Papers

We give a general framework for tomography of states that have bounded-extent with respect to a structured class of states. Let $\textsf{C}$ be a family of $n$-qubit states such that: $(i)$ $\textsf{C}$ is succinctly representable and $(ii)$ there is a weak agnostic learner of $\textsf{C}$. We give a tomography protocol for an unknown state $|\psi\rangle$ that is promised to admit a decomposition of the form $|\psi\rangle = \sum_i c_i |\phi_i\rangle$, where $|\phi_i\rangle \in \textsf{C}$ with bounded $\ell_1$-norm of the coefficients (which we call extent). Our main contribution is to show that a weak agnostic learner for $\textsf{C}$ can be boosted into a tomography algorithm for states with bounded extent with respect to $\textsf{C}$. Our reduction is black-box and applies broadly across model classes. As an application, when $\textsf{C}$ is the class of stabilizer states, we obtain tomography algorithms for states with stabilizer extent $\xi$ up to trace distance $\varepsilon$, in time $\textsf{poly}(n,(\xi/\varepsilon)^{\log(\xi/\varepsilon)})$, which is improvable to $ \textsf{poly}(n,\xi,1/\varepsilon)$ assuming the algorithmic polynomial Freiman-Ruzsa conjecture in the high-doubling regime. When the unknown state $|\psi\rangle$ is arbitrary, we give an algorithmic decomposition result in the spirit of a weak regularity lemma for quantum states with respect to $\textsf{C}$ and show that the structure in $|\psi\rangle$ that is explainable by $\textsf{C}$ can be efficiently learned. Our main conceptual message is that agnostic learning of a structured base class automatically yields learnability of its low-complexity linear span.

Recent advances have revealed that topology can further enrich the universality classes of quantum phase transitions, thereby extending beyond the traditional paradigms of statistical and condensed matter physics. However, multicriticality between topologically distinct quantum critical lines remains insufficiently explored. In this Letter, we systematically construct and investigate a novel class of topologically enforced Lifshitz multicritical points in one dimensional chiral symmetric fermionic systems. Such multicriticality is driven solely by changes in the topology of neighboring critical lines, beyond previously recognized multicritical points that are typically induced by changes in critical exponents. More importantly, the topologically enforced multicriticality identified here can host robust topological degeneracies while surprisingly exhibiting a breakdown of the Li Haldane bulk boundary correspondence-a phenomenon we elucidate through a simple physical picture.

While damped spin dynamics is important for the understanding of magnetic materials, clear signatures of quantum corrections to the Gilbert damping mechanism remain elusive. We propose a route to distinguish quantum and classical Gilbert spin damping using ferroelectric control of a magnetic dimer. Ab initio calculations for dimers on ferroelectric substrates show that polarization reversal switches the inter-spin exchange between ferromagnetic and antiferromagnetic regimes. We formulate a magnetization-based diagnostic that relates magnetization traces to entanglement dynamics, which enables ferroelectrical on/off control of dimer entanglement. Material-informed quantum Landau-Lifshitz-Gilbert simulations illustrate how the signature of magnetization dynamics can, in principle, be used to infer the existence of quantum Gilbert spin damping. This minimal and non-volatile platform connects first-principles modeling to experimentally accessible observables and provides a starting point for voltage-controlled quantum entanglement in magnetic spin networks.

The performance of quantum error correction (QEC) codes is limited by the underlying physical noise. Theoretical studies show that coherent and stochastic noise have different effects when performing QEC with either surface or repetition codes. We use the bitflip repetition code, realized in a transmon quantum processor, as a testbed to experimentally study the impact of injecting coherent versus stochastic errors on the logical performance. We adapt a scalable free-fermion simulator to simulate the experiments and we modify a subset sampling technique to efficiently sample stochastic noise in the quantum circuit. In the experiment, we do not observe the difference in logical fidelity predicted by simulation for either the distance-3 or distance-5 repetition codes. We hypothesize that this discrepancy could be explained by small drifts in qubit frequencies, which introduce phase-coherent noise that `stochastifies' the injected coherent errors. Our work contributes to advancing an understanding of how coherent errors affect experimental QEC.

