Coulomb corrections to the conventional strong-field approximation (SFA) theory (the lowest-order term of the $S$-matrix expansion) for nonsequential double ionization are considered by calculating higher-order terms of the $S$-matrix expansion that take into account multiple Coulomb interactions of the first-ionized electron with the ionic core while the second electron is still in its ground state. For a Ne atom in a linearly polarized laser field, the distribution of the components of the final electron momenta parallel to the field polarization is presented based on the $S$-matrix expansion up to the sixth order, which involves up to four Coulomb interactions between the parent ion and the first-ionized electron before it collides with the second bound electron. The calculated electron momentum distribution is significantly modified compared with the outcome of the conventional SFA. It is consistent with experimental results and a semiclassical simulation that fully takes into account the effect of the Coulomb potential on the first-tunneled electron. Our analysis shows that multiple Coulomb interactions of the first-ionized electron with the ionic core significantly modify the distribution of the final momenta by favoring larger and nearly equal momenta, in line with experimental results and semiclassical simulations.

Through the examination of energy level crossings among the fine-structure manifolds of the $(n=4-5)d^6$ and $(n=4-5)d^8$ configurations in a number of highly charged ions (HCIs), we identify forbidden transitions that can be suitable for making single-ion-based optical clocks. These clock transitions exhibit quality factors ranging between ${10}^{16}$ and ${10}^{18}$, which are larger than most of the previously proposed HCI clock candidates. They also show high sensitivity to the temporal variation of the fine-structure constant and violation of the local Lorentz symmetry invariance. Detailed assessments of the Zeeman, Stark, black-body radiation, and electric quadrupole shifts associated with the above-proposed clock transitions are conducted to establish a typical order of magnitudes of their fractional uncertainties due to the systematic effects, which are found to be at the ${10}^{-19}$ level.

Photoionization through single-photon absorption by two synchronous, linearly chirped, oppositely circularly polarized, attosecond pulses is known [N. J. Strandquist, Jr., and J. M. Ngoko Djiokap, Phys. Rev. A 106, 043110 (2022)] to create reversible spiral patterns in the momentum distribution of the ejected electron when the two pulses have equal but opposite chirp rates. Here we extend this study by demonstrating how this reversible spiral pattern can be controlled by varying the chirp rates as well as the time delay between the pulses. For two synchronous pulses, we find that using arbitrary chirp rates for each attosecond pulse can create a reversible spiral pattern identical to the one produced by equal but opposite chirp rates when adjusting the carrier-envelope phase difference. By adding a nonzero time delay between the two pulses, we show that the reversible spiral pattern can be controlled by using the accumulated linear Ramsey spectral phase to manipulate the chirp-induced linear or quadratic spectral phases of the photoelectron. Possible applications of such exquisite manipulation of both linear and quadratic spectral phases include manipulation of the photoelectron wave packet group delay.

The diffusion and localization of particles in lattice potentials are essential topics in the study of quantum states of matter. As two distinct mechanisms, flat-band localization (FBL) caused by destructive interference and Anderson localization (AL) by strong disorder can both prohibit particle transport and lead to an insulator state. The realization and characterization of the two different insulating phases necessitate the ability to shape the lattice potential and measure particle transport at the single-site level. By using spatial momentum as an artificial dimension, ultracold quantum gas in a momentum lattice provides an ideal platform to achieve single-site resolution. Here, we demonstrate that the transition from flat-band localization to Anderson localization can be realized and quantitatively studied in a Bose-Einstein condensate in a one-dimensional momentum lattice. The flat-band localization is realized in a one-dimensional Tasaki model, while the transition to Anderson localization is achieved by imposing a strong enough disorder potential and is characterized by stark features of particle transport from an initial state in an experimentally realistic finite-size system. Submitted in parallel with Zeng et al., this article provides experimental details on the realization of an effective model and preparation of the initial state as well as a theoretical study of the transition with experimental parameters.

A recent experiment has demonstrated the formation of a supersonic region in a convergent two-dimensional flow of a condensate of cesium atoms. The theoretical description of this effect has made use of stationary solutions to the Gross-Pitaevskii equation with a three-body dissipative term. Here we further develop that description, focusing on a different stationary solution, linear stability analysis, and properties of the time-dependent “resistive” state.

