We study theoretically the lifetimes of attractive and repulsive Fermi polarons, as well as the molecule at finite momentum in three dimensions. To this end, we develop a technique that allows for the computation of Green's functions in the whole complex frequency plane using exact analytical continuation within the functional renormalization group. The improved numerical stability and reduced computational cost of this method yield access to previously inaccessible momentum-dependent quasiparticle properties of low-lying excited states. While conventional approaches like the non-self-consistent $T$-matrix approximation method cannot determine these lifetimes, we are able to find the momentum-dependent lifetime at different interaction strengths of both the attractive and repulsive polaron as well as the molecule. At weak coupling our results confirm predictions made from effective Fermi liquid theory regarding the decay of the attractive polaron, and we demonstrate that Fermi liquidlike behavior extends far into the strong-coupling regime where the attractive polaron and molecule exhibit a $p^4$ momentum scaling in their decay widths. Our results offer an intriguing insight into the momentum-dependent quasiparticle properties of the Fermi polaron problem, which can be measured using techniques such as Raman transfer and Ramsey interferometry.

We report on the continuity equations for linear momentum and energy associated to a recently introduced electromagnetic formulation based on classical dipolar sources [Eur. Phys. J. Plus 138, 1034 (2023)]. When connected to the mass-polariton quasi-particle dynamics, these equations provide a consistent microscopic description of the local optical energy and momentum transfer inside dielectric media, called microscopic mass-polariton formulation. This procedure also unveils the true microscopic origin of the long-known Abraham optical force density as an interplay between induced dipoles and mechanical stresses generated within the material.

We propose a scheme aimed at achieving spatiospectral control over spontaneous emission within a four-level atom-light coupling system interacting with optical vortices carrying orbital angular momentum (OAM). The atom comprises a ground level and two excited states coupled with two laser fields, forming a V subsystem where the upper states exclusively decay to a common fourth state via two channels. By investigating various initial states of the atom and considering the presence or absence of quantum interference in spontaneous emission channels, we analyze how the characteristics of the OAM-carrying vortex beam imprint onto the emission spectrum. The interplay between the optical vortex and the quantum system, including its environment modes, induces a wide variety of spatiospectral behavior, including two-dimensional spectral-peak narrowing, spectral-peak enhancement, spectral-peak suppression, and spontaneous emission reduction or quenching in the spatial azimuthal plane. Our findings shed light on the dynamics of atom–vortex-beam light interactions and offer insights into the manipulation of emission properties at the quantum level.

We investigate one- and two-photon scattering in a one-dimensional waveguide coupled to a giant atom within the non-Markovian regime using the resolvent approach. The non-Markovian behavior gives rise to an atom-photon bound state that cannot be excited by a single incident photon. However, the bound state can be excited via the two-photon scattering process described by multichannel scattering theory, from which an analytical trapping probability of a photon in the bound state can be achieved. Additionally, we analyze the two-photon scattering process, obtaining the analytical expressions for scattered states. As non-Markovian effects strengthen, two peaks appear in the incoherent power spectrum, attributed to the system behaving as a leaky cavity formed by the giant atom's coupling points. Through the analysis of second-order correlation functions, we observe the bunching behavior for transmitted photons, antibunching behavior for reflected photons, and the distinctive retrieval behavior at the coupling points' separation.

We present a multimode theory of squeezed-state generation in resonant systems valid for arbitrary pump power and including pump depletion. The Hamiltonian is written in terms of asymptotic-in and -out fields from scattering theory, capable of describing a general interaction. As an example we consider the lossy generation of a highly squeezed state by an effective second-order interaction in a silicon nitride ring resonator point coupled to a waveguide. We calculate the photon number, the Schmidt number, and the second-order correlation function of the generated state in the waveguide. The treatment we present provides a path forward to study the deterministic generation of non-Gaussian states in resonant systems.

We propose a quantum battery realized with a few interacting particles in a three-well system with different on-site energies, which could be realized with ultracold-atom platforms. We prepare the initial state in the lowest-energy well and charge the battery using a spatial-adiabatic-passage–based protocol, enabling the population of a higher-energy well. We examine the charging under varying interaction strengths and reveal that the consideration of collective charging results in an intriguing oscillatory behavior of the final charge for finite interactions, through diabatic evolution. Our findings provide an opportunity for building stable and controllable quantum batteries.