In this work, we present constructions of quantum circuits to implement general measurements on quantum hardware. Firstly, we investigate a quantum circuit ansatz by following the Naimark extension with a universal set of gates, such as controlled-NOT and single-qubit gates; we call it a Naimark measurement. We present a circuit ansatz framed by the Naimark extension, leaving single-qubit gates with parameters, and apply a classical optimizer to determine their parameters to approximate a desired quantum measurement. Secondly, we relax the Naimark measurement with quantum neural-network (QNN) circuits, employing parameterized quantum circuits. We present hybrid Naimark-QNN measurements by incorporating QNN circuits into Naimark measurements. Thirdly, we also consider fully QNN measurements with shallow parameterized circuits. Then, we compare the constructed measurement circuits, Naimark, hybrid Naimark-QNN, and fully QNN measurements, for strategies of state discrimination, such as minimum-error and maximum-confidence measurements. We demonstrate that QNN circuits can efficiently and effectively achieve near-optimal quantum measurements with fewer training iterations.

Constructor theory is a proposal to extend quantum information theory beyond both quantum theory and computation, to cover more general machines than programmable computers – called constructors. It consists of newly conjectured physical principles that can be expressed as constraints on what tasks are possible, what are impossible, and why. These principles also determine the repertoire of the universal constructor, which is a programmable machine that can perform all physically possible tasks. The principles of constructor theory have novel physical content that supplements current dynamical laws, leading to new predictions for experimental tests. In this paper, we review the main experimental proposals to test the principles of constructor theory and discuss their implications for existing theories of physics and for their successors.

Quasiparticle poisoning bottlenecks superconducting qubits, limiting coherence and the scalability of quantum processors. In this work, we systematically investigate quasiparticle poisoning in superconducting qubits under three infrared (IR) shielding configurations, ranging from a dedicated multi-layer design to a simplified implementation. By measuring quasiparticle-induced parity switching, we demonstrate a suppression of the switching rate by over four orders of magnitude via the implementation of improved shielding. In the best configuration, the rate decreases over time following cooldown and reaches 0.069$\,$Hz on day 34, corresponding to an anticipated quasiparticle density per Cooper pair of $1.88\times10^{-11}$. To our knowledge, this represents the lowest quasiparticle density reported in the literature to date. The remaining quasiparticle population is likely dominated by sporadic phonon bursts stemming from mechanical stress release in the on-chip films, as well as from the surrounding environment. The effective qubit temperature follows the phonon bath down to 17$\,$mK, enabling initialization errors of $\sim 0.01\%$ for 3$\,$GHz qubits. These results demonstrate that proper IR shielding and thermalization are essential for suppressing quasiparticle poisoning and enabling high-coherence, scalable superconducting qubit systems.

Ising machines are a promising approach to solve combinatorial optimization problems. They map these problems onto the Ising model and search for low-energy configurations. However, navigating the rugged energy landscapes of these systems remains difficult. To improve this navigation, classical adiabatic annealing has been proposed in the literature as a heuristic optimization method for classical Ising machines. Using this technique, the Hamiltonian of the Ising machine is gradually transformed from an easily solvable Hamiltonian to the target Hamiltonian. However, its purported effectiveness is primarily motivated by an analogy to quantum adiabatic annealing, and systematic benchmarking has remained limited. In this work, we analyze the classical adiabatic annealing technique using continuation methods. Motivated by insights from this analysis, we propose an optimized annealing strategy we refer to as hybrid classical adiabatic annealing. We benchmark our proposed strategy using MaxCut instances with up to 800 spins and problems with external fields, for which it achieves a marginal improvement for a limited set of problems. We conclude that, although theoretically motivated and occasionally beneficial, the hybrid strategy does not offer a sufficient practical advantage over simpler, existing techniques.

