Fluctuation theorems establish exact relations for nonequilibrium dynamics, profoundly advancing the field of stochastic thermodynamics. In this work, we extend quantum fluctuation theorems beyond the traditional thermodynamic framework to quantum multipartite information dynamics, where both the system and the environment are multipartite without assuming any thermodynamic constraints. Based on the two-point measurement scheme and the classical probability, we establish the fluctuation theorem for the dynamics of classical multipartite mutual information. By extending to quasiprobability, we derive quantum fluctuation theorems for multipartite coherence and quantum correlations, presenting them in both integral and detailed forms. Our theoretical results are illustrated and verified using three-qubit examples, and feasible experimental verification protocols are proposed. These findings uncover the statistical structure underlying the nonequilibrium quantum information dynamics, providing fundamental insights and alternative tools for advancing quantum technologies.

The notion of antidistinguishability captures the possibility of ruling out certain alternatives in a quantum experiment without identifying the actual outcome. Although extensively studied for quantum states, the antidistinguishability of quantum channels remains largely unexplored. In this work, we investigate the single-shot antidistinguishability of unitary operations. We analyze two scenarios: antidistinguishability with single-system probes and with entangled probes. For sets of three unitaries, we first prove that all maximally entangled states are equivalent in their performance as probes. In the qubit case, we further establish that maximally entangled probes are always sufficient for perfect antidistinguishability: if a set of three unitaries acting on two-dimensional Hilbert space is antidistinguishable with either a single-system or nonmaximally entangled probe, then it is also antidistinguishable with a maximally entangled one. However, in higher dimension, this sufficiency fails. From dimension 3, there exists a set of unitaries that are antidistinguishable with a nonmaximally entangled probe or a single-system probe but not with a maximally entangled probe. We also establish that the union of two antidistinguishable sets of three unitaries acting on a two-dimensional Hilbert space also forms a set of antidistinguishable unitaries. Lastly, we provide methods to construct antidistinguishable unitaries from non-antidistinguishable ones.

While most of the existing quantum information engines assisted by Maxwell's demon harness thermal fluctuations, those that rectify only quantum fluctuations have recently been constructed. We propose an alternative type of quantum information engine that harnesses only quantum fluctuations to achieve cumulative energy storage and unidirectional transport of a particle. This unidirectional transport makes a stark contrast with the case without Maxwell's demon where the motion of a particle is confined to a finite region due to Bloch oscillations. We find a trade-off relationship between the maximum power and the maximum velocity. With an improved definition of efficiency that includes all possible energy flows in the engine cycle, we numerically demonstrate the absence of a trade-off relationship among power, efficiency, and power fluctuations that is present for classical heat engines and classical information engines. We also evaluate the influence of experimentally unavoidable measurement imprecision on the performance of the quantum Maxwell's demon.

We present a framework for linear combination of unitaries (LCU) style decomposition tailored to structured sparse matrices, which frequently arise in the numerical solution of partial differential equations (PDEs). While LCU is a foundational primitive in both variational and fault-tolerant quantum algorithms, conventional approaches based on the Pauli basis can require a number of terms that scale quadratically with matrix size. We introduce the Sigma basis, a compact set of simple, nonunitary operators that can better capture sparsity and structure, enabling decompositions with only polylogarithmic scaling in the number of terms. We develop both numerical and semianalytical methods for computing Sigma-basis decompositions of arbitrary matrices. Given this new basis is comprised of nonunitary operators, we leverage the concept of unitary completion to design efficient quantum circuits for evaluating observables in variational quantum algorithms and for constructing block encodings in fault-tolerant quantum algorithms. We compare our framework with related techniques such as unitary dilation, and other sparsity and structure exploiting block-encoding methods, and demonstrate its efficacy and generality. We illustrate our framework on several PDE examples and show an exponential improvement in decomposition size while retaining circuit efficiency. We also prescribe how our framework can be readily generalized by incorporating other unitary and nonunitary operators or “things” to expand or modify the Sigma basis and tailor the decomposition for specific problems to gain maximum efficiency.

Given a Calderbank-Shor-Steane code, it is sometimes necessary to modify the code by adding an arbitrary number of physical qubits and parity checks. Motivations may include concatenating codes, embedding low-density parity check codes into finite-dimensional Euclidean space, or reducing the weights of parity checks. During this embedding, it is essential that the modified code possesses an isomorphic set of logical qubits as the original code. However, despite numerous explicit constructions, the conditions under which such a property holds true are not known in general. Therefore, using the language of homological algebra, we provide a unified framework that guarantees a natural isomorphism between the output and input codes. In particular, we explicitly show how previous works fit into our framework.

