arXiv subjects

Wei Nie

Publications and source records attributed to Wei Nie.

18 recordsLinked to original sources

arXiv2025

Hybrid Quasi-Bound State in the Continuum at Topological Quantum Optics Interface

Topological manipulation of light provides a versatile toolbox for photonic technologies. Here, we show that a topological atom array can induce photon localization in a waveguide via symmetry-protected light-matter interaction. Long-lived photon-atom entanglement reveals the existence of a novel topological quasi-bound state in the continuum (quasi-BIC). This hybrid light-matter quasi-BIC is formed at a critical coupling condition via collectively induced absorption, which is produced by quantum interference between edge and bulk states. We uncover the time-reversed relation between topological quasi-BIC and light amplification. Interestingly, one can realize a directional ultranarrow amplifier by means of critical coupling. Our work demonstrates an unconventional quasi-BIC at a topological quantum optics interface with potential applications in quantum devices.

quant-ph↗

arXiv2025

Light Manipulation via Tunable Collective Quantum States in Waveguide-Coupled Bragg and Anti-Bragg Superatoms

A many-body quantum system which consists of collective quantum states, such as superradiant and subradiant states, behaves as a multi-level superatom in light-matter interaction. In this work, we experimentally study one-dimensional superatoms in waveguide quantum electrodynamics with a periodic array of superconducting artificial atoms. We engineer the periodic atomic array with two distinct nearest-neighbor spacings, i.e., $d$=$λ_0/2$ and $d$=$λ_0/4$, which correspond to Bragg and anti-Bragg scattering conditions, respectively. The system consists of eight atoms arranged to maintain these specific interatomic distances. By controlling atomic frequencies, we modify Bragg and anti-Bragg superatoms, resulting in distinctly different quantum optical phenomena, such as collectively induced transparency and a broad photonic bandgap. Moreover, due to strong waveguide-atom couplings in superconducting quantum circuits, efficient light manipulations are realized in small-size systems. Our work demonstrates tunable optical properties of Bragg and anti-Bragg superatoms, as well as their potential applications in quantum devices.

quant-ph↗

arXiv2025

DiagnosisArena: Benchmarking Diagnostic Reasoning for Large Language Models

The emergence of groundbreaking large language models capable of performing complex reasoning tasks holds significant promise for addressing various scientific challenges, including those arising in complex clinical scenarios. To enable their safe and effective deployment in real-world healthcare settings, it is urgently necessary to benchmark the diagnostic capabilities of current models systematically. Given the limitations of existing medical benchmarks in evaluating advanced diagnostic reasoning, we present DiagnosisArena, a comprehensive and challenging benchmark designed to rigorously assess professional-level diagnostic competence. DiagnosisArena consists of 1,113 pairs of segmented patient cases and corresponding diagnoses, spanning 28 medical specialties, deriving from clinical case reports published in 10 top-tier medical journals. The benchmark is developed through a meticulous construction pipeline, involving multiple rounds of screening and review by both AI systems and human experts, with thorough checks conducted to prevent data leakage. Our study reveals that even the most advanced reasoning models, o3, o1, and DeepSeek-R1, achieve only 51.12%, 31.09%, and 17.79% accuracy, respectively. This finding highlights a significant generalization bottleneck in current large language models when faced with clinical diagnostic reasoning challenges. Through DiagnosisArena, we aim to drive further advancements in AI's diagnostic reasoning capabilities, enabling more effective solutions for real-world clinical diagnostic challenges. We provide the benchmark and evaluation tools for further research and development https://github.com/SPIRAL-MED/DiagnosisArena.

cs.CL↗

arXiv2024

Collectively induced transparency and absorption in waveguide QED with Bragg atom arrays

Collective quantum states, such as subradiant and superradiant states, are useful for controlling optical responses in many-body quantum systems. In this work, we study novel collective quantum phenomena in waveguide-coupled Bragg atom arrays with inhomogeneous frequencies. For atoms without free-space dissipation, collectively induced transparency is produced by destructive quantum interference between subradiant and superradiant states. In a large Bragg atom array, multi-frequency photon transparency can be obtained by considering atoms with different frequencies. Interestingly, we find collectively induced absorption (CIA) by studying the influence of free-space dissipation on photon transport. Tunable atomic frequencies nontrivially modify decay rates of subradiant states. When the decay rate of a subradiant state equals to the free-space dissipation, photon absorption can reach a limit at a certain frequency. In other words, photon absorption is enhanced with low free-space dissipation, distinct from previous photon detection schemes. We also show multi-frequency CIA by properly adjusting atomic frequencies. Our work presents a way to manipulate collective quantum states and exotic optical properties in waveguide QED systems.

