Nonreciprocal quantum batteries, leveraging unidirectional energy transfer from charger to battery, demonstrate enhanced energy storage efficiency through their inherent directionality. We present an optimized nonreciprocal quantum battery architecture incorporating a quantum mediator between the battery and the charger to catalyze energy transfer. This mediator-enabled design significantly improves upon conventional direct-coupling configurations. Through comparative analysis of two distinct driving protocols (classical coherent driving versus quadratic temporal pulse excitation), we establish fundamental performance criteria for mediator-enhanced nonreciprocal quantum battery. Our results indicate that this proposed model expresses superior advantages over the previous conventional battery models without adding a mediator between the battery and the charger. Furthermore, we observe that under the classical driving, the decay rates of the charger and the battery could influence the relationship between the battery performance and the spectral width of the shared reservoir. Specifically, when the decay rates are weak, the battery performance and the spectral width of the shared reservoir would show a negative correlation. However, as the decay rates increase, this relationship would shift to a positive correlation. In contrast, under quadratic temporal pulse, the spectral width and the battery performance could represent a consistent positive correlation regardless of the decay rates of the charger and the battery.

We propose an approach for quantum amplitude estimation (QAE) designed to enhance computational efficiency while minimizing the reliance on quantum resources. Our method leverages quantum computers to generate a sequence of signals, from which the quantum amplitude is inferred through classical postprocessing techniques. Unlike traditional methods that use quantum phase estimation, which requires numerous controlled unitary operations and the quantum Fourier transform, our method avoids these complex and resource-demanding steps. By integrating quantum computing with classical postprocessing techniques, our method significantly reduces the need for quantum gates and qubits, thus optimizing the utilization of quantum hardware. We present numerical simulations to validate the effectiveness of our method and provide a comprehensive analysis of its computational complexity and error. This hybrid strategy not only improves the practicality of QAE but also broadens its applicability in quantum computing.

Advanced theoretical techniques that combine the linearized coupled-cluster method, configuration-interaction method, and perturbation theory are used to calculate energy levels, ionization potentials, electron affinities, field isotope shifts, and static dipole polarizabilities of the superheavy elements Lv and Ts, along with their lighter analogs Te, I, Po, and At. Calculations for the heavy elements, Po, At, Lv, and Ts, are used to address the gaps in the experimental data. Calculations for the lighter elements, Te and I (and partly Po and At), are used to demonstrate the accuracy of the calculations.

We investigate a one-dimensional quantum system with a self-similar arrangement of $\delta$-function potential barriers, exhibiting discrete scale invariance. The singular potential induces kinematically enforced symmetry breaking at $x=0$, decoupling the positive and negative spatial regions and leading to nonsymmetric zero-energy states. We demonstrate that the system supports a unique zero-energy wave function, which, although it is not square integrable, decays to zero at infinity and acts as a bound-like state with self-similar properties under discrete scaling transformations, akin to Efimov physics but limited to a single state. In momentum space, this wave function exhibits a threshold singularity at low momenta, with behavior depending on the scaling exponent $\alpha$: power-law divergence and log-periodic modulations for $0<\alpha <1$, logarithmic divergence for $\alpha =1$, and a finite limit for $\alpha >1$, which may be observable through time-of-flight or spectroscopic measurements in cold-atom experiments. The system's continuous spectrum, starting at zero energy, lacks discrete bound states. These findings highlight the role of singular potentials in generating scale-invariant quantum phenomena and provide a minimal framework for studying discrete scale symmetry and its potential experimental signatures.

We study localization and topological properties in spin-1/2 nonreciprocal Aubry-André chain with SU(2) non-Abelian artificial gauge fields. The results reveal that, different from the Abelian case, mobility rings will emerge in the non-Abelian case accompanied by the non-Hermitian topological phase transition. As the non-Hermitian extension of mobility edges, such mobility rings separate Anderson-localized eigenstates from extended eigenstates in the complex energy plane under the periodic boundary condition. Based on the topological properties, we obtain the exact expression of the mobility rings. Furthermore, the corresponding indicators such as inverse participation rate, normalized participation ratio, winding number, non-Hermitian spectral structures, and wave functions are numerically studied. The numerical results are in good agreement with the analytical expression, which confirms the emergence of mobility rings.

The quantum nonlinear Maxwell-Bloch equations for a single-mode laser with a two-level active medium are solved in the LED regime without adiabatic elimination of the medium polarization, when the population fluctuation spectrum is much narrower than the radiation and polarization spectra. It is shown that population fluctuations significantly increase the output power and collective Rabi splitting of a superradiant LED.

