We investigate a Lieb lattice of quantum emitters coupled to a two-dimensional waveguide network and demonstrate that this system supports an energetically isolated flat band, enabling localization despite the presence of long-range photon-mediated couplings. We then explore the two-excitation dynamics in both the soft-core and hard-core interaction regimes, which arise from the nonlinearity of the emitters. In the soft-core regime, we observe interaction-induced photon transport within the flat band, mediated by the formation of bound photon pairs. In the hard-core regime, corresponding to the two-level atom limit, we instead find the emergence of metastable exciton-like dressed states involving both flat and dispersive bands. Our findings highlight how the interplay between the collective behavior of emitters and effective photon-photon interactions can provide a platform for studying highly correlated photonic states in flat-band systems.

Electromagnetically-induced-transparency (EIT) cooling is a well-established method for preparing trapped-ion systems in their motional ground state. However, isolating a three-level system, as required for EIT cooling, is often challenging or impractical. Nonetheless, multilevel systems can inherently host dark states. In this work we extend the EIT cooling framework to such multilevel systems. We develop a formalism to accurately determine the cooling rate in the weak-sideband-coupling regime and provide an approximate estimate for cooling rates beyond this regime, without the need for explicit simulation of the motional degree of freedom. We clarify the connection between the cooling rate and the absorption spectrum, offering a pathway for efficient near-ground-state cooling of ions with complex electronic structures.

We show unexpected behavior in simulations of generalized squeezing performed with finite-dimensional truncations of the Fock space: even for extremely large dimensions of the state space, the results depend on whether the truncation dimension is even or odd. This situation raises the question of whether the simulation results are physically meaningful. We demonstrate that, in fact, the two truncation schemes correspond to two well-defined, distinct unitary evolutions whose generators are defined on different subsets of the infinite-dimensional Fock space. This is a consequence of the fact that the generalized squeezing Hamiltonian is not self-adjoint on states with finite excitations, but possesses multiple self-adjoint extensions. Furthermore, we present results on the spectrum of the squeezing Hamiltonians corresponding to even and odd truncation sizes that elucidate the properties of the two different self-adjoint extensions corresponding to the even and odd truncation schemes. To make the squeezing operator applicable to a physical system, we must regularize it using other terms that depend on the specifics of the experimental implementation. We show that the addition of a Kerr interaction term in the Hamiltonian leads to uniquely converging simulations, with no dependence on the parity of the truncation size, and demonstrate that the Kerr term indeed renders the Hamiltonian self-adjoint and thus physically interpretable.

The honeycomb Fock-state lattice (FSL) constructed by the three-mode Jaynes-Cummings model has been proven powerful in simulating novel states of matter and engineering robust quantum devices. This setting is scalable in the number of coupled atoms with enriched physics. Here, we explore a dice FSL constructed by the Fock states in the three-mode Tavis-Cummings model where two atoms are symmetrically coupled to three cavity modes. By introducing Floquet-engineered phased hoppings between cavity modes, we construct the Haldane model on the dice FSL. This system exhibits quantum anomalous Hall bands with Chern numbers up to $\pm 2$ and hosts multiple analytically solvable chiral edge states. The dice-Haldane term can realize a spin-1 quantum circulator with photons routed by the collective atomic state, enabling the generation of multipartite entangled states. We also investigate the strain effects and the dynamics within the dice flat band that supports bulk circulating modes. These findings establish the dice FSL as a versatile and highly tunable platform for exploring topological phases of quantized light and engineering quantum devices with enhanced performance.

Giant atoms enable precise control over single-photon dynamics in waveguide-based quantum circuits through spatially distributed interactions with the guided electromagnetic modes. Recent advancements in the realm of superconducting circuits allow for experimental implementation of giant atoms. In this work, we describe a microscopic model of a transmon qubit coupled to a transmission line and show that its Hamiltonian maps onto a generalized form for giant-atom-waveguide interactions. We demonstrate the generation of a frequency comb from a system comprising a single-photon Gaussian pulse incident on a cavity with giant-atom mirrors coupled to a one-dimensional waveguide. The finesse of this single-photon frequency comb can be significantly improved by using giant atoms instead of point atoms. Furthermore, this high-finesse cavity enables a substantial enhancement of the peaks in the comb spectra when the photon pulse is initially inside the giant-atom cavity. Our work provides a platform for the design of advanced quantum devices for high-resolution spectroscopy and quantum computation.

