The task of finding an element in an unstructured database is known as spatial search and can be expressed as a quantum-walk evolution on a graph. In this article, we modify the usual search problem by adding an extra trapping vertex to the graph, which is only connected to the target element. We study the transfer efficiency of the walker to a trapping site, using the search problem as a case study. Thus, our model offers no computational advantage for the search problem, but focuses on information transport in an open environment with a search Hamiltonian. The walker evolution is a mix between classical and quantum-walk search dynamics. The balance between unitary and nonunitary dynamics is tuned with a parameter, and we numerically show that, depending on the graph topology and the connectivity of the target element, this hybrid approach can outperform a purely classical or quantum evolution for reaching the trapping site. We show that this behavior is only observed in the presence of an extra trapping site, and that, depending on the topology and a tunable parameter controlling the strength of the oracle, a hybrid regime composed of 90% coherent dynamics can lead to either the highest or worst transfer efficiency to the trapping site. We also relate the performance of a hybrid regime to the entropy's decay rate. As the introduction of nonunitary operations may be considered noise, we interpret this phenomenon as a noise-assisted quantum evolution.

Squeezing as a quantum resource for quantum metrology is robust against decoherence and dissipation, while the conventional nonlinear two-photon quantum Rabi model (QRM) provides a squeezing resource immune to the divergence problem of the preparation time of the probe state (PTPS). However, the critical point of the two-photon QRM is locally restricted to one single point, which hinders a wider application. In the present work we propose to combine the Stark coupling with the two-photon QRM to realize a tunable critical point so that the nonlinear critical quantum metrology can be globalized. As demonstrated by the diverging quantum Fisher information (QFI) the protocol enables us to acquire a high measurement precision in a wide range of coupling parameters rather than locally at a single critical point. Moreover, we find that the QFI not only manifests criticality but also exhibits universality. As a particular merit of our protocol, a strong squeezing can be globally retained as the leading quantum resource, while at the same time the PTPS remains in a finite order.

We present theoretical results on state-selective total and angular-differential cross sections for single-electron-capture and excitation occurring in the ${\mathrm{He}}^{+}+\mathrm{He}$ collisions using the four-body boundary-corrected continuum intermediate state approximation in both prior and post forms. The theoretical cross sections are reported in the energy range of 50–2500 keV/amu. The purpose of the present study is to investigate the relative importance of the intermediate ionization continuum of the two electrons in the projectile and target. In the prior form, the effect of the dynamic electron-electron correlation is taken into account through the complete perturbation potentials. In this form, the final channel is described by the Coulomb continuum states of the electrons and projectile in the field of the target. Similarly, in the post form, the interaction of the electrons with the target and projectile is represented by the Coulomb continuum functions. The initial state of the two electrons in helium is considered to be a one-active-electron target. Therefore, the initial state of the active electron is described by the Roothaan-Hartree-Fock wave function, which is a more sophisticated single-electron wave function for the target. State-selective total and angular-differential cross sections are presented and compared with experimental and previous theoretical data where available. The differential cross sections exhibit minima and maxima in the projectile scattering angles, which are more pronounced in the region of high impact energy. The position of such minima moves towards smaller scattering angles. This structure demonstrates quantum matter wave scattering in atomic collision physics. We also investigated the projectile excitation for the same collision and compared it with other theoretical models.

We theoretically and experimentally investigate the Rabi pulling effect in an integrating sphere cold-atom clock (ISCAC). Rabi pulling in an ISCAC is caused by magnetic-sublevel transitions between hyperfine states and is related to the amplitude of the microwave pulse, the bias magnetic field, and the density distribution of cold atoms. Theoretical analysis shows the Rabi closed-loop scheme reduces microwave power fluctuation sensitivity by two orders compared to the Ramsey scheme. Experimentally, the Rabi closed-loop scheme achieves a long-term frequency stability of $1.9\times {10}^{-15}$ at an averaging time of $200000$ s.

We present a bound-continuum ionization model combined with numerical simulations to investigate the asymmetric features of Autler-Townes (AT) splitting in the ionization spectra of hydrogen atoms, induced by a spectrally phase-modulated ultrashort pulse. This model incorporates a resonance-enhanced two-photon ionization process, enabling transitions from the ground electronic state to the continuum state via the first excited electronic state through the absorption of two photons. By comparing our model predictions with exact numerical simulations based on time-dependent electronic wave-packet calculations, we demonstrate that the characteristics of the AT doublets, shaped by the spectral phase, emerge from the competing effects of selective population of dressed states and the transition amplitude to the continuum. In addition, through a perturbative analysis of the photoelectronic spectrum and the application of the Magnus expansion, we reveal a correlation between the number of AT fringes, resonant states, and pulse area, while drawing insights from bound states. This work enhances our understanding of how the spectral phase can be utilized to explore bound-state effects in ultrafast ionization dynamics.