The weak limit theorem (WLT), the quantum analog of the central limit theorem, is foundational to quantum walk (QW) theory. Unlike the universal Gaussian limit of classical walks, deriving analytical forms of the limiting probability density function (PDF) in higher dimensions has remained a challenge since the one-dimensional (1D) Konno distribution was established. Previous explicit PDFs for two-dimensional (2D) models were limited to specific cases whose fundamental nature was unclear. This paper resolves this long-standing gap by introducing the notion of maximal speed $v_{\max }$ as a critical parameter. We demonstrate that all previous 2D solutions correspond to a degenerate regime where $v_{\max }=1$. We then present the first exact analytical representation of the limiting PDF for the physically richer, unexplored regime $v_{\max }<1$ of a general class of 2D two-state QWs. Our result reveals 2D Konno functions that govern these dynamics. We establish these as the proper 2D generalization of the 1D Konno distribution by demonstrating their convergence to the 1D form in the appropriate limit. Furthermore, our derivation, based on spectral analysis of the group-velocity map, analytically resolves the singular asymptotic structure: we explicitly determine the caustics loci where the PDF diverges and prove they define the boundaries of the distribution's support. By also providing a closed-form expression for the weight functions, this work offers a complete description of the 2D WLT.

High-dimensional entanglement is a cornerstone of quantum information science, yet its characterization remains hindered by resource-intensive tomography and fragmented detection frameworks. In this work we propose an entanglement criterion from mutually unbiased equiangular tight frames, which integrates and extends existing approaches grounded in mutually unbiased bases and equiangular measurements [Morelli et al., Phys. Rev. Lett. 131, 170201 (2023)]. This criterion provides rigorous quantitative links to key entanglement properties, facilitating both qualitative evaluation of the Schmidt number and quantitative estimation of entanglement fidelity. Notably, it requires significantly fewer global projections compared to full tomography, thereby substantially lowering the experimental complexity in high-dimensional systems. Evaluated under realistic depolarizing and dephasing noise scenarios, the proposed method demonstrates an advantageous balance between measurement efficiency and robustness to noise, outperforming prior approaches. Therefore, this criterion may serve as a unified analytical framework for quantifying entanglement in complex quantum systems.

We introduce the paradigm of replacement-type quantum gates. This type of gate introduces input qubits, candidate qubits, and output qubits. The candidate qubits are prepared such that a displacement conditional on the input qubit results in the targeted output state. Finally, the circuit continues with the output qubits constructed from the candidate qubits instead of the input qubits, thus the name “replacement-type gate.” We present examples of replacement-type $X$ and $\mathrm{CNOT}$ gates realized with spin qubits and with neutral atom qubits with error rates predicted near the threshold of the XZZX surface code. By making use of the extended Hilbert space, including the position of the particles, these gates approximately preserve the innate noise bias of the qubits. The gate preserves the noise bias which motivates advanced quantum computer architectures with quantum error correction.

Quantum repeaters have promised efficient scaling of quantum networks for over two decades. Despite numerous platforms proclaiming functional repeaters, the realization of large-scale networks remains elusive, indicating that the resources required to do so were thus far underestimated. Here, we investigate the dependence of the resource scaling of networks on realistic experimental errors. Using a nested repeater protocol based on the purification protocol by Bennett et al. [Phys. Rev. Lett. 76, 722 (1996)], we provide an analytical approximation of the polynomial degree of the resources consumed by entanglement routing. Our error model predicts substantially stricter thresholds for efficient network operation than previously suggested, requiring two-qubit gate errors below 1.3% for resource scaling with polynomial degree below 10. The analytical model presented here provides insight into the reason why previous experimental implementations of quantum repeaters failed to scale efficiently and inform the development of truly scalable systems, highlighting the need for high-fidelity local two-qubit gates. We employ our analytical approximation of the scaling exponent as a figure of merit to compare different platforms and find that trapped ions and color centers in diamond currently provide the best route towards large-scale networks.

We report an iterative algorithm to retrieve accurate real-space information from gas phase ultrafast diffraction measurements with missing data at low momentum transfer. The algorithm operates in a manner similar to phase retrieval algorithms, which transform signals back and forth between the signal domain and the Fourier transform domain and apply constraints to retrieve the missing phase. Our algorithm retrieves missing data that is not accessible experimentally by applying a real-space constraint that requires only an approximate a priori knowledge of the shortest and longest internuclear distances in the molecule. We demonstrate successful retrieval of the missing data in simulated data and in experimentally measured electron diffraction signals of photodissociated iodobenzene molecules.