quant-ph↗

arXiv2023

Non-Hermitian Waveguide Cavity QED with Tunable Atomic Mirrors

Optical mirrors determine cavity properties by means of light reflection. Imperfect reflection gives rise to open cavities with photon loss. We study an open cavity made of atom-dimer mirrors with a tunable reflection spectrum. We find that the atomic cavity shows anti-$\mathcal{PT}$ symmetry. The anti-$\mathcal{PT}$ phase transition controlled by atomic couplings in mirrors indicates the emergence of two degenerate cavity supermodes. Interestingly, a threshold of mirror reflection is identified for realizing strong coherent cavity-atom coupling. This reflection threshold reveals the criterion of atomic mirrors to produce a good cavity. Moreover, cavity quantum electrodynamics with a probe atom shows mirror-tuned properties, including reflection-dependent polaritons formed by the cavity and probe atom. Our work presents a non-Hermitian theory of an anti-$\mathcal{PT}$ atomic cavity, which may have applications in quantum optics and quantum computation.

quant-ph↗

arXiv2022

Deep Learning-based Protoacoustic Signal Denoising for Proton Range Verification

Objective: Proton therapy offers an advantageous dose distribution compared to the photon therapy, since it deposits most of the energy at the end of range, namely the Bragg peak (BP). Protoacoustic technique was developed to in vivo determine the BP locations. However, it requires large dose delivery to the tissue to obtain an averaged acoustic signal with a sufficient signal to noise ratio (SNR), which is not suitable in clinics. We propose a deep learning-based technique to acquire denoised acoustic signals and reduce BP range uncertainty with much lower doses. Approach: Three accelerometers were placed on the distal surface of a cylindrical polyethylene (PE) phantom to collect protoacoustic signals. In total 512 raw signals were collected at each device. Device-specific stack autoencoder (SAE) denoising models were trained to denoise the input signals, which were generated by averaging 1, 2, 4, 8, 16, or 32 raw signals. Both supervised and unsupervised learning training strategies were tested for comparison. Mean squared error (MSE), signal-to-noise ratio (SNR) and the Bragg peak (BP) range uncertainty were used for model evaluation. Main results: After SAE denoising, the MSE was substantially reduced, and the SNR was enhanced. Overall, the supervised SAEs outperformed the unsupervised SAEs in BP range verification. For the high accuracy detector, it achieved a BP range uncertainty of 0.20 +/- 3.44 mm by averaging over 8 raw signals, while for the other two low accuracy detectors, they achieved the BP uncertainty of 1.44 +/- 6.45 mm and -0.23 +/- 4.88 mm by averaging 16 raw signals, respectively. Significance: We have proposed a deep learning based denoising method to enhance the SNR of protoacoustic measurements and improve the accuracy in BP range verification, which greatly reduces the dose and time for potential clinical applications.

physics.med-ph↗

arXiv2021

Dissipative Topological Phase Transition with Strong System-Environment Coupling

A primary motivation for studying topological matter regards the protection of topological order from its environment. In this work, we study a topological emitter array coupled to an electromagnetic environment. The photon-emitter coupling produces nonlocal interactions between emitters. Using periodic boundary conditions for all ranges of environment-induced interactions, the chiral symmetry inherent to the emitter array is preserved. This chiral symmetry protects the Hamiltonian, and induces parity in the Lindblad operator. A topological phase transition occurs at a critical photon-emitter coupling related to the energy spectrum width of the emitter array. Interestingly, the critical point nontrivially changes the dissipation rates of edge states, yielding a dissipative topological phase transition. In the protected topological phase, edge states suffer from environment-induced dissipation for weak photon-emitter coupling. However, strong coupling leads to robust dissipationless edge states with a window at the emitter spacing. Our work shows the potential to manipulate topological quantum matter with electromagnetic environments.

quant-ph↗

arXiv2021

Nonreciprocal single-photon band structure

We study single-photon band structure in a one-dimensional (1D) coupled-resonator optical waveguide (CROW) which chirally couples to an array of two-level quantum emitters (QEs). The chiral interaction between the resonator mode and the QE can break the time-reversal symmetry without the magneto-optical effect. As a result, a nonreciprocal single-photon edge state, band gap and flat band appear. By using such a chiral QE-CROW system, including a finite number of unit cells and working in the nonreciprocal band gap, we achieve frequency-multiplex single-photon circulators with high fidelity and low insertion loss. The chiral QE-light interaction can also protect one-way propagation of single photons against backscattering. Our work opens a new door for studying nonreciprocal photonic band structure and exploring its applications in the quantum regime.

quant-ph↗

arXiv2021

Majorana-like oscillation for edge states in one-dimensional topological chain with dissipative couplings

