In briefSeparability does not validate zero-noise extrapolation: factorial diagnostics on dynamic quantum circuits
SummaryThe paper runs a pre-specified 2^3 factorial experiment on three IBM dynamic quantum circuits to test whether separately amplifying gate, latency, and mid-circuit measurement errors yields a reliable zero-noise limit. It separates observable separability, response-model adequacy, and calibration, finding that weak interactions do not guarantee an accurate limit. Multi-knob extrapolations show smaller median errors, yet most original strategies still exclude the known ideal value for several observables. The authors present this as a diagnostic of the implemented response surface, not a certification of channel independence or mitigation accuracy.
In briefTwo bosons with density-assisted tunnelling on a tilted 1D lattice
SummaryThis paper studies how two bosons move in a tilted one-dimensional optical lattice when both standard and density-assisted tunnelling are present. The relative sign of the two tunnelling processes strongly shapes the dynamics, creating reinforcing and competing regimes. Without onsite interaction, early entanglement growth scales the same way with the density-assisted tunnelling amplitude, while finite interaction breaks the symmetry between the two regimes. At equal tunnelling amplitudes, the doublon and singlon sectors fully decouple.
Muhammad S. Hasan, Vikash Mittal, Tomasz Sowi\'nski
In briefA framework for checking finite-key security in COW quantum key distribution
SummaryThis paper presents a modular simulation framework that analyzes finite-key security in Coherent-One-Way (COW) quantum key distribution by separating device modeling, finite experimental statistics, and security inference. The framework is compared with experimentally reported COW-QKD operating points and with the Kato and Azuma-Hoeffding finite-key methods. It also shows that jointly optimizing the mean photon number and receiver splitting fraction increases the model-predicted secure-key rate.
Aryan Kuntal, Utkarsh Giradkar, Mudit Chaudhary et al.
In briefDynamical Mean-Field Theory for Real Materials Using Quantum Computer-Based Variational Time Evolution
SummaryThe paper builds a hybrid quantum-classical workflow combining density functional theory and dynamical mean-field theory to study CaCuO2, a parent compound of high-temperature cuprate superconductors. A variational quantum compressed time evolution algorithm serves as the impurity solver, run on an IBM Heron quantum device to compute the time-dependent Green's function. Using error mitigation and Lehmann representation fitting, the authors extract the density of states and resolve key spectral function features. However, they find the numerical accuracy needed for full DMFT self-consistency exceeds current hardware, suggesting practical applications will require post-NISQ devices.
Stefan Wolf, Johannes Selisko, Timo Eckstein et al.
In briefStructured light for addressable two-qubit gates in medium-sized ion crystals
SummaryThis paper gives a theoretical description of an addressable entangling-gate scheme recently implemented by Faorlin et al. Using laser beams that propagate perpendicular to the ion chain with structured light gradients, the scheme drives axial phonons, avoids spectral mode crowding, and reduces crosstalk. The authors derive closed-form expressions for the leading gate errors from thermal motional fluctuations and dephasing noise, and identify parameters that could lower the motional error from about 10^-3 to 10^-5.
In briefParallel quantum teleportation on IBM hardware using a five-qubit AME(5,2) state
SummaryThe paper demonstrates parallel teleportation of two qubits on the IBM superconducting processor ibm_pittsburgh using the five-qubit absolutely maximally entangled state AME(5,2). The authors build three-qubit Clifford decoders and apply XY4 dynamical decoupling with classical Pauli frame correction. After three rounds, the final entanglement fidelities are 0.704±0.028 and 0.680±0.022, with lower bounds above the separability threshold of 1/2.
In briefBlack holes as quantum information systems: how information leaves evaporating black holes
SummaryThis paper reviews and analyses quantum information-theoretic approaches to black hole evaporation aimed at the information paradox. It focuses on the Page-time paradox and the Hayden-Preskill model, which treats the black hole as a finite-dimensional quantum system described by a quantum circuit. The authors identify fast scrambling dynamics and entanglement as a resource as the two key features underpinning information release in this model.
In briefDimension-free inequalities that limit the local spectra of pure three-party quantum states
SummaryThis paper studies the quantum marginal problem, which asks how local and global properties of a multipartite quantum system must fit together. The authors introduce a new family of inequalities that bound the local spectra allowed for a pure tripartite state. The number of inequalities grows with system dimension, and they hold for arbitrary dimensions. For equal local dimensions up to 4, the family yields the complete set of eigenvalue inequalities.
WhyIntroduces dimension-free spectral inequalities for pure tripartite states, giving a complete set for local dimension up to four, advancing the quantum marginal problem.
In briefFirst-principles study of Co-doped Janus HfSSe monolayers as Li and Na battery anodes
SummaryThis paper uses first-principles density functional theory to study pristine and Co-doped Janus HfSSe monolayers as anode materials for Li-ion and Na-ion batteries. Co doping strengthens alkali-metal binding and raises theoretical capacities from 555.43 to 776.19 mAh/g for Li and from 370.29 to 582.14 mAh/g for Na. The authors also report average open-circuit voltages and minimum migration barriers, and conclude that Co-doped Janus HfSSe is a promising anode material.
