We study the two-point correlation functions and the bipartite entanglement in the ground state of the exactly solvable variable-range extended Ising model of qubits in the presence of a transverse field on a one-dimensional lattice. We introduce the variation in the range of interaction by varying the coordination number $\mathcal{Z}$ of each qubit, where the interaction strength between a pair of qubits at a distance $r$ varies as approximately $r^{-\alpha }$. We show that the algebraic nature of the correlation functions is present only up to $r=\mathcal{Z}$, above which it exhibits short-range exponential scaling. We also show that at the critical point, the bipartite entanglement exhibits a power-law decrease (approximately ${\mathcal{Z}}^{-\gamma }$) with increasing coordination number irrespective of the partition size and the value of $\alpha$ for $\alpha >1$. We further consider a sudden quench of the system starting from the ground state of the infinite-field limit of the system Hamiltonian via turning on the critical Hamiltonian and demonstrate that the long-time-averaged bipartite entanglement exhibits a qualitatively similar variation (approximately ${\mathcal{Z}}^{-\gamma }$) with $\mathcal{Z}$.

Indefinite causal order (ICO), in which the order of quantum operations is placed in a coherent superposition, has been demonstrated to enhance various information-processing tasks. Here we investigate its impact on the thermodynamic processes generated by thermalizing quantum channels. We consider a two-level system interacting with two thermal baths under a quantum SWITCH, with the channel order controlled coherently by an ancillary qubit. We derive closed-form expressions for the effective inverse temperature ${\beta }_f$ of the postselected system state for both identical and distinct bath temperatures, and identify the control-qubit parameters that maximize heating or cooling. Our analysis reveals how the diagonal and coherent components of the control-qubit state contribute separately to the temperature shift, and how their interplay enables departures from the thermal response attainable under protocols with a definite causal order within the thermodynamic setting considered here. Bath asymmetry enhances these effects, while reduced purity of the control qubit state suppresses them. These results provide a systematic framework for assessing SWITCH-based thermalization in the setting of indefinite causal order, and identify control-qubit coherence as a tunable resource.

We demonstrate coherent control of motional dynamics in trapped Rydberg ions engineered to exhibit a conical intersection between adiabatic potential-energy surfaces. Using quantum optimal control, an optimally shaped electric field drives the motional wave packet between prescribed spatial configurations on microsecond timescales. Localized nonadiabatic coupling breaks the symmetry of the dynamics and produces a directed trajectory: after only a few early passages through the conical intersection region, the packet proceeds toward the target with high fidelity. In contrast, in the Born-Oppenheimer limit, where such coupling is absent, the optimized control yields symmetric, multicycle oscillations rather than a comparably directed displacement. While both approaches reach the target at the chosen final time, the underlying trajectories are qualitatively different. This work demonstrates that engineered conical intersections can serve as a potential control resource for directional motional dynamics, complementing pulse-shaping methods in trapped-ion systems. This directional motion of the ions, enabled by the conical intersection, may provide a route toward improved control of motional states in trapped-ion quantum information processing.

Angular distributions of K-shell photoelectrons from CO molecules ionized by 20 keV photons are studied experimentally and theoretically in the molecular frame of reference. At this high photon energy, nondipole contributions to the light-matter interaction induce a strong forward-directed emission of the photoelectrons, which is only slightly modulated by scattering from the molecular potential. In addition, we observe a recently predicted asymmetry in the photoelectron emission distributions with respect to the polarization direction [Phys. Rev. Lett. 123, 243201 (2019)], which is caused by a rotational recoil of the nuclei imposed by the fast photoelectrons and high-energy photons. By addressing the C and O atoms separately in CO, we are able to resolve the molecular site that experiences this rotational kick, which was not possible in the previous study of ${\mathrm{N}}_2$ molecules. Our experimental results are explained by ab initio electronic structure calculations augmented by a semiclassical modeling of the rotational-recoil effect.