We present a theoretical investigation of cross-Kerr nonlinearities and associated four-wave mixing (FWM) in an $N$-type four-level coherent system. By pairing the probe field with another field, the system involves $\mathrm{\Lambda }$ and V types of electromagnetically induced transparency (EIT) which correspond to two cross-Kerr nonlinearities. Our analysis reveals that both the cross-Kerr nonlinearities and associated FWMs exhibit significant enhancement accompanied by compressed linewidths with increasing the detuning of the third field, though their enhancement behaviors differ remarkably. For the cross-Kerr nonlinearity and the associated FWM arising from the probe-coupling $\mathrm{\Lambda }$-type EIT, the positions of the enhanced nonlinearities remain essentially unchanged with increasing signal detuning, and their magnitudes grow monotonically with the signal detuning. In contrast, for those from the probe-signal $V$-type EIT, the positions of the nonlinearities shift with the increasing coupling detuning, forming a two-photon resonance between the probe and coupling fields, while their magnitudes first increase and then decrease with the coupling detuning.

Tensor networks offer a valuable framework for implementing Lindbladian dynamics in many-body open quantum systems with nearest-neighbor couplings. In particular, a tensor network Ansatz known as the locally purified density operator employs the local purification of the density matrix to guarantee the positivity of the state at all times. Within this framework, the dissipative evolution utilizes the Trotter-Suzuki splitting, yielding a second-order approximation error. However, due to the Lindbladian dynamics' nature, employing higher-order schemes results in nonphysical quantum channels. In this work, we leverage the gauge freedom inherent in the Kraus representation of quantum channels to improve the splitting error. To this end, we formulate an optimization problem on the Riemannian manifold of isometries and find a solution via the second-order trust-region algorithm. We validate our approach using two nearest-neighbor noise models and achieve an improvement of orders of magnitude compared to other positivity-preserving schemes. In addition, we demonstrate the usefulness of our method as a compression scheme, helping to control the exponential growth of computational resources, which thus far has limited the use of the locally purified Ansatz.

We investigate the transport properties of quantum walks on a multihierarchical network which is built by a replication of the dual Sierpinski gasket in the form of a regular dendrimer. The efficiency of the transport is monitored through the exact and the average return probabilities, which are obtained by implementing a continuous-time quantum walk (CTQW) model. All these probabilities (classical and quantum) are determined by knowing the eigenvalues and eigenvectors of the connectivity matrix. For our networks the complete eigenvalue spectrum is determined iteratively, a process that facilitates the analysis of very large networks. The classical return probability can be separated into two distinct components which depend on the underlying topologies: the dual Sierpinski gasket and the dendrimer. The quantum walks show strong localization effects, which are more accentuated when the starting node is peripheral. The quantum long-time average probability is determined analytically, depending solely on the generation numbers of our fractal and dendrimer. For networks with generation number of dual Sierpinski gasket higher than 5 the long-time probability keeps the same and depends only on the spectral dimension of the fractal.

Entanglement is fundamental to quantum mechanics, and accurate certification of entangled states in a device-independent manner is crucial to the functioning of secure quantum information processing. Previous research on entanglement certification primarily relies on projective measurements, while experimental certification of entangled states based on nonprojective measurements remains an unexplored area. In this work, we experimentally certify the two-qubit maximally entangled state using three-outcome nonprojective measurements in the one-sided device-independent scenario. Based on the maximal violation of steering inequality, we can experimentally self-test both the maximally entangled state and the nonprojective measurements performed by the untrusted party. Furthermore, we also experimentally demonstrate that this approach is highly robust when white noise is introduced into the states and measurements. Our work enables further insight into the quantum state certification with nonprojective measurements.

We show that iteration of a $\mathrm{few}(\sim N^{1/4}$) unitary steps of Grover's algorithm suffices to perfectly prepare a Dicke state of $N$ atoms in a cavity. We also show that a few subsequent Grover steps can be employed to generate GHZ and Cat states. The Grover iteration is physically realized by global qubit rotations and by the phase shift of single photons reflected on the cavity. Our protocols are deterministic and require no individual addressing of the atoms. A detailed error analysis accounting for spatial mode matching of the photon to the cavity, spontaneous emission, mirror scattering, and the finite bandwidth of the photon mode is used to predict the fidelity of the prepared states as a function of system parameters and atom-cavity cooperativity. The fidelity can be increased by heralding on detection of the reflected photon.

Quantum reservoir computing (QRC) is a low-complexity learning paradigm that combines the inherent dynamics of input-driven many-body quantum systems with classical learning techniques for nonlinear temporal data processing. Optimizing the QRC process and computing device is a complex task due to the dependence of many-body quantum systems on various factors. To explore this, we introduce a strongly interacting spin model on random regular graphs as the quantum component and investigate the interplay between static disorder, interactions, and graph connectivity, revealing their critical impact on quantum memory capacity and learnability accuracy. We tackle linear quantum and nonlinear classical tasks, and identify optimal learning and memory regimes through studying information localization, dynamical quantum correlations, and the many-body structure of the disordered Hamiltonian. In particular, we uncover the role of previously overlooked network connectivity and demonstrate how the presence of quantum correlations can significantly enhance the learning performance. Our findings thus provide guidelines for the optimal design of disordered analog quantum learning platforms.

Quantum simulators hold promise for solving many intractable problems. However, a major challenge in quantum simulation, and quantum computation in general, is to solve problems with limited physical hardware. Currently, this challenge is tackled by designing dedicated devices for specific models, thereby allowing one to reduce control requirements and simplify the construction. Here we suggest a method for quantum simulation in circuit QED that provides versatility in model design and complete control over its parameters with minimal hardware requirements. We show how these features manifest through examples of quantum simulation of Dirac dynamics, which is relevant to the study of both high-energy physics and two-dimensional materials. We conclude by discussing the advantages and limitations of the proposed method.

