We establish a comprehensive theoretical framework for coherent quantum speed limits (QSLs), deriving fundamental bounds on the rate of quantum evolution that explicitly isolate the contribution of quantum coherence. By applying Hölder's inequality for matrix norms to the Liouville–von Neumann equation, we construct two infinite families of QSLs for general unitary dynamics. These bounds are characterized by coherence measures based on Schatten $p$-norms and Hellinger distance, respectively, defined with respect to the instantaneous energy eigenbasis. Unlike traditional Mandelstam-Tamm bounds, our approach disentangles the quantum state's coherence structure from the Hamiltonian's energy scale. Using the Landau-Zener model accelerated by shortcuts to adiabaticity, we demonstrate that coherence functions as a critical kinematic resource: achieving faster evolution entails maintaining a state with high coherence relative to the instantaneous basis. Our results provide a resource-theoretic perspective on time-energy uncertainty, offering insights into the fundamental limits of quantum control and information processing.

Arbitrary manipulation of quantum states is a key challenge for quantum information processing in qubit-boson systems. Here, we demonstrate that universal quantum state control can be achieved by simultaneously inducing both rotations and displacements in phase space. An amplified gear effect with linear coupling and squeezing drive is introduced to precisely guide phase-space trajectories, resulting in multiple in situ acceleration pathways for control operations and a significant reduction in dissipative effects. By utilizing the characteristics of phase-space trajectories, we have further developed two general drive mechanisms and proposed a flexible optimization framework that can incorporate various pulse designs to improve robustness against parameter fluctuations. Our findings open alternative avenues for exploring arbitrary quantum state spaces, advancing quantum metrology and error correction in qubit-boson systems.

Entanglement is a key feature in many quantum technologies, including secure communication protocols and quantum computing. However, detecting it in mixed quantum states remains a challenging task. While the positive partial transposition (PPT) and computable cross-norm and realignment criteria are well-established tools for entanglement detection in general, and are especially effective in Bell-diagonal states, their connection to the underlying group structure of this state family has not been fully explored. In this work, we analyze the PPT and realignment criteria for Bell-diagonal states from a group-theoretic point of view. Our results demonstrate that the group structure of Bell-diagonal states provides a clear framework for analyzing and computing these two entanglement-detection criteria, thereby highlighting the connection between entanglement and group structure. This unified perspective offers insights into the mathematical and physical properties of entanglement in structured quantum systems and ties the PPT and realignment criteria for Bell-diagonal states to experimental procedures.

Using a two-step optical excitation scheme, we investigated the symmetric transition spectroscopy in rubidium Rydberg microwave electric-field detection. The study employed two microwave sources to achieve cascade coupling of the $78S_{1/2}\to 78P_{3/2}\to 79S_{1/2}$ transitions, with optical excitation states corresponding to $78S_{1/2}$ and $79S_{1/2}$, respectively. Due to the selection-rule-determined symmetry of the doubly microwave-coupled Rydberg levels, we found they maintain excellent symmetry for microwave field detection, despite the fact that the cascade transitions extend in opposite directions, one toward higher energies and the other toward lower energies. With nearly equal electric dipole moments for adjacent microwave transitions, this symmetric system enables microwave field measurements at wider transition frequencies with comparable sensitivity, also allowing dual-frequency channel-hopping measurements with equal gain, particularly advantageous for a simplified frequency-agile detection system, even at the same optical excitation.

The question of whether quantum tunneling imposes a finite time delay is a fundamental and contested issue, prominently debated in strong-field atomic ionization. Here we extend this debate to the molecular domain by investigating the tunneling dissociation time of the proton in ${\mathrm{H}}_2{}^{+}$. Through numerical solution of a two-level time-dependent Schrödinger equation and analysis via the backpropagation method, we discover a significant and tunable delay in the proton's emergence. Crucially, we demonstrate that this delay is not intrinsic but is primarily governed by the relative timescales of two motions. The delay's sign is determined by the competition between the laser cycle and the molecular rotational period: It is positive when the laser cycle is shorter than half the rotational period and negative in the opposite regime. Our work underlines the importance of tunneling dissociation delay by revealing its physical origin, establishing laser-driven molecular rotation as a powerful control knob and tunneling delay as a real-time probe of ultrafast rotational dynamics.

