This work uncovers a fundamental connection between doped stabilizer states, a concept from quantum information theory, and the structure of eigenstates in perturbed many-body quantum systems. We prove that for Hamiltonians consisting of a sum of commuting Pauli operators, i.e., stabilizer Hamiltonians, and a perturbation composed of a limited number of arbitrary Pauli terms, the eigenstates can be represented as doped stabilizer states with small stabilizer nullity. This result enables the application of stabilizer techniques to a broad class of many-body systems, even in highly entangled regimes. Building on this, we develop efficient classical algorithms for tasks such as finding low-energy eigenstates, simulating quench dynamics, preparing Gibbs states, and computing entanglement entropies in these systems. Our work opens up new possibilities for understanding the robustness of topological order and the dynamics of many-body systems under perturbations, paving the way for novel insights into the interplay of quantum information, entanglement, and many-body systems.

We experimentally compute relativistic and correlation effects in the atomic properties by using a superconducting qubit processor. Specifically, we compute the relativistic ground-state energies and magnetic-dipole hyperfine structure constants for four Li-like atomic systems ranging from very light to moderately heavy to very heavy in terms of nuclear charge. A symmetry-conserving Bravyi-Kitaev transformation is used to reduce the original six-qubit problem to a four-qubit problem, which is experimentally contrived by reducing the hardware requirement by employing a virtual two-qubit gate. It enables the simulation of four-qubit circuits using two physical qubits with additional circuit evaluations. The ground-state wave functions, required for computing atomic properties, are obtained by using quantum state tomography. Our results show that the averaged relative errors for the ground-state energies are $\approx 0.3\pm 1\%$. However, for the hyperfine structure constants, the mean values of the relative errors are less than $15\%$, with their estimated upper bound of relative errors of $\approx \pm 10\%$ (with the exception of $7.2\pm 47\%$ for neutral ${}^7\mathrm{Li}$). Notably, our results for the hyperfine structure constants exhibit higher sensitivity to errors as compared to energies; a trend which we also confirm through additional numerical simulations.

We investigated the convoy electron yields resulting from bombardments of amorphous carbon foils with 3.5-MeV/atom ${\mathrm{C}}_n^{+}$ ($n=1$–3) cluster ions. The target thickness ranged from 3.0 to $29.7\mu \mathrm{g}/{\mathrm{cm}}^2$. A detailed analysis of the thickness dependence revealed that for bombardments with ${\mathrm{C}}_2^{+}$ and ${\mathrm{C}}_3^{+}$ ions, the convoy electron yield per atom, $Y_n/n$, decreases with increasing target thickness and ultimately reaches an asymptotic value. The asymptotic value showed clear proportionality to the cluster size, $n$, indicating the presence of positive vicinity effects of $Y_n\propto n^2$. We found that the escape length of the convoy electrons for ${\mathrm{C}}_3^{+}$ and ${\mathrm{C}}_2^{+}$ is much longer than that of the ${\mathrm{C}}^{+}$ bombardment. The present result suggests that the enhancement of the escape length could be the origin of this vicinage effect on the convoy electron yield.

Homonuclear molecules have emerged as a crucial component in the pursuit of frequency standards, offering a promising avenue for the discovery of new physics phenomena that transcend the standard model. They also provide a unique approach to constraining variations in fundamental constants over time, thereby complementing the capabilities of atomic clocks. A notable challenge faced by molecular and single atomic quantum systems is the management of blackbody radiation (BBR), which introduces significant systematic errors and is challenging to regulate effectively. To address this issue, we perform ab initio quantum chemical calculations to accurately determine the potential energy curve and the polarizability tensor for the ground state of the ${\mathrm{N}}_2^{+}$ molecular ion, one of the most promising candidates for searching for variation of $m_e/m_p$ and creating frequency standards. We then calculate the BBR shifts affecting the vibrational levels of the ground electronic $X^2{\mathrm{\Sigma }}_g^{+}$ state, marking a substantial contribution towards the precise experimental measurements.

