Papers

Qubit leakage is a noticeable source of errors for quantum computing. In quantum processors, leakage excitations traveling between qubits generate correlated errors and perturb gate implementations. Leakage mobility can also be utilized for creating dedicated leakage removal pathways and removal units. To quantitatively characterize leakage mobility and to guide better design of processor architectures, we study here leakage dynamics in transmons with tunable couplers through numerical and analytical methods. Even if the couplers are tuned to cancel the single-excitation exchange or the ZZ interaction, the leakage hopping rates still persists in the range of 0.8-10 MHz due to transmon nonlinearity. In typical operation regimes, however, transmon frequency detuning localizes leakage excitations. The next-nearest-neighbor transmons can be still be near-resonant opening leakage tunneling channels. To suppress longer-range hopping, we find that the frequency spread of the next-nearest-neighbor transmons needs to be in the range of 1-4 MHz. Utilizing leakage mobility, we propose two passive leakage removal units. One is based on a tunable coupler and a pumped transmon, and another on a junction readout scheme. Based on realistic experimental parameters, our results on selectively mobilizing or localizing leakage excitations are readily applicable in superconducting quantum devices.

The chirality-induced spin selectivity (CISS) effect has been invoked to explain recent reports of differences in the time-resolved EPR signals between chiral and achiral molecules. However, the microscopic origin of these differences and their connection to CISS remains contested, particularly since these systems lack a metal interface. Here we introduce an intramolecular spinterface-like mechanism that naturally arises within donor-chiral bridge-acceptor (D–$\chi$B–A) complexes and quantitatively reproduces experimentally reported observed spin polarization in time-resolved EPR studies. In our two-electron Lindblad model, the photoexcited charge-transfer electron traversing the chiral bridge exchanges with the residual donor electron, which acts as a localized magnetic moment analogous to an induced magnetic moment on an electrode surface. The resulting through-bridge charge current produces an effective solenoidal field at the donor–bridge interface, breaking spin degeneracy and directional symmetry, thus enabling spin-selective transport without invoking intrinsic spin-orbit coupling on the bridge. We show that the interplay between this current-induced field, donor thermalization (which breaks time-reversal symmetry), and bridge spin mixing yields tens-of-percent polarization over realistic experimental conditions and charge-transfer time scales, matching reported CISS signatures in triads and DNA hairpins. By explicitly resolving the dependence on solenoidal coupling strength, temperature, and spin-mixing rates, the model identifies the regime in which internal spinterfaces can generate robust CISS-like spin filtering. These findings demonstrate that CISS-like signals in isolated D–$\chi$B–A complexes are fully compatible with a spinterface mechanism, providing a unified conceptual framework for interpreting both device-based and molecule-internal CISS platforms.

High-fidelity quantum gates are essential for scalable quantum computation. However, at short durations, short-timescale waveform distortions break the time-reflection symmetry of control pulses, preventing the precise closure of cyclic evolution. This mechanism renders conventional symmetric protocols intrinsically over-constrained. Conventional strategies typically rely on smoothing the pulse envelopes or embedding the interaction pulse within a longer qubit pulse to bypass short-timescale distortions, which inevitably leads to a persistent speed-fidelity trade-off. To overcome this limitation, we introduce a cyclic control strategy based on parameter-space expansion, which restores controllability by incorporating an additional degree of freedom. We experimentally demonstrate this approach in a superconducting controlled-Z gate, achieving robust suppression of coherent errors without increasing gate duration, reducing the average coherent error from 0.27% to 0.12% across multiple two-qubit gates, as validated by cross-entropy benchmarking. Our results establish a general route to fast, high-fidelity cyclic quantum gates beyond the conventional speed-fidelity trade-off.

