Quantum annealing correction (QAC) models provide a promising approach for mitigating errors in quantum annealers. Previous studies have established that QAC models are crucial for ensuring the robustness of the ground state of the Ising model on hardware. In this work, the effects of QAC models incorporating replicas with additional interactions, specifically, the penalty spin model and the stacked model, are investigated for problems characterized by a small energy gap between the ground and first excited states during quantum annealing, a well-known bottleneck to reaching the ground state. The results demonstrate that these QAC models can obtain the optimal solution within short annealing times by exploiting diabatic transitions, even for problems with a small energy gap. These findings highlight the potential of QAC models as practical near-term algorithms for hardware subject to runtime limitations and control noise.

Simulating chemical reactions exhibits a pronounced unevenness in computational difficulty: While equilibrium reactant and product geometries are often tractable, transition-state (TS) geometries frequently display strong multireference character that challenges both classical solvers and coherent quantum state-preparation methods. We introduce a dissipative continuation protocol for preparing electronic ground states near TS geometries within a hybrid classical-quantum workflow. In the intended setting, classical electronic-structure methods supply an approximate TS geometry, a computationally motivated continuation path, and a locally compatible active-space representation along that path. Starting from a warm start at a tractable geometry on the same aligned path, the quantum routine transports the state toward the TS using orbital-gauge-aligned Hamiltonians and engineered dissipative cooling primitives that repeatedly contract population into the instantaneous low-energy sector. We prove that, for continuation paths satisfying a Lipschitz smoothness condition and a localized eigenstate thermalization hypothesis–motivated downward-drift condition within the relevant energy window, the ground state at the target geometry can be prepared to total energy error ${\varepsilon }_E$ with total ideal cooling-step complexity $\tilde{O}(C_{\mathrm{DK}}^2{N}_o^2/{\varepsilon }_E)$. Equivalently, for an intensive target error ${\varepsilon }_{\mathrm{int}}:={\varepsilon }_E/N_o$, the ideal cooling-step complexity is $\tilde{O}(C_{\mathrm{DK}}^2{N}_o/{\varepsilon }_{\mathrm{int}})$. Here $C_{\mathrm{DK}}$ quantifies ground-state rotation along the aligned path. The corresponding logical gate count is obtained by multiplying this primitive count by the cost of implementing one dissipative step, which is polynomial in the block-encoding size of the Lindbladian under standard Lindblad-simulation algorithms. This identifies a structured regime in which dissipative continuation provides a conditional route to ground-state preparation at strongly correlated TS geometries.

Nonadiabatic holonomic quantum computation (NHQC) offers intrinsic resilience to certain control imperfections. However, conventional nonadiabatic holonomic protocols are constrained by the fixed-pulse-area condition, which limits flexibility and prolongs duration of small-angle gates. Here we experimentally demonstrate a brachistochrone nonadiabatic holonomic single-qubit gate scheme in a trapped ${}^{40}\mathrm{Ca}^{+}$ ion and realize the construction of the $\sqrt{X}$ gate under the conventional NHQC, brachistochrone NHQC (BNHQC), and composite BNHQC (CBNHQC) protocols. By characterizing the performance of the gate in the presence of dissipation, Rabi-frequency errors and detuning errors, we show that BNHQC and CBNHQC outperform conventional NHQC, and BNHQC can offer a favorable balance between operation speed and robustness. It further shows that keeping high fidelity and strong robustness requires a reduction of the accumulated population of excited state in the evolution process. These results demonstrate the favorable balance between operation speed and robustness offered by time-optimal holonomic control, and they support further exploration of such schemes in trapped-ion platforms.