By calculating the dynamical structure factor of the two-dimensional doped attractive Fermi-Hubbard model with Rashba spin-orbit coupling (SOC), we not only investigate collective modes and single-particle excitations of the system during the phase transition between the Bardeen-Cooper-Schrieffer superfluid and topological superfluid, but also propose a universal method to measure the pairing gap in an optical lattice system. Our numerical results show that the area of the molecular excitation peak at the transferred momentum $\mathbf{q}=[\pi ,\pi ]$ is proportional to the square of the pairing gap in the system with Rashba SOC. In particular, this method is very sensitive to the pairing gap. We verify that this method is universal to measure the pairing gap in a doped optical lattice with Rashba SOC. These theoretical results are important for experimentally measuring the pairing gap and studying the topological superfluid in an optical lattice.

The vortex beam carrying orbital angular momentum has attracted great attention because of its novel properties and various applications. For a traditional vortex beam, the phase changes along the azimuthal direction with the law of periodicity. As is known, besides the periodicity, the quasiperiodicity also draws interest, bringing inspiration to the area where the periodicity is applied. In this paper, we try to break the periodicity of the traditional vortex beam, and we propose a kind of Fibonacci vortex beam based on the Fibonacci sequence with quasiperiodicity. The Fibonacci vortex beam is generated in experiment, and the orbital angular momentum spectrum of the Fibonacci vortex beam is further analyzed. Subsequently, the focal property of the beam is investigated in detail. The transverse energy flow in the focal plane is with spiral distribution like a comet in a curved orbit, and it can transport particles to a specified location along a certain spiral path. The multiple Fibonacci vortex beam is further proposed to generate fan-blade-like transverse energy flow in the focal plane, which can be applied in attracting or sweeping particles with high efficiency. This work breaks the periodicity of the vortex beam, which is inspirational in studying the vortex beam and optical angular momentum, and it can also be applied in various areas such as optical trapping and manipulation.

Strong long-range coupling between distant cantilevers is vital to cantilever-based quantum information processing. Here, we present an effective approach for establishing strong coupling between two distant cantilevers and generating the corresponding entanglement by utilizing phonon-squeezing-induced quantum criticality, where the phonon squeezing is achieved through frequency-doubling electrical regulation of the spring constant. Our system comprises three cantilever mechanical resonators connected in series by voltage, with the middle cantilever modulated by voltage and coupled to spin qubits. With current experimentally accessible parameters, by exploiting the combined effects of phonon squeezing and quantum criticality, we can significantly enhance the coupling strength between the polariton and the cantilever mechanical resonator by two or more orders of magnitude, all while maintaining a constant connection voltage. Similar to the Raman process, the polariton is virtually excited under conditions of large detuning, enabling indirect strong coupling between the two spatially separated cantilever mechanical resonators. We find that even if the distance between the cantilever resonators is increased by more than two orders of magnitude, the coupling remains strong with the connection voltage unchanged. On this basis, we demonstrate the generation of entanglement between two macroscopic cantilevers separated by long distances and clearly show through the calculations that the system decay has a minimal effect on quantum entanglement for a range of parameters. Apart from that, we assess the feasibility of the proposed method utilizing currently available technology. The present approach is expected to offer immunity to the high energy consumption and noise associated with elevated voltages, paving the way for quantum information and computation with cantilever mechanical resonator architecture.

We investigate the influence of the presence of a dielectric medium on the energy shift for a uniformly moving atom in blackbody radiation. The atomic energy-level shift usually depends on the temperature of thermal radiation, the atomic velocity, the refractive index of the medium, and the atomic polarizability. Analytical and numerical analyses indicate that the presence of the dielectric medium has profoundly disturbed the behavior of the atomic energy shifts, especially when the atomic speed is greater than the speed of light in the medium. Our work further suggests that the combination of a medium and atomic relativistic center-of-mass motion can provide insight into the radiative properties of atom-field coupling system.