We present a low-cost implementation of lambda-enhanced gray molasses cooling in a nonstandard beam geometry and with an inexpensive laser locking setup that only provides limited coherence of the Raman laser beams. In contrast to the established use of resource-intensive phase-locking methods, our laser system uses two independent lasers, frequency- locked to a spectral feature produced by an electromagnetically induced transparency (EIT) resonance. We show that this approach achieves sufficient coherence to enable effective gray molasses cooling without the need for costly GHz electronics, significantly reducing the complexity and cost of experimental setups and represents a step toward more accessible cold atom technologies. Furthermore, the cooling remains efficient even with a nonoptimal beam geometry, typical of cold-atoms quantum computing platforms based on optical tweezers. A wave-function Monte Carlo analysis supports the experimental findings, offering insight into the cooling dynamics of this unconventional scheme.

To reveal a microscopic mechanism for the anomalous minimization and dependence of the superfluid critical velocity on a moving obstacle potential in an atomic Bose-Einstein condensate [Kwon et al., Phys. Rev. A 91, 053615 (2015)], we introduce a considerably simplified model of superflow along a step potential. The energy spectrum and wave functions of the lowest-energy excitations in this system are well described by the semiclassical analysis based on the Bogoliubov theory. We found that the critical velocity is minimized and becomes zero when the potential height equals the hydrostatic chemical potential, which corresponds to the critical point of the local condensation phase transition inside the step potential. In a finite-size system, the critical velocity $v_{\mathrm{c}}$ obeys a power-law scaling with system size $L_x$ as $v_{\mathrm{c}}\propto L_x^{-0.963}$. This criticality provides an explanation of the power-law scaling of the minimum critical velocity observed in the experiment.

A tenet of contemporary physics is that novel physics beyond the Standard Model lurks at a scale related to the Planck length. The development and validation of a unified framework that merges general relativity and quantum physics is contingent upon the observation of Planck-scale physics. Here, we present a fully quantum model for measuring the nonstationary dynamics of a nanogram-mass mechanical resonator, which will slightly deviate from the predictions of standard quantum mechanics induced by modified commutation relations associated with quantum gravity effects at low-energy scalar. The deformed commutator is quantified by the oscillation frequency deviation, which is amplified by the nonlinear mechanism of the detection field. The measurement resolution is optimized to a precision level that is 15 orders of magnitude below the electroweak scale.

We propose a scheme to achieve efficient frequency conversion for a single photon propagating in a one-dimensional conventional waveguide by exploiting the quantum interference induced by the scale of a V-type giant atom (GA) characterized by the distance between the two coupling points as well as single-photon transition pathways originating from the coupling between the GA and the resonator. The presence of photons in the resonator triggers the frequency conversion of photons. The scattering spectra and the conversion contrast are studied in both the Markovian and non-Markovian regimes. The disappearance of frequency conversion is rooted in the complete suppression of the emission from the excited state to either of the lower states in the $n+1$ subspace, where $n$ is the photon number of the resonator, and the non-Markovianity-induced nonreciprocity is found under specific conditions. Altering the photon number $n$ induces the nonreciprocal transmission of single photons in the waveguide and hence enhances the conversion probability.

The Adler equation is a well-known one-dimensional model describing phase locking and synchronization. Motivated by recent experiments using optomechanical oscillators, we extend this model to include overtone-synthesized sinusoidal coupling with adiabatic temporal modulation. This extension gives rise to unique topological features such as an integer-valued winding number, discontinuous phase-slip transitions, and hysteretic and nonreciprocal phase dynamics. We further extend the analysis to the quantum regime, where we obtain a counterintuitive result: a continuously valued winding number. This behavior arises from averaging over different winding-number components in a closed-system Thouless pump. Moreover, hysteretic dynamics—suppressed within the quantum adiabatic approximation—is recovered in nonadiabatic calculations, where Landau-Zener-Stückelberg oscillations induce the nonreciprocal phase evolution observed in classical systems.

