We investigate the spectral and topological properties of an atomic chain of red phosphorus. We reveal the separation of flat-band states from the rest of the system and calculate its energy bands analytically. The topological properties of the system are established through the evaluation of the Berry (Zak) phase of the energy bands, revealing nontrivial topology. The Berry phase depends on the relative strength of the hopping parameters and exhibits dual energy-dependent topological phase transitions. Remarkably, the emergence of inert band edges provides a direct spectral signature of these transitions, acting as energy-resolved indicators of the redistribution of topological charge between bands. The existence of the associated edge states is proved numerically for finite lattices. The theoretical predictions, particularly the band structure and the existence of edge states, are further confirmed by numerical simulations of red phosphorus through a phononic lattice in the form of a highly structured aluminum plate.

We present a matrix product state (MPS) method for including decoherence processes in calculations involving waveguide quantum electrodynamics (QED) using density matrices. The approach is based on collision quantum optics, where the many-body state of the waveguide is represented using discrete time bins, which are then efficiently encoded using an MPS chain. Our method is a generalization of previous MPS methods, and we demonstrate how one can efficiently extend the method to density matrices, allowing for the inclusion of various loss processes in the form of Lindblad terms in the Liouvillian superoperator responsible for the relevant dissipation dynamics. As an application of the theory, we study various waveguide QED systems and the influence of emitter pure dephasing (which is one of the most important processes in real systems) on the light-matter interactions, including a two-level system (TLS) in a semi-infinite waveguide with time-delayed feedback, two spatially separated TLSs with finite delays, and finally the scattering of few-photon Fock pulses on a TLS. In addition to emitter pure dephasing, we also show how to include off-chip radiative decay, and show how it differs qualitatively from pure dephasing.

Modern experiments in resonators are moving to ever more extreme quantum regimes, posing major challenges to established theoretical approaches, such as so-called few-mode models. While these models have driven major insights for traditional regimes, they are now hitting their limitations for highly open cavities and extended systems, as encountered in cavity experiments with molecules and solid-state systems. Here, we present a method that significantly extends the conceptual underpinning of these discrete-mode models, promoting them to a systematic treatment. We develop an ansatz which allows to quantize the resonator's resonances with position-resolved discrete modes, thus naturally incorporating losses in the formalism. Such a construction effectively unifies key ideas from pseudomodes and quantized quasinormal modes theory. We further present a criterion for construction of the ansatz parameters at every point in space and semianalytically benchmark the resulting solution for a paradigmatic one-dimensional example resonator.

The Gottesman-Kitaev-Preskill (GKP) error correcting code uses a bosonic mode to encode a logical qubit and has the attractive property that its logical Clifford gates can be implemented using Gaussian unitary gates. In contrast, a direct unitary implementation of the $T$ gate using the cubic phase gate has been shown to have a logical error floor unless the GKP codestate has a biased-noise profile. In this work, we propose a method for on-demand noise biasing based on a standard GKP error-correction circuit. This on-demand biasing circuit can be used to bias the GKP codestate before a $T$ gate and return it to a nonbiased state afterward. With the on-demand biasing circuit, we prove that the logical error rate of the $T$ gate can be made arbitrarily small as the quality of the GKP codestates increases. We complement our proof with a numerical investigation of the cubic phase gate subject to a phenomenological noise model, showing that the $T$ gate can achieve average gate fidelities above $99\%$, with 12 dB of GKP squeezing without the use of postselection. Moreover, we develop a formalism for finding optimal unitary representations of logical diagonal gates in higher levels of the Clifford hierarchy that is based on a framework of “polynomial phase stabilizers” whose exponents are polynomial functions of one of the quadrature operators. This formalism naturally extends to multiqubit logical gates and even to number-phase bosonic codes, providing a powerful algebraic tool for analyzing non-Clifford gates in bosonic quantum codes.

