Digitizing an adiabatic evolution is a strategy able to combine the good performance of gate-based quantum processors with the advantages of adiabatic algorithms, thus providing a hybrid model for efficient quantum information processing. In this work we develop validity conditions for high-fidelity digital adiabatic tasks. To this end, we assume a digitizing process based on the Suzuki-Trotter decomposition, which allows us to introduce a digitized adiabatic theorem. As a consequence of this theorem, we show that the performance of such a hybrid model is limited by the fundamental constraints on the adiabatic theorem validity, even in ideal quantum processors. We argue how our approach predicts the existence of intrinsic nonadiabatic errors reported by Barends et al. [Nature (London) 534, 222 (2016)] through an empirical study of digital annealing. In addition, our approach allows us to explain the existence of a scaling of the number of Suzuki-Trotter blocks for the optimal digital circuit with respect to the optimal adiabatic total evolution time, as reported by Mbeng et al. [Phys. Rev. B 100, 224201 (2019)] through robust numerical analysis of digital annealing. We illustrate our results through two examples of digitized adiabatic algorithms, namely, the two-qubit exact-cover problem and the three-qubit adiabatic factorization of the number 21.

Nonadiabatic holonomic quantum computation (NHQC) has shown promise in mitigating control errors, but requires additional methods to further eliminate the effects of decoherence errors. Existing NHQC schemes capable of combating both types of errors often necessitate auxiliary qubits, thereby increasing qubit resource consumption. This paper proposes nonadiabatic holonomic quantum gates based on a three-level dressed state space, which have inherent insensitivity to decoherence and eliminate the need for auxiliary qubits. Through numerical simulations, the presented gates within the dressed-state framework display enhanced resistance to both control field errors and decoherence errors. Moreover, we discuss the implementation of our approach on the nitrogen-vacancy center in diamond, demonstrating its feasibility and potential for geometric quantum computation.

Differential elastic electron scattering cross sections of trichlorofluoromethane ($\mathrm{C}{\mathrm{Cl}}_3\mathrm{F}$) were measured over a broad energy range spanning 30 to 800 eV in the angular range of 20° to 150°. The experimental results were compared with calculations using the IAM-SCAR+I model. Satisfactory agreements between both data sets were found for electron energies above 200 eV within experimental uncertainties, whereas significant deviations of up to 100% were observed at electron energies below 60 eV. In addition to the measurements of differential elastic-scattering cross sections, total inelastic-scattering cross sections of $\mathrm{C}{\mathrm{Cl}}_3\mathrm{F}$ were calculated using the spherical complex optical potential model. These calculations closely match experimental total ionization cross sections available in the literature for energies below 50 eV. The sum of the experimental total elastic-scattering cross sections and the theoretical total inelastic-scattering cross sections aligns very well with the total electron scattering cross sections of $\mathrm{C}{\mathrm{Cl}}_3\mathrm{F}$ measured by other groups across the entire energy range (30 to 800 eV), demonstrating the consistency among these three cross sections.

Rydberg state excitation of atoms and molecules induced by femtosecond laser fields has attracted considerable attention due to its critical role in processes such as neutral atom acceleration and near-threshold harmonic generation. In this study, we experimentally investigate the dissociative Rydberg state excitation of ${\mathrm{H}}_2$ and CO molecules induced by a femtosecond laser pulse centered at 400 nm. Coincidence measurements are conducted for the resulting photoelectrons, ionic, and Rydberg fragments. Electron-nuclear correlations are observed by analyzing the joint electron-nuclear energy spectrum, which shows multiple diagonal lines spaced by photon energy, indicating that the observed dissociative Rydberg state excitations are primarily accessed via multiphoton resonance excitation. The excitation pathways of ${\mathrm{H}}_2$ and CO molecules are explored in detail. Interestingly, the dissociative Rydberg state excitations of ${\mathrm{H}}_2$ and CO molecules exhibit distinct behavior compared to their respective dissociative double ionization channels. This notable difference is attributed to electron-nuclear correlations in photon energy sharing and is further explained through an analysis of the relevant potential energy curves. Our findings contribute to a deeper understanding of the dissociative Rydberg state excitation of molecules in femtosecond laser fields.

