Generating and manipulating Dirac points in artificial atomic crystals has received attention, especially in photonic systems due to their ease of implementation. In this Letter, we propose a two-dimensional photonic crystal made of a Kekulé lattice of pure dielectrics, where the internal rotation of cylindrical pillars induces optical Dirac-degeneracy breaking. Our calculated dispersion reveals that the synchronized rotation reverses bands and switches parity as well so as to induce a topological phase transition. Our simulation demonstrates that such topologically protected edge states can achieve robust transmission in defect waveguides under deformation, and therefore provides a pragmatically tunable scheme to achieve reconfigurable topological phases.

The chaotic light source is one of the most crucial foundations in optical physics studies and photonic devices. The microcavity provides the predominant solution of compact chaotic light sources in integrated photonics. Still, its prefixed feature has severely ruled out access to tuning for meeting the ever-increasing demands of the general-purpose chaotic light source in engineering. Here we report a demonstration of a chaotic light source with a switchable bandpass–band-stop chaotic emission and tunable bandwidth in a spinning microcavity anti-parity-time (anti-$\mathcal{PT}$). system. In addition, the arrangement of anti-$\mathcal{PT}$ microcavity presents several phenomena such as loss-induced chaotic emission and two different chaotic emissions from one microcavity light source. Such advantages offer another possible way to advance multiplex photonic devices and on-chip chaotic light source fabrication. These results provide a promising approach for the tunable chaotic source and serve as tools for applications in secure communications, electromechanical switching, and exploring non-Hermitian physics.

Electric Rydberg-atom interferometry has been performed with helium atoms in coherent superpositions of the $1s56s{}^{3}S_1$ and $1s57s{}^{3}S_1$ Rydberg levels. The experiments were carried out in a longitudinal geometry with the atoms traveling at 2000 m/s in pulsed supersonic beams. After laser photoexcitation from the $1s2s{}^{3}S_1$ metastable level, coherent manipulation of the population of the Rydberg states was achieved using sequences of microwave pulses. The difference in the static electric dipole polarizabilities of the $1s56s{}^{3}S_1$ and $1s57s{}^{3}S_1$ levels allowed superpositions of external momentum states to be generated when inhomogeneous electric fields were used to exerted forces on the atoms prepared in superpositions of these internal states. Interference fringes, with contributions arising from the spatial separation of these Rydberg-atom wave packets in the direction of propagation of the atomic beam, were identified through changes in the internal-state populations as the magnitudes and durations of the time-dependent electric-field gradient pulses were adjusted. The maximal displacement of the atomic wave packets for which interference fringes were observed was $\sim 0.75\mathrm{nm}$, limited by the longitudinal velocity spread in the atomic beam and the characteristics of the inhomogeneous electric-field distribution in the apparatus. The experimental data are in good quantitative agreement with the results of numerical calculations of the time evolution of the atomic states under the experimental conditions.

We here develop a thin-shell approximation of the Mie scattering problem for a spherical multilayer structure consisting of central core, a spacer layer, and a thin layer with radially anisotropic dielectric function. This thin layer can, for example, represent a uniform layer of adsorbed dyes at a fixed distance from a spherical nanoparticle, with an effective anisotropic dielectric tensor to account for dye-orientation effects. This geometry with the spacer layer was recently shown to be necessary to precisely account for all electromagnetic effects in such systems [C. Tang, B. Auguié, and E. C. Le Ru, Phys. Rev. B 103, 085436 (2021)]. The Mie theory solution involves Bessel functions of complex order, which are not commonly available in many numerical calculations. We show that this hurdle is overcome in the thin-shell approximation, where the solution is of similar complexity to that of isotropic Mie theory with only spherical Bessel functions of integer order. We also apply this approximation to the calculation of the optical absorption in each individual layer. Using the dye-on-metal-nanoparticle system as illustration, we show that the thin-shell predictions agree extremely well with the full solution for experimentally relevant parameters, and can therefore be used instead. This speeds up the numerical implementation and will simplify further analytical developments.