We present an analytical study of a two-dimensional photonic lattice that simultaneously incorporates fractional coupling, parity-time ($\mathcal{PT}$) symmetry, and nonreciprocal interactions. The system features a checkerboard arrangement of alternating gain and loss sites, with asymmetric coupling amplitudes between sublattices. The dynamics are governed by a fractional discrete Laplacian as introduced by [O. Ciaurri et al., arXiv:1507.04986; O. Ciaurri et al., Adv. Math. 330, 688 (2018)], capturing long-range interactions. We derive a closed-form dispersion relation that explicitly depends on the product of forward and backward coupling strengths, as well as the fractional exponent. Our analysis reveals that increasing nonreciprocity or fractionality can significantly enhance the stability of the $\mathcal{PT}$-symmetric phase, pushing the threshold for $\mathcal{PT}$ breaking to higher gain or loss values. We also compute the participation ratio analytically, showing that nonreciprocity reduces mode delocalization. These results suggest a mechanism for tuning light stability and localization in photonic systems, with potential applications in the design of nonreciprocal and robust optical devices.

We study the phenomenon of quantum backflow in tight-binding systems with complex couplings, considering different boundary conditions and lattice sizes. Backflow is an intrinsically nonclassical effect where the density flux associated with a particle described by the superposition of wave functions with, say, positive momentum, acquires negative values. We calculate the superposition of positive-momentum states that gives rise to the strongest backflow in the system. We also evaluate the bounds on the total amount of probability that flows in the opposite direction of the particle's momentum.

Variational quantum algorithms (VQAs) have emerged as a leading paradigm that extracts practical computation from near-term intermediate-scale quantum devices, enabling advances in quantum chemistry simulations, combinatorial optimization, and quantum machine learning. However, the performance of VQAs is highly sensitive to the design of the ansatzes. To be effective, ansatzes must be expressive enough to capture target states but shallow enough to be trainable. We propose a genetic algorithm-inspired framework for designing ansatzes that achieve high expressibility while maintaining shallow depth and low parameter count. Our approach evolves ansatzes through mutation and selection based on an expressibility metric. The circuit generated by our framework consistently demonstrates high expressibility at any target depth and performs comparably to traditional ansatz design approaches. In this work, we present a problem-agnostic, scalable solution for ansatz design, producing expressive, low-depth circuits that need to be designed only once and can serve a wide range of applications.

This study explores the excitation and ionization of an atomic beam as a pathway to optimize focused ion beams (FIBs) for high-precision applications. Leveraging the unique advantages of Rydberg excitation followed by field ionization—specifically its ability to minimize velocity and position dispersions—we present a method to generate ion beams with good performance at low energies. A custom lua program, integrated into the simion simulation platform, models the intricate processes of particle distributions, laser excitation, and Rydberg ionization. This integrated approach incorporates essential parameters such as excitation and ionization rates, Stark shifts, Doppler effects, and electric fields, enabling a detailed analysis of ion-beam properties. Our simulations demonstrate the influence of critical factors such as the chosen Rydberg state, ionization region characteristics, and velocity dispersions on the final ion-beam quality. By optimizing these parameters, we achieve significant reduction of the axial energy spread and the longitudinal extent of the ionization region. This framework bridges theoretical modeling and experimental validation, offering a comprehensive toolkit for the development of next-generation ion sources and advancing FIB technologies across various scientific domains.

We compute the bound and resonant states of hydrogen-like muonic ions ($\mu \mu p$, $\mu \mu d$, $\mu \mu t$), three-body muonic molecular ions ($pp\mu$, $pd\mu$, $pt\mu$, $dd\mu$, $dt\mu$, $tt\mu$), and four-body double-muonic hydrogen molecules ($\mu \mu pp,\mu \mu dd,\mu \mu tt$) using an extended stochastic variational method combined with complex scaling. The approach provides a unified treatment of bound and quasibound states and achieves an energy accuracy better than $0.1\mathrm{eV}$ across all systems studied. Complete spectra below the corresponding $n=2$ atomic thresholds are obtained, including several previously unresolved shallow resonances in both three- and four-body sectors.