Rydberg atom arrays are a promising platform for quantum optimization, encoding computationally hard problems by reducing them to independent set problems with unit-disk graph topology. In the work of Nguyen et al., PRX Quantum 4, 010316 (2023), a systematic and efficient strategy was introduced to encode multiple problems into a special unit-disk graph: King's subgraph. However, King's subgraphs are not the optimal choice in two dimensions. Due to the power-law decay of Rydberg interaction strengths, the approximation to unit-disk graphs in real devices is poor, necessitating postprocessing that lacks physical interpretability. In this work we develop an encoding scheme that can universally encode computationally hard problems on triangular lattices, based on our innovative automated gadget search strategy. Numerical simulations demonstrate that, for a benchmark instance, quantum optimization on triangular lattices reduces independence-constraint violations by nearly two orders of magnitude compared to King's subgraphs, substantially alleviating the need for postprocessing in experiments.

We investigate charging dynamics in many-body quantum batteries by examining the relationship between instantaneous charging power and the emergence of bipartite, tripartite, and multipartite quantum correlations across different battery-charger configurations. We find that the charging power reaches its maximum before the correlation measures peak, revealing a temporal separation between rapid energy transfer and the buildup of quantum correlations. We further study the role of interaction structure using local and many-body charging Hamiltonians under both unconstrained and constrained charging Hamiltonians, in which the total available charging resources are fixed to scale proportionally with the number of spins, thereby isolating the influence of interaction geometry and particle participation on the charging dynamics. In the unconstrained case, the enhanced charging energy observed for higher-order interactions originates primarily from the larger energy scale of the charging Hamiltonian. Under constrained conditions, however, increasing the interaction order alone provides no advantage over parallel charging when interaction and local spin-flip contributions are balanced, whereas interaction-dominated protocols significantly enhance charging performance, highlighting the importance of collective many-body dynamics. Fully collective interactions are found to yield the largest enhancement in charging power together with stronger multipartite correlations, while partially collective interactions provide only limited improvements. Finally, extending the interaction range through next-nearest-neighbor couplings suppresses charging power, demonstrating that, under constrained energetic resources, charging performance is governed primarily by interaction structure, particle participation, and collective many-body dynamics rather than by interaction order alone.

While binary atomic Bose-Einstein condensates (BECs) are typically prone to collapse under strong interspecies attraction, it has been shown that higher-order fluctuation corrections, known as Lee-Huang-Yang corrections, can stabilize the mixture. In this work we demonstrate an alternative stabilization mechanism based on kinetic energy. Specifically, we consider a one-dimensional mixture of a quasi-BEC and a Tonks-Girardeau (TG) gas and show that the kinetic energy of the TG component can counteract the interspecies attraction, thereby preventing collapse. This balance leads to the formation of a self-bound quantum droplet, which exhibits two distinct regimes: a low-density droplet and a high-density droplet. We argue that these regimes are smoothly connected by a crossover. Furthermore, an analysis of the derivatives of the ground-state energy and bulk modulus reveals that the transition from a miscible mixture to the droplet phase is of third order. Our findings extend the theoretical understanding of quantum droplets in low-dimensional quantum gases, and the proposed system may be experimentally accessible within current ultracold-atom platforms.

We investigate hard-core bosons at half filling on a three-leg ladder under a uniform artificial gauge field. By analyzing current patterns and correlation functions, we uncover a rich quantum phase diagram containing multiple superfluid and insulating phases. In bosonic ladder systems, increasing the gauge flux typically destabilizes the Meissner phase and leads to vortex phases characterized by circulating currents. In the present system, however, we find that charge-density-wave (CDW) phases emerge precisely in such a flux regime despite the presence of only an on-site interaction, where vortex states are naturally expected and are indeed realized in nearby parameter regions. While part of this behavior can be qualitatively understood from a strong-coupling perspective, we also identify an isolated CDW region that cannot be connected to such limits. Furthermore, upon increasing the artificial gauge flux, we observe a reentrant sequence of quantum phase transitions, CDW $\to$ vortex-superfluid $\to$ CDW, revealing a strong competition between the vortex phase and the density-wave order.