Far-field spatial coherence dictates the interference properties of scattered light and thermal emission. Traditionally, these phenomena are treated through disjointed paradigms: classical scattering descriptions assume cold objects lacking quantum fluctuations, idealized quantum scattering schemes ignore dissipation, and semiclassical fluctuational electrodynamics relies on phenomenological noise currents, precluding the consistent treatment of incident quantum states. Here, we develop a first-principles framework based on the modified Langevin noise formalism to unify the scattering of quantum light and the intrinsic thermal emission of finite dissipative objects. We demonstrate that the outgoing far-field spatial coherence separates into an algebraic superposition of two geometry-driven mechanisms, coupled by the global unitarity of the radiation-matter dynamics. The first mechanism, elastic scattering, acts as a non-unitary spatial filter, mode-selectively attenuating and reshaping incident quantum correlations. The second mechanism, thermal emission, originates from localized material dissipation and projects the object's absorption profile into the far field, providing a quantum-vectorial derivation of the macroscopic van Cittert-Zernike theorem. Applying this framework across optical regimes, we determine operational bounds for lossy quantum photonics. Under chaotic thermal illumination, we analytically demonstrate thermal cloaking at equilibrium and show that a passive sink casts a structured thermal shadow geometrically identical to a primary emitter. Under coherent illumination, we derive a thermodynamic phase diagram bounding macroscopic phase correlations, demonstrating that subwavelength nanostructures undergo substantial coherence degradation compared to bulk objects. Finally, under spatially entangled illumination...

We develop a quantized screw-mode mechanism for chirality-induced spin selectivity (CISS). The corresponding quantum, termed a heliciton, is a screw-symmetric environmental excitation with phase $\phi-qz$, longitudinal momentum $\hbar q$, and energy $\hbar\Omega_q$. Its absorption and emission convert the static local chiral vertex developed in our preceding work into an inelastic resonant scattering process. In first Born approximation, absorption maps $\uparrow,k$ to the $\downarrow,k+q$ sideband, whereas emission maps $\downarrow,k$ to the $\uparrow,k-q$ sideband. The two outputs share the sampled-current overlap $\mathcal J_\chi(k)$ but differ in ladder factors, final momenta, and detunings. With spectral factors $\mathcal S_+$ and $\mathcal S_-$, $P_{\rm sb}=[\mathcal S_--\mathcal O(T)\mathcal S_+]/ [\mathcal S_-+\mathcal O(T)\mathcal S_+]$, where $\mathcal O(T)=\exp[-\hbar\Omega_q/(k_BT)]$. An isolated emission or absorption resonance yields $P_{\rm sb}\simeq+1$ or $-1$, respectively, in the resolved sideband sector. Reversing the screw handedness interchanges the spin identities of the two sidebands while leaving their spectral and occupation weights unchanged, and therefore reverses $P_{\rm sb}$ at every temperature. At high temperature, absorption and emission have nearly equal occupation weights; at low temperature, absorption is exponentially suppressed while spontaneous emission remains. Liquid-nitrogen temperature can already produce a pronounced asymmetry for higher-$\Omega_q$ modes. Thus a spatially resolved Dirac wave with spin-dependent helical conserved current couples locally to a heliciton and produces thermally weighted spin- and momentum-resolved sidebands without an ad hoc spin-dependent potential.

Quantum discord captures quantum correlations beyond entanglement and can remain finite even when the entanglement vanishes. We investigate the transient nonequilibrium dynamics and steady-state behavior of quantum discord and classical correlations in a double quantum dot (DQD) system coupled to fermionic reservoirs. By employing a quantum Langevin equation formalism, we obtain the exact reduced density matrix of the system, enabling a comprehensive analysis of its quantum and classical correlations under nonequilibrium conditions. The influence of system-reservoir coupling strength, spectral bandwidth, thermal bias, and varying initial state on both the transient dynamics and steady-state correlations is systematically analyzed. Quantum discord remains finite in the nonequilibrium steady state over a broad parameter range. Although thermal gradients reduce the overall magnitude of correlations, quantum discord persists and exhibits greater resilience. These results demonstrate that nonequilibrium electronic transport, together with the environmental spectral properties and reservoir asymmetry, provides an effective means of controlling nonclassical correlations in mesoscopic systems and establishes quantum discord as a robust hallmark of open fermionic quantum devices.