The exact wave function of an isolated three-body resonance at finite scattering length is obtained for two identical particles interacting with another one via a pairwise zero-range potential. The corresponding universal spectrum is studied as a function of the scattering length. The universality of the results is illustrated by considering a model with finite-range interactions.

Yet another important family of temporal optical solitons, the fractional-order optical solitons (FOSs), can be generated by the interplay between fractional-order dispersion and self-phase modulation due to Kerr nonlinearity in a fiber laser cavity, which provides a promising avenue for exploring unique soliton dynamics in fractional-order nonlinear systems. We theoretically investigate the stationary properties of vector fractional-order optical solitons (VFOSs) in a fractional-order dispersion birefringent optical fiber, and then the dynamics of VFOSs in a fractional-dispersion-dominant mode-locked fiber laser. Investigating the formation dynamics of the FOSs, we find that the vector soliton tails are decaying nonexponentially, and the frequency chirps of two orthogonal polarization components complement each other. Due to the varied fractional phase profiles, the temporal pulse, spectral profile, central frequency offset, time-bandwidth product, and energy-width scaling are closely associated with the Lévy index α $(1<\alpha <2)$. The spectral profiles of the mode-locked VFOSs evolve from the fish-fin structure with no sidebands $(\alpha =1.1)$ to the hyperbolic-secant shape with noticeable sidebands $(\alpha =1.7)$, and a spectral-shifting feature is observed during the VFOS formation in the cavity, generation of asymmetric sidebands, and complex dispersion wave radiation. We discuss in detail the polarization dynamics of the VFOSs for $\alpha =1.1$ and 1.7. Our findings will offer significant insight into both the fundamental working principle and the fascinating nonlinear dynamics of the fractional-order optical soliton laser.

We present a general, nonperturbative method for deriving effective Hamiltonians of arbitrary order for periodically driven systems based on an iterated integration-by-parts technique. The resulting family of effective Hamiltonians reproduces the well-known Floquet-Magnus expansion, now enhanced with explicit error bounds that quantify the distance between the exact and approximate dynamics at each order, even in cases where the Floquet-Magnus series fails to converge. We apply the method to the semiclassical Rabi model and provide explicit error bounds for both the Bloch-Siegert Hamiltonian and its third-order refinement. Our analysis shows that, while the rotating-wave approximation more accurately captures the true dynamics than the Bloch-Siegert Hamiltonian in most regimes, the third-order approximation ultimately outperforms both.

Recent advances in laser theory have demonstrated that a quantum enhancement is possible for the production of coherence $\mathfrak{C}$ by a continuous-wave laser device. Curiously, natural families of laser models that achieve Heisenberg-limited scaling for coherence produce the most coherence when the beam exhibits sub-Poissonian photon statistics. In this work, we provide an analytical treatment of those novel families of laser models by considering a parameter regime that permits a linearization. We characterize the dynamics of each laser system and find that some of the intuitions from standard laser theory may be applied here. Specifically, the intracavity number dynamics are well described as an Ornstein-Uhlenbeck process, while the intracavity phase dynamics are well described in terms of a physically realizable ensemble of pure states, which evolve according to pure phase diffusion. Unlike a standard laser, however, we find that the pure states comprising the ensemble in the Heisenberg-limited lasers are substantially phase squeezed. From our dynamical analysis, we deduce various quantities of the beam for each laser family, including the first- and second-order Glauber coherence functions, intensity noise spectrum, Mandel-$Q$ parameter, and coherence $\mathfrak{C}$. In addition, inspired from these phase diffusion dynamics, we derive an upper bound on laser coherence $\mathfrak{C}\lesssim 1.1156{\mu }^4$—which is tighter by a factor of $3/8$ when compared to that derived in Baker et al. [Nat. Phys. 17, 179 (2021)]—by making one of the assumptions of that paper slightly stronger.

We introduce an ergotropy-based formulation of quantum thermodynamics, which provides a strong connection between average heat and von Neumann entropy. By adopting this formulation, we can reinterpret the infinitesimal average heat in terms of the infinitesimal change of the passive state associated with the density operator behind the quantum dynamics. Like entropy, this leads to a heat concept that is invariant under passive state transformations. As an application, the average heat can be used as a general non-Markovianity measure for unital maps. Moreover, a positive-semidefinite temperature naturally emerges in an out-of-equilibrium ergotropy-based scenario. Concerning the infinitesimal average work, it arises as an infinitesimal variation of ergotropy, as well as an extra passive work contribution in the case of a time-dependent Hamiltonian. As illustrations, we consider the thermodynamics of a single-qubit open system in the cases of generalized amplitude-damping and phase-damping channels.