Negative states are an intrinsic property of relativistic quantum theory and related to antiparticles in the context of the Dirac sea concept. We show that negative states can dominantly contribute to the diffraction amplitude in the quantum dynamics of the two-photon Kapitza-Dirac effect. We draw our conclusion by investigating solutions from time-dependent perturbation theory, where the perturbative solutions are in match with numeric solutions of the relativistic quantum system and also with the numeric and analytic solutions from the relativistic equations of motion of a classical point-like electron in an external standing-wave light field. While our numeric solutions assume a strong laser field, the analytic solutions indicate that negative state coupling remains dominant for arbitrary low-field amplitudes, where in the single-photon case (Compton scattering) negative state coupling can be mathematically associated with the interaction of a virtual electron-positron pair in the context of a quantized theory in old-fashioned perturbation theory.

Robust and efficient eigenstate preparation is a central challenge in quantum simulation in the noisy intermediate-scale quantum (NISQ) era and beyond. The Rodeo Algorithm (RA) [Choi et al., Phys. Rev. Lett. 127, 040505 (2021)] offers exponential convergence to a target eigenstate but suffers from poor performance when the initial state has low fidelity with the desired eigenstate, limiting its scalability. In this work, we introduce a fusion method that preconditions the RA by an adiabatic ramp and modular subsystem fusion, enabling high-fidelity state preparation across large many-body systems. Numerical simulations of the spin-1/2 XX chain demonstrate that this hybrid preconditioning restores the RA's exponential convergence and dramatically reduces computational cost. The method's efficiency is governed by boundary size, making it ideally suited for one-dimensional (1D) and quasi-1D architectures such as trapped-ion chains and neutral-atom arrays. The fusion method thus defines a scalable framework for high-fidelity quantum state preparation across both present and future generations of quantum hardware.

Noise-robust holonomic gates realized by the adiabatic non-Abelian geometric phase play a key role in quantum information processing. However, previous holonomic gates were realized via real pulses applied to Hermitian quantum systems. Here we extend the general form of non-Abelian holonomy to the non-Hermitian degenerate quantum systems. In addition, we show that the non-Abelian geometric phases can be generated via adiabatic cyclic evolution of the four-level tripod quantum system driven by complex pulses. Notably, this phase is purely geometric, obtained via the single-loop multipulse approach, and is employed to realize a set of universal holonomic gates. Furthermore, we demonstrate that this geometric quantum gate is robust against systematic errors from small perturbations in pulse parameters.

We investigate the ${\mathrm{O}}^{+}$: ${\mathrm{C}}^{+}$: ${\mathrm{O}}^{+}$ fragmentation channel of ${\mathrm{CO}}_2^{3+}$ produced in slow collisions with ${\mathrm{Ar}}^{q+}$ projectiles ($4\le q\le 16$, velocities $\approx 0.3$ a.u). Using the native-frames method, we disentangle the sequential and concerted break-up processes and their corresponding kinetic energy release (KER) distributions. Ab initio potential energy curves of ${\mathrm{CO}}_2^{3+}$ are calculated and mapped to the KER spectra to identify the underlying electronic states involved in the fragmentation. While the sequential KER distributions remain nearly unchanged for across the projectile charge range, the concerted KER distributions exhibit pronounced but non-systematic variations with projectile charge. For low charge projectiles an additional feature at $\approx 15.5\mathrm{eV}$ is seen in the concerted KER distribution, which, in past works, has been attributed to sequential processes. The branching ratio shifts in favor of sequential break-up as $q$ increases, consistent with expectations from classical descriptions of electron capture. Departures from a monotonic increase with $q$ are observed for specific projectiles, indicating that, in addition to the projectile charge, its electronic structure must also be taken into account to understand capture induced fragmentation.

We measure the photon emission induced by energetic Ne and He ions transmitted through thin single crystalline Si foils. The emitted photons are detected with a delay line microchannel plate detector. Our measurements show that photon emission detectable from the rear surface of the membranes is multiple times more likely than photon emission from the front surface of the membrane. It can be deduced that photon emission from electronic deexcitation of the sample can only play a minor role, while the vast majority of detected photons are emitted by excited projectiles freely decaying behind the sample. Utilizing shadowing effects, we can show that a large proportion of excited projectiles travels several centimeters before decaying. The photons observed in the present approach are another accessible observable reporting on ultrafast processes during ion-matter interaction.