The traveling salesman problem (TSP) is a classic NP-hard problem. Held–Karp dynamic programming~\cite{held1962dynamic, bellman1962dynamic} solves it exactly in $O(n^2 2^n)$ time, a barrier that has stood for over six decades. Whether quantum computing can surpass $O^*(2^n)$ is a central open question. The authors of~\cite{ambainis2019quantum}\ (SODA~2019) claimed a query complexity of $O^*(1.727^n)$, but we identify a structural counting error: when corrected, their scheme requires $\Omega^*(2^n)$ queries and offers no advantage over classical Held–Karp. We design a quantum divide-and-conquer framework: partition $n$-vertex set into $k$ subsets, classically precompute shortest paths within each, then search over all $k$-partitions via quantum minimum finding. We prove $k=3$ achieves $O^*(1.890^n)$, and $k=4$ attains the global optimum $O^*(1.866^n)$, the first quantum algorithm to surpass $O^*(2^n)$ for general TSP. To convert the query bound into a time-complexity advantage, we overcome the oracle-construction bottleneck by preparing a set partition state, requiring $O(n^2)$ gates and $O(n)$ depth. Leveraging structured state preparation, we achieve a total time complexity of $O^*(1.866^n)$. Qiskit simulations on $n=6,7$ achieve $98.9\%$ and $100\%$ accuracy.

This study investigates the analytical solvability of the Klein-Gordon and Duffin-Kemmer-Petiau (DKP) equations for a scalar particle interacting with a transcendental $\alpha$-attractor-type potential, $V(x) = V_0 e^{a \tanh(bx)}$. We first address the problem of integrability within the framework of Picard-Vessiot theory. By analyzing the differential field extensions associated with the system, we demonstrated that the differential Galois group is the full special linear group $SL(2, \mathbb{C})$. Given that this group is not solvable, we provide rigorous proof for the non-existence of Liouvillian solutions, effectively ruling out any expression in terms of primitives and elementary functions. Building upon this result, we further establish that wavefunctions cannot be represented as finite compositions or transformations of classical special functions, such as those of the Bessel, Whittaker, or Heun families. This second conclusion is supported by the “double-transcendence” of the potential; we prove via the Hermite-Lindemann theorem that no rational coordinate transformation $z(x)$ exists that could map the physical equation into an ordinary differential equations(ODE) with rational coefficients. Consequently, the $\alpha$-attractor potential is strictly non-integrable and lies entirely outside the landscape of solvable relativistic quantum systems.

Quantum software bugs often yield silent, incorrect outputs rather than explicit errors, making them particularly difficult to detect and repair with conventional techniques. Although large language models (LLMs) have shown strong performance on classical software engineering tasks, their ability to debug quantum code remains largely unexplored. To bridge this gap, we propose QBugLM, a multi-agent framework that automates the quantum software debugging pipeline, from taxonomy-driven bug injection to LLM-based detection and repair, and finally to simulation-based validation, for framework-agnostic OpenQASM 3.0 programs. We further conduct a comprehensive case study using QBugLM to benchmark two LLMs, Claude 4.6 Sonnet and Qwen3 Coder Next, across different prompting strategies, bug categories, and quantum programs. Our results show that iterative feedback is critical, as a single retry raises Pass@1 from below 25% to above 80%. Moreover, simpler structured prompting can even outperform Chain-of-Thought and ReAct for reasoning-capable models under fixed-resource constraints. Our work takes initial steps toward benchmarking LLM capabilities for debugging quantum programs and offers practical insights to support future efforts in automated quantum software repair.