We present a first-principles $S$-matrix framework for multiphoton ionization driven by arbitrary quantum states of light, retaining the full spatial structure of the light fields. Within this framework, we show that the utilization of momentum-entangled photon pairs emitted by ultrathin nonlinear crystals can enhance resonant two-photon ionization cross sections by more than two orders of magnitude relative to an uncorrelated reference state. The enhancement stems from the broad distribution of the transverse momentum and is captured only by a nonparaxial treatment, while strongly underestimated in the paraxial approximation. Atom-specific estimates for resonant two-photon ionization in sodium indicate that the predicted effect should be observable with currently available photon-pair sources.

We present a model for a topological quasicrystalline system that is suitable for realization in cold atom experiments. We define the model in terms of complex momentum-space couplings that break time-reversal symmetry (TRS) and detail how it may be experimentally realized using two-photon Raman couplings. In the weak-potential limit, we study the model analytically by calculating the band structure over a “quasi-Brillouin zone” (QBZ). We find symmetry-protected Dirac cones, which are gapped by a TRS-breaking term, resulting in a Chern number $\mathcal{C}=1$. This provides a direct analogy to the Haldane model, but now in a quasicrystalline setting. We also infer the number of states below the topological gap from the QBZ area. We verify our analysis with numerical calculations of periodic approximants to our system, constructing a phase diagram in parameter space that shows a topological region extending beyond the weak-potential regime. We also find examples of narrow Chern bands with the potential for hosting strongly correlated physics. Our work raises questions about the nature of localization and strongly correlated states in Chern bands in quasiperiodic systems.

Since the dawn of the space age, observations of energetic particles in planetary radiation belts have been interpreted within a diffusive transport framework, even though the dominant processes that populate and deplete these belts—such as injections and moon-driven absorption—produce particle distributions that are highly structured and spatially localized. This exposes a fundamental question: How can coherent phase-space structures evolving under collisionless dynamics give rise to observational signatures that appear consistent with diffusion-based transport? Here, we show that diffusionlike behavior inferred from radiation belt observations can arise solely from an observational phase-mixing effect, independent of stochastic wave-particle transport. As orbiting spacecraft sweep across neighboring drift shells while trapped particles undergo electromagnetic drifts, measurements inevitably sample regions with slightly different drift frequencies. This converts spatially localized drift-phase structures into rapidly decorrelating temporal signals, making them observationally indistinguishable from those produced by stochastic wave-particle processes. We derive the associated correlation function analytically and show that the effective lifetime of these structures is only a few drift periods. Consequently, even highly localized injections rapidly lose coherence, preventing spacecraft from resolving fine-scale structure in the distribution function. These results show that collisionless dynamics can produce observational signatures that mimic diffusive transport on timescales shorter than those expected from radial transport, limiting the inference of particle acceleration processes and leading to biased transport rates and inaccurate long-term flux predictions. This calls for a reassessment of diffusion-based interpretations inferred from sparse in situ measurements of radiation belts at Earth, across the solar system, and in the recently discovered radiation belts of ultracool brown dwarfs.

Precision measurements of molecules offer an unparalleled paradigm to probe physics beyond the standard model. The rich internal structure within these molecules makes them exquisite sensors for detecting fundamental symmetry violations, local position invariance, and dark matter. While trapping and control of diatomic and a few very simple polyatomic molecules have been experimentally demonstrated, leveraging the complex rovibrational structure of more general polyatomics demands the development of robust and efficient quantum control algorithms. In this study, we present reinforcement-learning quantum-logic spectroscopy (RL-QLS), a general, reinforcement-learning-designed quantum-logic approach to prepare molecular ions in single, pure quantum states. The reinforcement-learning agent optimizes the pulse sequence, each followed by a projective measurement, and probabilistically manipulates the collapse of the quantum system to a single state. The performance of the RL-QLS control algorithm is numerically demonstrated for the polyatomic molecule ${\mathrm{H}}_3{\mathrm{O}}^{+}$ with 130 thermally populated eigenstates and degenerate transitions within inversion doublets, as well as for ${\mathrm{CaH}}^{+}$ under the disturbance of environmental thermal radiation. We expect that the developed theoretical framework can be readily implemented for quantum control of polyatomic molecular ions with densely populated structures, thereby facilitating experimental tests of fundamental theories.