Md. Muktadir Hasan, Md. Mafizul Islam, and Ahmed Zubair
In briefPolarization signatures of mixed scalar and pseudoscalar axion-like particle photon couplings
SummaryThis paper studies photon conversion into a single axion-like particle with both scalar and pseudoscalar photon couplings, using a finite linearly polarized laser pulse. Changing the collision angle between the strong pulse and the probe scans the resonant ALP mass. The two conversion amplitudes interfere, so conversion probability and polarization rotation depend on the difference between the probe polarization and coupling angles. These dependences provide polarization-resolved signatures of mixed couplings.
SummaryThe paper shows that several potential-energy functions based on the exponential e^{-αr} (α>0) are either equivalent or identical to the Tietz potential. Some of these potentials contain redundant parameters. Removing them does not affect their performance in describing the vibration-rotation spectra of diatomic molecules.
In briefMeasurement incompatibility limits in Bayesian quantum estimation beyond quadratic loss
SummaryThis paper studies how measurement incompatibility affects single-shot Bayesian multiparameter quantum estimation. It shows that the minimum joint loss can exceed the separately optimised bound by at most a factor of two. Using the generalised Barnum–Knill inequality, the authors extend this bound to a wider class of additive losses, including periodic losses such as the sine loss and unbounded losses such as absolute loss.
Francesco Albarelli, Stefano Chessa, Jes\'us Rubio
In briefA q-inspired radial quantum model: extends a one-dimensional q-deformation to a rotationally covariant framework and studies its observable effects.
SummaryThe paper deforms only the radial derivative while keeping tangential derivatives unchanged, and constructs self-adjoint frame-momentum operators. It derives a rotationally invariant uncertainty bound with a correction proportional to the mean distance from the center. For weak deformation, the leading harmonic-oscillator energy shifts split levels with different orbital angular momenta while preserving rotational degeneracy.
In briefOptimal circuits for arbitrary quantum transformations using parallel controlled rotations
SummaryThis paper presents a quantum-circuit synthesis protocol that realizes any n-qubit unitary transformation up to a diagonal factor, using bitstring-conditioned rotations with tunable angle and axis as native operations. The resulting circuit is optimal in gate count and depth for such systems. The authors demonstrate the method experimentally on two qubits in a few-mode superconducting circuit, reporting an average gate fidelity of 97.6% for Haar-random unitaries.
Heikki Suominen, Suman Kundu, Heidi Kivij\"arvi et al.
In briefSelf-consistent closure method for predicting dense many-body spectra from microscopic data
SummaryThe paper introduces multi-resolvent self-consistency (MRSC) equations that separate an exact algebraic hierarchy from an approximate finite-parameter closure. On the free-fermion benchmark the exact identities are reproduced, and in a blind test on the interacting Ising chain the predictions fall within 0.35% to 0.97% of the probes. The authors also present a diagnostic chain for local rotational invariance window conditions, described as a finite-order framework rather than a proof of universal emergence.
In briefBroader orbital-angular-momentum range in thin-film photon-pair sources
SummaryThis paper examines photon pairs generated in a 7-micrometer-thick lithium niobate film and compares them with a 500-micrometer periodically poled lithium niobate crystal under identical pump conditions. The thin-film source shows a much broader orbital angular momentum spectrum, with an azimuthal Schmidt number almost 9 times larger, decoupled from the frequency spectrum. The authors perform quantum-state tomography in selected two- and four-dimensional subspaces, demonstrating high-purity maximally entangled states. The results suggest thin nonlinear films are a promising platform for high-dimensional quantum state generation.
In briefRelativistic strong quantum Mpemba effect: how acceleration reverses quantum relaxation order
SummaryThis paper studies a two-level detector coupled to a massless scalar field and relaxing via the Unruh effect. For a pair of isospectral initial states, relaxation curves that do not cross in inertial motion show a Mpemba crossing above a threshold acceleration. At a higher, precisely tuned acceleration, the initially more distant state relaxes faster because it has no overlap with the slowest decay mode. The authors also show that acceleration can switch the relaxation bottleneck between population and coherence modes.
In briefOptimal approximate quantum conversion via a taut-string geometric principle
SummaryThe paper studies optimal approximate state conversion in quantum resource theories. It shows that such problems in non-uniformity, bipartite pure-state entanglement, and pure-state coherence reduce to one of four elementary taut-string constructions. The framework covers many distinguishability measures, including trace distance, unitarily invariant norms, and quantum relative entropy. The increment vector of the taut string determines both the optimal error and a canonical optimal state.
WhyUnifies diverse approximate resource conversion problems under four taut-string constructions, covering many divergences with a rigorous theoretical framework of substantial scope.
In briefCertified benchmark of quantum LDPC decoders against non-degenerate maximum-likelihood decoding
SummaryThe paper presents a framework that certifies whether non-degenerate maximum-likelihood decoding succeeds on individual sampled shots under circuit-level noise, offering a common reference for comparing decoders and codes. Bounds on minimum correction costs in the true and competing logical classes label each shot as success, failure, or undecided. On two bivariate bicycle codes, best-first ordered statistics decoding closely tracks this benchmark but leaves some ML-correctable shots uncorrected.
Michele Banfi, Marco Ferrari, Antonino Favano et al.