Stokes parameters play a vital role in the study of photons, electrons, and other elementary particles. Superposition of phase singularities in an orthogonal polarization basis leads to the creation of Stokes singularities. It has been established that these phase singularities carry orbital angular momentum of light and hence the study of Stokes singularities is significant. The superposition of orbital-angular-momentum states, depending on the chosen basis, leads to the formation of different types of Stokes singularities such as polarization singularities and Poincaré singularities. These are subsets of Stokes singularities. There is a plethora of applications that has emerged in recent years for both phase and polarization singularities. Spin to orbital-angular-momentum conversion is possible by the use of a $q$ plate. In fact, a $q$ plate can convert a scalar beam into a phase or polarization vortex and a polarization singularity into another polarization singularity. But the process of the inter- or intraconversion of Stokes vortices has not been reported so far. This article discusses this aspect and the invariance of various topological parameters that occur in this process.

We investigate steady-state thermal transport and photon statistics in a nonequilibrium hybrid quantum system, in which a qubit shows longitudinal and quadratic coupling with an optical resonator. Our calculations are conducted with the method of the quantum dressed master equation combined with full counting statistics. The effect of negative differential thermal conductance is unravelled at finite temperature bias, which stems from the suppression of cyclic heat transitions and large mismatch of two squeezed photon modes at weak and strong qubit-resonator hybridizations, respectively. The giant thermal rectification is also exhibited at large temperature bias. It is found that the asymmetric composition of the hybrid system by spin and boson roles and negative differential thermal conductance show the cooperative contribution. Noise power and skewness, as typical current fluctuations, exhibit global maximum with strong hybridization at small and large temperature bias limits, respectively. Moreover, the effect of photon quadrature squeezing is discovered in the strong hybridization and low-temperature regime, which shows asymmetric response to two bath temperatures. These results would provide some insight to thermal functional design and photon manipulation in qubit-resonator hybrid quantum systems.

We consider the reversible processes between two one-to-one correlated measurement outcomes which underlie both problem solving and quantum nonlocality. In the former case, the two outcomes are the setting and the solution of the problem; in the latter, they are those of measuring a pair of maximally entangled observables whose subsystems are space separate. We argue that the quantum description of these processes mathematically describes the correlation but leaves the causal structure that physically ensures it free of violating the time symmetry required of the description of a reversible process. It would therefore be incomplete and could be completed by time symmetrizing it. This is done by assuming that the two measurements evenly contribute to selecting the pair of correlated measurement outcomes. Time symmetrization leaves the ordinary quantum description unaltered but shows that it is the quantum superposition of unobservable time-symmetrization instances whose causal structure is completely defined. Each instance is a causal loop: Causation goes from the initial to the final measurement outcome and then back from the final to the initial outcome. In the speedup, all is as if the problem solver knew in advance half of the information about the solution she will produce in the future and could use this knowledge to produce the solution with fewer computation steps. In nonlocality, the measurement on either subsystem retrocausally and locally changes the state of both subsystems when the two were not yet spatially separate. This locally causes the correlation between the two future measurement outcomes.

The performance of variational quantum algorithms relies on the success of using quantum and classical computing resources in tandem. Here, we study how these quantum and classical components interrelate. In particular, we focus on algorithms for solving the combinatorial optimization problem MaxCut, and study how the structure of the classical optimization landscape relates to the quantum circuit used to evaluate the MaxCut objective function. In order to analytically characterize the impact of quantum features on the critical points of the landscape, we consider a family of quantum circuit ansätze composed of mutually commuting elements. We identify multiqubit operations as a key resource and show that overparameterization allows for obtaining favorable landscapes. Namely, we prove that an ansatz from this family containing exponentially many variational parameters yields a landscape free of local optima for generic graphs. However, we further prove that these ansätze do not offer superpolynomial advantages over purely classical MaxCut algorithms. We then present a series of numerical experiments illustrating that noncommutativity and entanglement are important features for improving algorithm performance.

Drawing independent samples from a probability distribution is an important computational problem with applications in Monte Carlo algorithms, machine learning, and statistical physics. The problem can be solved in principle on a quantum computer by preparing a quantum state that encodes the entire probability distribution followed by a projective measurement. We investigate the complexity of adiabatically preparing such quantum states for the Gibbs distributions of various classical models including the Ising chain, hard-sphere models on different graphs, and a model encoding the unstructured search problem. By constructing a parent Hamiltonian, whose ground state is the desired quantum state, we relate the asymptotic scaling of the state preparation time to the nature of transitions between distinct quantum phases. These insights enable us to identify adiabatic paths that achieve a quantum speedup over classical Markov chain algorithms. In addition, we show that parent Hamiltonians for the problem of sampling from independent sets on certain graphs can be naturally realized with neutral atoms interacting via highly excited Rydberg states.