We theoretically investigate the impact of spectral leakage on harmonic intensity and phase by numerically solving the one-dimensional time-dependent Schrödinger equation (TDSE) for a model ${\mathrm{He}}^{+}$ ion. We show that spectral leakage is an intrinsic and ubiquitous issue in TDSE-based simulations of high-order harmonic generation. Its impact becomes increasingly pronounced with increasing laser peak intensity and wavelength. By analyzing the coupling terms in the dipole acceleration, we identify the physical origin of this effect as post-pulse oscillations of the dipole response. These oscillations give rise to artificial spectral leakage in the calculated harmonic spectra. By applying window functions to dipole acceleration in the time domain, the impact of spectral leakage can be efficiently reduced. However, most window functions cause a reduction in harmonic intensity and introduce errors in harmonic phase. Here, we demonstrate that several window functions are well suited for TDSE simulations, as they effectively mitigate spectral leakage while accurately regaining both the harmonic intensity and the phase.

We present a theoretical investigation of collective spontaneous emission of two identical two-level atoms side-coupled to a one-dimensional semi-infinite waveguide. The presence of the waveguide boundary naturally induces a feedback interference mechanism. Our results reveal that the collective spontaneous emission rate of the two atoms can be effectively suppressed or enhanced by this interference mechanism, depending on whether the atoms are initially prepared in a symmetric or antisymmetric state. Remarkably, the maximum collective emission rate can reach twice that observed in the case of an infinite waveguide, which arises from Purcell enhancement induced by the waveguide boundary. Further analysis of the two-atom collective dynamics reveals that, under appropriate conditions, an atom-photon bound state can be formed, leading to the confinement of emitted photons within the atom-atom or atom-boundary interspace. These results offer potential applications in quantum information processing based on waveguide quantum electrodynamics.

A quantum battery is considered as a one-dimensional spin-1/2 chain, which can be described by the $XY$ Heisenberg Hamiltonian. An external magnetic field is applied to charge the quantum battery. The results demonstrate that the counterrotating-wave terms play an important role in the performance of the quantum battery, including enhancing the maximum stored energy and charging power, and improving the charging precision. Some quasimomentum canonical modes play an important role in the charging process. The analytical expressions of the maximum stored energy, charging power, and charging precision are derived. Especially, for the pure counterrotating-wave terms, the “behavior” expressions can be employed to obtain the optimal values of the parameters. This study provides a potential way to design high stored energy and fast charging quantum batteries.

We formulate a geometric framework in which physical laws emerge from restricted access to microscopic information. Measurement constraints are modeled as a gauge symmetry acting on density operators, inducing a gauge-reduced space of physically distinguishable states. In the case of quantum thermodynamics, this construction leads to a gauge-invariant formulation in which the invariant entropy admits a stochastic description and satisfies a general detailed fluctuation theorem. From this result, we derive an integrated fluctuation theorem and a Clausius-like inequality that unifies the first and second laws in terms of invariant work and coherent heat. Entropy production is identified with the relative entropy between forward and backward probability measures on the gauge-reduced space of thermodynamic trajectories, revealing irreversibility as a geometric consequence of limited observability. The third law emerges as a singular zero-temperature limit in which thermodynamic orbits collapse and entropy production vanishes. Since the framework applies to arbitrary information constraints, it encompasses energy-based thermodynamics as a particular case of more general measurement scenarios.

The study of nonclassicality is essential to understand the quantum-to-classical transition in physical systems. Recently, a witness of nonclassicality has been proposed, linking the ability of a system (the mediator) to create quantum correlations between two quantum probes with its nonclassicality, intended as the existence of at least two noncommuting variables. Here we propose an inequality that quantitatively links the increase in quantum correlations between the probes to a function of the noncommutativity of the mediator's observables. We test the inequality for various degrees of nonclassicality of the mediator, from fully quantum to fully classical. This quantum-to-classical transition is simulated via a phase-flip channel applied to the mediator, inducing an effective reduction of the noncommutativity of its variables. Our results provide a general framework for witnessing nonclassicality, assessing the nonclassicality of a system via its intrinsic properties, independently of the specific chosen interaction dynamics.