We report the observation of a dimensional crossover of a $p$-wave Feshbach resonance in an ultracold, spin-polarized ${}^6\mathrm{Li}$ Fermi gas confined by a one-dimensional optical lattice. Using high-resolution atom-loss spectroscopy, we resolve the orbital doublet associated with the $m_{\ell }=0$ and $|m_{\ell }|=1$ scattering channels over a wide range of lattice depths. In the weak-confinement regime, the atom loss signal associated with the $|m_{\ell }|=1$ branch is stronger, consistent with the twofold orbital degeneracy of the three-dimensional system. As the lattice confinement increases, the relative loss weight of the two orbital branches evolves continuously toward the quasi-two-dimensional limit, indicating a progressive suppression of relative motion along the lattice direction. In addition, we observe a systematic confinement dependence of the orbital splitting between the two resonance branches. These results provide an experimental characterization of orbital-dependent $p$-wave scattering in reduced dimensions and motivate future microscopic studies of confined anisotropic scattering.

Higher-order exceptional points (EPs) are non-Hermitian degeneracies at which three or more eigenvalues and eigenvectors simultaneously coalesce. EPs typically require fine-tuning of multiple parameters, whereas symmetry protection can reduce the dimensionality of the parameter space required for their realization. Here, we show that gauge flux provides a route to symmetry-controlled higher-order EPs. Using a three-level loop-interaction system formed by coupling a single-mode waveguide to an orbital-angular-momentum (OAM) waveguide, we demonstrate that a gauge flux can be introduced through mode rotation induced by a trench in the OAM waveguide. In the absence of gauge flux, the system lacks the symmetry required to support higher-order EPs. By contrast, a gauge flux of $\pi /2$ induces a non-Hermitian chiral symmetry, giving rise to a third-order EP. By tuning the coupling strength, we further realize switching between third- and second-order EPs. Our results establish gauge flux as an alternative degree of freedom for realizing and manipulating higher-order non-Hermitian degeneracies.

We study two spatially separated boundary subsystems coupled to a common structured environment under relative motion within a Gaussian open-system framework. By integrating out the environment, we obtain an influence functional governed by a dressed environmental correlator evaluated at the boundary positions. Its retarded and Hadamard components govern coherent mediation and correlated fluctuations, respectively. Relative motion activates the leading resonant contribution to correlated decoherence through Doppler-shifted spectral overlap of the boundary excitations. For identical boundary dispersions, this contribution has an ideal narrow-linewidth onset at $v>2u_{\varphi }$. Below this value, no resonant momentum shell exists, whereas above it a finite shell opens and produces an enhanced correlated-decoherence contribution. Finite spectral linewidth generates subthreshold tails and rounds the ideal onset into a crossover centered on the same kinematic condition. The leading resonant contributions to motion-induced excitation production and correlated decoherence probe the same on-shell environmental structure. The proposed readout of this two-subsystem reduced-dynamics signature uses either differential-coherence measurements or a two-node noise cross-spectrum.

Dissipative phase transitions are strongly shaped by the symmetries of the Liouvillian, yet a clear understanding of the quantitative impact of weak and strong symmetries on critical behavior is presently lacking. We study a squeezed-photon model with single- and two-photon losses, realizing weak and strong symmetries in the simplest possible setting. The two symmetries exhibit identical Gaussian static fluctuations, whereas the order parameter and the asymptotic decay rate display distinct scaling behaviors. Our one-loop Keldysh analysis, together with cumulant-expansion numerics, reveals sharply different critical scaling with respect to the thermodynamic scaling parameter. This shows that weak and strong symmetries lead to distinct dynamical universality classes despite originating from the same symmetry group in the closed system. Our results provide a clear quantitative demonstration that strong symmetries fundamentally reshape dissipative criticality.