Ab initio calculations of the parallel component of the magnetic dipole hyperfine structure (HFS) constant have been carried out for hydroxyl radical isotopologues [${}^{16,17}\mathrm{OH}$(D)] over the internuclear distance range $R\in [0.6,1.8]\AA$. For the ground electronic state $X^2\mathrm{\Pi }$, the HFS functions were evaluated for contributions induced by both oxygen and hydrogen nuclei. In addition, the hydrogen-induced HFS curve was calculated for the excited $A^2{\mathrm{\Sigma }}^{+}$ state. The quantum-chemistry study employs a four-component relativistic coupled-cluster method, including excitations up to the triple level, namely: the contribution of triple-cluster amplitudes was studied both perturbatively and through fully iterative calculations. The resulting oxygen- and hydrogen-induced HFS functions represent the most accurate and reliable theoretical predictions to date exhibiting excellent agreement with semiempirical curve for hydrogen-induced HFS derived from high-resolution spectroscopic data for the lowest vibrational levels ($v\in [0,2]$) of the electronic $X^2\mathrm{\Pi }$ state. Vibrationally averaged ab initio values are consistent with experimental values within $1\%$ for all states considered. Furthermore, the internuclear distance range over which the HFS curves are defined has been extended beyond that of previous studies, thereby providing a robust foundation for accurate HFS treatments of higher-lying rovibrational levels of OH isotopologues within both adiabatic and nonadiabatic frameworks.

The light-induced-phase (LIP) model offers an elegant interpretation of how a dressing laser field modulates the line shape of an absorption resonance. However, its central assumption of adiabatic evolution—no population change—limits its validity to weak fields, precluding its application in the strong-field regime, where pronounced diabatic dynamics occur. To overcome this limitation, we generalize the conventional LIP model within the instantaneous-Floquet-state (IFS) formalism. The validity of this Floquet-generalized LIP (FGLIP) model is quantified by a Floquet adiabaticity parameter $\xi$ and demonstrated across a wide range of laser parameters. The deviation of resonance line shape from the FGLIP model is due to amplitude modification and phase shift arising from diabatic transitions between IFSs, namely diabatic corrections. Numerical simulations of helium $1s2p$ absorption show that the resonance line shapes are quantitatively reproduced, via incorporating diabatic corrections in the FGLIP model, from adiabatic $(\xi \ll 1)$ to highly diabatic regimes. Moreover, by leveraging $\xi$ as a control criterion, we demonstrate complete cyclic modulation of the helium $1s2p$ resonance line shape—traversing from symmetric Lorentzian to asymmetric Fano and back—via coherent accumulation of a $2\pi$ LIP shift by tuning the intensity of the dressing infrared laser pulse, all within the adiabatic regime. This work provides both a fundamental understanding of Floquet diabatic dynamics and a practical tool for achieving coherent optical control of quantum systems.

We theoretically propose a quantum heat engine using a setup consisting of a ring-trapped Bose-Einstein condensate placed in a Fabry-Pérot cavity where the optical field carries orbital angular momentum. We first show that the cavity-enhanced light-atom coupling leads to the emergence of polaritonic modes whose character can be reversibly switched between photonlike and phononlike by detuning sweeps, allowing work extraction governed by distinct reservoirs. We investigate the dependence of the engine efficiency on the orbital angular momentum. Beyond ideality, we discuss finite-time scenarios based on shortcuts to adiabaticity such that the efficiency retains its ideal-operation value, despite finite-time operation. Our analysis identifies orbital angular momentum as a control knob that can reconfigure the performance of such quantum heat engines.

Supersolids—exotic quantum states that combine superfluid flow with crystalline order—have recently been realized in quantum degenerate gases, yet a direct quantitative measurement of their superfluid fraction and understanding of their topological properties have remained elusive. In this work we show that the nonequilibrium dynamics of a spin-orbit coupled dipolar Bose-Einstein condensate under $\mathcal{PT}$-symmetric driving and dissipation generates an oscillating current whose frequency exhibits a strong dependence on the superfluid fraction of the underlying supersolid. This dynamical response further reveals topological phase transitions between distinct supersolid phases characterized by their spin textures. Our findings establish a platform for exploring supersolids with topological properties and provide deep insight into their nonequilibrium behavior beyond conventional closed-system scenarios.

This paper investigates the ground states and complex dynamics of vortices in spin-orbit-coupled Bose-Einstein condensates subjected to a position-dependent detuning. By scanning the detuning gradient and solving the coupled Gross-Pitaevskii equations, we obtain static vortex lattice structures containing one to six vortices. When the detuning gradient is quenched below its initial value, these vortex lattices exhibit novel periodic rotation motion, with the stability persisting for up to 1000 ms. Notably, depending on the quenched gradient, the twin vortices exhibit two distinct modes: a scissorslike oscillation and unidirectional clockwise rotation. We quantitatively analyze this dynamics and establish direct correspondence between the rotation and the underlying magnetic field gradients experienced by the condensates. When the quenched detuning gradient exceeds its initial value, new vortices are generated. Our findings not only elucidate the rich response of vortices to synthetic magnetic fields but also provide a potential theoretical scheme for the development of ultracold-atom-based magnetic-field gradiometers.

