Achieving high-fidelity two-qubit gates is crucial for spin qubits in silicon-based double quantum dots. However, these gates are sensitive to charge noise in experimental settings, which remains a significant challenge. Geometric gates, which utilize pure geometric phases for gate operations, are a promising approach to achieving robust control. In this work, we theoretically propose a feasible strategy to implement geometric two-qubit gates for silicon-based spin qubits considering experimental control environments. By operating in the suitable region where the local magnetic field gradient is significantly larger than the exchange interaction, we can implement both entangling and nonentangling geometric gates through analytical and numerical methods. It is found that the geometric gates obtained are highly compatible with existing experimental techniques using electric dipole spin resonance in silicon. Moreover, the implemented geometric controlled-$Z$ (CZ) gates can achieve fidelities exceeding 99% under experimental noise levels and the gate times are as short as 20 ns. Our work paves the way for the realization of high-fidelity geometric two-qubit gates for spin qubits in silicon.

Cooling of atomic motion is a crucial tool for many branches of atomic physics, ranging from fundamental physics explorations to quantum information and sensing. For trapped ions, electromagnetically-induced-transparency (EIT) cooling has received attention for the relative speed, low laser power requirements, and broad cooling bandwidth of the technique. However, in applications where the ion used for cooling has hyperfine structure to enable long coherence times, it is difficult to find a closed three-level system in which to perform standard EIT cooling. Here, we demonstrate successful EIT cooling on ${}^{25}\mathrm{Mg}^{+}$ by the addition of an extra laser frequency; this method can be applied to any ion with nonzero nuclear spin. Furthermore, we simultaneously EIT cool all axial modes in mixed-species crystals ${}^9\mathrm{Be}^{+}\text{−}{}^{25}\mathrm{Mg}^{+}$ and ${}^9\mathrm{Be}^{+}\text{−}{}^{25}\mathrm{Mg}^{+}\text{−}{}^9\mathrm{Be}^{+}$ through the ${}^{25}\mathrm{Mg}^{+}$ ion. This demonstrates the viability of EIT cooling in architectures where the laser-cooled species can host high-fidelity hyperfine qubits.

The complex eigenenergies and nonorthogonal eigenstates of non-Hermitian systems exhibit unique topological phenomena that cannot appear in Hermitian systems. Representative examples are the non-Hermitian skin effect and exceptional points. In a two-dimensional parameter space, topological classifications of nonseparable bands in multiband non-Hermitian systems can be established by invoking a permutation group, where the product of the permutation represents state exchange due to exceptional points in the space. We unveil in this work the role of pseudo-Hermitian lines in non-Hermitian topology for multiple bands. In particular, the nonseparability of non-Hermitian multibands can be topologically nontrivial without exceptional points in two-dimensional space. As a physical illustration of the role of pseudo-Hermitian lines, we examine a multiband structure of a photonic crystal system with lossy materials. Our work builds on the fundamental and comprehensive understanding of non-Hermitian multiband systems and also offers versatile applications and realizations of non-Hermitian systems without the need to consider exceptional points.

A double quantum dot coupled to an optical cavity is a prototypical example of a nontrivial open quantum system. Recent experimental and theoretical studies show that this system is a candidate for single-photon detection in the microwave domain. This motivates studies that go beyond just the average current, and also take into account the full counting statistics of photon and electron detections. With this in mind, here we provide a detailed analysis of the waiting time statistics of this system within the quantum jump unraveling, which allows us to extract analytical expressions for the success and failure probabilities, as well as for the interdetection times. Furthermore, by comparing single- and multiphoton scenarios, we infer a hierarchy of occurrence probabilities for the different events, highlighting the role of photon interference events in the detection probabilities. Our results therefore provide a direct illustration of how waiting time statistics can be used to optimize a timely and relevant metrological task.

In this article, we present a succinct algorithmic framework via alternating quantum walks, unifying quantum spatial search, state transfer, and uniform sampling on a large class of graphs. Using the framework, we can achieve exact uniform sampling over all vertices and perfect state transfer between any two vertices, provided that eigenvalues of Laplacian matrix of the graph are all integers. Furthermore, if the graph is vertex transitive as well, then we can achieve deterministic quantum spatial search that finds a marked vertex with probability $100\%$. In contrast, existing quantum search algorithms generally have a certain probability of failure. Even if the graph is not vertex transitive, such as the complete bipartite graph, we can still adjust the algorithmic framework to obtain deterministic spatial search, which thus shows the flexibility of it. Besides unifying and improving plenty of previous results, our work provides results on more graphs. The approach is easy to use since it has a succinct formalism that depends only on the depth of the Laplacian eigenvalue set of the graph, and may shed light on the solution of more problems related to graphs.