We present an approach for evaluating Wannier functions, offering an alternative perspective on their role in many-body systems. Unlike traditional methods, such as the maximally localized Wannier functions approach, which focuses on minimizing the function tails, our approach emphasizes these tails. Using perturbative analytical approximations and extensive numerical simulations on an exactly solvable model, we address nonstandard Hubbard terms and demonstrate their critical influence on many-body dynamics. Specifically, we study tunneling dynamics in arbitrary double-well potentials, moving beyond the standard Hubbard model to include nonstandard terms such as density-induced tunneling and pair tunneling. Our results reveal that these terms significantly modify the dynamics predicted by the standard Hubbard model: Density-induced tunneling modifies the single-particle tunneling parameter ${\mathrm{\Omega }}_0$, while pair tunneling enables coherent propagation not captured by the standard model. We show that the discrepancies between the standard and nonstandard Hubbard models grow with increasing interaction strength, potentially leading to novel transport behaviors. However, at lower interaction strengths, both models converge, as nonstandard terms become negligible. These findings have important implications for phenomena such as superconductivity in twisted bilayer graphene and metal-insulator transitions. Our model aligns well with numerical simulations of lowest-band parameters and is strongly supported by experimental observations of second-order atom tunneling in optical double-well potentials. This strong agreement with experimental data highlights the accuracy and potential of our approach in providing a more comprehensive framework for describing complex many-body systems than the standard Hubbard model.

Gottesman-Kitaev-Preskill (GKP) qubits, known for their exceptional error-correction capabilities, are highly coveted in quantum computing. However, generating optical GKP qubits has been a significant challenge. Measurement-based methods, where a portion of entangled squeezed vacuum modes are measured with photon number resolving detectors heralding a desired state in the undetected modes, have emerged as leading candidates for optical GKP qubit generation due their minimal resource requirements. While the current measurement-based methods can produce high-quality GKP qubits, they suffer from low success probabilities limiting experimental realization. The heart of the problem lies in the duality of photon number resolving measurements, being both the source of nonlinearity needed to generate quality GKP qubits and the component driving down their probability of successful production. Our method, breeding approximate squeezed coherent state superpositions created by generalized photon subtraction, overcomes this problem by supplementing two photon number resolving measurements with a single high success probability homodyne measurement. This scheme achieves success probabilities $\ge {10}^{-5}$, two orders of magnitude higher than strictly photon number resolving measurement based methods, while still producing states with high fidelity, possessing error-correction capabilities equivalent to up to a 10 dB squeezed GKP qubit. This breakthrough significantly advances the practical use of the optical GKP qubit encoding.

The ab initio approach is used to evaluate the excitation energies of the $2s2p{}^{2S+1}{P}_J$ states from the ground state as well as the $2s2p{}^{3}P_1\to 2s2p{}^{3}P_0$ and $2s2p{}^{3}P_2\to 2s2p{}^{3}P_1$ transition energies for selected Be-like highly charged ions over a wide range: from ${\mathrm{Ar}}^{14+}$ to ${\mathrm{U}}^{88+}$. The issue of a strong level mixing due to the proximity of states with the same symmetry is addressed by applying the QED perturbation theory for quasidegenerate levels. The employed approach combines a rigorous perturbative QED treatment up to the second order with electron-electron correlation contributions of the third and higher orders calculated in the Breit approximation. The higher-order QED effects are estimated using the model-QED-operator approach. The nuclear-recoil and nuclear-polarization effects are taken into account as well. The performed calculations are accompanied with a thorough analysis of uncertainties due to uncalculated effects. The most accurate theoretical predictions for the excitation and transition energies in Be-like ions are obtained, which, in general, are in perfect agreement with the available experimental data.

The electronic stopping power of Fe ions traveling through Fe is investigated using nonequilibrium simulations of the electronic response via real-time time-dependent density functional theory. The role of core electrons of both projectiles and host atoms on the electronic stopping power are investigated by explicitly incorporating core electrons in simulations. This study finds that the effect of the projectile's core electrons on electronic stopping power surpasses that of the core electrons of the target atoms. The steady-state charges of projectiles with varying electron configurations are calculated to assess the Bethe formula's applicability. Furthermore, the electronic stopping power of the projectiles traversing through Fe along the channeling trajectory is studied. The results show that the charges captured by channeling projectiles exhibit a polarization effect in the medium- and high-velocity regimes, leading to a high electronic stopping power.

The atomic comagnetometer is capable of reducing the effect of magnetic-field variations through comparing the synchronous measurement results from at least two magnetometers. A new configuration of comagnetometer is based on an ensemble of identical atoms or molecules, and possesses the ability to suppress the magnetic-field-gradient-induced systematic effect. We present a comprehensive analysis on the systematic effects of a single-species cesium atomic comagnetometer. Experimental results reveal that the dominant systematic effect arises from the light shift. We propose a method to suppress the light-shift-induced systematic effect, combined with quantitative investigations on other sources of systematic effects. The optimized system is able to search for the hypothetical spin-dependent gravitational energy of a proton at a level of ${10}^{-19}$ eV.