$L$-subshell x-ray production cross sections induced by electron impact were determined for La, Ce, Pr, and Nd in the incidence energy range of 5.7–25 keV. The experiments were carried out by irradiating thick samples in a field-emission scanning electron microscope equipped with an energy-dispersive spectrometer. The x-ray spectra were then analyzed using a previously developed optimization software, which accounts for bulk effects through a model for the ionization depth distribution function. The x-ray production cross sections obtained were compared with theoretical predictions, using different relaxation data reported in the literature. A good agreement is obtained for the $L_2$ and $L_3$ subshells when the distorted-wave Born approximation model is used along with the relaxation parameters reported by Perkins et al. [Technical Report UCRL-50400, Vol. 30, Lawrence Livermore National Laboratory, Livermore, CA, 1991]. However, for the $L_1$ subshell, the theoretical curves systematically underestimate the measurements in the high-energy region, evincing the need for further determinations of the fluorescence yield coefficient for this subshell.

We employ an all-particle multireference Fock-space relativistic coupled-cluster (FSRCC) theory to study the $5s^2{}^1{S}_0-5s5p{}^{3}P_0^o$ clock transition in both fermionic and bosonic isotopes of Sr. We compute the excitation energies for several low-lying states, E1 and M1 transition amplitudes, hyperfine reduced matrix elements, and isotope shifts using FSRCC theory. Further, using our results on E1, M1, and hyperfine structure (HFS) reduced matrix elements, we calculate the lifetime of the metastable clock states for ${}^{87}\mathrm{Sr}$ and ${}^{88}\mathrm{Sr}$. Furthermore, we employ perturbed relativistic coupled-cluster (PRCC) theory to compute the ground state electric dipole polarizability of Sr. To improve the accuracy of our results, we incorporate the corrections from the relativistic and quantum electrodynamical (QED) effects, and perturbative triples to all our calculations. Moreover, we employ large bases to ensure the convergence of the computed properties. Our computed excitation energies are in good agreement with the experimental data for low-lying excited states. Our results for E1, M1, and HFS reduced matrix elements are within the experimental error bars, however, with slight difference from the previous calculations due to more accurate treatment of electron correlations in FSRCC theory. Our computed lifetime of the clock state for ${}^{87}\mathrm{Sr}$ is within the error bars of the available experimental results, whereas for ${}^{88}\mathrm{Sr}$ it is an order of magnitude smaller than the only available calculation [R. Santra et al., Phys. Rev. A 69, 042510 (2004)] using model potential. Our PRCC result for the ground state polarizability is in good agreement with the experiment, and smaller than previous calculations. Our results on isotope shift factors are consistent with available experimental results for intercombination transitions. From detailed analysis of the results, we find that the corrections from the Breit interaction, QED effects, and perturbative triples are crucial to get accurate clock transition properties in Sr. Moreover, valence-valence electron correlation is important to get accurate energies and properties of Sr.

Laser-induced tunneling ionization underlies a broad class of strong-field phenomena in attosecond physics. A key quantity in this process is the transverse tunneling exit position, which influences both the phase of the continuum wave packet and the subsequent electron dynamics. In this work, we show that the intracycle interference between directly ionized electron wave packets provides a sensitive probe of the transverse tunneling exit position in molecules. By numerically solving the time-dependent Schrödinger equation for the aligned ${\mathrm{N}}_2$ molecule, we observe a pronounced, alignment-dependent asymmetry in the intracycle interference pattern of the photoelectron momentum distribution. Analysis based on adiabatic theory reveals that this asymmetry originates from the transverse shift of tunneling exit position. The exit position is reconstructed from the interference patterns with picometer-scale precision and is consistent with the result obtained from the electron density distribution of the molecular orbital.