We investigate the superradiant phase transition of a Fermi gas in a double-cavity systems with unbalanced decay rates. By self-consistently solving the steady-state equation for the cavity fields via a mean-field approach, we determine the superradiant phase diagram for low particle filling. By comparing with the case where only one cavity is present, we show that in a double-cavity system, if superradiance is already established in one cavity, the other cavity is more likely to enter the superradiant phase. This phenomenon is explained by calculating the density of states at the Fermi surface and the effective pumping strength experienced by the atoms. The results show that although the density of states is suppressed when superradiance is built in one cavity, the spatial redistribution of fermions in the cavity field significantly enhances the effective pumping strength of the other cavity, thereby facilitating its transition to the superradiant phase.

We study the geometric phase accumulated during nonadiabatic charging of different driven open quantum systems serving as quantum battery models. We provide a full numerical analysis of dynamics under different types of noises typically reported in superconducting circuit implementations. We complement the study with analytic results derived in the limiting case of no noise (i.e., isolated systems). We compute the nonunitary geometric phase acquired by the quantum batteries during the transition and show that there is a direct relation between the accumulated geometric phase and the integral of the stored energy during the transition. Finally, we perform the same analysis on a bipartite quantum battery that relies on a dephased charger and find similar results. Our theoretical findings are within experimental reach using state-of-the-art techniques.

Standard quantum information theory is founded on the assumption that multiparty state space possesses a tensor-product structure. Anyons, as candidates for information carriers in fault-tolerant quantum computing, exhibit unique entanglement properties that differ from the conventional quantum systems, resulting from the absence of a tensor-product structure in their state spaces. Here we investigate the relationship between Bell nonlocality and entanglement in anyonic states. Specifically, we find that certain pure anyonic states with nonzero anyonic entanglement entropy (AEE) are local, yet exhibit nonlocality when subjected to collective measurements on multiple copies, a phenomenon known as superactivation of nonlocality, which is typically observed in conventional mixed states. To analyze this, we decompose the total entanglement of anyonic states into two distinct components: Conventional entanglement (CE), which arises from the tensor-product structure, and anyonic charge entanglement (ACE), which captures residual contributions. By studying their asymptotic behavior, we find that CE gradually increases and approaches AEE while ACE diminishes with the number of copies. Crucially, we show that for pure anyonic states, the presence of nonzero CE is a necessary and sufficient condition for the state to exhibit nonlocality, thereby providing a theoretical explanation for the observed superactivation of nonlocality. Our findings provide insights into the connection between entanglement and nonlocality in anyonic systems.

We report an experimental investigation of three-body fragmentation of ${{\mathrm{CO}}_2}^{2+}$ into ${\mathrm{C}}^{+}+{\mathrm{O}}^{+}+\mathrm{O}$ induced by 1 MeV/u ${\mathrm{C}}^{4+}$ ions using a cold-target recoil-ion momentum spectroscopy. With ion-ion coincidence measurement, the ${\mathrm{C}}^{+}+{\mathrm{O}}^{+}$ ion pair is identified. By taking advantage of the differences in momentum correlations among fragments from ${{\mathrm{CO}}_2}^{2+}$ and those from ${{\mathrm{CO}}_2}^{q+}$ $(q\ge 3)$, we are able to disentangle the contributions from ${{\mathrm{CO}}_2}^{2+}$. Consequently, the kinetic energy release (KER) distribution for the channel ${{\mathrm{CO}}_2}^{2+}\to {\mathrm{C}}^{+}+{\mathrm{O}}^{+}+\mathrm{O}$ is determined and compared with the available experimental and theoretical data. By filtering the events using an energy correlation map, the linear and molecular bending concerted fragmentation mechanisms, as well as the sequential fragmentation mechanism with ${\mathrm{CO}}^{+}$ as the intermediate, are identified with the aid of the kinetic energy distributions of the fragments and the Dalitz plots, and their relative branching ratios are evaluated. The linear concerted fragmentation with higher KER values was not observed in previous study of slow ion collisions. This difference indicates that the projectile velocity has a strong influence on the molecular fragmentation dynamics.