Motivated by recent cold-atom realizations of matter-wave waveguide QED, we study simple fermionic impurity models and discuss fermionic analogs of several paradigmatic phenomena in quantum optics, including formation of nontrivial bound states, (matter-wave) emission dynamics, and collective dissipation. For a single impurity, we highlight interesting ground-state features, focusing in particular on real-space signatures of an emergent length scale associated with an impurity screening cloud. We also present non-Markovian many-body effects in the quench dynamics of single- and multiple-impurity systems, including fractional decay around the Fermi level and multiexcitation population trapping due to bound states in the continuum.

Here we investigate the internal sublattice symmetry, and thus the enriched topological classification of bosonic Bogoliubov excitations of thermodynamically stable free-boson systems with nonvanishing particle-number-nonconserving terms. Specifically, we show that such systems well described by the bosonic Bogoliubov–de Gennes Hamiltonian can be in general reduced to particle-number-conserving (single-particle) ones. Building upon this observation, the sublattice symmetry is uncovered with respect to an excitation energy, which is usually hidden in the bosonic Bogoliubov–de Gennes Hamiltonian. Thus, we obtain an additional topological class, i.e., class AIII, which enriches the framework for the topological threefold way of free-boson systems. Moreover, a construction is proposed to show a category of systems respecting such a symmetry. For illustration, we resort to a one-dimensional prototypical model to demonstrate the topological excitation characterized by a winding number or symplectic polarization. By introducing the correlation function, we present an approach to measure the topological invariant. In addition, the edge excitation together with its robustness to symmetry-preserving disorders is also discussed.

The dynamics of a resonant, free-running ring laser, in the common case of a fast relaxation of atomic polarization, is unexpectedly highly singular. As shown in Politi et al. [Phys. Rev. Res. 5, 023059 (2023)], this is due to the closeness to a pure Hamiltonian dynamics ruled by a nonlinear wave equation, herein named the Klein-Gordon-Toda model. In this paper, we derive a quasi-Hamiltonian model which allows describing realistic systems. In particular, we identify two nearly conserved, energy-like quantities, which “naturally” exhibit an ultraslow dynamics confirmed and highlighted by numerical simulations. A minimal version of the quasi-Hamiltonian model is finally derived, which not only reproduces the laser thresholds, but also helps in understanding the origin of the nearly integrable character of the laser dynamics.

In this paper, we investigate the topological properties of breathing honeycomb plasmonic lattices consisting of silver nanoparticles with in-plane polarized modes. Eigenvalues of the Wilson loop matrix are employed to distinguish the topological properties of band gaps of our model. The calculation results demonstrate that the proposed model with in-plane polarization supports the obstructed atomic limit phase not only in the middle gap but also in the band gaps that are opened due to the vectorization of in-plane polarizations. The topological edge modes and corner modes are demonstrated by a ribbon supercell and a hexagonal finite-sized system, respectively. To reveal the differences between topological states that appear in different band gaps, we explore the robustness of these corner states by introducing two types of point defects in a finite-sized system. Our work reveals the inherent differences between the topological properties of two-dimensional nanoparticle arrays with in-plane or out-of-plane polarized modes and may extend the application and research of topological plasmonic system.

The departure of the quantum world from the classical regime is captured through the observation of nonclassical correlations manifested in the behaviors of subatomic systems. However, once the dimension of the system becomes substantially large, the quantum behavior begins to decline, and subsequently it starts following the predictions of classical physics. The macroscopic limit at which such quantum-to-classical transition occurs remains one of the long-standing questions in the foundations of quantum theory. There are evidences that the macroscopic limit to which the quantumness of a system persists depends on the degree of interaction due to the measurement processes. For instance, with a system having a considerably large Hilbert-space dimension, if the measurement is performed in such a way that the outcome of the measurement only reveals a coarse-grained version of the information about the individual level of the concerned system then the disturbance due to the measurement process can be considered to be infinitesimally small. Based on such coarse-grained measurement the dependence of Bell inequality violation on the degree of coarsening has already been investigated [H. Jeong, Y. Lim, and M. S. Kim, Phys. Rev. Lett. 112, 010402 (2014)]. In this paper, we first capture the fact that, when local realism is taken to be the defining notion of classicality, the effect of the degree of coarsening on the downfall of quantumness of a macroscopic entangled state can be compensated by testing a Bell inequality of a higher number of settings from a family of symmetric Bell inequalities if the number of settings is odd. However, in contrast, we show that such compensation cannot be seen when we witness such quantum-to-classical transition using symmetric Bell inequalities having an even number of settings. Finally, complementing the above result, we show that, when unsteerability is taken as the classicality, for both odd and even numbers of settings the degree of coarsening at which the quantum-to-classical transition occurs can be consistently pushed ahead by testing a linear steering inequality of a higher number of settings and observing its violation. We further extend our treatment for mixed macroscopic entangled states.