Generating strongly entangled states within multiparticle systems stands as a pivotal endeavor in quantum physics. It not only serves as a cornerstone for delving into the intrinsic properties of quantum mechanics but also provides indispensable quantum resources vital for the development of emerging quantum technologies that transcend classical capabilities. Here, we propose a method to manipulate the magnon-photon, magnon-phonon, and photon-phonon robust entanglement, and the tripartite entanglement involving magnon, photon, and phonon modes, within a hybrid cavity magnomechanical system, leveraging the interference effects induced by two counterpropagating pump lasers. We find that it becomes feasible to exert effective control over all three different types of bipartite quantum entanglement and the tripartite quantum entanglement by properly adjusting the phase difference between the two pump lasers. Moreover, this approach not only enhances these entanglements but also bolsters their resilience against thermal noise emanating from the surrounding environment. The outcomes of our research reveal a readily implementable technique for the manipulation and preservation of quantum entanglement. This technique is of paramount importance in numerous real-world applications that hinge on purely quantum resources, including noise-resistant quantum computing and high-precision quantum measurements.

There are various approaches to long-range quantum communication based on conceptually different forms of quantum repeaters. Here, we explore a quantum repeater scheme that employs quantum error correction (QEC) both on the flying (light) qubits and on the stationary (matter) qubits. The idea is to combine the benefits of encoded one-way and two-way schemes where effective channel transmission and loss scaling are enhanced by means of photon loss codes and encoded quantum memories, respectively, while sacrificing some of their advantages, such as high clock rates, independent of classical communication times (one-way), and potentially large segment lengths (two-way). More specifically, we illustrate, propose, and analyze such a quantum repeater using the bosonic Gottesman-Kitaev-Preskill (GKP) code, which naturally enables encoding and QEC of qudits, protecting them against transmission and memory loss, the latter, for instance, occurring on collective spin modes of atomic ensembles. While the encoded one-way and two-way schemes on their own either require very high repeater link coupling efficiencies and GKP squeezing or allow for experimentally more feasible, small values of these parameters, respectively, we find that there are intermediate parameter regimes where the combined repeater protocol is superior.

Nonequilibrium systems maintain spatiotemporal order through energy dissipation and entropy production. Here, we demonstrate this principle by engineering a quantum limit cycle that emerges from the interplay between a first-order absorbing-state phase transition and feedback mechanism coupling order and control parameters. The quantum limit cycle manifests dynamical correlations driven by multiplicative quantum noise and periodic traverses through tipping points, which act as a robust early-warning signal for state transitions. This periodic crossing results in the enhanced dynamical susceptibility and transient rise of long-range correlations near each tipping event and their subsequent disappearance away from it. These critical transitions are accompanied by a sharp increase in the energy dissipation rate, leading to a stepwise accumulation of dynamical entropy production over time. Our results provide a way for realizing dynamical fluctuations and long-range correlations in strongly interacting driven-dissipative open quantum systems.

Understanding how frustration and disorder shape relaxation in complex systems is a central problem in statistical physics and quantum annealing. Spin glass models provide a natural framework to explore this connection, as their energy landscapes are governed by competing interactions and constrained topologies. We investigate the nonexponential relaxation behavior of spin glasses on network architectures relevant to quantum annealing hardware—such as finite size Chimera, Pegasus, and Zephyr graphs—where embedding constraints and finite connectivity strongly modulate the distribution of barriers and metastable states. This slow relaxation arises from the combined effects of frustration and disorder, which persist even beyond the conventional spin glass transition. Within the Fortuin-Kasteleyn-Coniglio-Klein cluster formalism, the appearance of unfrustrated cluster regions gives rise to multiple relaxation scales, as distinct domains follow different dynamical pathways across a rugged energy landscape. This framework enables a broader characterization of spin glass energy landscapes and provides physical insight into how topological constraints, frustration, and disorder jointly govern relaxation dynamics in complex networks relevant to quantum annealing architectures.