We study diffraction of twisted matter waves—electrons and light ions carrying orbital angular momentum $\ell /\hslash =0,\pm 1,\pm 2,...$—by circular and triangular apertures. Within the scalar Kirchhoff-Fresnel framework, circular apertures preserve cylindrical symmetry and produce ringlike far-field profiles whose radii and widths depend on $\left|\ell \right|$ but are insensitive to its sign. In contrast, equilateral triangles break axial symmetry and yield structured patterns that encode both the magnitude and the sign of $\ell$. A transparent Fraunhofer mapping links detector coordinates to the Fourier plane, explaining the $\left(\right|\ell |+1)$-lobe rule and the sign-dependent rotation of the pattern. We validate these results for both ideal Bessel beams and localized Laguerre-Gaussian packets, and we cross-check them by split-step Fourier propagation of the time-dependent Schrödinger equation. From these analyses we extract practical design rules—Fraunhofer distance, lattice pitch, and detector sampling—relevant to OAM diagnostics with moderately relativistic electrons of $E_{\text{kin}}\sim 0.1$–5 MeV and light ions of $E_{\text{kin}}\sim 0.1$–1 MeV/u. Our results establish triangular diffraction as a simple, passive, and robust method for reading out the OAM content of structured quantum beams.

Rabi-coupled spinor Bose-Einstein condensates, with competing intra- and interspecies interactions, enable independent control of two- and three-body interactions. We show that coupling can also drive the system into a strongly nonlinear regime of saturating interaction. More precisely, the equation of state interpolates between low- and high-density regimes described by two different two-body scattering lengths. Interestingly, the transition can be determined by the strength of the coupling. We experimentally demonstrate this saturation phenomenon by measurements of the expansion of a Bose-Einstein condensate as a function of the detuning and of the strength of the Rabi coupling in spin mixtures of potassium 39.

We extend the Gross-Pitaevskii equation to incorporate the effect of quantum fluctuations onto the flow of a weakly interacting Bose-Einstein condensate. Applying this framework to an analog black hole in a quasi-one-dimensional, transonic flow, we investigate how acoustic Hawking radiation backreacts on the background condensate. Our results point to the emergence of stationary density and velocity undulations in the supersonic region (analogous to the black-hole interior) and enable to evaluate the change in upstream and downstream Mach numbers caused by Hawking radiation. These findings provide new insight into the interplay between quantum fluctuations and analog gravity in Bose-Einstein condensates.

The ${\mathbf{A}}^2$ term presents a fundamental challenge to realizing the superradiant phase transition (SPT) in cavity quantum electrodynamics. Here, we propose a hybrid quantum system enabling SPT regardless of the presence of the ${\mathbf{A}}^2$ term. The system consists of a qubit, a mechanical mode, and an optical cavity, where the qubit and mechanical mode constitute a quantum Rabi model, while the mechanical mode and cavity form an optomechanical system. Crucially, the auxiliary cavity introduces a switchable ${\mathbf{A}}^2$ term that effectively counteracts or even fully eliminates the original ${\mathbf{A}}^2$ effect. This allows controllable observation of SPT, diagnosed via the second-order equal-time correlation function $g^{\left(2\right)}\left(0\right)$ of phonons. Furthermore, the auxiliary cavity exponentially reduces the critical coupling strength, significantly relaxing experimental requirements. In addition, we show that phonons in the normal phase display bunching but are coherent in the superradiant phase. Interestingly, higher-order squeezing is found in both phases, with near-perfect higher-order squeezing achieved at the SPT point, establishing it as a probe for SPT behavior. Our work demonstrates that hybridizing optomechanics and cavity quantum electrodynamics provides a promising route to accessing SPT physics in the presence of the ${\mathbf{A}}^2$ term.

We propose and analyze a general scheme to engineer programmable and nonreciprocal interactions in an array of atoms coupled to a photonic waveguide. By subjecting each atom to a local harmonic frequency modulation with a defined phase ${\theta }_i$, we demonstrate the emergence of effective long-range couplings whose parameters are dynamically controllable. For atoms coupled to a conventional waveguide, the modulation dresses the atomic operators, leading to effective interactions governed by the Bessel function ${\mathcal{J}}_0$ whose argument depends on the phase differences $\mathrm{\Delta }{\theta }_{ij}$. For atoms coupled to a photonic crystal waveguide near its band edge, where the density of states is sharply varying, the modulation can be tuned to selectively activate the ${\mathcal{J}}_1^2$ term, which simultaneously scales both the coherent and dissipative components of the complex coupling strength ${\mathrm{\Gamma }}_{ij}$. Crucially, the spatial profile of the local modulation phases imprints a factor $exp\left(\mathrm{i}\mathrm{\Delta }{\theta }_{ij}\right)$ onto the waveguide-mediated coupling strength ${\mathrm{\Gamma }}_{ij}$, enabling the synthesis of nonreciprocal quantum interactions. Our approach thus provides a flexible toolbox for simulating a wide range of non-Hermitian Hamiltonians on waveguide-QED platforms.