Positivity preservation is naturally guaranteed in exact non-Markovian master equations for open quantum system dynamics. However, in many approximated non-Markovian master equations, the positivity of the reduced density matrix is not guaranteed. In this paper we provide a general class of time-local, perturbative, and positivity-preserving non-Markovian master equations generated from stochastic Schrödinger equations, particularly quantum-state-diffusion equations. Our method has an expanded range of applicability for accommodating a variety of non-Markovian environments. We show the positivity-preserving master equation for a three-level system coupled to a dissipative bosonic environment as a particular example to exemplify our general approach. We illustrate the numerical simulations with an analysis explaining why the previous approximated non-Markovian master equations cannot guarantee positivity. Our work provides a consistent master equation for studying the non-Markovian dynamics in ultrafast quantum processes and strong-coupling systems.

We provide a tool for measuring the Stokes parameters and the degree of polarization of single photons by employing second-order interference, namely, the Hong-Ou-Mandel (HOM) interferometer. It is shown that the technique is able to distinguish a partially polarized photon where the polarization state is coupled to an internal degree of freedom, such as time of arrival, from partial polarization due to external entanglement with the environment. The method does not directly resort to any kind of polarization-selective components and therefore is not limited by the extinction ratio of polarizers. Moreover, the technique can be generalized to any two-level encoding of quantum information in single photons, such as time-bin or orbital angular momentum qubits.

We develop the general framework of virtual resource distillation, an alternative distillation strategy proposed in Phys. Rev. Lett. 132, 050203 (2024), which extends conventional quantum resource distillation by integrating the power of classical postprocessing. The framework presented here is applicable not only to quantum states, but also to dynamical quantum objects such as quantum channels and higher-order processes. We provide a general characterization and benchmarks for the performance of virtual resource distillation in the form of computable semidefinite programs as well as several operationally motivated quantities. We apply our general framework to various concrete settings of interest, including standard resource theories such as entanglement, coherence, and magic, as well as settings involving dynamical resources such as quantum memory, quantum communication, and non-Markovian dynamics. The framework of probabilistic distillation is also discussed.

Entanglement distillation allows to convert noisy quantum states into singlets, which can, in turn, be used for various quantum technological tasks, such as quantum teleportation and quantum key distribution. Entanglement dilution is the inverse process: singlets are converted into quantum states with less entanglement. While the usefulness of distillation is apparent, practical applications of entanglement dilution are less obvious. Here, we show that entanglement dilution can increase the resilience of shared quantum states to local noise. The increased resilience is observed even if diluting singlets into states with arbitrarily little entanglement. We extend our analysis to other quantum resource theories, such as quantum coherence, quantum thermodynamics, and purity. For these resource theories, we demonstrate that diluting pure quantum states into noisy ones can be advantageous for protecting the system from noise. Our results demonstrate the usefulness of quantum resource dilution, and provide a rare example for an advantage of noisy quantum states over pure states in quantum information processing.

Cavity-magnon systems are emerging as a fruitful architecture for the integration of quantum technologies and spintronic technologies, where magnons are coupled to microwave photons via the magnetic-dipole interaction. Controllable, the photon-magnon (P-M) couplings provide a powerful means of accessing and manipulating quantum states in such hybrid systems. Thus, determining the relevant P-M couplings is a fundamental task. Here we address the quantum estimation problem for the P-M coupling strength in a double-cavity-magnon system with drive and dissipation. The effects of various physical factors on the estimation precision are investigated and the underlying physical mechanisms are discussed in detail. Considering that in practical experiments it is almost infeasible to perform measurements on the global quantum state of this composite system, we identify the optimal subsystem for performing measurements and estimations. Further, we evaluate the performance of different Gaussian measurements, indicating that optimal Gaussian measurement almost saturates the ultimate theoretical bound on the estimation precision given by the quantum Fisher information.