Simulation of quantum computing on supercomputers is a significant research topic, which plays a vital role in quantum algorithm verification, error-tolerant verification, and other applications. Tensor-network contraction based on density matrix is an important single-amplitude simulation strategy, but it is hard to execute on the distributed computing systems. In this paper, we studied the problem in detail, and propose a scheme based on cutting edges of undirected graphs. This scheme cuts edges of undirected graphs with large tree width to obtain many undirected subgraphs with small tree width, and these subgraphs contracted on different computing cores. The contraction results of slave cores are summarized in the master node, which is consistent with the original tensor-network contraction. Thus, we can simulate the larger scale quantum circuit than single core. Moreover, it is an NP-hard problem to find the global optimum cutting edges, and we propose a search strategy based on a heuristic algorithm to approach it. In order to verify the effectiveness of our scheme, we conduct tests based on the quantum approximation optimization algorithm (QAOA) and Shor's algorithm, and it can simulate a 120-qubit three-regular QAOA algorithm on a 4096-core supercomputer, which greatly exceeds the simulation scale on a single core of 100 qubits.

The formation of positive ions of antihydrogen ${\overline{\mathrm{H}}}^{+}$ via the three-body reaction (i) $e^{+}+e^{-}+\overline{\mathrm{H}}\to e^{-}+{\overline{\mathrm{H}}}^{+}$ is considered. In reaction (i), free positrons $e^{+}$ are incident on antihydrogen $\overline{\mathrm{H}}$ embedded in a gas of low-energy ($\approx$ meV) electrons and, due to the positron-electron interaction, a positron is attached to $\overline{\mathrm{H}}$ whereas an electron carries away the energy excess. We compare reaction (i) with two radiative attachment mechanisms. One of them is (ii) spontaneous radiative attachment, in which the ion is formed due to spontaneous emission of a photon by a positron incident on $\overline{\mathrm{H}}$. The other is (iii) two-center dileptonic attachment which takes place in the presence of a neighboring atom B and in which an incident positron is attached to $\overline{\mathrm{H}}$ via resonant transfer of energy to B with its subsequent relaxation through spontaneous radiative decay. It is shown that reaction (i) can strongly dominate mechanisms (ii) and (iii) for positron energies below 0.1 eV. In addition, it is shown that, at the energies considered, reaction (i) will not be influenced by annihilation and that the reaction $e^{+}+e^{+}+\overline{\mathrm{H}}\to e^{+}+{\overline{\mathrm{H}}}^{+}$ has a vanishingly small rate compared with reaction (i). We also compare the reaction (i) with the formation of ${\overline{\mathrm{H}}}^{+}$ in collisions between an antihydrogen atom and a positronium.

Popular approximations to the exchange-correlation (xc) energy of density-functional theory do not yield the spatial “step” structures in the exact xc potential which are necessary to describe dissociation and electron excitation with the Kohn-Sham (KS) system. Via the discontinuity in the derivative of the xc energy as a function of electron number I derive exact analytic expressions in terms of the KS single-particle energies for the height of the step in the xc potential between a variety of open- and closed-shell atoms within stretched molecules.

We investigate one-dimensional three-body systems composed of two identical bosons and one mass-imbalanced atom (impurity) with attractive two-body and three-body zero-range interactions. In the absence of three-body interaction, we give a complete phase diagram of the number of three-body bound states in the whole region of mass ratio and the ratio of intra- and intercomponent interaction strength via direct calculation of Skornyakov-Ter-Martirosyan equations. We demonstrate that other low-lying three-body bound states emerge when the mass of the impurity particle is different from other two identical particles. We obtain the binding energies together with the corresponding wave functions. When the mass of impurity atom is very large, there are at most three three-body bound states. In the presence of three-body zero-range interaction, we reveal that weak three-body interaction will not always induce one more three-body bound state. At some special parameter points, arbitrary small three-body interaction can generate one more three-body bound state. This corresponds to the transition of the number of three-body bound states induced only by two-body attractive interaction.