We discuss the idea of extracting energy from a quantum battery, applying a projective measurement on an auxiliary system. The battery is initially connected to the auxiliary system and allowed to interact with it. After some time, we execute a measurement on the auxiliary system which probabilistically projects the setup to a particular state, and the corresponding state of the battery is the final state. We consider the sum of the product of the energy difference between the initial and final states of the battery with the probability of getting that final state, where the sum is taken over all the preferable outcomes, that is, the outcomes which reduce the energy of the battery. We define the maximum value of this quantity as the distillable energy, where the maximization is taken over the time of interaction and auxiliary state and measurement basis parameters. Restricting ourselves to a particular uncountable set of states, we find that distillable energy is always higher than the ergotropy of the battery, irrespective of the presence or absence of entanglement between battery and auxiliary. We also compare the distillable energy with the energy extracted using the interaction between the battery and the auxiliary without any measurements. In comparison with the measurement-free scenario, we show that while measurement-based protocols do not provide any enhancement in the amount of extractable energy, they do yield a distinct advantage in terms of power, most notably in the case of distillable power, surpassing the power obtained without measurements. We show that the average of extracted energy overall measurement outcomes is independent of the applied measurement and equivalent to applying no measurement. Additionally, we find that the advantage in power for measurement-based energy extraction reduces with the increase in the size of the battery if the dimension of the auxiliary is kept fixed. Finally, we find that the ground state is the only state for which distillable energy is zero. We also analyze the behavior of the maximum value (maximization done over the same parameters as in the case of distillable energy) of the product of the probability of getting a particular suitable outcome and the energy difference of the corresponding initial and final states of the battery, which is referred to as maximum probabilistically extractable energy.

Identifying phase transition points is a fundamental challenge in condensed-matter physics, particularly for transitions driven by quantum interference effects such as Anderson and many-body localization. Recent studies have demonstrated that quantum coherence provides an effective means of detecting localization transitions, offering a practical alternative to full quantum state tomography and related approaches. Building on this idea, we investigate localization transitions through complementarity relations that connect local predictability, local coherence, and entanglement in bipartite pure states. Our results show that predictability serves as a robust and efficient marker for localization transitions. Crucially, its experimental determination requires exponentially fewer measurements than coherence or entanglement, making it a powerful tool for probing localization phase transitions.

Continuous-variable quantum secret sharing (CVQSS) based on discrete modulation is a viable alternative to Gaussian-modulated CVQSS due to its implementation simplicity. However, its theoretical performance remains far below the Gaussian-modulated counterparts. In this work we propose a CVQSS scheme based on constellation shaping, which enables near-Gaussian modulation effects by combining probabilistic and geometric constellation shaping with quadrature amplitude modulation (QAM). For the probabilistic shaping, binomial distribution and Boltzmann-Maxwell (BM) distribution are selected to adjust the occurrence probabilities of quantum states, and for the geometric shaping, triangular quadrature amplitude modulation (TQAM) is employed to optimize the geometric positions of the constellation points. Numerical simulations indicate that compared with other discrete-modulated CVQSS schemes, the proposed BM-distributed 16-TQAM scheme achieves the highest asymptotic secret key rate and the lowest detection error probability. Moreover, the optimal modulation variance of this scheme is higher than that of other schemes, demonstrating that the players can employ a larger modulation variance when preparing coherent states, thereby enhancing the signal-to-noise ratio of the whole system and providing a potential advantage in long-distance transmission.

We investigate the impulsive alignment of acetylene (${\mathrm{C}}_2{\mathrm{H}}_2$) molecules via resonant vibrational excitation using ultrashort infrared laser pulses. Focusing on two vibrational bands, the fundamental mode ${\nu }_3$ at 3 µm and the combination band ${\nu }_1+{\nu }_3$ at 1.5 µm, we compare theoretical predictions with experimental observations. Numerical simulations reveal that excitation of the ${\nu }_3$ band induces a pronounced and persistent planar alignment characteristic of resonant processes, akin to phenomena recently observed in iodine molecules. In contrast, alignment via the ${\nu }_1+{\nu }_3$ band is predominantly governed by nonresonant interactions due to the weaker transition dipole moment, resulting in a negligible resonant contribution. Experimental measurements at 1.5 µm confirm the dominance of nonresonant dynamics. These findings highlight the importance of dipole strength in resonant alignment and support the broader applicability of vibrationally driven alignment strategies in molecular control.