We investigate the effect of interferometer delay and imbalance on the performance of a BB84 time-bin quantum key distribution system. We simulate the impact of interference visibility on system performance and measure the visibility of a pair of interferometers as a function of their relative time delay and intensity imbalance. In addition, our analysis highlights the effect of laser chirp on system performance.

Population transfer via chirped rapid adiabatic passage is studied using open quantum and semiclassical models, with and without the rotating-wave approximation. A time-dependent variational approach based on the multiple-Davydov D$_2$ trial state is employed to simulate the quantum models with an arbitrary finite mean photon number. We examine the accuracy of both the semiclassical field description and the rotating-wave approximation. Robust population transfer is identified over a wide parameter regime controlled by the laser spectral chirp and is found to be insensitive to the spin–phonon coupling strength, Gaussian pulse area, and energy gap of the two-level system.

Adaptive Derivative-Assembled Problem-Tailored variational quantum eigensolvers (ADAPT-VQE) represent one of the most promising approaches for quantum chemistry on near-term quantum devices. However, their optimization is slow and may stall due to vanishing parameters and redundant operators in the ansatz. In this work, we propose a simple strategy of operator elimination that removes non-contributing operators from the pool once they are detected, enabling the optimization to continue progressing toward convergence. We examine two variants, with and without pool restoration after elimination, and find that the former converges more smoothly and faster than the latter and the standard ADAPT-VQE. To capture dynamical correlations between the active space and its environment, we combine ADAPT-VQE with our recently developed downfolding approach, the one-body downfolding framework (OBDF). In OBDF, the bare molecular Hamiltonian in the active space is replaced by a correlated effective Hamiltonian that incorporates dynamical correlation effects outside the active space. We benchmark our implementation on a linear \ce{H_6} chain, an \ce{H_6} lattice, an \ce{H_6} ring, and the \ce{N_2} molecule using the OpenFermion simulator. Our results show that operator elimination significantly reduces circuit depth and iteration count, and that OBDF-ADAPT-VQE yields energies closer to the full configuration interaction (FCI) reference than the standard approach within the same active space.

Deterministic single-photon sources are indispensable core devices for quantum information technology, yet high-performance implementation remains a long-standing bottleneck for linear optical quantum computing. We propose a feasible scheme for deterministic single-photon emission based on a $\triangle$-type three-level atom coupled to a single-mode cavity, driven by two classical external fields, which is adaptable to both strong and ultrastrong cavity-atom coupling regimes. Under continuous-wave driving, the system achieves excellent single-photon characteristics: the normalized equal-time second-order correlation function reaches $g^{(2)}(0)\sim10^{-6}$, with a photon indistinguishability of $98.73\%$ and a state purity of $99.95\%$ in the strong coupling regime, while the ultrastrong coupling regime further suppresses $G^{(2)}(0)\sim10^{-8}$, yielding an indistinguishability of $99.10\%$ and a purity of $99.99\%$. For pulsed driving in the ultrastrong coupling regime, the source realizes superior performance, with an emission efficiency, indistinguishability, and purity of $99.96\%$, $98.98\%$, and $99.99\%$ under resonant conditions, and $100\%$, $95.91\%$, and $99.93\%$ under detuned conditions, respectively. The near-ideal optical performance of the proposed scheme provides a viable route for constructing high-quality deterministic single-photon sources, which offers a promising solution to the limitations of conventional single-photon devices and facilitates the further development of quantum information science and fundamental quantum optical research.