In briefMotion, relativity and dark-matter effects on ion-trap clock phases and noise
SummaryThis paper develops a quantum theory linking systematic shifts and fluctuations in trapped-ion optical clocks to filter functions set by the pulse sequence. It covers laser frequency noise, recoil and Doppler shifts, micromotion, and state-dependent trap effects, along with relativistic corrections. The same framework is applied to hypothetical dark-matter signals. By analyzing ensemble-averaged phases and variances, it characterizes systematic and statistical contributions to clock accuracy and precision.
In briefWhy the Fer expansion of a driven spin cannot stop after the first term
SummaryThe paper studies the Fer expansion, which writes the propagator of a driven quantum system as an ordered product of exponentials. For su(2) in any representation, from a qubit to a spin of any size, the authors resum the Fer recursion into a closed map on curves in R^3. They prove that for a real-analytic drive, the expansion stops beyond the first factor only trivially, when the first exponential is already exact.
Lorenzo Bagnasacco, Daniel Burgarth, Vittorio Giovannetti et al.
In briefCooling more while dissipating less: a counterintuitive trade-off from thermodynamic geometry
SummaryThe paper shows that, from the same starting state, optimal driving can sometimes reach a colder or hotter target in the same time while dissipating less energy, or dissipate the same energy in less time. The authors name this near-equilibrium anomalous tradeoff (NEAT), study it in the slow-driving regime of open quantum systems, and establish necessary conditions and its geometric origin. They demonstrate NEAT in an exactly solvable qutrit model and in d-dimensional birth-death dynamics, and show it can improve Carnot engine performance.
Andrea Canzio, Vasco Cavina, Salvatore Raia et al.
In briefLocal-channel stability of classical Z₂ lattice gauge models
SummaryThe paper gives sufficient conditions under which classical Z₂ lattice gauge models on d-dimensional lattices remain two-way equivalent to their canonical flat ensemble under weak local perturbations at low temperature. It shows that sufficiently high-temperature states are instead equivalent to a product state. An optimized covariance between distant neighborhoods serves as an indicator distinguishing these two domains. These sufficient domains do not determine the full phase diagram.
WhyProves rigorous low- and high-temperature local-channel equivalence conditions for lattice gauge models, a novel theoretical advance with impact limited to a specialized subfield.
In briefConstant-depth quantum pricing of barrier options using a static oracle
SummaryThis paper proposes a quantum pricing framework for barrier options whose circuit depth does not grow with the number of monitoring dates. Using the Brownian reflection principle and Girsanov theorem, the path maximum is recast as a static joint distribution of terminal price and running supremum, so daily boundary checks are handled by one static bivariate oracle. In transpilation benchmarks for daily monitoring over 252 dates, the authors report a 98.59% reduction in CNOT count and a 98.02% reduction in two-qubit depth, with a 7.84% relative valuation error under an IBM Eagle noise model.
In briefSparse block encoding with low subnormalisation for quantum linear solvers on unstructured meshes
SummaryThis paper proposes a block encoding method for unstructured mesh solvers that decomposes the system matrix into a sum of 1-sparse matrices to reduce subnormalisation. It is evaluated on 2D and 3D CFD matrices from aerofoil, cavity, and duct meshes, with and without preconditioning. The authors report a near-constant subnormalisation factor as preconditioning infill levels increase, and show that reduced precision digitisation markedly lowers the number of multiplexed rotations.
Leigh Lapworth, Jarrett Smalley, Christoph S\"underhauf
In briefNumerical method for computing excited states of dipolar Bose-Einstein condensates using constrained gentlest ascent dynamics
SummaryThis paper proposes a numerical method based on constrained gentlest ascent dynamics (CGAD) to compute excited states of dipolar Bose-Einstein condensates, targeting constrained saddle points with any prescribed Morse index. The scheme combines a semi-implicit sine-pseudospectral discretization with an orthonormalization correction, and evaluates the nonlocal dipole-dipole terms via the nonuniform fast Fourier transform. It is applied to one-, two-, and three-dimensional systems. The authors report that excited states can persist even where the condensate's ground state becomes mean-field unstable.
In briefRandom Permanent and Hafnian Moments via Replica Method
SummaryThe paper rewrites permanents and Hafnians of random matrices as contour integrals, turning their moment computations into a replica calculation similar to mean-field spin glasses. For the 2k-th moment of N×N matrices with independent entries, it gives in closed form the growth rate, prefactor, and first 1/N correction, matching exact enumerations. At k=2 the replica-symmetric solution becomes unstable, separating a power-law bulk from a large-deviation tail, which is also computed. The results apply to boson sampling with single photons and squeezed light.
WhyRecasts random permanent and Hafnian moments as a replica calculation, giving closed-form growth rates and 1/N corrections matching exact enumerations, with implications for boson sampling.
Paolo Facchi, Angelo Mariano, Giorgio Parisi et al.
In briefAtmospheric channel model for QKD over satellite megaconstellations
SummaryThis paper builds an open atmospheric channel model for ground-to-satellite quantum optical links, combining altitude-dependent molecular and aerosol absorption with turbulence effects. The model is checked against data from missions such as Micius and Hispasat, and a hypothetical Starlink-based quantum network is assessed for single-photon transmittance, power balance, and uplink and downlink channel capacity. The authors report that the model predicts real data under simple atmospheric assumptions and offers practical design guidance for future quantum satellite missions.