The oscillation of Majorana modes with near zero energy plays a very important role for ascertaining Majorana fermions. The edge states, which also have almost-zero-energy in one-dimensional Su-Schrieffer-Heeger chain (SSHc), have been extensively studied for their topologically protected properties when the on-sites have dissipations induced by independent environments. We here show that common environments shared by each pair of the nearest neighbour sites in the SSHc can result in dissipative couplings between sites, and thus change topologically trivial phase to nontrivial one. The Majorana-like oscillation for the finite-size hybridizations of two non-Hermitian edge states with complex localization lengths can be induced by the dissipative coupling. The controllable topology parameter of the SSHc plays the role of the magnetic field in the nanowire for controlling Majorana oscillation. The measurement for the oscillation is proposed. Our study provides a new way to manipulate edge states and is experimentally feasible within current technology of superconducting quantum circuits.

quant-ph↗

arXiv2021

Topology-Enhanced Nonreciprocal Scattering and Photon Absorption in a Waveguide

Topological matter and topological optics have been studied in many systems, with promising applications in materials science and photonics technology. These advances motivate the study of the interaction between topological matter and light, as well as topological protection in light-matter interactions. In this work, we study a waveguide-interfaced topological atom array. The light-matter interaction is nontrivially modified by topology, yielding novel optical phenomena. We find topology-enhanced photon absorption from the waveguide for large Purcell factor, i.e., $Γ/Γ_0\gg 1$, where $Γ$ and $Γ_0$ are the atomic decays to waveguide and environment, respectively. To understand this unconventional photon absorption, we propose a multi-channel scattering approach and study the interaction spectra for edge- and bulk-state channels. We find that, by breaking inversion and time-reversal symmetries, optical anisotropy is enabled for reflection process, but the transmission is isotropic. Through a perturbation analysis of the edge-state channel, we show that the anisotropy in the reflection process originates from the waveguide-mediated non-Hermitian interaction. However, the inversion symmetry in the non-Hermitian interaction makes the transmission isotropic. At a topology-protected atomic spacing, the subradiant edge state exhibits huge anisotropy. Due to the interplay between edge- and bulk-state channels, a large topological bandgap enhances nonreciprocal reflection of photons in the waveguide for weakly broken time-reversal symmetry, i.e., $Γ_0/Γ\ll 1$, producing complete photon absorption. We show that our proposal can be implemented in superconducting quantum circuits. The topology-enhanced photon absorption is useful for quantum detection. This work shows the potential to manipulate light with topological quantum matter.

quant-ph↗

arXiv2021

Optical properties of a waveguide-mediated chain of randomly positioned atoms

We theoretically study the optical properties of an ensemble of two-level atoms coupled to a one-dimensional waveguide. In our model, the atoms are randomly located in the lattice sites along the one-dimensional waveguide. The results reveal that the optical transport properties of the atomic ensemble are influenced by the lattice constant and the filling factor of the lattice sites. We also focus on the atomic mirror configuration and quantify the effect of the inhomogeneous broadening in atomic resonant transition on the scattering spectrum. Furthermore, we find that initial bunching and persistent quantum beats appear in photon-photon correlation function of the transmitted field, which are significantly changed by filling factor of the lattice sites. With great progress to interface quantum emitters with nanophotonics, our results should be experimentally realizable in the near future.

quant-ph↗

arXiv2020

Bandgap-Assisted Quantum Control of Topological Edge States in a Cavity

Quantum matter with exotic topological order has potential applications in quantum computation. However, in present experiments, the manipulations on topological states are still challenging. We here propose an architecture for optical control of topological matter. We consider a topological superconducting qubit array with Su-Schrieffer-Heeger (SSH) Hamiltonian which couples to a microwave cavity. Based on parity properties of the topological qubit array, we propose an optical spectroscopy method to observe topological phase transition, i.e., edge-to-bulk transition. This new method can be achieved by designing cavity-qubit couplings. A main purpose of this work is to understand how topological phase transition affects light-matter interaction. We find that topological bandgap plays an essential role on this issue. In topological phase, the resonant vacuum Rabi splitting of degenerate edge states coupling to the cavity field is protected from those of bulk states by the bandgap. In dispersive regime, the cavity induced coupling between edge states is dominant over couplings between edge and bulk states, due to the topological bandgap. As a result, quantum interference between topological edge states occures and enables single-photon transport through boundaries of the topological qubit array. Our work may pave a way for topological quantum state engineering.