The emergence of multiple superradiant phases in Dicke lattice models has attracted considerable attention in the quantum optics community. However, a unified understanding of the origin of multistability and its relation to different superradiant phases is still lacking. Here, we develop a configuration-based understanding to classify the superradiant phases in Dicke lattices. We show that photon hopping naturally organizes the possible superradiant configurations according to the lattice symmetry, providing a unified interpretation of the nonequilibrium phase diagram and the emergence of multistability. For the dissipative four-site Dicke lattice, we obtain the complete phase diagram and identify the coexistence of up to four stable superradiant phases. The proposed classification is further extended to five- and six-site lattices. Moreover, we demonstrate that the same configuration-based understanding also applies to the closed Dicke lattice, where the ground state uniquely selects one of the allowed configurations. Finally, we show that different configurations may belong to either same or distinct nonequilibrium universality classes in the dissipative Dicke lattice, while they share the same equilibrium universality class in the closed Dicke lattice. Our results provide a unified picture for understanding equilibrium and nonequilibrium superradiant phase transitions in Dicke lattices.

Hybrid quantum platforms based on highly excited Rydberg atoms coupled to nanophotonics devices offer a promising route toward scalable quantum networks and integrated quantum technologies. However, the close proximity of Rydberg atoms to dielectric nanostructures makes these systems particularly susceptible to uncontrolled surface electric fields that can lead to a degradation of the excitation process. Here, we experimentally investigate Rydberg excitation of laser-cooled $^{87}$Rb atoms via the evanescent field of an optical nanofiber in the presence of fiber-guided red- and blue-detuned light fields as used to trap ground state atoms in fiber-based dipole traps. We observe a time evolution of the Rydberg excitation spectrum when both the dipole trapping fields are on and the additional spectral features that appear can be suppressed by applying an external oscillating electric field to the system, strongly indicating that surface charge accumulation is responsible for the observed spectral feature. The experimental results are reproduced qualitatively by a model that incorporates DC energy level shifts arising from electric fields generated by charges deposited on the nanofiber surface. We identify Rydberg-ground state collisional ionization, which is enhanced by the dipole trapping fields, as the dominant mechanism for charge generation. These results provide new insight into charge dynamics at dielectric nanophotonic interfaces and establish practical guidelines for mitigating surface charge-induced electric fields in fiber-integrated Rydberg quantum systems.

Quantum contextuality is a vital non-classical resource, yet illuminating the precise mechanisms through which it enables unconditional computational advantages remains a challenge. We translate graph-theoretic formulations of contextuality into an unconditional quantum memory advantage for formal language recognition. We define a promise problem on an exclusivity graph $G$ where any classical finite automaton respecting exclusivity requires $N \ge \chi(G)$ memory states, whereas a QFA requires a memory of dimension $d = \xi(G)$. The gap between these bounds isolates a structural, information-theoretic incompatibility between classical and quantum descriptions that we term representational contextuality. For Boolean orthogonality graphs, this exacts an exponential classical memory penalty ($d=\mathcal{O}(n)$ vs $N=2^{\Omega(n)}$). Finally, we demonstrate a sharp algorithmic phase transition: allowing the classical machine a finite confusability of mutually exclusive events reduces this exponential classical memory cost to $\mathcal{O}(n)$.

Superconducting quantum chips commonly utilize quarter-wavelength ({\lambda}/4) transmission line resonators as readout circuits. An analytical model for the accurate determination of resonance frequencies and coupling Q-factors of feedline-coupled superconducting resonators is introduced. The model leverages four-port microwave network analysis, integrating boundary conditions and conformal mapping techniques to compute even- and odd-mode impedances in edge-coupled coplanar waveguide (CPW) structures. Its versatility allows application to both planar and 3-D heterogeneous architectures, making it a powerful tool for resonator design. To validate the model, a test chip with {\lambda}/4 resonators of varying geometries is fabricated and measured in a cryogenic environment. Comparisons with finite element method (FEM) simulations and experimental measurements confirm the model's accuracy, with resonance frequencies and coupling Q-factors aligning closely across configurations. This proposed model facilitates the design of superconducting resonators in readout circuits for more effective, scalable, and adaptable quantum computing architectures.