We develop a paraxial theory of spin dynamics for twisted electrons traversing the entrance or exit fringe of an axially symmetric magnetic coil. Starting from the Foldy-Wouthuysen reduction, we identify a transverse Pauli coupling proportional to the fringe-field gradient. The scalar orbital dynamics is treated exactly through the Ermakov mapping, while the transverse spin coupling is included perturbatively, yielding explicit first-order transition amplitudes for general solenoidal profiles. Axial symmetry requires each spin flip to be accompanied by a compensating change of orbital angular momentum, while the coordinate-linear perturbation restricts each incoming oscillator mode to at most two neighboring radial sidebands. For 100-keV electrons in a 1-T field, the low-order examples considered give integrated spin-flip probabilities of order ${10}^{-9}$ per edge. The framework therefore quantifies mixing between spin and orbital angular momentum (OAM) in realistic magnetic lenses and provides a basis for controlling spin-OAM conversion using engineered sequences of magnetic-field edges.

The one-center Coulomb–Sturmian convergent close-coupling method is applied to proton collisions with the boron atom and singly charged carbon ion. Here we report an update to our target-structure implementation, in which configuration state functions are constructed using the method of coefficients of fractional parentage. To assess the quality of the structure models for the two targets, we present the excitation energies, oscillator strengths, and dipole polarizabilities obtained from the present configuration interaction calculations. Cross sections for total and state-selective target excitation and electron loss are calculated from 10 keV to 1 MeV. For both systems, the total excitation cross section is found to be dominated by excitation of the $2s$ subshell. This emphasizes the importance of a multi-electron description of the target in such scattering calculations. Comparisons with previous theoretical and experimental data are presented and discussed. In particular, we find that the present calculation for the electron-loss cross section in $p+{\text{C}}^{+}$ collisions is in good agreement with the available measurements across the entire overlapping incident-energy range.

Recent real-time, time-dependent density functional theory (TDDFT) calculations have reported an unexpected delayed growth of molecular dipole oscillations some time after an extreme-ultraviolet (XUV) pulse is applied. We show that numerical and analytical arguments suggest that this instability is an artifact of an incorrect nonlinearity introduced by the computational approach: Propagation with an adiabatic exchange-correlation approximation within the time-dependent Kohn-Sham equations of TDDFT tends to amplify initially small and pure sinusoidal oscillations in a system. On the other hand, when this same adiabatic approximation is used within the recent response-reformulated TDDFT, the instability is absent. The absorbing boundary condition plays a crucial role consistent with our argument. We demonstrate this explicitly on the ${\mathrm{N}}_2$ molecule subject to an XUV pulse, with a range of adiabatic functionals.

Double and triple photoionization of Be-like ${\mathrm{B}}^{+}$ ions have been studied in the photon-energy range from approximately 250 to 1300 eV. The method of merged photon and ion beams was employed and calculations were performed in support of the experiments making use of different theoretical approaches. The cross section ${\sigma }_{13}$ for net double ionization in the investigated photon-energy range is dominated by direct removal of one $K$-shell electron and subsequent single-Auger decay. $K$-shell ionization is described very well by theory. Accordingly, measured yields of ${\mathrm{B}}^{3+}$ photoproducts were normalized to theory to obtain absolute cross sections ${\sigma }_{13}$. Aside from the process of direct single ionization plus autoionization, ${\sigma }_{13}$ additionally contains contributions from photoexcited double-$K$-shell-vacancy ${\mathrm{B}}^{+}$ resonances, from direct double $L$-shell ionization, and from direct double ionization involving one $L$-shell and one $K$-shell electron. We show that, apart from single $K$-shell ionization with subsequent Auger decay, all these processes are of minor importance for ${\sigma }_{13}$. Nevertheless, the sensitivity of our experiment allowed us to observe the $2s^{2}2p3s{}^{1}P_1$ double-$K$-shell-vacancy resonance and to determine its energy, width, strength, and asymmetry parameter. Relativistic Hartree-Fock theory was employed to characterize the role of such resonances in ${\sigma }_{13}$. The cross section ${\sigma }_{14}$ for net triple ionization of ${\mathrm{B}}^{+}$ is expected to arise primarily from direct double $K$-shell ionization and subsequent single-Auger decay. The experimental cross section is found to be larger than theoretical predictions. Possible additional contributions to ${\sigma }_{14}$ such as $K$-shell ionization with accompanying $K$-shell excitation and subsequent Auger decay are discussed, as is the influence of metastable ions in the primary ${\mathrm{B}}^{+}$ ion beam.