Positron-molecule binding energies ${\varepsilon }_{\mathrm{B}}$ have been measured for over 100 molecules. They range from a few to greater than 300 meV. The complete set of ${\varepsilon }_{\mathrm{B}}$ values is presented including, where necessary, updated analyses of previous data to provide more accurate values of ${\varepsilon }_{\mathrm{B}}$. The result is a dataset of 85 distinct hydrocarbon molecules and 29 deuterated analogs with ${\varepsilon }_{\mathrm{B}}$ values ranging in precision from $\pm 3$ to $\pm 20$ meV. Linear regression analysis is used to estimate ${\varepsilon }_{\mathrm{B}}$ using the global molecular parameters polarizability $\alpha$, permanent dipole moment $\mu$, and the number of $\pi$ bonds $N_{\pi }$ associated aromatic molecules and those with unsaturated bonds. Use of an optimized expansion for the entire dataset predicts ${\varepsilon }_{\mathrm{B}}$ to within a root-mean-square error of $\approx 30$ meV. This expression can provide useful estimates of ${\varepsilon }_{\mathrm{B}}$ for molecular species similar to those in the existing dataset but for which ${\varepsilon }_{\mathrm{B}}$ has not been measured. Chemical species for which this regression analysis is not valid are discussed. Complementary analyses are made for restricted ranges of global parameters, and these empirical expressions provide additional insight into the underlying physical mechanisms for positron-molecule binding. The results are related to recent many-body theory calculations of the bound-state positron wave functions.

Interatomic potentials were measured for combinations of chemical elements relevant for nuclear fusion. Angular scans of the scattering yield were performed on a W(110) and a Fe(100) single crystal using $\mathrm{H}{\mathrm{e}}^{+}$ and ${{\mathrm{D}}_2}^{+}$ beams with energies of 3 keV/atom using a time-of-flight low-energy ion scattering setup. Information on the interatomic potentials was deduced by reproducing width and intensity of minima and maxima in the angular scans in molecular dynamics simulations by adjusting the assumed screening length with a correction factor. Results from experiments were compared to common interatomic potential models and density functional theory predictions. Our measurements show that the uncorrected Thomas-Fermi-Molière and the Ziegler-Biersack-Littmark potentials overestimate the interatomic potential for the studied combinations. In contrast, the Yamamura-Takeuchi-Kawamura potential yields values slightly below our experimental result. At the same time, density functional theory predictions agree well with our experimental results for the He cases while differing significantly for the D cases.

A twist between two periodic systems offers the possibility to drastically control quantum transport properties. At discrete sets of commensurate twisting angles, a moiré periodic pattern is formed, and the low-energy single-particle spectrum forms distinct bands and gaps. Here, we consider twisted systems at a commensurate angle made of two continuous-space periodic potentials. We devise a general approach, based on a hierarchy of energy scales, to derive effective tight-binding models that capture the energy spectrum, focusing on the case of square lattices. Localized states in the moiré unit cell are coupled by strong intracell and weak intercell tunnelings, generating a series of energy bands and subbands that correspond to distinct, periodic lattices. For sufficiently deep potentials, we find excellent agreement between the spectrum of the continuous-space system and the tight-binding approximation thus constructed. Our approach allows for the interpretation of moiré band structures and the extraction of parameters for the effective tight-binding models. Applications to the physics of many-body systems and extensions to other twisted models are also discussed.

To solve the difficulty in wavelength adaptability of external-cavity semiconductor lasers, external-cavity distributed feedback has been proven to be an effective method to achieve adaptive narrow-linewidth semiconductor lasers. For the structural design and precise manufacturing of adaptive semiconductor lasers, the principle of laser linewidth compression based on distributed feedback needs to be explored. In this article, we propose a theoretical model for analyzing the operational mechanism of the adaptive distributed-feedback semiconductor laser. Theoretical and experimental results show that achieving adaptive linewidth compression requires tens of or more feedback points. On the basis of sufficient feedback points, increasing the feedback length and ratio can achieve an ultranarrow laser linewidth and high side-mode suppression ratio. This work provides a model analysis tool for exploring the ideal configuration of adaptive narrow-linewidth semiconductor lasers, which paves the way for the design and manufacturing of high-performance semiconductor lasers.