Heterogeneous nucleation at surface edges is pervasive across nature and industry, yet the role of line pinning effect, arising from asymmetric capillary interactions at geometric singularities, remains poorly understood. Herein, we develop a generalized nucleation theory that explicitly incorporates edge pinning energy, thereby extending classical frameworks to account for nanoscale confinement and interfacial asymmetry. Through analytical treatment of droplet formation within geometrically defined nanopores, we derive a closed-form expression for the line pinning energy as a function of Laplace pressure, pore geometry, and wettability. This formulation reveals that line pinning effect can significantly reshape the nucleation energy landscape, introducing nontrivial dependencies on contact angle and pore morphology. Our results uncover a tunable, geometry-mediated mechanism for controlling nucleation barriers, offering predictive insight into phase transitions in confined environments and suggesting strategies for design in applications ranging from nanofluidics to crystallization control.

We introduce a minimal multiscale framework that links within-host virus dynamics to population-level susceptible-infectious-recovered-susceptible (SIRS) epidemiology through explicit, bidirectional coupling. At the microscopic layer, a two-variant quasispecies (master and mutant genomes with packaged virions) evolves on a fast timescale. At the macroscopic layer, two infectious classes (master- and mutant-infected), susceptible, recovered, and deceased individuals evolve slowly. The two scales are connected through transmission rates that depend on instantaneous virion abundance and through prevalence-weighted effective replication rates. Exploiting the timescale separation, we formalize a coarse-grained slow-fast closure: The genome-virion subsystem rapidly relaxes to quasisteady states that parametrize time-varying transmission in the slow epidemiological system. This yields an integrated expression for the basic reproduction number and sharp inequalities that delineate coexistence versus exclusion. A key prediction is a context-dependent error threshold that shifts with the prevalence ratio, enabling transient pseudo-error catastrophes driven by epidemic composition rather than intrinsic fidelity. Linearization reveals parameter regions with damped oscillations arising solely from the microscopic-macroscopic feedback. Two illustrative extremes bracket the model's behavior: An avirulent strongly immunizing strain that benignly replaces the master, and a hypervirulent weakly immunizing strain that self-limits via host depletion and collapses transmission. This framework yields testable signatures linking viral load, incidence, and within-host composition.

We propose a concept for a cryogenic source of atomic tritium at sub-Kelvin temperatures and energies suitable for magnetic trapping. The source is based on the dissociation of solid molecular ${\mathrm{T}}_2$ films below 1 K by electrons from a pulsed rf discharge, a technique recently demonstrated for atomic hydrogen, combined with buffer-gas cooling and magnetic confinement. We analyze the key processes limiting the source performance, adsorption, spin exchange, and recombination, and show that atomic tritium fluxes exceeding ${10}^{15} {\mathrm{s}}^{-1}$ at temperature of $\sim 200$ mK can be achieved. Such a source would enable Doppler-free two-photon $1S$–$2S$ spectroscopy in atomic tritium for high-precision measurements of the triton charge radius, providing a crucial benchmark for bound-state QED and improving the comparison between electronic, muonic, and scattering determinations of nuclear sizes in light systems. Beyond spectroscopy, using atomic tritium source avoids molecular final-state broadening in $\beta$ decay and is therefore necessary for next-generation neutrino-mass measurements; combined with detector technologies such as sub-eV resolution quantum sensors or cyclotron radiation emission spectroscopy, it enables an order-of-magnitude improvement compared to the current best experimental limit. Additionally, the source can be used to generate a beam of low-field-seeking deuterium atoms for loading magnetic traps, an important benchmark before trapping tritium atoms, which is useful for precision spectroscopy.

