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Yue Chang

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quant-ph Computation and Language cond-mat.mes-hall physics.optics

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preprint2026arXiv

YEZE at SemEval-2026 Task 9: Detecting Multilingual, Multicultural and Multievent Online Polarization via Heterogeneous Ensembling

This paper presents our system for SemEval-2026 Task 9: Detecting Multilingual, Multicultural and Multievent Online Polarization, which identifies polarized social media content in 22 languages through three subtasks: binary detection, target classification, and manifestation identification. We propose a heterogeneous ensemble of multilingual pretrained models, combining XLM-RoBERTa-large and mDeBERTa-v3-base. We investigate techniques such as multi-task learning, translation-based data augmentation, and class weighting to improve classification performance under severe label imbalance. Our findings indicate that independent task modeling combined with class weighting is more effective.

preprint2022arXiv

Accessing strongly-coupled systems without compromising them

The last decades have seen a burst of experimental platforms reaching the so-called strong-coupling regime, where quantum coherent effects dominate over incoherent processes such as dissipation and thermalization. This has allowed us to create highly nontrivial quantum states and put counterintuitive quantum-mechanical effects to test beyond the wildest expectations of the founding fathers of quantum physics. The strong-coupling regime comes with certain challenges though: the need for a large isolation makes it difficult to access the system for control or monitoring purposes. In this work we propose a way to access such systems through an engineered environment that does not compromise their strong-coupling effects. As a proof of principle, we apply the approach to the photon-blockade effect present in nonlinear resonators, but argue that the mechanism is quite universal. We also propose an architecture based on superconducting circuits where the required unconventional environment can be implemented, opening the way to the experimental analysis of our ideas.

preprint2019arXiv

Quadrupole Effects on Nuclear Magnetic Resonance Gyroscopes

Nuclear magnetic resonance gyroscopes that detect rotation as a shift in the precession frequency of nuclear spins, have attracted a lot of attentions. Under a feedback-generated drive, the precession frequency is supposed to be dependent only on the angular momentum and an applied magnetic field. However, nuclei with spins larger than 1/2, experience electric quadrupole interaction with electric field gradients at the cell walls. This quadrupole interaction shifts the precession frequencies of the nuclear spins, which brings inaccuracy to the rotation measurement as the quadrupole interaction constant $C_q$ is difficult to precisely measure. In this work, the effects of quadrupole interaction on nuclear magnetic resonance gyroscopes is theoretically studied. We find that, when the constant $C_q$ is small compared to the characteristic decay rate of the system, as the strength of the feedback-driving field increases, the quadrupole shift monotonically decreases, regardless of the sign of $C_q$. In large $C_q$ regime, more than one precession frequency exists, and the nuclear spins may precess with a single frequency or multi-frequencies depending on initial conditions. In this regime, with large driving amplitudes, the nuclear spin can restore the single-frequency-precession. These results are obtained by solving an effective master equation of the nuclear spins in a rotating frame, from which both the steady-state solutions and dynamics of the system are shown.

preprint2015arXiv

Deterministic Generation of Photon Pairs within the Bad Cavity Limit

The development, characterization and control of $N$-photon sources are instrumental for quantum technological applications. This work constitutes a step forward in this direction, where we propose a cavity quantum electrodynamics setup designed for the generation of photon pairs. We analyze it both via the scattering and master equation formalisms. From the connection between these two frameworks it naturally arises a physical criterion characterizing when weakly-driven systems behave as continuous antibunched two-photon sources. We find the optimal parameters for which our setup works as an efficient photon-pair source, showing also that it becomes a deterministic down-converter of single photons. We provide a specific implementation based on state-of-the-art superconducting circuits, showing how our proposal is within the reach of current technologies.

preprint2014arXiv

Regularized linearization for quantum nonlinear optical cavities: Application to Degenerate Optical Parametric Oscillators

Nonlinear optical cavities are crucial both in classical and quantum optics; in particular, nowadays optical parametric oscillators are one of the most versatile and tunable sources of coherent light, as well as the sources of the highest quality quantum-correlated light in the continuous variable regime. Being nonlinear systems, they can be driven through critical points in which a solution ceases to exist in favour of a new one, and it is close to these points where quantum correlations are the strongest. The simplest description of such systems consists in writing the quantum fields as the classical part plus some quantum fluctuations, linearizing then the dynamical equations with respect to the latter; however, such an approach breaks down close to critical points, where it provides unphysical predictions such as infinite photon numbers. On the other hand, techniques going beyond the simple linear description become too complicated especially regarding the evaluation of two-time correlators, which are of major importance to compute observables outside the cavity. In this article we provide a regularized linear description of nonlinear cavities, that is, a linearization procedure yielding physical results, taking the degenerate optical parametric oscillator as the guiding example. The method, which we call self-consistent linearization, is shown to be equivalent to a general Gaussian ansatz for the state of the system, and we compare its predictions with those obtained with available exact (or quasi-exact) methods.