Given the recent advances in quantum technology, the complexity of quantum states is an important notion. The idea of the Krylov spread complexity has come into focus recently with the goal of capturing this in a quantitative way. The present paper sheds light on the Krylov complexity measure by exploring it in the context of continuous-time quantum walks on graphs. A close relationship between Krylov spread complexity and the concept of limiting distributions for quantum walks is established. Moreover, using a graph optimization algorithm, quantum-walk graphs are constructed that have vertex states with minimal and maximal (long-time average) Krylov $\overline{\mathcal{C}}$ complexity. This reveals an empirical upper bound for the $\overline{\mathcal{C}}$ complexity as a function of Hilbert-space dimension and an exact lower bound.

We demonstrate a controllable and tunable topological beam splitter with a multiport based on the one-dimensional extended Su-Schrieffer-Heeger model, which supports the topological interface by introducing the nearest-neighbor (NN) coupling defect at the central site. The quantum state initially prepared at the interface can be transmitted with high fidelity to multiple output ports with equal or unequal probability on both sides of the model by modulating the NN coupling between the sites in the time domain. We show that the output port can be added by increasing the number of sublattices $a$. Especially, by setting the on-site potential energy, we can easily control the direction of the quantum state transfer process and ensure that this state is only transmitted to the multiple output ports on the left or multiple output ports on the right, which realizes the function of topological switching. Benefiting from the topological protection of the edge states, the quantum states can be transmitted with high fidelity even if there is the NN coupling disorder. Our work realizes a robust and multifunctional topological beam splitter.

The precision required to characterize a Hamiltonian is central to developing advantageous quantum computers, providing powerful advances in quantum sensing and crosstalk mitigation. Traditional methods to determine a Hamiltonian are difficult due to the intricacies of quantum systems, involving numbers of equations and parameters that grow exponentially with the number of qubits. To mitigate these shortcomings, in this paper, we introduce an innovative and effective procedure integrating a physics-informed neural network (PINN) with a freezing mechanism to learn the Hamiltonian parameters efficiently. Although PINN and experimental data alone would become impractical as $N$ increases, the mechanism we introduce freezes the interactions of most of the qubits, leaving just a qubit subsystem to be analyzed by the PINN method. Determination of all physical parameters is accomplished by analyzing the system by parts until completion. We validated the efficacy of our method using simulation data obtained from the IBM quantum computer to obtain the training data and we found that a PINN can learn the two-qubit parameters with high accuracy, achieving a median error of less than $0.1\%$ for systems of up to four qubits. We have successfully combined the PINN analysis of two qubits with the freezing mechanism in the case of a four-qubit system.

Many quantum systems display Markovian and non-Markovian behaviors with the information flow and backflow between the system and the surrounding environment. In this paper, we introduce a definition of the dynamics of open quantum systems called information trapping, which is a special case of the information flow. We show that under specific conditions, the information flow can exhibit behavior beyond Markovian or non-Markovian system dynamics. The physical reason behind this phenomenon may arise from the entanglement between the system and the environment, such that the rates of entangling and disentangling can equalize over time, influenced by the quantum memory of the system and environmental decoherence effects. This proposal is investigated by considering some witnesses of the behavior of the system dynamics such as fidelity, trace distance, the Holevo quantity, and Hilbert-Schmidt speed in the quantum teleportation and dense coding protocols based on the open quantum system consisting of an $XXZ$ chain Heisenberg affected by intrinsic decoherence. The main achievement of this work is focused on facilitating access to faithful quantum communication.

Spectroscopic measurements of the rotational distribution of ${}^{84}\mathrm{Sr}$ and ${}^{86}\mathrm{Sr}5sns{}^1{S}_0$ ultralong-range Rydberg molecular dimers created via photoassociation in a cold gas are reported. The dimers are produced by two-photon excitation via the $5s5p$ ${}^{1}P_1$ intermediate state. The use of singlet states permits detailed study of the roles that the initial atom-atom interaction, photon momentum transfer during Rydberg excitation, and sample temperature play in determining the spectral line shape and final dimer rotational distribution. The results are in good agreement with the predictions of a model that includes these effects. The present work further highlights the sensitivity of ultralong-range Rydberg molecule formation to the state of the initial cold gas.

The quantum electrodynamic formalism is presented for the systematic and exact in $Z\alpha$ derivation of nuclear recoil corrections in hydrogenic systems.