Multi-core quantum computing architectures have emerged as a promising solution to the qubit scalability limitations of monolithic NISQ devices. Quantum algorithms are expressed as quantum circuits composed of single- and two-qubit gates. However, circuit scheduling in multi-core quantum systems remains largely unexplored. Reducing overall execution time (makespan), increasing core utilization, and hiding communication latency behind computation depends on effective scheduling. In this paper, we first introduce a layered scheduling approach as a baseline where quantum gates within the same layer are executed in parallel, while layers themselves are executed sequentially. We then propose a greedy scheduling strategy which schedules each gate as soon as all its dependencies and required resources are available. This allows fine-grained parallelism across cores. Our evaluation shows that on real benchmarks, greedy scheduling achieves an average 40% reduction in makespan and improvement in core utilization. The results suggest that the use of intelligent circuit scheduling to exploit parallelism can greatly enhance the speed of circuit execution in multi-core quantum architectures.

We present a theoretical framework for spontaneous Raman scattering that fundamentally bridges quantum-mechanical and nonlinear-optical approaches. By conceptualizing spontaneous Raman scattering as a stimulated Raman gain or loss event seeded by the quantum vacuum field, we rigorously derive the spontaneous Raman cross-section directly from the third-order nonlinear susceptibility. Crucially, this framework predicts the existence of a hitherto unrecognized phenomenon: "spontaneous Raman loss" (sRL), which acts as the vacuum-seeded counterpart to stimulated Raman loss, complementing traditional spontaneous Raman scattering (spontaneous Raman gain, sRG). Furthermore, we establish a rigorous connection to the traditional Kramers-Heisenberg-Dirac (KHD) theory, revealing that the spontaneous process is governed by interference before a detector between the signal field emitted from molecules and the vacuum field itself that stimulates the molecules. This insight uncovers a direct correspondence between the sRG susceptibility and the rotating/counter-rotating interference terms in the KHD formula. Ultimately, we extend the foundational KHD theory by incorporating previously unrecognized essential terms, achieving perfect analytical agreement between the quantum mechanical and nonlinear optical descriptions of Raman scattering.

State-of-the-art two-qubit gates with trapped ions employ open-loop control that rely on simplified models to precompute control sequences. Our aim is to introduce closed-loop control for two-qubit gates to correct disturbances as they occur during the gate implementation. We introduce a spectator ion into the ion chain used for quantum logic processing, where it couples with the other ions through collective motional modes. The spectator ion's position is continuously monitored by driving dipole transitions and detecting the resultant fluorescence. We show that incorporating a spectator ion is feasible for linear Paul trap implementations and is expected to reduce the two-qubit gate Bell-state preparation infidelity by an order of magnitude with the deleterious effects of position monitoring being negligible compared to the thermal effects that exist in the system, even in the absence of the spectator ions. Mathematically, we describe driven ion-trap dynamics, including the spectator ion, by a stochastic quantum master equation involving the amplitude-modulation multimode-motional coupling gate, motional drift, thermal effects, recoil from photon scattering, spontaneous decay, and light shift. Our on-the-fly control method employs reinforcement learning with the reward function based on the actual geometric phase of the spectator ion. A key advantage of our approach is that we introduce a control method that involves `learning' and correcting disturbances happening in the trap on-the-fly, thus achieving high-fidelity gates. Our approach will lead to a significantly higher two-qubit gate fidelity at a reduced calibration overhead owing to the small parameter drift in the control system.