preprint2011arXiv

Analog of Electromagnetically Induced Transparency Effect for Two Nano/Micro-mechanical Resonators Coupled With Spin Ensemble

We study a hybrid nano-mechanical system coupled to a spin ensemble as a quantum simulator to favor a quantum interference effect, the electromagnetically induced transparency (EIT). This system consists of two nano-mechanical resonators (NAMRs), each of which coupled to a nuclear spin ensemble. It could be regarded as a crucial element in the quantum network of NAMR arrays coupled to spin ensembles. Here, the nuclear spin ensembles behave as a long-lived transducer to store and transfer the NAMRs' quantum information. This system shows the analog of EIT effect under the driving of a probe microwave field. The double-EIT phenomenon emerges in the large $N$ (the number of the nuclei) limit with low excitation approximation, because the interactions between the spin ensemble and the two NAMRs are reduced to the coupling of three harmonic oscillators. Furthermore, the group velocity is reduced in the two absorption windows.

preprint2011arXiv

Inherent Mach-Zehnder interference with "which-way" detection for single particle scattering in one dimension

We study the coherent transport of single photon in a one-dimensional coupled-resonator-array, "non-locally" coupled to a two-level system. Since its inherent structure is a Mach-Zehnder interferometer, we explain the destructive interference phenomenon of the transmission spectrums according to the effect of which-way detection. The quantum realization of the present model is a nano-electromechanical resonator arrays with two nearest resonators coupled to a single spin via their attached magnetic tips. Its classical simulation is a waveguide of coupled defected cavity array with double couplings to a side defected cavity.

preprint2010arXiv

Multi-Atomic Mirror for Perfect Reflection of Single Photons in A Wide Band of Frequency

A resonant two level atom doped in one dimensional waveguide behaves as a mirror, but this single-atom "mirror" can only reflect single photon perfectly at a specific frequency. For a one dimensional coupled-resonator waveguide, we propose to extend the perfect reflection region from a specific frequency to a wide band by placing many atoms individually in the resonators in a finite coordinate region of the waveguide. Such a doped resonator array promises us to control the propagation of a practical photon wave packet with certain momentum distribution instead of a single photon, which is ideally represented by a plane wave with specific momentum. The studies based on the discrete-coordinate scattering theory display that such hybrid structure indeed provides a near-perfect reflection for single photon in a wide band. We also calculated photon group velocity distribution, which shows that the perfect reflection with wide band exactly corresponds to the stopping light region.

preprint2009arXiv

Multi-Stability of Electromagnetically Induced Transparency in Atom-Assisted Optomechanical Cavities

We study how an oscillating mirror affects the electromagnetically induced transparency (EIT) of an atomic ensemble, which is confined in a gas cell placed inside a micro-cavity with an oscillating mirror in one end. The oscillating mirror is modeled as a quantum mechanical harmonic oscillator. The cavity field acts as a probe light of the EIT system and also produces a light pressure on the oscillating mirror. The back-action from the mirror to the cavity field results in several (from one to five) steady-states for this atom-assisted optomechanical cavity, producing a complex structure in its EIT. We calculate the susceptibility with respect to the few (from one to three) stable solutions found here for the equilibrium positions of the oscillating mirror. We find that the EIT of the atomic ensemble can be significantly changed by the oscillating mirror, and also that the various steady states of the mirror have different effects on the EIT.

preprint2008arXiv

Quantum Optomechanics with Single Atom

The recently increasing explorations for cavity optomechanical coupling assisted by a single atom or an atomic ensemble have opened an experimentally accessible fashion to interface quantum optics and nano (micro) -mechanical systems. In this paper, we study in details such composite quantum dynamics of photon, phonon and atoms, specified by the triple coupling, which only exists in this triple hybrid system: The cavity QED system with a movable end mirror. We exactly diagonalize the Hamiltonian of the triple hybrid system under the parametric resonance condition. We find that, with the rotating-wave approximation, the hybrid system is modeled by a generalized spin-orbit coupling where the orbital angular momentum operator is defined through a Jordan-Schwinger realization with two bosonic modes, corresponding to the mirror oscillation and the single mode photon of the cavity. In the quasi-classical limit of very large angular momentum, this system will behave like a standard cavity-QED system described by the Jaynes-Cummings model as the angular momentum operators are transformed to bosonic operators of a single mode. We test this observation with an experimentally accessible system with the atom in the cavity with a moving mirror.