Classical and wave properties of microlasers with the shape of a truncated pseudosphere are investigated through experiments and numerical simulations. These pseudosphere microlasers are surface-like organic microlasers with constant negative curvature, which were fabricated with high optical quality by direct laser writing. It is shown that they behave, in many ways, similar to two-dimensional flat disks, regardless of their different Gaussian curvature. We derive the monodromy matrices for geodesics on the pseudosphere and demonstrate that the periodic geodesics are marginally stable. Actually, due to the rotational symmetry, the pseudosphere is an integrable system with marginally stable dynamics.

We demonstrate the dynamical Talbot effect caused by optical diffraction from standing surface acoustic waves (SAWs). The Talbot effect is a wave interference phenomenon in the Fresnel regime, and we observe it with a fiber-based scanning optical interferometer on a SAW Fabry-Perot cavity. By studying the interferometric signal at 1 GHz, next to the usual phase term we discover the existence of an amplitude-modulated term which vanishes at periodic positions when we displace the acoustic device relative to the beam focus. With this, we reveal the optical Talbot effect where, despite the curved wavefronts of the optical field, the conventional Talbot length appears. Finally, we propose to use the amplitude modulation as a different way of imaging surface acoustic waves.

In quantum dynamics, the Loschmidt amplitude is analogous to the partition function in the canonical ensemble. Zeros in the partition function indicate a phase transition, while the presence of zeros in the Loschmidt amplitude indicates a dynamical quantum phase transition. Based on the classical-quantum correspondence, we demonstrate that the partition function of a classical Ising model is equivalent to the Loschmidt amplitude in non-Hermitian dynamics, thereby mapping an Ising model with variable system size to the non-Hermitian dynamics. It follows that the Yang-Lee zeros and the Yang-Lee edge singularity of the classical Ising model correspond to the critical times of the dynamic quantum phase transitions and the exceptional point of the non-Hermitian Hamiltonian, respectively. Our work reveals an inner connection between Yang-Lee zeros and non-Hermitian dynamics, offering a dynamic characterization of the former.

This paper presents a hybrid quantum-classical approach to prime factorization. The proposed algorithm is based on the variational quantum eigensolver (VQE), which employs a classical optimizer to find the ground state of a given Hamiltonian. A numerical study is presented, evaluating the performance of the proposed method across various instances on both IBM's real quantum computer and its classical simulator. The results demonstrate that the method is capable of successfully factorizing numbers up to 253 on a real quantum computer and up to 1 048 561 on a classical simulator. These findings show the potential of the approach for practical applications on near-term quantum computers.

While the concept of entanglement for distinguishable particles is well established, defining entanglement and nonlocality in systems of indistinguishable particles, which require the use of the (anti)symmetrization postulate, remains challenging, and multiple approaches have been proposed to address this issue. In this work we study the problem of detecting genuine tripartite entanglement among systems of indistinguishable bosons. A genuine entangled state is one that cannot be separable under any bipartition, where separability in the indistinguishable regime is defined by the existence of single-particle properties within each subsystem, without the possibility of knowing which property belongs to which subsystem. We use an algorithm that allows us to search for these single-particle properties and consequently rank states according to their degree of separability. In particular, we introduce a state of indistinguishable bosons with properties analogous to those of the standard Greenberger-Horne-Zeilinger state.

Geometry and dimensionality have played crucial roles in our understanding of the fundamental laws of nature, with examples ranging from curved space time in general relativity to modern theories of quantum gravity. In quantum many-body systems, the entanglement structure can change if the constituents are connected differently, leading to altered bounds for correlation growth and difficulties for classical computers to simulate large systems. While a universal quantum computer can perform digital simulations, an analog-digital hybrid quantum processor offers advantages such as parallelism. Here, we engineer a class of high-dimensional Ising interactions using a linear one-dimensional ion chain with up to eight qubits through stroboscopic sequences of commuting Hamiltonians. In addition, we extend this method to noncommuting circuits and demonstrate the quantum XY and Heisenberg models using Floquet periodic drives with tunable symmetries. The realization of higher-dimensional spin models offers new opportunities ranging from studying topological phases of matter or quantum spin glasses to future fault-tolerant quantum computation.