Optical lattice clocks have set records in clock precision and accuracy. Continuing to advance their performance, via probing as many atoms as possible for the longest interrogation time affordable, requires experimentally and theoretically studying a many-body lattice system. Motivated by recent experimental results on a Fermi-degenerate three-dimensional optical lattice clock [W. R. Milner et al., Science 388, 503 (2025)], we present a theoretical overview of Ramsey and Rabi spectroscopy in one-dimensional chains. At realistic experimental temperatures and confinement conditions, atoms are spatially localized into small chains of approximately one to five atoms. We show that in the presence of spin-orbit coupling induced by the clock laser, the spectroscopy observables are modified by superexchange interactions within each chain, and depend strongly on the length of the chain. The thermal distribution of chain lengths thus plays a key role in the spectroscopy measurements. Our results offer insight into observable many-body effects in state-of-the-art lattice clocks and suggest new directions for optimizing clock performance.

The search for superconductivity with unconventional pairing symmetry has been a central focus in the study of strongly correlated electron systems. In this work, we report a numerically exact study of the spin-triplet pairing in a two-dimensional Hubbard model with repulsive interactions, employing the determinant quantum Monte Carlo method. The model includes next-nearest-neighbor and third-nearest-neighbor hopping terms and maintains spin balance. By tuning the fermion filling close to a type-II Van Hove singularity (VHS) in the model, we numerically investigate the ordering tendencies of several possible pairing channels with different symmetries. Our numerical results provide clear evidence of the spin-triplet $p$-wave pairing instability approaching low temperatures, as revealed by the vertex contribution to the pairing susceptibility. This signature becomes increasingly pronounced as the interaction strength increases in the weak to intermediate regime. We further find that, near the type-II VHS, the dominant spin-spin correlations in the system are ferromagnetic, suggesting its close relation to the spin-triplet pairing instability. Our findings offer a reliable approach to realize spin-triplet $p$-wave superfluidity in the repulsive Hubbard model from an unbiased numerical perspective.

Exploring gravitational interactions between objects with small masses has become increasingly timely. Concurrently, oscillators with masses ranging between milligrams and grams in cavity optomechanical systems sparked interest for probing gravity and even investigating gravity-induced decoherence within massive mechanical systems. Here we present a measurement scheme for probing gravity in a microwave optomechanical setup that incorporates periodic gravitational modulation between the test mass and the driven source mass at the milligram scale. Optomechanically induced transparency (OMIT) can be utilized to sense the gravitational interactions between test masses and source masses. Specifically, the relative variation in the height of the OMIT peak, expressed as $|1+r{e}^{i\varphi }{|}^2-1$, where $r$ represents the ratio of the amplitude of the gravitational driving force to the radiation pressure force of the probe tone and $\varphi$ denotes their phase difference, can reach up to 2.3% under plausible experimental conditions. This work may facilitate cavity-optomechanical probing of gravitational coupling between milligram-scale mechanical oscillators, a mass regime where modifications to gravity, evidence for extra dimensions, or gravity-induced entanglement may emerge.

This work introduces an all-dielectric chiral metasurface capable of efficiently generating a range of cylindrical vector vortex beams (CVVBs) and complex polarization structures such as optical Stokes skyrmions. The metasurface incorporates two chiral unit cells, one responsive to left circularly polarized light and the other to right circularly polarized light, demonstrating 77% circular dichroism and 72% cross-polarization conversion efficiency. It employs the geometric phase principle to achieve precise phase modulation. This design supports multifunctionality under both circularly and linearly polarized illumination, producing vortex beams with distinct topological charges for circularly polarized light and intricate first-order CVVBs for varying linear polarization angles. Furthermore, encoding tailored phase profiles onto the metasurface's subarrays facilitates the generation of optical skyrmions, expanding its applicability. This compact metasurface enables advancements in optical communications, quantum information processing, and high-resolution imaging, contributing to next-generation photonic technologies.

Quantum correlations based on quantum interference effects, such as unconventional quantum antibunching, have attracted significant attention due to their potential for generating high-quality single-quantum sources. Here, we propose an all-solid-state scheme to realize and control directional quantum correlations in a hybrid cavity electromagnonic system. We find that, through directional pumping of the nonlinear microwave resonator, quantum squeezing occurs exclusively along the pump direction. In the forward-input case, the system can achieve the strongest photon and magnon antibunching under the corresponding optimal parametric conditions. Furthermore, by adjusting the cavity-magnon coupling strength, an effective switch between strong photon antibunching and strong magnon antibunching can be realized. In contrast, in the backward-input case, quantum antibunching cannot be observed due to the absence of quantum squeezing. Consequently, directional quantum squeezing causes bosonic modes with different input directions to follow distinct transition pathways, thereby generating different quantum interference effects and ultimately enabling nonreciprocal unconventional quantum antibunching. Our work provides a pathway for realizing quantum correlations in cavity electromagnonic systems.