A striking feature of cavity quantum electrodynamics is the existence of atom-photon bound states, which typically form when the coupling between the atom and its environment is strong enough that the atom can “grab” an emitted photon and re-absorb it, resulting in a virtual cloud surrounding the atom. Here, we demonstrate the existence of bound states that instead form in the case of weak coupling. Specifically, we show that when a quantum emitter is weakly coupled to a structured reservoir exhibiting topologically protected surface states, hybridizations between these states and the emitter can form, resulting in midgap bound states. We illustrate this using a semi-infinite extension of the Su-Schrieffer-Heeger (SSH) model as our reservoir. First, we diagonalize the bare semi-infinite SSH chain and reveal a winding number that predicts that only the edge state on the finite side of the chain survives the semi-infinite extension. Then, after coupling the quantum emitter to this end of the chain, we analyze the modified emitter spectrum and reveal the existence of bound states in three parameter regions. Two of these represent the usual strong-coupling bound states, while the third gives the weak-coupling bound states with eigenvalue appearing in the SSH band gap, and which exhibit partial sublattice localization. We demonstrate that oscillations between the weak-coupling bound states can be used to transfer the particle from the emitter into the lattice in a predictable and reversible manner. We briefly consider the potential realization of our model in two experimental platforms.

Quantum state discrimination enables the accurate identification of quantum states, which are generally nonorthogonal. Among various strategies, minimum-error discrimination and unambiguous state discrimination exhibit contextuality-enhanced success probabilities that surpass classical bounds, offering significant advantages for quantum sensing and communication. However, in practice, both error and failure outcomes can occur, suggesting the need for a unified strategy that incorporates both aspects while exploring the potential for contextuality enhancement. In this work we theoretically demonstrate contextuality enhancement in quantum state discrimination under a fixed failure probability. We show that this enhancement disappears within a certain intermediate range of failure probabilities—a phenomenon absent in conventional strategies, where both minimum-error and unambiguous discrimination consistently outperform the noncontextual bound for equal priors. Moreover, we analyze how the existence of this nonenhancement region depends on the confusability of the quantum states, which corresponds to their fidelity in a quantum model. We further extend the discussion to the noisy state discrimination, which even encompasses the maximal-confidence discrimination. In this extended discussion, we observe that the nonenhancement region tends to disappear with increasing noise strength.

Quantum annealing is a promising algorithm for solving combinatorial optimization problems. It searches for the ground state of the Ising model, which corresponds to the optimal solution of a given combinatorial optimization problem. The guiding principle of quantum annealing is the adiabatic theorem in quantum mechanics, which guarantees that a system remains in the ground state of its Hamiltonian if the time evolution is sufficiently slow. According to the adiabatic theorem, the annealing time required for quantum annealing to satisfy the adiabaticity scales inversely proportional to the square of the minimum energy gap between the ground state and the first excited state during time evolution. As a result, finding the ground state becomes significantly more difficult when the energy gap is small, creating a major bottleneck in quantum annealing. Expanding the energy gap is one strategy for improving the performance of quantum annealing; however, its implementation in actual hardware remains difficult. This study proposes a method for efficiently solving instances with small energy gaps by introducing additional local terms to the Hamiltonian and exploiting the diabatic transition remaining in the small energy gap. The proposed method achieves an approximate quadratic speedup of the exponential scaling exponent in time to solution compared to the conventional quantum annealing. In addition, we investigate the transferability of the parameters obtained with the proposed method.

Nonstabilizerness, or “magic,” is a resource for universal quantum computation in most fault-tolerant architectures; access to states with nonstabilizerness allows for nonclassically simulable quantum computation to be performed. Quantifying this resource for unknown states is therefore essential to assessing their utility in quantum computation. The stabilizer Rényi entropies have emerged as a leading tool for achieving this, having already enabled one efficient algorithm for measuring nonstabilizerness. In addition, the stabilizer Rényi entropies have proven useful in developing connections between nonstabilizerness and other quantum phenomena. In this work, we introduce an alternative algorithm for measuring the stabilizer Rényi entropies of an unknown quantum state. First, we show the existence of a state, produced from the action of a channel on $\alpha$ copies of some state $\rho$, that encodes the $\alpha$-stabilizer Rényi entropy of $\rho$ into its purity. We detail several methods of applying this channel, and then, by employing existing purity-measuring algorithms, provide an algorithm for measuring the $\alpha$-stabilizer Rényi entropies for all integers $\alpha >1$. This algorithm is benchmarked for qubits and the resource requirements compared to other known algorithms. Finally, a nonstabilizerness-entanglement relationship is shown to exist in the algorithm, demonstrating a relationship between the two resources, before an instance of resource hiding is found.