We show that the motion of spin-polarized impurity (ferron) in ultracold atomic gas is characterized by a certain critical velocity which can be traced back to the amount of spin imbalance inside the impurity. We have calculated the effective mass of ferron in two dimensions. We show that the effective mass scales with the surface of the ferron. We discuss the impact of these findings; in particular, we demonstrate that ferrons become unstable in the vicinity of a vortex.

The measurement of weak continuous forces exerted on a mechanical oscillator is a fundamental problem in various physical experiments. It is fundamentally impeded by quantum back-action from the meter used to sense the displacement of the oscillator. In the context of interferometric displacement measurements, we here propose and demonstrate the working principle of a scheme for coherent back-action cancellation. By measuring the amplitude quadrature of the light reflected from a detuned optomechanical cavity inside which a stiff optical spring is generated, back-action can be canceled in a narrow band of frequencies. This method provides a simple way to improve the sensitivity in experiments limited by quantum back-action without injection of squeezed light or stable homodyne readout.

We investigate the dynamic evolution and thermodynamic process of a driven quantum system immersed in a finite-temperature heat bath. A Born-Markovian quantum master equation is formally derived for the time-dependent system with discrete energy levels. This quantum master equation can be applied to situations with a broad range of driving speeds and bath temperatures and thus be used to study the finite-time quantum thermodynamics even when nonadiabatic transition and dissipation coexist. The dissipative Landau-Zener model is analyzed as an example. The population evolution and transition probability of the model reveal the importance of the competition between driving and dissipation beyond the adiabatic regime. Moreover, local maxima of irreversible entropy production occur at intermediate sweep velocity and finite temperature, which the low-dissipation model cannot describe.

We study the possibility of varying the measured lifetime of a decaying particle based on the technique of weak value amplification in which an additional filtering process called postselection is performed. Our analysis made in a direct measurement scheme presented here shows that, for simple two-level systems, the lifetime may be prolonged more than three times compared to the original one, while it can also be shortened arbitrarily by a proper choice of postselection. This result is consistent with our previous analysis on the possible prolongation of the lifetime of $B$ mesons that may be observed in laboratories, and suggests room for novel applications of weak-value amplification beyond precision measurement conventionally considered.

It is impossible to mask an arbitrary quantum state into the correlations between two subsystems such that the original information is completely unknown to each local system. This is the no-masking theorem proposed by Modi et al. [K. Modi, A. K. Pati, A. Sen(De), and U. Sen, Phys. Rev. Lett. 120, 230501 (2018)]. In this work, we propose the concept of $k$-uniform quantum information masking in multipartite systems and indicate the relation between quantum error-correcting codes (QECCs) in heterogeneous systems and quantum information masking. As a consequence, we show that the no-masking theorem is a special case of the quantum Singleton bound for QECCs in heterogeneous systems essentially, and we give a more general no-masking theorem in multipartite systems based on the quantum Singleton bound. We also solve two open questions proposed by Li and Wang [M.-S. Li and Y.-L. Wang, Phys. Rev. A 98, 062306 (2018)]. That is, an arbitrary state of level $d$ cannot be masked in a tripartite system of level $d$ such that the marginal states are not proportional to identity, and an arbitrary state of level $d$ cannot be masked in a tripartite system of level $n$ with $n<d$. Further, we give some methods for constructing new QECCs from old QECCs in heterogeneous systems.

The electronic stopping power of zinc oxide for protons is presented over a wide range of velocities by using real-time time-dependent density functional theory. We calculated the electronic stopping power of energetic protons for both channeling and off-channeling trajectories, and revealed the microcosmic mechanism of semicore $3d$-electron excitation in ZnO. In the low-energy regime, the stopping power obtained from channeling geometry is in a quantitative agreement with the measured data, which reproduced not only the experimental threshold velocity of the stopping power, but also the deviation from velocity-proportional electronic stopping power which is considered to be caused by excitation of the tightly bound $3d$ electrons. In the high-energy regime, we examined the impact parameter dependence of semicore $3d$-electron excitation of ZnO, and showed that the stopping power obtained from off-channeling geometry greatly improves the simulation results in comparison with the channeling results. We also demonstrated that the electronic energy loss of protons is not only related to the number of electrons excited, but also associated with the energy distribution of excited electrons and holes after collisions.