By means of a diffusion Monte Carlo technique, we study one-dimensional unbalanced mixtures of fermionic ytterbium atoms (${}^{173}\mathrm{Yb}$ and ${}^{171}\mathrm{Yb}$). This means clusters in which the total number of ${}^{173}\mathrm{Yb}$ particles is different from the sum of all the atoms belonging to the ${}^{171}\mathrm{Yb}$ isotope. Our aim will be to check the possibility of having self-bound arrangements beyond the balanced compositions reported in previous literature rather than exploring all the situations in which that could be possible. In that vein, we focused mainly on mixtures in which the atoms belonging to one isotope are spin polarized, while the spins of the particles in the other isotope are evenly distributed in two sets. What we found was that, even though self-bound droplets are possible for different compositions, the most stable ones are clusters with a slight excess of attractively interacting ${}^{171}\mathrm{Yb}$ particles with different spins with respect to the number of spin-polarized ${}^{173}\mathrm{Yb}$ atoms. Clusters in which the number of repulsively interacting unequal-spin ${}^{173}\mathrm{Yb}$ atoms are in excess with respect to the spin-polarized ${}^{171}\mathrm{Yb}$ particles have a very narrow stability range.

We present and discuss a type of nonlinear diffraction wave (NLDW) induced by the strong cross-phase-modulation (XPM) effect between the femtosecond pump wave (FW) and its second-harmonic wave (SHW), observed experimentally in periodically poled lithium niobate (PPLN) nonlinear gratings. We develop a modified femtosecond pulse propagation model that describes the evolution of FW and SHW under the participation of the XPM effect. This model is numerically solved using the split-step Fourier transformation method, and the results successfully explain the experimentally observed XPM-NLDW phenomenon. The discovery and analysis of XPM-NLDW will provide a deeper insight into the synergic nonlinear effects arising from the interaction of a femtosecond laser pulse with the PPLN crystal and stimulate the exploration of many other unknown phenomena existing in this regime of nonlinear optics.

We develop a theoretical framework to describe how zero-photon detection may be utilized to enhance optomechanical laser cooling via the anti-Stokes interaction and, somewhat surprisingly, enable cooling via the Stokes interaction commonly associated with heating. Our description includes both pulsed and continuous measurements as well as optical detection efficiency and open-system dynamics. For both cases, we discuss how the cooling depends on the system parameters such as detection efficiency and optomechanical cooperativity, and we study the continuous-measurement-induced dynamics, contrasting with single-photon-detection events. For the Stokes case, we explore the interplay between cooling and heating via optomechanical parametric amplification, and we find the minimum efficiency required to cool a mechanical oscillator via zero-photon detection. This work serves as a companion article to our recent experiment [E. A. Cryer-Jenkins et al., Phys. Rev. Lett. 134, 073601 (2025)], which demonstrated enhanced laser cooling of a mechanical oscillator via zero-photon detection on the anti-Stokes signal. The cooling techniques developed here can be applied to a wide range of areas including nonclassical state preparation, quantum thermodynamics, and avoiding the often unwanted heating effects of parametric amplification.

Recently published works have shown that the multiple temporal compression (MTC) method is a more efficient approach for generation of multiple bright solitons in stacked waveguides, in comparison to the traditional soliton-fission technique. In the present paper, we performed systematic computer simulations of the appropriate generalized nonlinear Schrödinger equation to extend the MTC method for generation of dark solitons through controlled interactions of bright solitons in waveguiding systems with the normal group-velocity dispersion. Further, the generated dark solitons are demonstrated to be useful for accurately governing the dynamics of bright solitons generation in complex systems based on stacked waveguides. Therefore, we report scenarios that provide mitigation or switching of the energy transfer during bright-soliton collisions, along with the ability of the cascaded MTC processes to increase the number of generated solitons. These results underscore the potential of the MTC as a versatile method for managing the propagation dynamics of multiple temporal bright and dark solitons produced by a single input pulse, with possible applications for the design of optical devices.