We study Floquet thermalization in a periodically driven quantum non-integrable Ising chain by combining two operational diagnostics: subsystem thermalization and work statistics. For generic interacting Floquet systems, stroboscopic dynamics lead to heating toward an infinite-temperature state at low driving frequencies, to a prethermal state during the crossover regime, and then to a finite-temperature state at high driving frequencies. We show that reduced density matrices of small subsystems provide a precise measure of local equilibration and clearly resolve prethermal plateaus. In parallel, we analyze the statistics of work performed over a Floquet cycle using both the characteristic function of work with and without the two-point measurements, and the related fluctuation theorem, which captures coherent contributions and deviations from thermal equilibrium. By comparing these two diagnostics within the same Floquet setting, we demonstrate that work statistics encode the same dynamical crossover that governs subsystem thermalization. Our results establish a unified and experimentally accessible framework for characterizing Floquet thermalization, prethermal regimes, and coherent energy absorption in interacting quantum systems.

Artificial intelligence (AI) and quantum information (QI) are rapidly co-evolving. AI is becoming a practical tool for learning, designing, controlling, and verifying quantum systems, while QI offers new computational models, representational structures, and learning-theoretic questions for AI. This survey reviews the interface from both directions. In the AI for QI direction, we organize recent progress around the central tasks of extracting information from limited measurements, training and discovering quantum algorithms, stabilizing noisy hardware, automating experimental and programming workflows, and extending learning-based methods to sensing and networking. In the QI for AI direction, we examine how quantum computation and quantum-inspired structures affect learning through algorithmic speedups, expressivity, trainability, generalization, neural-network design, and tensor-network representations. We close by identifying cross-cutting challenges in reproducibility, scalability, hardware realism, and co-design, arguing that progress will depend on tighter integration of theory, experiment, and hybrid quantum–classical systems.

Quantum steering ellipsoid (QSE) provides a faithful representation of a two-qubit state. When extended to tripartite systems, the steerability from a trusted party to different receivers is subject to volume monogamy relations, which only constrain the total steerability but cannot individually eliminate the steerability of an untrusted third party, leaving a potential channel for information leakage via steering. Here, we show that this residual steerability can be completely suppressed by selectively engineering bound states in local qubit-environment subsystems, without compromising the steerability between trusted parties. Specifically, when bound states are formed in the subsystems formed by the trusted parties and their environments but absent in the untrusted one, the untrusted party's QSE volume decays to zero, while the trusted party's QSE volume remains finite. Our results establish selective bound-state engineering as a mechanism for extreme volume monogamy, with potential applications in secure quantum communication with an untrusted third party.

We present a variational derivation of the Wallis product and its reciprocal from the four-dimensional singular harmonic oscillator. The inverse-square interaction is absorbed into an effective angular parameter $\nu$, so that the lowest exact energy in a fixed sector is $E_{4d,\mathrm{exact}}=\hbar\omega(\nu+2)$. Motivated by the radial Kustaanheimo–Stiefel relation $r=\rho^2$ between the four-dimensional oscillator and the three-dimensional Coulomb problem, we use the quartic trial family $R_a(\rho)=N\rho^\nu e^{-a\rho^4}$. The minimized variational energy yields an accuracy ratio governed by adjacent Gamma functions. In the large-$\nu$ semiclassical limit, this ratio approaches unity. Restricting $\nu$ to the odd sequence $\nu=2n-1$ gives the standard Wallis product, whereas the even sequence $\nu=2n$ gives its reciprocal form. The Coulomb-dual interpretation further relates the two branches to integer and half-integer effective angular sectors in the dual Coulomb/MICZ description. The result shows that Wallis-type infinite products persist under an inverse-square deformation of the oscillator and arise from a common Gamma-function structure in radial variational dynamics.