quant-ph↗

arXiv2020

Topologically Protected Quantum Coherence in a Superatom

Exploring the properties and applications of topological quantum states is essential to better understand topological matter. Here, we theoretically study a quasi-one-dimensional topological atom array. In the low-energy regime, the atom array is equivalent to a topological superatom. Driving the superatom in a cavity, we study the interaction between light and topological quantum states. We find that the edge states exhibit topology-protected quantum coherence, which can be characterized from the photon transmission. This quantum coherence helps us to find a superradiance-subradiance transition, and we also study its finite-size scaling behavior. The superradiance-subradiance transition also exists in symmetry-breaking systems. More importantly, it is shown that the quantum coherence of the subradiant edge state is robust to random noises, allowing the superatom to work as a topologically protected quantum memory. We suggest a relevant experiment with three-dimensional circuit QED. Our study may have applications in quantum computation and quantum optics based on topological edge states.

quant-ph↗

arXiv2019

Superposition of macroscopically squeezed states with enhanced squeezing in cavity optomechanical system at single-photon level

We propose an efficient approach to generate the superposed macroscopically squeezed states with enhanced squeezing in a two-mode optomechanical system. This can be achieved by introducing a sinusoidal modulation to either the cavity frequencies or the coupling strengths between two cavity modes. The squeezement of the oscillator can be significantly enhanced to 12.16 dB with single photon, once the relative ratio of coupling strength is optimized under proper conditions. Further enhanced squeezing can be obtained by carefully adjusting the system parameters. In terms of the Wigner quasi-probability distribution, we show the squeezed error ellipses and interference fringes of the Yurke-Stoler-type squeezed states, denoting the squeezing and superposition properties. Our state generation scheme show reliable performance and robust resistance to finite environmental fluctuations, which implies applications for both fundamental interest and practical value.

quant-ph↗

arXiv2018

Photon transport mediated by an atomic chain trapped along a photonic crystal waveguide

We theoretically investigate the transport properties of a weak coherent input field scattered by an ensemble of $Λ$-type atoms coupled to a one-dimensional photonic crystal waveguide. In our model, the atoms are randomly located in the lattice along the crystal axis. We analyze the transmission spectrum mediated by the tunable long-range atomic interactions, and observe the highest-energy dip. The results show that the highest-energy dip location is associated with the number of the atoms, which provides an accurate measuring tool for the emitter-waveguide system. We also quantify the influence of a Gaussian inhomogeneous broadening and the dephasing on the transmission spectrum, concluding that the highest-energy dip is immune to both the inhomogeneous broadening and the dephasing. Furthermore, we study photon-photon correlations of the reflected field and observe quantum beats. With tremendous progress in coupling atoms to photonic crystal waveguides, our results may be experimentally realizable in the near future.

quant-ph↗

arXiv2017

Photon scattering by an atomic ensemble coupled to a one-dimensional nanophotonic waveguide

We theoretically investigate the quantum scattering of a single-photon pulse interacting with an ensemble of $Λ$-type three-level atoms coupled to a one-dimensional waveguide. With an effective non-Hermitian Hamiltonian, we study the collective interaction between the atoms mediated by the waveguide mode. In our scheme, the atoms are randomly placed in the lattice along the axis of the one-dimensional waveguide, which closely corresponds to the practical condition that the atomic positions can not be controlled precisely in experiment. Many interesting optical properties occur in our waveguide-atom system, such as electromagnetically induced transparency (EIT) and optical depth. Moreover, we observe that strong photon-photon correlation with quantum beats can be generated in the off-resonant case, which provides an effective candidate for producing non-classical light in experiment. With remarkable progress in waveguide-emitter system, our scheme may be feasible in the near future.

quant-ph↗

arXiv2017

Scaling of geometric phase versus band structure in cluster-Ising models

We study the phase diagram of a class of models in which a generalized cluster interaction can be quenched by Ising exchange interaction and external magnetic field. We characterize the various phases through winding numbers. They may be ordinary phases with local order parameter or exotic ones, known as symmetry protected topologically ordered phases. Quantum phase transitions with dynamical critical exponents z = 1 or z = 2 are found. Quantum phase transitions are analyzed through finite-size scaling of the geometric phase accumulated when the spins of the lattice perform an adiabatic precession. In particular, we quantify the scaling behavior of the geometric phase in relation with the topology and low energy properties of the band structure of the system.

cond-mat.stat-mech↗

arXiv2015

Simulation and Detection of Photonic Chern Insulators in One-Dimensional Circuit Quantum Electrodynamics Lattice

We introduce a simple method to realize and detect photonic topological Chern insulators with one-dimensional circiut quantum electrodynamics arrays. By periodically modulating the couplings of the array, we show that this one-dimensional model can be mapped into a two-dimensional Chern insulator model. In addition to allowing the study of photonic Chern insulators, this approach also provides a natural platform to realise experimentally Laughlin's pumping argument. Based on scattering theory of topological insulators and input-output formalism, we show that the photonic edge state can be probed directly and the topological invariant can be detected from the winding number of the reflection coefficient phase.

quant-ph↗