Liquid crystals are well-known for their nonlinear orientational optical properties, in particular self-focusing as a result of optically induced reorientation magnitude, which relies on dynamic phase spatial modulation. Here we report on optical self-focusing of a purely geometric nature. The effect is demonstrated using a uniformly oriented liquid crystal half-wave plate illuminated by a fully polarized collimated beam. The effect is shown to be driven by spin angular momentum deposition and its magnitude scales with the amount of spin angular momentum carried by the incident beam. The experimental and modeling results encompass both material and wave aspects as well as the optomechanical process that drives the phenomenon, thus enriching the nonlinear spin-orbit photonics toolbox.

We investigate steady-state entanglement and steering in a three-dimensional cavity magnomechanics system. From the system's equations of motion, we derive the linearized Lyapunov equation for steady states, introduce logarithmic negativity to quantify entanglement, and apply a quantization method for Gaussian states with continuous variables to measure steering. Numerical simulations reveal that steady-state entanglement and steering can be established between various system components—such as the two cavity modes, the cavity mode and magnon mode, and the cavity mode and phonon mode—by selecting experimentally feasible detunings, dissipation rates, and coupling rates. We develop a three-dimensional cross-cavity model to study bipartite and tripartite entanglement and explore parameter adjustments to achieve both one-way and two-way steering. Additionally, we confirm the system's strong robustness to temperature variations. This work provides a platform for studying entanglement and steering beyond squeezed optical drives and has potential applications in quantum information processing and quantum sensing.

The giant-atom topological-waveguide-QED systems have recently emerged as a promising platform for manipulating light-matter interactions. The combination of the multiple-point couplings and topological phase effect could lead to rich physical phenomena and effects. Here, we study single-photon scattering in a Su-Schrieffer-Heeger (SSH) waveguide coupled to either one or two two-level giant atoms. We assume that each giant atom is coupled to the waveguide via two coupling points and hence there exist four and sixteen coupling configurations for the single-giant-atom case and two-giant-atom separate coupling case, respectively. By solving the single-photon scattering problem in the real space, we obtain the exact expressions of the single-photon scattering amplitudes. It is found that a single photon in the SSH waveguide can be completely reflected or transmitted by choosing proper coupling configurations, coupling-point distances, atomic resonance frequency, and dimerization parameter. In addition, under proper parameter conditions, the scattering spectra are periodically modulated by the coupling-point distances. We also find that the collective behavior of the two giant atoms can be adjusted by quantum interference effect and topological effect and that the single-photon scattering spectra can exhibit the Lorentzian, super-Gaussian, electromagnetically induced transparencylike, and asymmetric Fano line shapes for some coupling configurations. This work will inspire the development of controllable single-photon devices based on the giant-atom topological-waveguide-QED systems.

Waveguide quantum electrodynamics (wQED) with giant atoms provides a distinctive opportunity to quantum simulation of many-body physics through its unique decoherence-free interactions. This study presents a theoretical framework for simulating the diagonal Aubry-André-Harper (AAH) model in the context of giant-atom wQED. The proposed scheme employs photonic modes in the waveguide to not only mediate interactions between atoms but also to detect the energy spectrum of the atom array. To illustrate the effectiveness of this approach, we present a simulation of the Hofstadter butterfly spectrum with high precision. Furthermore, for an incommensurate AAH atomic chain, we demonstrate that the photon transmission spectrum can accurately distinguish between the many-body localized phase and the extended phase. The method presented here is also applicable to the simulation of other types of 1D atomic chains based on giant-atom wQED.

Understanding how macroscopic systems exhibit irreversible thermal behavior has been a longstanding challenge, first brought to prominence by Boltzmann. Recent advances have established rigorous conditions for isolated quantum systems to equilibrate to a maximum entropy state, contingent upon weak assumptions. These theorems, while powerful, applied for a sudden quench. However, natural processes involve finite-time perturbations or quenches, which raises a crucial question: Can these systems still equilibrate under more realistic, finite-time dynamics? In this work, we extend the established results to account for finite-time quenches, demonstrating that, even under finite-time perturbations, the system will equilibrate provided it populates many significant energy levels. While the mathematical proof is more intricate than in the instantaneous case, the physical conclusion remains the same: sufficient perturbation leads to equilibration. Our results provide a broader and more physically realistic framework for understanding thermalization in isolated quantum systems.