In photoionization, the nondipole interactions induce forward-backward asymmetric photoelectron energy along the laser propagation direction. By employing nondipole modified strong-field approximation, we attribute this emission-direction-dependent photoelectron energy to the displacement induced by the magnetic component of a laser pulse. The displacement induced by the magnetic field gives rise to a phase difference between the electron wave packets with different ionization instants. It results in a shift of the interference fringes, manifesting as the asymmetric photoelectron energy along the laser propagation direction. By numerically solving the time-dependent Schrödinger equation, we demonstrate that the time-resolved displacement with picometer resolution is traced from the time-delay-dependent asymmetric photoelectron energy in attosecond photoelectron interferometry. The cycle-averaged displacement is retrieved from the intercycle interference and dynamic interference. Moreover, we show that the magnetic field induced momentum also results in emission-direction-dependent photoelectron energy. From the asymmetric photoelectron energy in the attosecond streaking spectrum, the time-resolved momentum induced by the magnetic field is revealed.

We propose to shape attosecond pulses in the extreme ultraviolet (xuv) by creating and tuning a spectral minimum in the high-order harmonic generation (HHG) spectrum by using two gas jets. We show that the HHG spectrum is greatly modulated by moving the first gas jet upstream from the laser focus while the second gas jet is located at the laser focus and its pressure is low, thus the xuv attosecond pulse can be effectively shaped. This does not depend much on the profile of the gas density. Phase matching of HHG is determined by the interplay of the geometric phase and the single-atom induced dipole phase when the pressure of the first gas jet is low, while phase matching is mostly caused by reshaping of the driving laser in the first gas jet when it has the high pressure. We also show that the HHG spectrum cannot be modified much when pressures of both gas jets are high. This work provides an alternative approach to shape xuv attosecond pulses based on the available technique for generation of HHG.

Optomechanical (OM) cavities simultaneously localize photons and phonons, thus enhancing their mutual interaction through radiation-pressure force. This acousto-optic interaction can be quantified by means of the optical-frequency shift per mechanical displacement $G$. The aforesaid frequency shift can also be related to the vacuum OM coupling rate $g_0$, where only photoelastic and moving-boundary effects are commonly taken into account. However, the thermo-optic and thermal-expansion effects may also play a role since the material forming the OM cavity could be heated by the presence of photons, which should naturally affect the mechanical properties of the cavity. In this work, we introduce a theoretical approach to determine how thermal effects change the canonical OM coupling rate. To test the model, a complete set of optical-thermal-mechanical simulations was performed in two OM crystal cavities fabricated from two different materials: silicon and diamond. Our results lead us to conclude that there is a non-negligible thermal correction that is always present as a negative shift to the OM coupling rate that should be considered in order to predict more accurately the strength of the OM interaction.

We study the feasibility of sub-shot-noise interferometry with imperfect detectors, starting from twin Fock states and two-mode squeezed vacuum states. We derive analytical expressions for the corresponding phase uncertainty. We find that one can achieve phase shift measurements below the standard quantum limit, as long as the losses are smaller than a given threshold, and that the measured phase is close enough to an optimal value. We provide our analytical formulas in a python package, accessible online.

We study the stability of counterdiabatic drive by computing the joint dependence of the probability of nonadiabatic transitions $P_{\eta }\left(\delta \right)$ on the adiabatic parameter $\delta$ and on the normalized amplitude of the adiabatic gauge potential (AGP) $\eta$ in the Landau-Zener-Stückelberg-Majorana model. We show that the Dykhne-Davis-Pechukas formula cannot be readily applied since the AGP introduces a singularity in the Hamiltonian which makes the wave function multivalued in the complex-time plane. This can be understood as the non-Abelian Aharonov-Bohm phase introduced by the AGP and leads to the counterdiabatic correction of the Landau-Zener formula. In particular, it shows that, unlike the nonperturbative suppression of transitions in the adiabatic limit $\delta \to 0$, the probability is only perturbatively suppressed in the counterdiabatic limit $\eta \to 1$. We then consider the extension of our results to integrable time-dependent quantum Hamiltonians. We prove that the AGP satisfies the flatness constraint which characterizes integrability in these models, which allows us to derive simple expressions for the AGP and the probability of transitions $P_{\eta }\left(\delta \right)$ near adiabatic or counterdiabatic evolution in three- and four-state integrable examples.