We experimentally investigate long-range electron-electron correlation across the two atomic sites of an argon dimer in its dissociative double ionization induced by a linearly polarized 400-nm femtosecond laser field. The correlation between the two electrons, ionized at two atomic sites, is revealed through analysis of the joint kinetic energy spectra and the momentum distributions. Notably, one of the two electrons exhibits a pronounced redshift in the low-kinetic-energy region, in contrast to the electron energy spectrum observed in single ionization of argon dimers. This distinctive spectral feature is corroborated by theoretical simulations, which attribute the redshift to the differing intensity dependence of the kinetic energy distributions of the two electrons, as well as to the influence of electron-electron correlation during the ionization process.

Topological effects, known for their robustness against considerable perturbation, disorder, and defects, are believed to promote emerging quantum technologies. However, topological enhancement and protection could play a crucial role within coherence time, out of which decoherence mostly washes out the quantum feature. It motivates us to accelerate topological effects to achieve effective protection and optimal control of quantum information. Taking the prototypical Thouless pumping as an example, quantized transport of particles in a cyclic adiabatic evolution faces a challenge: slow driving may exceed the coherent time, while fast driving may break quantization. To address this dilemma, we propose to add a control Hamiltonian to speed up Thouless pumping using shortcuts to adiabaticity. Compared to traditional Thouless pumping, our fast quantum pumping scheme not only enables a substantial reduction of pumping time, but also effectively suppresses wave-packet diffusion. Furthermore, we demonstrate the resilience of our protocol to moderate noise levels in both momentum and real space. Our study settles the notoriously critical problem of practical quantum pumping.

Stability of elongated (“slender”) quantum droplets (QDs) with embedded unitary and multiple vorticity is a problem that was not solved previously. In this work, we propose a solution which relies upon the use of the spatial modulation of the interspecies scattering length in the binary Bose-Einstein condensates, in the form of a two-dimensional axisymmetric Gaussian, shaped by means of the optical Feshbach resonance. The corresponding effective nonlinear trapping potential supports completely stable elongated QDs with vorticity $S=0$ and partly stable families of elongated QDs with $S=1,2,3,4$ (other nonlinear systems do not maintain stability of vortex droplets with $\ge 2$). We systematically analyze effects of the amplitude and width of the Gaussian modulation, as well as the total number of atoms, on the shape and stability of the QDs, some effects being explained analytically. Collisions between identical QDs with $S=1$ moving in opposite directions along the central axis leads to their merger into still more elongated breathing QDs with the same vorticity, while collisions between QDs with $S=\pm 1$ are quasielastic. Moving modulation profiles are able to adiabatically rotate the trapped elongated QDs. Application of a torque to the vector QD sets in the gyroscopic regime of robust precession, which realizes a macroscopic spin-orbit-coupling effect.

Classical and quantum states can be distinguished by entanglement entropy, which can be viewed as a measure of quantum resources. Entanglement entropy also plays a pivotal role in understanding computational complexity in simulating quantum systems, especially in tensor network states related methods. However, stabilizer states formed solely by Clifford gates can be efficiently simulated with the tableau algorithm according to the Gottesman-Knill theorem, although they can host large entanglement entropy. In this work, we introduce the concept of nonstabilizerness entanglement entropy which is basically the minimum residual entanglement entropy for a quantum state by excluding the contribution from Clifford circuits. It can serve as a new practical measure of difficulty in the classical simulation of quantum many-body systems, which takes both entanglement and nonstabilizerness into consideration. We discuss why it is a better criterion than previously proposed metrics such as stabilizer Rényi entropy when measuring the difficulty in the classical simulation with tensor network states related method. We also show numerical results of nonstabilizerness entanglement entropy with concrete quantum many-body models. The concept of nonstabilizerness entanglement entropy expands our understanding of the “hardness” in the classical simulation of quantum many-body systems.

We show that in finite dimensions, around any $m$-partite product state ${\rho }_{\mathrm{prod}}={\rho }_1\otimes \cdots \otimes {\rho }_m$, there exists an ellipsoid of separable states centered around ${\rho }_{\mathrm{prod}}$. This separable ellipsoid contains the separable ball proposed in previous works, and the volume of the ellipsoid is typically exponentially larger than that of the ball due to the hierarchy of eigenvalues in typical states. We further generalize this ellipsoidal criterion to a trace formula that yields separable region around all separable states, and further study biseparability. Our criteria not only help numerical procedures to rigorously detect separability, but they also lead to a nested hierarchy of stochastic local operations and classiccal communication (SLOCC)-stable subsets that cover the separable set. We apply the procedure for separability detection to three-qubit X states, genuinely entangled four-qubit states mixed with noise, and the one-dimensional transverse-field Ising model at finite temperature to illustrate the power of our procedure for understanding entanglement in physical systems.