In this paper we study localized states in a monitored evolution on a finite graph and how they are distinguished from the delocalized states in terms of the transition probabilities and the mean transition times. Monitoring is performed by repeated projective measurements with respect to a single quantum state. Our constructive approach is based on a mapping from a set of energy levels and an eigenvector basis onto the monitored evolution matrix. The eigenvalues of the latter are distributed over the complex unit disk and the corresponding transition probabilities decay quickly in the quantum Zeno regime at frequent measurements. A localized basis favors the return to the initial state, while a delocalized basis favors transitions between different states. This provides a practical criterion to identify localized states by measuring the mean transition time.

The lower bound of estimated precision for a coherent parameter unitarily encoded in closed systems has been obtained, and such a lower bound is inversely proportional to the fluctuation of the encoding operator. In this paper, we first derive some general results regarding the lower bound of estimated precision for a dissipative parameter, which is nonunitarily encoded in open systems, by combining the law of error propagation and the non-Hermitian linear response theory. This lower bound is related to the correlation of the encoding dissipative operator and the evolution time. We next demonstrate the utility of our general results by considering three different kinds of nonunitary encoding processes, including particle loss, relaxation, and dephasing. We finally compare the lower bound with the quantum Fisher information obtained by tomography and find they are consistent in the regime where the non-Hermitian linear response applies. This lower bound can guide us to find the optimal initial states and detecting operators to significantly simplify the measurement process.

Among the surprising features of quantum measurements, the problem of distinguishing and antidistinguishing general quantum measurements is fundamentally appealing. Unlike classical systems, quantum theory offers entangled states and peculiar state update rule of the postmeasurement state, which gives rise to four distinct scenarios for distinguishing (and antidistinguishing) quantum measurements: (i) probing single systems and without access to the postmeasurement states, (ii) probing entangled systems and without access to the postmeasurement states, (iii) probing single systems with access to the postmeasurement states, and (iv) probing entangled systems with access to the postmeasurement states. In these scenarios, we consider the probability of distinguishing (and antidistinguishing) quantum measurements sampled from a given set in the single-shot regime. For some scenarios, we provide the analytical expressions of distinguishability (and antidistinguishability) for qubit projective measurements. We show that the distinguishability of any pair of qubit projective measurements in scenario (iii) is always greater than its values in scenario (ii). Interestingly, we find certain pairs of qubit nonprojective measurements for which the optimal distinguishability in scenario (ii) is achieved using a nonmaximally entangled state. It turns out that, for any set of measurements, distinguishability (and antidistinguishability) in scenario (i) is always less than or equal to in any other scenario, while it reaches its highest possible value in scenario (iv). We establish that the relations form a strict hierarchy, and there is no hierarchical relation between scenarios (ii) and (iii). In particular, we introduce different variants of the well-known “trine” qubit measurement to construct pairs (and triples) of qubit quantum measurements such that they are perfectly distinguishable (and antidistinguishable) in scenario (ii) but not in scenario (iii) and vice versa. Additionally, we present qubit measurements that are perfectly distinguishable (and antidistinguishable) in scenario (iv) but not in any other scenario.

Using quantum measurements to extract information from states is a matter of routine in quantum science and technologies. A recent work [Phys. Rev. Lett. 133, 040202 (2024)] reported the finding that the symmetric structures of a state can be harnessed to dramatically reduce the sample complexity in extracting information from the state. However, due to the presence of noise, the actual state at hand is often corrupted, making its symmetric structures distorted before the execution of quantum measurements. Here, using the methodology of quantum metrology, we identify the optimal measurement that can retrieve maximum information of a symmetric state from its corrupted copies. We show that this measurement can be found by solving a semidefinite program in generic cases and can be explicitly determined for a large class of noise models covariant under the symmetry group in question. The results of this study nicely complement the recent work by providing a method to optimally utilize the distorted symmetric structures of corrupted states for information retrieval.