Sergio G\'andara G\'andara, Javier Vecino-Pe\~nas, Ana Fern\'andez-Vilas et al.
In briefTrapped-ion quantum repeater node tested over a 17 km city fiber
SummaryThis paper demonstrates a trapped-ion quantum repeater node that creates photonic entanglement over a 17 km fiber running across a city, going beyond lab-only prototypes. The node uses two atomic ions coupled to an optical cavity, and the authors first characterize the long fiber channel and the ion-photon entanglement distributed over it. They then implement a repeater-node protocol that entangles a local photon with a remote photon. The results indicate the technology can run on existing city-scale fiber and is a step toward distributed quantum repeater networks.
In briefControlled-Z gates in transmon circuits using two auxiliary states
SummaryThis paper proposes controlled-Z (CZ) quantum gates that use two higher excited states, |02⟩ and |20⟩, activated by selective Floquet coupling in transmon circuits. Two protocols are presented: a nonadiabatic round trip through a bright auxiliary superposition and adiabatic evolution along a zero-energy dark state. Numerical simulations report high average gate fidelities for both, and phase control extends the approach to geometric CZ gates.
In briefNarrowband Nonreciprocal Transmission in a Doppler-Broadened Multilevel Atomic System
SummaryThis paper theoretically studies narrowband nonreciprocal light transmission in a Doppler-broadened five-level M-type atomic medium. After Doppler averaging, the system keeps a narrow electromagnetically induced transparency window, narrower than that of a standard three-level Λ system. The transparency window shows strong direction dependence, with high forward transmission and strong suppression in reverse. Transparency linewidth and forward-backward transmission can be tuned by two independent driving fields while the central frequency stays nearly fixed. The authors suggest the scheme suits frequency-selective filtering and compact vapor-cell nonreciprocal devices for quantum networks.
In briefExact finite-N first-order transitions: how they are suppressed or terminated
SummaryThis paper studies first-order transitions that arise from symmetry-protected ground-state crossings at finite particle number. The authors establish exact Juddian crossings for arbitrary finite N in one- and two-photon anisotropic Dicke models, showing that coupling-matrix eigenvalues set local instability thresholds and the determinant fixes the exact crossing. In the one-photon model, the overlap of coherent branches vanishes in the thermodynamic limit, suppressing the transition cusp. In the two-photon model, squeezed states lose normalizability at spectral collapse, terminating the transition line at finite N.
In briefBidirectional Path Integral Monte Carlo for Estimating Quantum Circuit Amplitudes
SummaryThe paper proposes an approximate classical algorithm for estimating transition amplitudes of quantum circuits. It samples Feynman paths by random walks started from both the input and output states, combined with Multiple Importance Sampling to reduce variance. Empirical results show faster convergence than a forward-only sampling approach, and the method is demonstrated on quantum circuits with up to 4096 qubits.
In briefSearching for axion dark matter with superconductor-spin hybrid magnetometers
SummaryThis paper studies axions, a dark matter candidate predicted by theories beyond the Standard Model, which could be detected in laboratories through a pseudomagnetic field. The authors built a broadband magnetometer by coupling a ferrite spin sensor to a superconducting quantum interference device readout, reaching sub-100 aT/Hz^1/2 sensitivity at tens of kHz. It sets the most stringent terrestrial limits on the axion-electron coupling in the 5 to 60 kHz range.
In briefMultimode parametric amplifier for K-band quantum measurements
SummaryThis paper demonstrates a K-band nondegenerate three-wave-mixing amplifier built from a multimode resonator containing an array of 500 SNAILs. It achieves continuous 20 dB gain from 19.6 to 25.6 GHz with pump frequencies below 32.2 GHz. The amplifier also reports a 3-dB bandwidth of 2.6 to 11.7 MHz at 20 dB gain and an average added noise of 0.73 quanta in the 20-22 GHz band. The authors state it offers a practical route to state-of-the-art K-band readout of superconducting qubits.
In briefAxion dark matter detection in non-Markovian noise
SummaryThis paper proposes a noise-tolerant quantum-metrology scheme using coupled 129Xe spin ensembles to search for axion dark matter, which interacts very weakly with standard-model particles. The authors report that, in an experimentally accessible parameter regime, the scheme's ideal exclusion limit on the axion coupling constant is several orders of magnitude stronger than conventional methods. They also find that when a bound state appears in the spectrum, the limit asymptotically recovers its ideal value under non-Markovian dynamics, while it deteriorates significantly under the Markovian approximation.
In briefSingle-photon time qubit: quantum-vacuum control and complementarity of the arrow of time
SummaryThis paper formulates and experimentally tests a single-photon time qubit using phase-resolved interferometry with two coherently seeded entangled nonlinear biphoton sources. By inverting the pump-seed phase during pair creation from the quantum vacuum, the authors reverse the stimulated evolution direction, enabling single-qubit control and tomography on a temporal Bloch sphere. They also report a complementarity relation between which-branch information recorded by vacuum fluctuations and the visibility of the interference.