Non-Hermitian cavity magnomechanics, which incorporates the magnon-photon and magnon-phonon interactions simultaneously, enables rich physical phenomena, including exceptional-point-enhanced sensing, and offers pathways toward topological transitions and nonreciprocal quantum transformation. These interactions exert a pivotal influence on the optical response of a weak probe field and pave the way for novel applications in quantum technologies. In this work we consider a yttrium-iron-garnet (YIG) sphere coupled to a microwave cavity. The magnon mode of the YIG sphere is directly excited through microwave field coupling, whereas the cavity mode is probed via a weak-field interrogation scheme. The direct interaction of a traveling field with the magnon mode induces gain in the system, thereby establishing non-Hermitian dynamics. The parity-time ($\mathcal{PT}$)-symmetric behavior of a hybrid non-Hermitian cavity magnomechanical system is designed and investigated. Eigenvalue spectrum analysis demonstrates that a third-order exceptional point (${\mathrm{EP}}_3$) emerges under tunable effective magnon-photon coupling when the traveling field is oriented at an angle of $\pi /2$ relative to the cavity's $x$ axis. The photonic spin Hall effect (PSHE) in a reflected probe field is subsequently examined in such a system. Under balanced gain and loss conditions and in the presence of effective magnon-phonon coupling, tunable effective magnon-photon coupling enables coherent control of the PSHE across the broken $\mathcal{PT}$-symmetric phase, at the ${\mathrm{EP}}_3$ and in the $\mathcal{PT}$-symmetric phase. Investigation reveals that the PSHE can be significantly enhanced or suppressed via effective magnon-photon coupling. The influence of intracavity length on the PSHE is further explored, providing an additional parameter for fine-tuning the transverse shift. These findings establish a direct correspondence between the PSHE and the underlying non-Hermitian eigenvalue spectrum. They further demonstrate that non-Hermitian cavity magnomechanical platforms provide a pathway to tunable photonic functionalities, with immediate prospects for quantum switching and precision sensing.

We consider the phenomenon of resonant radiation emitted by solitonlike wave packets in quadratic crystals and demonstrate the key role of the group-velocity dispersions, at the fundamental frequency and second harmonic, respectively, without any contribution from higher-order dispersions. In particular our approach allows us to predict a mechanism of primary resonance around the fundamental frequency component. Our theoretically predicted resonances are found to be in excellent agreement with numerical simulation of the propagation in a wide range of parameter values.

We investigate superradiant quantum phase transitions in a Dicke trimer model consisting of two types of hoppings, i.e., photon hoppings and atom hoppings. In the superradiant regime, the system can exist in two distinct phases: normal and frustrated superradiant phases, which are governed by both types of hoppings. Particularly, the interplay between these hoppings gives rise to interesting effects, such as triggering superradiance with much lower coupling strengths when both hoppings exhibit the same tendency. In contrast, with opposite tendencies, the competition between hoppings leads to a first-order phase transition between two different superradiant phases with translational symmetry broken. These findings enable the system to undergo a sequence of transitions across three phases by changing the coupling strength. Our work provides deep insights into competing interactions and quantum phase transitions in multicavity systems with geometric structures.

We propose the concept of amplified quantum nondemolition measurement of a quadrature amplitude of optical field. Similarly to standard quantum nondemolition measurement, it does not introduce a backaction noise into the measured quadrature. At the same time, it provides a noiseless amplification of this quadrature. We propose a possible practical implementation of this concept based on the nondegenerate optical parametric amplifier. We show that, assuming demanding but realistic values of the optical squeezing and losses, a sensitivity several times better than the standard quantum limit can be achieved.

Identifying the precise moment when a quantum channel undergoes a change is a fundamental problem in quantum information theory. We study how accurately one can determine the time at which a channel transitions to another. We investigate the quantum limit of the average success probability in unambiguous discrimination, in which errors are completely avoided by allowing inconclusive results with a certain probability. This problem can be viewed as a quantum process discrimination task, where the process consists of a sequence of quantum channels; however, obtaining analytical solutions for quantum process discrimination is generally extremely challenging. In this paper, we propose a method to derive lower and upper bounds on the maximum average success probability in unambiguous discrimination. In particular, when the channels before and after the change are unitary, we show that the maximum average success probability can be analytically expressed in terms of the length of the channel sequence and the discrimination limits for the two channels.