We examine the non-Markovian dynamics and the generation of quantum coherence and entanglement within a triple-layer graphene (TLG) system embedded in a planar microcavity. Using time-dependent perturbation theory, we derive an exact analytic solution for the system and demonstrate how the confined electromagnetic field mediates quantum correlations between the graphene layers. We employ three complementary measures; the relative entropy of coherence (REC) to quantify quantum coherence, the tangle to assess tripartite entanglement, and a non-Markovianity measure derived from the REC to characterize quantum memory effects. Our analysis reveals that these quantum resources exhibit remarkable sensitivity to various control parameters. Specifically, we demonstrate that the number of cutoff modes, the spatial positioning of the layers, the momentum parameter, and the interlayer rotation angles provide effective control over coherence, entanglement, and memory effects. We further show that these measures exhibit an exceptional sensitivity to the rotation angle between the layers. Ultimately, our results establish cavity-confined TLG as a highly tunable platform for exploring vacuum-mediated quantum phenomena, providing a framework for the precise manipulation of quantum correlations in graphene-based photonic and optoelectronic devices.

The characterization of the quantum critical properties of genuine non-Hermitian many-body systems remains ambiguous as neither the state considered nor the definition of expectation values is unique. In this work, we investigate the quantum critical properties of two models of non-Hermitian XY spin chains with magnetic field. Using exact solutions, we systematically investigate the parameter dependence of the energy, the magnetization as well as the long-distance asymptotic behavior of static correlation functions. We compute expectation values within the standard formalism of quantum mechanics as well as within biorthogonal quantum mechanics and take two different states which one might reasonably consider to be the analog of the ground state of a Hermitian model. The critical properties, including such fundamental characteristics as the phase diagram, depend on both the formalism used as well as the state considered. We provide arguments in favor of the use of standard quantum mechanics. Which state to be taken in computations, depends on the (hypothetical) experimental preparation of the system.

We theoretically investigate circular dichroism in the ion yield following $1+1+1$ ionization of 3-methylcyclopentanone using femtosecond linearly chirped laser pulses, inspired by recent experiments by Das et al. [Phys. Chem. Chem. Phys. 27, 8043 (2025)]. To this end, we numerically solve the time-dependent Schrödinger equation and evaluate the total population in the Rydberg states at the end of the second absorption step. The A-band transition in the first absorption step is treated using state-of-the-art quantum-chemical calculations, whereas the second absorption step is described via an effective model. Within our framework, we identify the interplay between the first and second absorption step as the key explanation for the experimentally observed chirp dependence of the anisotropy. By elucidating this mechanism for the chirp-enhanced signal, our findings contribute towards the development of improved control schemes for chiral molecules.

In this work we show that long-range interactions can be significantly beneficial for implementing shortcuts to adiabaticity (STA) in many-body open quantum critical systems driven out of equilibrium, as well as for charging quantum batteries in the presence of dissipation. In sharp contrast to short range interactions where passage through criticality may demand STA control with non-zero interactions between infinitely distant spins, using the example of a Kitaev chain with long-range couplings, we find that the corresponding control may involve involve interaction strength with decays algebraically with distance. In case of non-unitary control, the advantage of long-range interactions manifest through reduction in the cost of STA. We further propose a modified STA technique aimed at charging a quantum battery in the presence of dissipation, in which case long-range interactions may enhance the resultant ergotropy. Our results establish long-range interactions as a valuable resource for quantum control, with direct implications for quantum technologies.

Continuous-variable quantum key distribution (CV-QKD), which uses quadratures of the electromagnetic field, enables practical quantum communication using standard telecommunication technologies. Unidimensional CV-QKD (UD-CVQKD) simplifies the implementation by restricting modulation to a single quadrature. In this work, we experimentally demonstrate a free-space Gaussian-modulated UD-CVQKD system operating under a high detector electronic-noise regime (1.4 shot-noise units). The system employs polarized coherent states with signal and local oscillator co-propagating in the same spatial mode in orthogonal polarizations, ensuring stable interference. System security is analyzed under both untrusted (UTD) and trusted (TD) detector noise models. While no positive secret key rate is obtained under the UTD model, the TD model enables secure key generation over a finite range of modulation variances, highlighting the critical role of detector trust in high-noise conditions. A maximum secret key rate of 270 kbps is achieved at an optimal modulation variance of 11.57. Furthermore, secure operation requires high-transmittance (low-loss) channels under such noise conditions. This study demonstrates the practical feasibility of free-space UD-CVQKD in realistic high electronic-noise detection constraints and highlights detector electronic noise as a key limiting factor in practical systems.