In briefFrequency-comb biphoton sources explain nonlocal state reduction via induced coherence
SummaryThis paper proposes an open-system, measurement-defined framework within linear relativistic quantum electrodynamics to explain how entangled superpositions in spacelike-separated regions yield nonlocal correlations without superluminal action or ad hoc wavefunction collapse. It is realized with two spacelike-separated nonlinear crystals driven by a multi-mode frequency comb and a narrow coherent laser. The authors derive an exact spatial-dephasing Lindblad master equation and report a wave-particle-entanglement relation, P^2 + E^2 + V^2 = 1, linking the work to induced coherence and quotient measurement theory.
In briefStabilizer Rényi moments beyond entanglement: how they decay in critical quantum chains
SummaryThis paper studies how stabilizer Rényi moments decay with distance in critical quantum chains described by two-dimensional conformal field theories. These moments depend on the choice of operator basis and cannot be fully determined by entanglement spectra. The authors derive an exact entanglement baseline for reductions of pure stabilizer states and a symmetry selection rule for the charged contribution. In an exact Ising example, an on-site rotation changes the full decay exponent while leaving every subsystem entanglement spectrum unchanged. For Ising intervals at index two, the authors give an exact Pfaffian representation and compare the charged amplitude with a candidate conformal boundary calculation; the data support the prediction, but linking it to the lattice limit still requires endpoint matching and control of the order of limits.
In briefWhether discrete time crystals survive in small cavity QED systems
SummaryThis paper studies discrete time crystal (DTC) behavior in a periodically driven open Dicke model with a finite number of atoms. Non-mean-field fluctuations cause the decay rate and amplitude of transient DTCs to vary non-monotonically as the atom number grows. The authors find that the second-order cumulant expansion fails to capture finite-size dynamics, while a stochastic truncated Wigner approximation is accurate, and they identify three dynamical regimes using it and the Monte Carlo wave function method.
In briefExplainer: How lattice cut direction shapes symmetry in a Rényi entanglement ensemble (quantum Monte Carlo study)
SummaryThis paper examines whether microscopic details of a lattice bipartition survive in the second Rényi entropy ensemble at a critical point. Using quantum Monte Carlo simulations of the square-lattice J-Q3 model at the Néel–valence-bond-solid transition, the authors measure magnetic and dimer order parameters. For an axis-aligned cut, the VBS component perpendicular to the boundary is inequivalent to the parallel one, while a 45-degree tilted cut makes the two equivalent within numerical accuracy. The authors attribute this contrast to differing microscopic symmetries of the Rényi twist defect.
WhyShows microscopic lattice bipartition information survives in the Rényi-2 ensemble, supported by QMC comparisons on the J-Q3 model, with notable implications for entanglement studies.
In briefJoint Logical Measurements for Group Surface Codes via Smooth Hybrid Lattice Surgery
SummaryThis paper introduces smooth hybrid lattice surgery for group surface codes, using merge and split operations along smooth boundaries to perform joint logical measurements. The code patches may use identical or different finite groups, including non-Abelian ones. The central result is that these operations realize a logical K-coset measurement, generalizing the joint logical parity measurement of ordinary surface codes. The authors give explicit measurement circuits, correction procedures for nonidentity outcomes, and examples including generalized controlled multiplication and preparation of T, CZ, CCX, and CS magic states.
In briefHollow-core fiber's low nonlinearity for multiplexing quantum entanglement with classical DWDM signals
SummaryThis paper compares single-mode fiber and photonic-bandgap hollow-core fiber of equal length deployed in a campus network. It tests whether polarization-entangled photons can coexist with high-power dense wavelength-division multiplexed classical signals. The authors report that hollow-core fiber suppresses background noise by about two orders of magnitude while preserving high-fidelity entanglement distribution.
In briefBayesian method that corrects photon loss in optical quantum circuits, including photon collisions
SummaryPhoton loss is the main noise source in linear optical quantum circuits, distorting detector counts away from the ideal output distribution. The authors model raw counts as multinomial observations under per-photon binomial loss and jointly infer the ideal distribution and loss rate via a Bayesian posterior, extending to outputs with photon collisions. On simulated data from the Perceval simulator (n=4 photons, m=20 and m=10 modes), the method achieves lower KL divergence than recycling and postselection baselines in the no-collision benchmark.
In briefQuantum attacks on two Feistel-type block cipher designs
SummaryThis paper proposes new quantum attacks on two Feistel-type constructions, New Structure IV and the lightweight block cipher LBlock, under the quantum chosen-plaintext attack model. For New Structure IV, the authors build an 8-round quantum distinguisher and an r(r>12)-round key-recovery attack that reduces time complexity by a factor of 2^{n/2} compared with prior work. For LBlock, they construct a 9-round distinguisher extended to an r(r>15)-round key-recovery attack, and reduce the 15-round attack's time complexity from O(2^38) to O(2^26) by shrinking the subkey guess space.