We overcome the long-standing noninvasive measurability (NIM) challenge in Leggett-Garg tests by exploiting the causal structure of quantum field theory (QFT). Our protocol uses three independent ensembles of the vacuum state, each measured by a different pair of observers at spacelike-separated events, yielding the three two-time correlators. By placing these events at positions $(0,0)$, $(\tau,L)$, and $(2\tau,2L)$ with $L>\tau+2\tau_0$, we rigorously ensure that no measurement can influence another. We investigate the vacuum state of a free massive scalar field in 1+1 dimensions, employing the dichotomic observable $Q(f)=\operatorname{sign}(\phi(f))$ where $\phi(f)$ is the smeared field. In the Heisenberg picture, the time evolution is absorbed into a translation of the time-window function, allowing us to derive the two-time correlation function $C(\tau,L)$ and the Leggett-Garg parameter $K_3=2C(\tau,L)-C(2\tau,2L)$. For non-overlapping time windows, we find that the correlation function decays exponentially with $\tau$ for a massive field. For overlapping windows, our numerical computation for a rectangular time window yields $K_3<1$ across the entire mass range, firmly establishing that the vacuum does not violate the LGI. Thus, under strict noninvasive conditions, the vacuum shows no violation of macrorealism, in stark contrast to its well-known violation of spatial Bell inequalities. Our spacelike-separated protocol provides the first LGI test in QFT with rigorously satisfied NIM, setting a methodological benchmark for future studies and highlighting the fundamental distinction between spacelike entanglement and temporal macrorealism in relativistic quantum fields.

Quantum illumination offers a significant theoretical advantage for target detection in high background noise environments. However, its practical deployment in free-space channels is hindered by atmospheric turbulence. Stochastic fluctuations in atmospheric turbulence inevitably degrade the quantum signature, rendering the real-time evaluation of quantum advantage under such dynamic conditions a critical yet unresolved challenge. To circumvent the reliance on costly direct turbulence measurements, we propose a physics-driven framework that integrates Kolmogorov-Arnold networks directly bridge macroscopic meteorological observations with microscopic quantum channel dynamics. Trained on 105,120 samples from 12 climatically diverse sites and validated on 26,280 unseen samples from three extreme boundary conditions (arid continental, tropical maritime, high-altitude plateau), our approach establishes a physically consistent mapping from standard meteorological variables to the temporal evolution of the quantum advantage. This end-to-end system dynamically quantifies the degradation of quantum advantage across diverse turbulence conditions. Our results provide a rigorous theoretical and data-driven pathway for environmental adaptation, facilitating the transition of quantum radar networks from proof-of-principle demonstrations to all-weather operational systems.

This study establishes a theorem that provides sufficient criteria for identifying terms in any time-independent Hamiltonian that have no influence on local dynamics, local observables, or any local phenomena, without any approximation. The usefulness of this theorem is demonstrated by predicting the behavior of three systems. The first system consists of multiple qubit chains with Ising interactions. The second system is formed by a single qubit chain, differentiated by the substitution of Dzyalonshinskii-Moriya (DM) interaction for the last Ising interaction. The predictions were verified by analytically deriving the reduced dynamics of both systems. A third system was also considered, namely, a short qubit chain with a transverse magnetic field on the intermediary environment qubit. This transverse magnetic field signals that the commutation relation required by our theorem no longer holds. The third system's local dynamics were also derived analytically, demonstrating that all Hamiltonian constituents contributed to the reduced dynamics. The physical consequences of our theorem's inapplicability were also explored using this third system by analyzing the entanglement dynamics between the qubits that do not directly interact. The results showed that the entanglement is caused by an emergent coupling between the two non-directly interacting subsystems. This emergent coupling arises from the non-commutativity of the intermediate interactions connecting the two subsystems. When searching for these emergent couplings, our theorem can eliminate intermediate interactions that will not produce them.

We develop a unified treatment of scattering and discrete spectra for the one-dimensional Dirac equation with scalar and vector interactions. Under the spin-symmetry condition, the coupled first-order Dirac system maps exactly onto an effective Sturm–Liouville (Schrö\-din\-ger-like) problem for a single spinor component. This mapping provides a convenient framework for analyzing transmission, reflection, and analytic continuation. As an explicit application, we consider effective interactions of hyperbolic Pöschl–Teller type and exploit supersymmetric quantum mechanics and shape invariance to obtain a closed-form expression for the transmission probability. The bound-state spectrum is then recovered from the poles of the analytically continued transmission amplitude, reproducing known results and offering a unified description of scattering and bound states. For the barrier configuration, we briefly comment on the resulting pole pattern in the complex momentum plane and its connection with resonance and quasi-normal-mode behavior. Moreover, we use the chiral transformation to relate the spin- and pseudospin-symmetry sectors and translate results between them without repeating the full derivation.