We consider bosons with weak contact interactions in a harmonic trap and focus on states at the lowest Landau level. Motivated by the known nontrivial phase-space topography of the energy functional of the corresponding Gross-Pitaevskii equation, we explore Husimi distributions of quantum energy eigenstates in the classical phase space of the Schrödinger field. With interactions turned off, the energy levels are highly degenerate and the Husimi distributions do not manifest any particular localization properties. With interactions turned on, the degeneracy is lifted, and a selection of energy levels emerges whose Husimi distributions are localized around low-dimensional surfaces in the phase space.

In this work we aim to clarify theoretically the spatial coherence properties of the x-ray beam in the focal plane after interaction with a variable line space (VLS) grating. Assuming that the VLS grating is oriented horizontally, we are interested in the coherence properties of the beam in the vertical dispersion direction. We first consider a fully spatially coherent x-ray beam illuminating the grating. We show that the spatial coherence properties in the focal plane depend on the bandwidth of the incoming radiation. Being fully spatially coherent up to the VLS grating, the spatial coherence properties degrade in the focal plane of the VLS grating. We attribute this to coupling of the spatial and frequency components in the focal plane of the grating. Next, we examine partially coherent x-ray beams incident on a VLS grating. We assume that this radiation is of the Gaussian Schell-model type and obtain an analytical expression for the spatial coherence properties of the beam in the focal plane of the VLS grating for such a field. Next, we consider a monochromator setting that is provided by installing slits in the focal plane of the VLS grating and examine the degree of coherence in this case. Finally, we evaluate the degree of coherence at different apertures of the exit slits, assuming coherent illumination of the grating and a bandwidth of $1.7\times {10}^{-4}$.

We present experimental results on tuning biphoton frequency by introducing a detuned coupling field in spontaneous four-wave mixing (SFWM), and examine its impact on the pairing ratio. This tunability is achieved by manipulating the inherent electromagnetically induced transparency (EIT) effect in the double-$\mathrm{\Lambda }$ scheme. Introducing a detuned coupling field degrades the efficiency of EIT-based stimulated four-wave mixing, which in turn reduces the biphoton pairing ratio. However, this reduction can be mitigated by increasing the optical power of the coupling field. Additionally, we observe that blue- and red-detuning the biphoton frequency results in distinct temporal profiles of biphoton wave packets due to phase mismatch. These findings provide insights into the mechanisms of frequency-tunable biphoton generation via SFWM, and suggest potential optimizations for applications in quantum communication and information processing.

Assisted by the probe gain, we propose a scheme to realize the amplified unidirectional broadband reflection in a one-dimensional defective atomic lattice. In this system, some lattice cells are intentionally designed to prevent atom trapping and exhibit a periodic distribution, in order to break the spatial symmetry of light propagation and form a well reflection band. While the filled lattice cells of ${}^{87}\mathrm{Rb}$ atoms are driven into the closed three-level $\mathrm{\Delta }$-type configuaration, which can realize the amplification of the probe field. By optimizing parameters and reasonable settings, it is obvious that our scheme not only yields a flexible and adjustable broadband unidirectional reflection amplification, but also has reduced the requirement for probe gain and greatly shortened the length of defective atomic lattices.

We investigate the correspondence between classical noise and quantum environments. Although it is known that classical noise can be mapped to quantum environments for pure dephasing and infinite-temperature dissipation processes, we show how finite-temperature dissipation can be also described using classical noise by introducing auxiliary systems and conservation. Taking a two-level system as an example, we construct the so-called central spin model with its couplings fluctuating with the classical noise and then acquire its statistical-average dynamics which captures the dissipation beyond infinite temperature. By adjusting the number of auxiliary systems and their initial states, the noise-based model reproduces both Markovian and non-Markovian evolution. We also find that different quantities of the two-level system are governed by different model parameters, indicating that the constructed model is an effective simulator for specific observables rather than an equivalent form of a realistic open system. In addition, the model is also applicable to investigate topical mechanisms of open systems, e.g., negative temperatures and asymmetric equidistant quenches.