In briefEngineering XY and ZZ interactions between two remote superconducting qubits via a multimode waveguide
SummaryThis paper studies how qubit frequency assignments and multimode interference in a finite multimode waveguide can be used to engineer effective XY and ZZ interactions between two superconducting qubits. It finds that a single-mode waveguide cannot suppress both interactions to zero, while odd and even mode configurations yield very different interaction types. Full-Hamiltonian simulations show XY-dominated SWAP dynamics and ZZ-dominated CZ-type dynamics, establishing a frequency assignment criterion for selecting the interaction type.
In briefA new approximation method for open spin systems, showing long-range order far from equilibrium
SummaryThe paper introduces an SU(2)-covariant truncated-Wigner method that maps dissipative spin systems onto stochastic dynamics with one Bloch sphere per site, for arbitrary spin S. Applied to 400-site two-dimensional dissipative anisotropic XY lattices, it finds that vortex-antivortex proliferation destroys the staggered-XY phase for nearest-neighbour coupling, while algebraically decaying long-range interactions stabilize an extended Z2-ordered phase. The authors present the first beyond-mean-field steady-state phase diagram for this model, showing reentrant loss of order at strong coupling and closure of the ordered region beyond α≈3.5.
WhyProposes an SU(2)-covariant truncated-Wigner method, giving the first beyond-mean-field steady-state phase diagram, validated against exact and tensor-network benchmarks.
Igor Timofeev, Dawid A. Hryniuk, Marzena H. Szyma\'nska
In briefControlling topological criticality in an SSH chain with non-Hermitian impurities
SummaryThis paper studies the topological phase of a one-dimensional Su-Schrieffer-Heeger chain containing a finite concentration of non-Hermitian substitutional impurities. The authors propose a deterministic way to shift the phase boundary by using site-dependent non-reciprocal hopping, where breaking the impurities' internal symmetry moves the critical point. Finite-size scaling yields correlation length exponents for symmetric and asymmetric cases, and an impurity-induced real-to-complex spectral transition is also reported.
In briefField test of a self-contained 10 km mobile quantum network link sharing one optical aperture
SummaryThe study demonstrates a free-space optical system over a 10.31 km link from a mobile platform to a ground station, using one shared aperture for both decoy-state BB84 quantum key distribution and bidirectional classical laser communication. The classical link uses Manchester-coded on-off keying with error-packet retransmission. The quantum link achieved an average quantum bit error rate of 2.512% and an average secret key rate of 644 bps. The distilled keys were then used to send AES-256 encrypted images over the classical channel.
In briefQuantum algorithm for high-dimensional nonlinear stochastic equations using Carleman linearization
SummaryThis paper proposes a quantum algorithm for high-dimensional nonlinear stochastic differential equations, using Carleman linearization to convert the nonlinear system into a linear one. Auxiliary processes approximate the tensor powers of the state, and the expectations of the resulting system are solved with a quantum ODE solver. When the nonlinear and noise terms are sufficiently small, the linearization error decreases exponentially with the truncation order, and the required number of queries scales as polylog(N). A numerical demonstration on a Langevin-dynamics-related equation confirms the exponential decay of the error.
In briefStudying non-classical correlations in the tW system using negativity and geometric quantum discord
SummaryThis paper phenomenologically studies a mixed-dimensional qubit-qutrit system formed in leading-order tW production at 13 TeV in the leptonic final state. Two missing neutrinos are reconstructed with conditional normalizing flows, and a joint spin density matrix is derived from angular distributions of the decay products. Non-classical correlations are quantified with Peres-Horodecki negativity and geometric quantum discord, including the effects of Standard Model contributions and two reducible backgrounds.
In briefA natural-transformation view of the Choi-Jamiołkowski isomorphism
SummaryThis paper revisits the Choi-Jamiołkowski isomorphism, the channel/state duality of quantum information theory, through the lens of naturality in the sense of Eilenberg and MacLane. For finite-dimensional Hilbert spaces, it identifies a unique Choi map natural in both spaces that maps completely positive maps to density operators without requiring an entangled input state. The author also shows how the standard Choi-Jamiołkowski formulas express this naturality.
In briefQuantum-classical hybrid optimization methods, drawing lessons from classical decomposition
SummaryThis survey uses classical decomposition to examine how quantum and physics-inspired solvers can be integrated into hybrid quantum-classical algorithms. It distinguishes formal decomposition, reformulation and reduction, and computational orchestration, asking what each transformation preserves and what certificates the inner solver supplies. The authors find that the analyzed studies show conditional component benefits, but do not establish transferable end-to-end superiority over strong classical comparators.
In briefAssignment maps: mappings that set up correlated initial states for open quantum systems
SummaryThis paper studies an open quantum system S coupled to an environment E. It establishes a one-to-one correspondence between completely positive trace-preserving maps from S to E and assignment maps that initialize the composite system SE in a possibly correlated state before unitary evolution. The authors show these assignment maps preserve Hermiticity and trace but not global positivity. They also give a necessary and sufficient condition for a local state of S to lie in the domain where such maps are valid.
In briefAllocating Measurement Shots Across Assertions When Debugging Quantum Circuits
SummaryThis paper studies how to distribute a fixed number of measurement shots across multiple mid-circuit assertions in statistical assertion-based quantum debugging. It proposes and evaluates four allocation strategies (equal split, static weight, adaptive entropy routing, and sequential retirement) within the QDB debugger on CUDA-Q. The strategies are tested on different circuits under noise-free and depolarizing noise conditions. The adaptive strategies concentrate shots on high-uncertainty assertions, substantially reducing total shot usage while maintaining comparable debugging confidence.