In classical settings, the Mpemba effect occurs when a hotter system cools faster than an initially colder one. In quantum systems, this effect can be reinterpreted exploiting the concept of symmetries, with the asymmetry of a subsystem playing the role of temperature. A quantum Mpemba effect arises when a more asymmetric state restores the symmetry faster than a less asymmetric one. Previous work mainly focuses on closed systems characterized by thermal equilibration and Hamiltonian symmetries. In this paper, we analyze the dynamics of asymmetry in an open quantum many-body system featuring symmetry breaking and uncover dynamical behavior that appears to be unique to these settings. In the symmetric phase, we demonstrate the existence of a quantum Mpemba effect, which emerges as a direct consequence of a non-monotonic evolution of the asymmetry. In the broken-symmetry phase, we analyze the imbalance between the system's ability to increase or to decrease its asymmetry. Our results extend the notion of quantum Mpemba effects to open quantum many-body systems exhibiting symmetry-breaking phase transitions and establish them as a platform for observing and controlling anomalous relaxation phenomena.

Continuous-time Quantum Annealing (QA) is a strategy for preparing the ground state of nontrivial many-body systems. In its standard form, the dynamics is generated by a time-dependent interpolation between a simple driving Hamiltonian and the target problem Hamiltonian, usually implemented through a linear schedule. This approach faces the crucial bottleneck of small spectral gaps, which may require exponentially long annealing times to ensure adiabaticity. Here, we show how to implement quantum control over the annealing schedule in a frustrated Ising ring, one of the simplest models exhibiting an exponentially small bottleneck gap. By optimizing smooth continuous-time annealing schedules with a dressed-CRAB approach, and using a digitized representation of the dynamics to efficiently evaluate gradients, we construct protocols that strongly outperform standard fixed schedules. The optimized dynamics bypasses the bottleneck through a strongly nonadiabatic mechanism, leading to efficient ground-state preparation despite the exponentially small minimum gap. In particular, the annealing time required to reach a fixed residual-energy threshold is found to grow linearly with system size rather than exponentially. We further examine a lowest-order variational counter-diabatic correction and find that, once schedule optimization is allowed, it does not lead to any improvement.

We experimentally demonstrate an improved optical biasing scheme for superconducting nanowire single-photon detectors (SNSPDs), which employs a cryogenic InGaAs-InP photodiode (PD) as a local bias source. It is found that, under illumination from a stable external light source, this PD generates a stable photocurrent in a cryogenic environment (~2.3 K), with fluctuations in the photocurrent primarily attributed to fluctuations in the incident optical power. Furthermore, by screening and effectively blocking stray photons leaking from the PD, which give rise to background dark counts, we have achieved an SNSPD exhibiting an ultra-low intrinsic dark count rate of 1e-4 cps. Utilizing this improved optical biasing technique, our SNSPD achieved performance comparable to that obtained under conventional electrical biasing: a system detection efficiency of 80.7%, a background dark count rate of 32.6 cps, and a minimum timing jitter of 57.5 ps. These results indicate that cryogenic-PD-based optical biasing serves as a viable, low-noise, and low-jitter alternative to traditional electrical biasing. Moreover, this work offers useful design guidance for the future development of PD-based low-noise bias sources and for the construction of all-photonic SNSPD systems tailored for high-precision quantum photonics applications.