The emergence of powerful deep generative models based on diffusion and flow matching has enabled the learning and modeling of complex distributions. Learning quantum distributions, however, remains challenging due to the inherent difficulty of accurately modeling the meaningful physical properties of quantum states. We propose Quantum Flow Matching (QFM), a novel generative model designed to learn quantum distribution by utilizing spin Wigner function and flow matching. By converting density matrix into the spin Wigner function and leveraging functional flow matching to learn distributions in function space, QFM enables accurate and effective learning of multi-qubit quantum distributions. We demonstrate the effectiveness of our method by evaluating physical quantities such as trace, purity, and entanglement entropy of the generated quantum states, accurately capturing the underlying physics of the given quantum distributions.

The fidelity of a quantum gate is sensitive to small deviations in the physical control parameters. Unfortunately, it is generally difficult to exactly model the implemented Hamiltonian for a set of user-defined parameters, necessitating on-device calibration. Here, we present an active learning framework based on Bayesian optimization with a Gaussian Process surrogate to find the optimal parameter set. We validate the technique through numerical calibration of the laser amplitude and frequencies that implement the trapped-ion Mølmer Sørensen gate. We show that a Gaussian process can model the Hamiltonian dynamics. The addition of active learning accelerates the discovery of the optimal parameter set with speed and final fidelity dependent on the quantum projection noise of the data. These results establish the utility of active learning and surrogate models for quantum calibration and control.

Finding exact solutions to the quantum many-body problem is computationally intractable (QMA-hard). Traditional approximations for electrons in an atom or molecule – density functional theory and wavefunction methods – have been indispensable, but their development shows signs of saturation: DFT functionals have proliferated without converging toward the exact functional, and strong correlation remains largely unsolved after decades of effort. This position paper argues that machine learning represents the most promising path forward – not as a proof of logical necessity, but as a decision-theoretic argument: ML succeeds whether the underlying problems are truly hard or merely lack simple analytical solutions. We reframe recent traditional method development as “hand-crafted machine learning” that has exhausted the hypothesis space accessible to human intuition. Significant challenges remain, but these have clear research paths forward, unlike the fundamental barriers facing traditional approaches. ML-based approaches merit strategic priority in quantum chemistry's next phase.

Intramolecular electron transport in biological systems is typically described as a diffusive hopping process, according to the semi-classical rate theories of Marcus and Hopfield combined with classical Pauli-type master equations. However, the possibility that non-trivial quantum mechanical effects could play a functional role in the transport dynamics in certain biomolecular processes has attracted increasing attention. Here, we extend the quantum mechanical model of open system dynamics by the Lindblad equation to a key biological component, the long chains of redox centers based on iron-sulfur clusters or heme groups that are widespread in many biological organisms, where they realize the cellular respiration. This approach allows to explore a wide range of physical parameters, showing key features of electron transport in these multi-domain protein structures. We pay particular attention to heat and entropy transfer between the electrons and the protein bath, which constitutes a benchmark of physical realism for the models. Electron currents, average transfer times and relative efficiency of the transport process are also explicitly characterized.

We study the problem of extracting a quantum complexity resource from a mixed Gaussian state of the multimode light. We present the first complete, certificate-checked solution to this problem in a genuinely coupled sector. We carry this out for the two-mode case, the smallest case in which modes are genuinely coupled. Even in this case the solution is highly nontrivial, and we rigorously prove that it cannot be given in a closed form.