In briefCounterexamples to the total-current Hohenberg-Kohn conjecture
SummaryThis paper gives three counterexamples to the total-current Hohenberg-Kohn conjecture, which holds that the ground-state density and total current determine the scalar and vector potentials. It studies two spinless fermions in three dimensions and constructs Hamiltonians whose ground states have zero total current but nonzero magnetic field. Complex conjugation yields a second Hamiltonian with the same density and zero current but reversed magnetic field, disproving the conjecture.
WhyConstructs three counterexamples disproving the total-current Hohenberg-Kohn conjecture, including explicit and monopole-based cases, with substantial implications for DFT foundations.
In briefOptimal four-copy detector for the three-tangle and its fault-tolerant cost
SummaryThis paper studies how to detect the three-tangle, a measure of genuine tripartite entanglement that separates GHZ-type from W-type entanglement in pure three-qubit states. The authors identify a statistically optimal one-sided four-copy detector with click probability τ3²/48, compared with τ3²/256 for earlier constructions, reducing required repetitions by a factor of 16/3. They give ancilla-free circuits using 15 CNOT gates and an 11-CNOT variant, and show a tradeoff between statistical efficiency and circuit cost that persists under fault-tolerant encoding.
Federico Tom\'as B. P\'erez, Berta Casas, I-Chi Chen et al.
In briefPlasmonic metasurfaces that switch optical quantum interference between bunching and anti-bunching
SummaryThe paper presents a composite quantum plasmonic metasurface that acts as an ultrathin non-unitary beamsplitter. By changing the incident photon frequency or the design dimensions, it can produce either bosonic bunching or fermionic anti-bunching of single photons. The photon-photon interactions are analyzed with a quantum coalescence metric. The authors state the approach could support fundamental non-classical light studies and quantum optical logic gates for quantum computing and communications.
Lawrence M. Qin, Sky Semone, Matthew J. Brandsema et al.
In briefLow-temperature optical comparison of Er³⁺, Tm³⁺, and Eu³⁺ molecular complexes
SummaryThis paper compares the cryogenic optical properties of Er³⁺, Tm³⁺, and Eu³⁺ molecular complexes in the same ligand environment. Spectral hole burning appears in the Eu³⁺ complex but not in the Er³⁺ or Tm³⁺ complexes. Laser-induced local heating and slow thermal recovery over seconds to tens of seconds are reported for the Er³⁺ and Tm³⁺ powders, and the authors argue heating alone cannot explain the contrast, pointing instead to ion-dependent relaxation and decoherence linked to electronic structure and environmental coupling.
In briefQuantum fluctuations and phase-space dynamics of an AFM-driven carbon nanotube oscillator
SummaryThe paper models the fundamental flexural mode of a carbon nanotube driven by an atomic force microscope as a harmonic quantum Brownian oscillator coupled to a thermal environment. It derives the reduced dynamics in phase space, where the Wigner function evolves under dissipation, forced displacement, and bath-induced fluctuations. For a Drude memory kernel, covariances are written as explicit finite sums over three characteristic roots. The authors also examine interference attenuation of two-packet superpositions and the integrated negative part of the Wigner function as a measure of nonclassicality.
In briefNext phase of quantum energy science: from mechanisms to applications
SummaryThis paper organizes a growing field spanning quantum batteries, molecular and excitonic energy transport, polaritonics, quantum materials and nuclear control, all of which use quantum states and engineered environments to control energy. It proposes a framework linking mechanisms, functions, capabilities and applications. The authors identify five elementary functions (Excite, Hold, Release, Transfer, Transform) and three engineering capabilities (Storage, Routing, Conversion) along with their performance metrics.
Florian Metzler, Matt K. Lilley, Matthew C. DeCapua et al.
SummaryThis paper presents a dielectric structure, designed by inverse design, that surrounds a quantum emitter to push photon-collection efficiency toward unity. The device collects emission from the full 4π solid angle and reshapes it adiabatically into a collimated beam. The authors experimentally demonstrate the ray bending that collimates omnidirectional emission in two dimensions.
In briefChip-based switch that isolates qubit readout noise
SummarySuperconducting quantum computers need fast, accurate readout, which relies on cryogenic amplifiers that add thermal noise able to disrupt qubits, so ferrite isolators are typically used. This study places a chip-scale microwave switch, a tunable inductive bridge, in the readout chain of a fixed-frequency transmon, pulsing it to conduct only during readout. Switching did not noticeably change qubit coherence, residual excited-state population, or readout fidelity. When broadband noise mimicking amplifier thermal photons was injected, the switch suppressed resulting dephasing by more than 30 dB, consistent with its measured on-off ratio, suggesting it could replace readout-chain isolators on chip.
In briefA group-theory method for computing multi-invariants of certain stabilizer states
SummaryThis paper studies multi-invariants, a multi-partite generalization of Rényi entropies, for simple stabilizer states under an arbitrary replica symmetry group. The authors develop a group-theoretic technique that evaluates these invariants by counting intersections among cosets of the replica group. The method streamlines calculations for graph states with two GHZ-like nodes and certain generalizations. It is best suited to cases where the quantum state is simple but flexibility in the choice of replica group is needed.