Quantum computing offers several algorithms for computing the ground state of a problem Hamiltonian. Algorithms in the Fault-Tolerant Quantum Computing (FTQC) regime, such as Quantum Phase Estimation (QPE) and Quantum Signal Processing (QSP), are the most desirable because they offer optimal asymptotic scaling. In the Noisy Intermediate Scale Quantum (NISQ) regime, the most realistic approaches involve Variational Quantum Eigensolver (VQE) algorithms and their variants. A central difference between the two regimes is that FTQC algorithms do not prepare the ground state via direct state transition. Instead, they build a project that identifies the ground state using ancillary qubits that flag the target subspace. The desired state is then recovered via amplitude amplification or post-selection. In this work, we propose a VQE ansatz whose structure is more similar to that of an FTQC algorithm. We introduce the Projector Variational Ansatz (PVA), which incorporates the projector structure into the adaptive variational setting. Depending on its parametrization, this ansatz can be equivalent to either an Adaptive Derivative-Assembled Pseudo-Trotter (ADAPT)-VQE when all ancilla mixing angles vanish, or to an Intermediate Scale Quantum (ISQ)-QSP quantum circuit structure. We benchmarked PVA against an ADAPT-VQE baseline using both qubit-excitation and fermionic-operator pools. We propose an implementation in which an L-layer PVA circuit is designed using 3L + 1 parameters and requires only one ancilla and two additional CNOT gates per Pauli generator used in ADAPT. Our experimental results show that this first proposal for PVA converges using fewer CNOT gates than the standard ADAPT-VQE on the tested system.

We study thermal quantum correlations and coherence in Heisenberg $XY$ model with anisotropic interactions under a uniform magnetic field $ B $. Using concurrence $C$, local quantum uncertainty (LQU), Bell-Clauser-Horne-Shimony-Holt (CHSH) nonlocality $ \mathbb{B}$, and coherence $C_l$ as quantifiers, we analyze how magnetic anisotropy $ \delta_m $, coupling anisotropy $ \delta_c $, Dzyaloshinskii-Moriya (DM) interaction $ D $, temperature $ T $, and magnetic field $ B $ modulate quantum resources. At low temperatures and relevant magnetic fields, the entanglement is maximized, but exhibits sudden death for $ \delta_m = 0 $, which turns into a smooth decay as $ \delta_m $ increases, highlighting its stabilizing role. LQU shows that stronger anisotropy suppresses quantum correlations, while $ \mathbb{B} $ induces a non-monotonic response peaking at a critical field $ B_c $. Bell-CHSH nonlocality violations ($ \mathbb{B} > 2 $) persist below $ B_c $, but thermal noise ($ T \geq 1 $) suppresses them. Coherence $ C_l $ is most robust to thermal fluctuations, especially for high \( \delta_m \), which also dampens abrupt quantum phase transitions. The DM interaction is essential for entanglement generation, with $ D $ and anisotropy synergistically enhancing correlation resilience. We identify a hierarchy of thermal degradation: nonlocality ($ \mathbb{B} $) vanishes first, followed by entanglement ($ C $), then general quantum correlations (LQU), while coherence $ C_l $ persists the longest. These results demonstrate tunable control of quantum resources via anisotropy and external parameters, providing insights for the design of robust spin-based quantum technologies.

Multipartite entanglement forms the core of many networking applications. In the near-term future, it is expected that multipartite distribution will be achieved first through star topologies, making it important to understand the noise incurred during the distribution process. In such networks, elementary links are created stochastically and successful links must be stored while waiting for the remaining links, causing memory decoherence that depends on the random waiting times. We derive analytical expressions for both the average noise and its distribution, when distributing GHZ states under memory dephasing in star networks. We study and compare two distribution protocols: the factory and piecemaker protocol. Furthermore, we find expressions for the case of a global cut-off (allowing fast optimization of the cut-off without requiring Monte Carlo simulations) and extend the analysis for the factory protocol to depolarizing noise for arbitrary states.