We demonstrate the time-resolved detection of dynamical phase transitions (DPTs) in lattice-confined spinor gases subject to a priori unknown time-variant interactions, via the temporal behaviors of both the system energy and spinor phases extracted from the observed spin dynamics. Using this technique, we describe the observed nonequilibrium spin dynamics, governed by intricate spin-spatial couplings, across a range of conditions. This work also introduces a diagnostic tool that can quickly identify DPTs without requiring observations over at least a full period of the spin dynamics. Our approach can naturally extend to other complex systems subject to time-dependent parameters, such as Floquet systems under driven magnetic fields, driven interactions, or spin-flopping fields, with potential applications in the study of DPTs in nonintegrable models.

The superradiant phase transition in the dissipative Dicke lattice model, driven by on-site collective atom-photon couplings and intersite photon hopping, is a cornerstone of nonequilibrium quantum many-body physics. However, little is still known about the influence of boundaries in experimental achievable systems of finite size. Here we investigate the dissipative superradiant phase transition in the Dicke lattice model with a small number of sites and reveal a striking sensitivity of this model to the nature of the boundary conditions. Under open boundary conditions, we observe qualitatively distinct behavior, including the absence of homogeneous superradiance, a strongly shifted critical coupling, and an enlarged range of hopping strengths over which steady states remain stable, in sharp contrast to that with periodic boundary conditions. Our results demonstrate the crucial influence of boundary effects on the stationary phases of dissipative lattice models, which offers intriguing opportunities for studying these phenomena in near-term experimental realizations of such models in quantum optics and circuit QED.

We present a theoretical study of the two-particle spectrum $\omega \left(K\right)$ for the chiral waveguide QED setup of an array of two-level atoms directionally interacting with photons propagating along the waveguide. We demonstrate that for each pair center-of-mass momentum $K$ there exist distinct solutions with $\mathrm{Im}\omega \le 0$ in the two-particle spectrum, corresponding to bound, antibound, and resonance states, in addition to the continuum of scattering states. Contrary to previous studies, which showed the bound and resonance-state spectra only over a limited range of $K$, the calculated spectrum is consistent across all $K$ values. An interesting finding is that the real part of the spectrum $\text{Re}\omega \left(K\right)$ in the chiral model is gapless. The calculated dispersion law $\omega \left(K\right)$ provides an effective model for the bound photon pairs also in a finite-size array, manifesting the topological non-Hermitian skin effect.

Many-body quantum systems with local interactions undergo “sudden death of entanglement” at high temperatures, whereby thermal states become classical mixtures of product states. We investigate whether symmetry constraints can prevent this phenomenon. We prove that strongly symmetric thermal states (canonical ensemble) of generic Hamiltonians with on-site Abelian symmetries remain entangled with nonzero entanglement negativity at arbitrarily high temperatures, under mild conditions on the symmetry actions and the charge sector of the strong symmetry. Our results extend to weakly symmetric thermal states (Gibbs ensemble) under superselection rules, which restrict state decompositions to be symmetric. In particular, we show that fermionic Gibbs states evade sudden death of entanglement and have persistent fermionic negativity at high temperatures, proving along the way some existing conjectures about fermionic entanglement. These findings demonstrate that global symmetry correlations can preserve quantum entanglement despite thermal decoherence, providing new insights into the interplay between symmetry and quantum information in thermal equilibrium.