 2D trap that supports uniform light-atom interaction over exceptionally long, field-free distances. We extend our discussion to $n=6$, $n=8$ designs with similar uniformity but multiple zero-field lines. With its strong gradient for magnetic trapping, the ferromagnetic devices also enable new quantum optical scenarios featuring interactions between co-guided atoms and photons at ONF interfaces.

physics.atom-ph↗

arXiv2024

Optical Routing via High Efficiency Composite Acoustic Diffraction

Acousto-optical modulation (AOM) is a powerful and widely used technique for rapidly controlling the frequency, phase, intensity, and direction of light. Based on Bragg diffraction, AOMs typically exhibit moderate diffraction efficiency, often less than 90\% even for collimated inputs. In this work, we demonstrate that this efficiency can be significantly improved using a composite (CP) setup comprising a pair of 4-F-linked AOMs, enabling beamsplitting with fully tunable splitting amplitude and phase. The efficiency enhancement arises from two effects, termed "momentum echo" and "high-order rephasing," which can be simultaneously optimized by adjusting the relative distance between the two AOMs. This method is resource-efficient, does not require ultra-collimation, and maintains control bandwidth. Experimentally, we achieved a diffraction efficiency exceeding 99\% (excluding insertion loss) and a 35 dB single-mode suppression of the 0th-order beam, demonstrating a full-contrast optical router with a switching time of less than 100~nanoseconds. Theoretically, we formulate the dynamics of CP-AOM in terms of multi-mode quantum control and discuss extensions beyond the $N=2$ configuration presented in this work. The substantially enhanced performance of CP-AOMs, coupled with reduced acoustic amplitude requirements, may significantly advance our ability to accurately control light at high speeds with low-loss acousto-optics.

physics.optics↗

arXiv2023

Composite picosecond control of atomic state through a nanofiber interface

Atoms are ideal quantum sensors and quantum light emitters. Interfacing atoms with nanophotonic devices promises novel nanoscale sensing and quantum optical functionalities. But precise optical control of atomic states in these devices is challenged by the spatially varying light-atom coupling strength, generic to nanophotonic. We demonstrate numerically that despite the inhomogenuity, composite picosecond optical pulses with optimally tailored phases are able to evanescently control the atomic electric dipole transitions nearly perfectly, with $f>99\%$ fidelity across large enough volumes for {\it e.g.} controlling cold atoms confined in near-field optical lattices. Our proposal is followed by a proof-of-principle demonstration with a $^{85}$Rb vapor -- optical nanofiber interface, where the excitation by an $N=3$ sequence of guided picosecond D1 control reduces the absorption of a co-guided nanosecond D2 probe by up to $\sim70\%$. The close-to-ideal performance is corroborated by comparing the absorption data across the parameter space with first-principle modeling of the mesoscopic atomic vapor response. Extension of the composite technique to $N\geq 5$ appears highly feasible to support arbitrary local control of atomic dipoles with exquisite precision. This unprecedented ability would allow error-resilient atomic spectroscopy and open up novel nonlinear quantum optical research with atom-nanophotonic interfaces.

physics.optics↗

arXiv2022

Composite acousto-optical modulation

We propose a composite acousto-optical modulation (AOM) scheme for wide-band, efficient modulation of CW and pulsed lasers. We show that by adjusting the amplitudes and phases of weakly-driven daughter AOMs, diffraction beyond the Bragg condition can be achieved with exceptional efficiencies. Furthermore, by imaging pairs of AOMs in a counter-propagating configuration, high contrast switching of output orders can be achieved at the driving radio frequency (rf) limit, thereby enabling efficient bidirectional routing of a synchronized mode-locked laser. Here we demonstrate a simplest example of such scheme with a double-AOM setup for efficient diffraction across an octave of rf bandwidth, and for routing a mode-locked pulse train with up to $f_{\rm rep}=400$~MHz repetition rate. We discuss extension of the composite scheme toward multi-path routing and time-domain multiplexing, so as to individually shape each pulses of ultrafast lasers for novel quantum control applications.

physics.optics↗