We propose a non-Hermitian Floquet photonic lattice formed by a physical resonator coordinate and a synthetic frequency coordinate. A two-step modulation protocol realizes a chiral walk in this physical-synthetic plane, with a real synthetic flux controlling loop interference and imaginary gauge fields controlling non-reciprocal envelopes. We show that anomalous corner pairs at quasienergies zero and \(\pi/T\) exhibit three distinct layers of physics. A non-Bloch higher-order construction predicts whether the \(0/\pi\) corner pair exists under open boundaries. The imaginary gauge fields select where the right eigenmodes accumulate. The real flux controls the local interference matrix element that determines whether the doubled-period optical response is visible. As a result, the same topological coexistence sector can be bright, skin-dark, or flux-dark in a local optical measurement. We further show that the complex gauge can tune an exceptional point of the two-period corner propagator. At this point the anomalous response keeps its doubled-period sign alternation, but its envelope becomes algebraic because of a Jordan block. These results provide a photonic route to separate topological existence, skin-selected localization, optical visibility, and defective two-period dynamics in a non-Hermitian synthetic dimension.

The solution of large-scale eigenvalue problems is crucial in nuclear many-body theory, where Hamiltonian matrices often reach extremely large dimensions. Quantum computing opens new perspectives for addressing such demanding problems. Although the Quantum Phase Estimation algorithm offers, in principle, a systematic route to matrix diagonalization, its practical deployment demands levels of coherence and error correction that current quantum hardware cannot yet support. A viable near-term strategy is instead to exploit quantum annealing, which enables the recasting of eigenvalue problems into quadratic unconstrained binary optimization formulations that can be addressed by existing annealing-based processors. Here, we propose a hybrid quantum-classical algorithm that combines quantum annealing and classical deflation to iteratively extract the full eigenspectrum of both standard and generalized eigenvalue problems. We benchmark this method on eigenvalue problems arising from the Equation of Motion Phonon Method performing calculations on real quantum hardware. Our approach illustrates the capabilities and limitations of near-term quantum devices in addressing nuclear eigenvalue problems.

We investigate the emergence of chaotic Bohmian trajectories in a three-mode superposition of the ground and first excited states of a two-dimensional anisotropic harmonic oscillator. The analysis focuses on the interference-induced phase structure of the wavefunction, which determines the Bohmian velocity field through its phase gradient. We show that the spatial extent of chaotic motion is controlled by the temporal coherence of the interference pattern, set by the detuning between oscillator modes. Near resonance, slow beating generates long-lived phase-gradient structures that repeatedly stretch and fold nearby trajectories, leading to more spatially extended chaotic regions. In contrast, strong detuning produces rapid temporal decorrelation of the phase field and confines chaotic dynamics to localized regions of configuration space. To quantify this behavior, we use a dimensionless coherence parameter comparing the beating time scale with a characteristic transport time. The results identify temporal coherence of the interference-induced phase field as a useful diagnostic for chaotic transport in low-dimensional Bohmian systems.

We investigate the effect of light on quantum metric-mediated intrinsic nonlinear Hall conductivity in Berry dipole semimetals. We discover that light induces a tunable asymmetry in the off-diagonal part of the quantum metric, which is manifested by an asymmetry in the quantum metric dipole. We show that the nonlinear response can be tuned directly by the light amplitude. In particular, we note that the direction of the nonlinear Hall signal changes when the light amplitude is increased beyond a threshold value. Light thus emerges as a promising stimulus to control the quantum geometric response in topological semimetals.