We explore the feasibility of realizing Dicke states in qubit arrays with always-on isotropic Heisenberg coupling between adjacent qubits, assuming a single Zeeman-type control acting in the $z$ direction on an actuator qubit. The Lie-algebraic criteria of controllability imply that such an array is not completely controllable, but satisfies the conditions for subspace controllability on any subspace with a fixed number of excitations. Therefore, a qubit array described by the model under consideration is state-to-state controllable for an arbitrary choice of initial and final states that have the same Hamming weight. This limited controllability is exploited here for the time-efficient dynamical generation of an $a$-excitation Dicke state $|D_a^N\rangle$ ($a=1,2,...,N-1$) in a linear array with $N$ qubits starting from a generic Hamming-weight-$a$ product state. To dynamically generate the desired Dicke states—including $W$ states $|W_N\rangle$ as their special ($a=1$) case—in the shortest possible time with a single local $Z$ control, we employ an optimal-control scheme based on the dressed chopped random basis (dCRAB) algorithm. We optimize the target-state fidelity over the expansion coefficients of smoothly varying control fields in a truncated random Fourier basis; this is done by combining Nelder-Mead-type local optimizations with the multistart-based clustering algorithm that facilitates searches for global extrema. In this manner, we obtain the optimal-control fields for Dicke-state preparation in arrays with up to nine qubits. Based on our numerical results, we find that the shortest possible state-preparation times scale as $\mathcal{O}\left(N^{2.08}\right)$ for $W$ states and $\mathcal{O}\left(N^{1.78}\right)$ for $a=2$ Dicke states. Finally, we demonstrate the robustness of our dCRAB-based state-engineering scheme against various types of imperfections of relevance for its anticipated experimental implementation.

We investigate the electronic structure of ${\mathrm{AgF}}_2, {\mathrm{AgFBF}}_4$, AgF, and ${\mathrm{Ag}}_2\mathrm{O}$ using x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) at the Ag $L_3$ edge. XAS results were compared with density functional theory computations of the spectra, allowing an identification of main features and an assessment of the theoretical approximations. Our RIXS measurements reveal that ${\mathrm{AgF}}_2$ exhibits charge-transfer (CT) excitations and $dd$ excitations, analogous to those observed in ${\mathrm{La}}_2{\mathrm{CuO}}_4$. We propose to use the ratio of $dd$ to CT spectral weight as a measure of the covalence of the compounds and provide explicit equations for the weights as a function of the scattering geometry for crystals and powders. The measurements at the metal site $L_3$ edge and previous measurement in the ligand $K$ edge reveal a striking similarity between the fluoride and cuprate materials, with fluorides somewhat more covalent than cuprates. These findings support the hypothesis that silver fluorides are an excellent platform to mimic the physics of cuprates, providing a promising avenue for exploring high-$T_c$ superconductivity and exotic magnetism in quasi-two-dimensional (${\mathrm{AgF}}_2$) and quasi-one-dimensional (${\mathrm{AgFBF}}_4$) materials.

By means of cellular dynamical mean-field theory (CDMFT), we study how short-range correlations drive the breakdown of the self-consistent perturbation theory in two-dimensional systems and the most relevant physical consequences associated with it, such as the CDMFT Mott transition. To this aim, we first derive in a structured and consistent way the Bethe-Salpeter equation (BSE) formalism at the CDMFT level in all physical channels, explicitly addressing the important aspect of the related Ward identities. In this context, we perform systematic calculations of the BSE for the two-dimensional Hubbard model at half filling at intermediate coupling. Our study illustrates how the divergence of a fundamental building block of the BSE in the charge channel, the two-particle irreducible vertex, systematically occurs at lower interactions than in the (purely local) DMFT case. We establish that these divergences are a prerequisite for the CDMFT Mott instability in two dimensions, which occurs at larger interaction values, and explicitly demonstrate that both are driven by short-ranged antiferromagnetic spin fluctuations.