The propagation effects reshaping the excitation pulse are known to exhibit a strong influence on the high-harmonic generation (HHG) in solid-state media. Previous measurements showed that the midinfrared pulse dynamics, most importantly the nonlinear loss and spectral broadening, can dampen or even extinguish the highest harmonic peaks. Despite the importance of these effects, their inclusion in the HHG modeling has been so far restricted to one-dimensional propagation and/or very thin samples. This work demonstrates an approach where the driving pulse is simulated with a full spatial and temporal resolution in samples of realistic thickness while the material interfaces are included as well. We show that the HHG spectrum measured in the transmission geometry is greatly affected by the Fresnel reflections causing interference in the vicinity of the material surface, and we find that different parts of the harmonic spectra originate from different regions of the material sample. Our results underline the importance of realistic and comprehensive simulations in the interpretation of high-harmonic generation from solids in the transmission geometry.

Schrödinger cat states, which are superpositions of macroscopically distinct states, are potentially critical resources for upcoming quantum information technologies. In this paper we introduce a scheme to generate entangled Schrödinger cat states in a nonrelativistic electric dipole system situated on a two-dimensional plane, along with an external potential and a uniform strong magnetic field perpendicular to the plane. Additionally, our findings demonstrate that this setup can lead to the phenomenon of collapse and revival of entanglement for a specific range of our model parameters.

We give two upper bounds to the mutual information in arbitrary quantum estimation strategies. The first is based on some simple Fourier properties of the estimation apparatus. The second is derived using the first, but, interestingly, depends only on the Fisher information of the parameter, so it is valid even beyond quantum estimation. We illustrate the usefulness of these bounds by characterizing the quantum phase estimation algorithm in the presence of noise. In addition, for the noiseless case, we extend the analysis beyond applying the bound and we discuss the optimal entangled and adaptive strategies, clarifying inaccuracies appearing on this topic in the literature.

Quantum probes, such as single- and two-qubit probes, can accurately measure the temperature of a bosonic bath. The current investigation assesses the precision of the temperature estimate by using quantum Fisher information and the accompanying quantum signal-to-noise ratio. Employing an ancilla as a mediator between the probe and the bath improves thermometric sensitivity by transmitting temperature information into the probe qubit's coherences. In addition, we analyze two interacting qubits that were initially entangled or separated as quantum probes for various environmental configurations. Our findings show that increased precision is gained when the probe approaches its steady state, which is determined by the coupling between the two qubits. Furthermore, we can obtain high-efficiency temperature estimation for any low temperature by changing the interaction between the two qubits.

There is a pressing need for more accurate computational simulations of the optoelectronic properties of defects in materials to aid in the development of quantum sensing platforms. In this work, we explore how quantum computers could be effectively utilized for this purpose. Specifically, we develop fault-tolerant quantum algorithms to simulate optically active defect states and their radiative emission rates. We employ quantum defect embedding theory to translate the Hamiltonian of a defect-containing supercell into a smaller, effective Hamiltonian that accounts for dielectric screening effects. Our approach integrates block-encoding of the dipole operator with quantum phase estimation to selectively sample the optically active excited states that exhibit the largest dipole transition amplitudes. We also provide estimates of the quantum resources required to simulate a negatively charged boron vacancy in a hexagonal boron nitride cluster. We conclude by offering a forward-looking perspective on the potential of quantum computers to enhance quantum sensor capabilities and identify specific scenarios where quantum computing can resolve problems traditionally challenging for classical computers.

We report on the experimental and theoretical investigation of alignment echoes of ${\mathrm{N}}_2\mathrm{O}$ molecules induced by a pair of time-delayed femtosecond laser pulses with different polarizations. When circularly polarized kick pulses are applied, the alignment echoes in the laser propagation direction are activated, giving rise to $k$-alignment echoes. In these cases, the conventional 2π phase-space analysis, where molecules are restricted to rotate in the plane perpendicular to the laser propagation direction, cannot capture the complete echo information. Thus, we consider the rotational dynamics of molecules in the three-dimensional space and adopt a full phase-space analysis involving evolution in both azimuthal and polar directions, termed 4π phase-space analysis, to reveal the underlying physical mechanism of $k$-alignment echoes. Its mechanism results from a joint contribution of the filamentation in both azimuthal and polar phase spaces. Our classical and quantum simulations are consistent with the experimental observations.