The nonlinear dynamics of a mechanical resonator in an optomechanical system with linear, quadratic and cubic photon-vibration interactions (with respect to mechanical displacements) in a modulated driving field under conditions of adiabatic elimination of the optical field is studied. Based on the constructed bifurcation diagrams of the mechanical coordinate and the largest Lyapunov exponent as a function of the modulation amplitude, as well as power spectra, phase portraits and Poincare sections, regions of regular and chaotic dynamics of the optomechanical system are identified. It is also shown that for a certain modulation amplitude in the presence of all three types of interactions, chaotic dynamics of the mechanical resonator (oscillator) is realized, which is replaced by quasi-periodic oscillations in the absence of cubic interaction, and the system returns to chaotic behavior if only linear interaction remains. This non-monotonic dependence of chaotic dynamics on the order of nonlinearity originates from the interplay between parametric driving and effective potential reshaping and manifests that nonlinearity does not always enhance chaos. For an optomechanical system in a membrane-in-the-middle configuration, where only quadratic photon-vibration interaction is present, it is demonstrated that at small modulation amplitudes the mechanical oscillator exhibits quasi-periodic motion in each of the wells of a symmetric two-minimum potential, whereas large modulation amplitudes lead to chaotic motion, involving interwell transitions.

Nonreciprocal transmission (classical nonreciprocity) in optomechanical systems based on asymmetric Fabry-Perot (F-P) cavities has been theoretically proposed and experimentally demonstrated. However, nonreciprocal quantum effects, particularly nonreciprocal quantum entanglement, remain unexplored in such systems. Here, we propose to generate nonreciprocal optomechanical entanglement in an asymmetric F-P cavity and discuss the connection between the nonreciprocal transmission and nonreciprocal quantum entanglement. We reproduce the nonreciprocal transmission spectra by solving the quantum Langevin equations, and then discuss the optimal parameters to achieve nonreciprocal optomechanical entanglement in the system. We show that a greater and more robust optomechanical entanglement can be approached in the asymmetric F-P cavities, in comparing with the symmetric cavities. Furthermore, we find that the degrees of classical and quantum nonreciprocities do not exhibit positive correlation as expected. Our work shows that the classical and quantum nonreciprocities can be realized simultaneously in the asymmetric F-P cavities, which provide a platform to explore the connection between classical and quantum nonreciprocities.

Superconducting circuit devices require electrical interconnects between different circuit elements on the chip, for which conventional device architectures use a combination of two structural elements: airbridges to connect non-adjacent elements in the base layer, and bandages to connect the electrodes forming the Josephson junctions to the base layer. Bandages introduce unwanted parasitic material interfaces and increase the manufacturing complexity. Here, we overcome the limitations imposed by bandages by establishing all electrical interconnects with airbridges of varying size fabricated in a single step. The airbridges show a high yield and mechanical stability over a wide range of sizes from $0.5\,\mu\mathrm{m}$ to $4\,\mu\mathrm{m}$ in width and from $5\,\mu\mathrm{m}$ to $40\,\mu\mathrm{m}$ in length, and show low loss when integrated in coplanar waveguide resonators and transmon qubits. Measured relaxation times up to more than $250\,\mu\mathrm{s}$ in standard transmon geometries show that the process achieves high coherence while substantially easing and accelerating device fabrication.

Quantum simulation requires highly accurate input states. Gutzwiller-projected Bardeen-Cooper-Schrieffer (BCS) states provide physically motivated input states for solving strongly correlated lattice models, but their preparation on a quantum computer is hindered by the non-trivial nature of the Gutzwiller projection. We construct scalable quantum algorithms for this task by combining a circuit construction for arbitrary BCS states with the amplitude amplification for Gutzwiller projection (AAGP) procedure. AAGP yields a quadratic reduction in the number of projection queries compared with measurement-based postselection and leads to substantially improved fault-tolerant resource scaling. For projected BCS states optimized for the square-lattice $t$-$J$ model, we find that the projected-state weight decreases exponentially with system size, but the quadratic improvement is still large enough at physically relevant finite sizes to make a decisive practical difference. In particular, for a 100-site benchmark, AAGP reduces the required number of projection queries by about seven orders of magnitude. These results establish AAGP as an enabling input-state preparation protocol for projected BCS states in quantum simulation.