Bartlomiej Czech, Yichen Feng, Jonathan Harper et al.
In briefRényi multi-entropy of graph states and the n→1 limit
SummaryThis paper studies Rényi multi-entropy, a generalization of Rényi entropy to pure states of more than two parties, for qubit graph states. It is defined by a replica contraction at integer n, with the multi-entropy as the n→1 limit. The authors show that at every odd n the contraction equals 2^(-k/2), define a class of collision-controlled graphs with a polynomial rank sum, and obtain a natural polynomial continuation to n=1. They show this continuation is not an entanglement monotone, since a Z measurement on one qubit of an odd ring can increase it.
WhyShows odd-replica graph-state multi-entropy reduces to finite-field ranks and that the n→1 continuation is not an entanglement monotone, a notable theoretical result.
In briefCavity models for SU(2) gauge theory: a few-mode quantum model of glueballs
SummaryThe paper adapts cavity quantum electrodynamics methods to pure SU(2) gauge fields, deriving a cavity Hamiltonian in Coulomb gauge with only three localized bosonic modes. Unlike the non-interacting electromagnetic case, this model has a nontrivial spectrum whose lowest-energy states are bound composite gauge particles called glueballs. The authors extend the framework to one-dimensional arrays of coupled cavities, discussing driven glueball condensates and clustering of multi-glueball states, and propose experimental exploration with superconducting quantum circuits.
Lucia Valor, Jacquelin Luneau, Klaus Liegener et al.
In briefPolynomial-time classical simulation of lossy BosonSampling
SummaryThis paper presents a classical algorithm that simulates BosonSampling in polynomial time when a constant fraction of input photons survives photon loss. Under the fixed-loss model, it samples from a distribution close to the target within a given total variation error, with high probability over random interferometers. The result greatly extends the provably simulable regime, including the experimentally relevant linear-survival case, and is also extended to uniform transmission loss.
WhyExtends provable simulability of lossy BosonSampling from sqrt(εN) to any constant surviving fraction, a major regime expansion; correctness of the Haar-averaged analysis needs scrutiny.
In briefSpectral signatures of hidden order and hidden quantum critical points
SummaryThis paper studies hidden-order phases, which break symmetry yet cannot be detected by standard local two-point correlators. Using a minimal model of doped spin chains, the authors show that these phases can be probed through dynamical two-point response functions measurable by RIXS and neutron scattering. Numerical results identify spectral fingerprints of the hidden-order phase, its hidden quantum critical point, and a class of gapless symmetry-protected topological phases.
Reja H. Wilke, Henning Schl\"omer, Sebastian Paeckel et al.
In briefNambu-Goldstone Bosons and Quantum Fisher Information: how symmetry breaking links quantum information measures
SummaryThis paper shows that the quantum Fisher matrix for ground states of systems with continuous symmetries is equivalent to the Nambu-Goldstone bosons produced by broken generators. The information metric defined by the Fisher matrix is shown to match the Zamolodchikov metric that defines the system's coset space. The authors also relate the Uhlmann curvature from multi-parameter estimation to the charge density matrix distinguishing type-A and type-B Nambu-Goldstone bosons, illustrate these connections with examples, and discuss extension to finite temperature.
In briefRearranging many atoms in any direction at once, using moving light patterns
SummaryThe authors move many individual atoms in parallel, in any direction, by generating changing holograms with one spatial light modulator. They introduce a training-free, warm-start weighted Gerchberg-Saxton algorithm that generates holograms in real time with performance comparable to neural-network methods. Using these methods, they assemble ytterbium atoms into a 2078-site kagome lattice with 99.0% mean filling and demonstrate three-dimensional rearrangement between array layers.
In briefBoundary-sensitive quantum order on non-amenable lattices, where boundary effects induce bulk order
SummaryThe paper studies quantum systems on non-amenable lattices, whose boundaries make up an extensive fraction of the system. The authors combine boundary-retaining iDMRG with an exact symmetry-fixing duality to examine p<5 state clock models on the coordination-3 infinite Cayley tree. They report an intermediate phase between ordered and disordered phases, where bulk order is induced by an arbitrarily weak boundary field rather than by conventional spontaneous symmetry breaking.
In briefQuantum Algorithms for Optimal Control of Long-Horizon Linear Systems
SummaryThis paper proposes quantum algorithms for finite-horizon continuous-time linear-quadratic regulation (LQR), a foundational optimal control problem. Instead of solving the nonlinear Riccati equation, it reformulates the problem as a multiple-shooting linear system and proves a condition-number bound independent of the horizon under stabilizability and detectability assumptions. Under sparse block-encoding and state-preparation assumptions, query and gate complexities scale polylogarithmically with system size and control duration. Results are established for damped mass-spring chains and supported by numerical experiments.
Xiajie Huang, Cristina \'Alvarez Yuste, Nikita Guseynov et al.
In briefSupervised learning via quantum Hamiltonian embeddings: encoding training data into one parameterized Hamiltonian whose approximate ground state sets the classification rule
SummaryThis paper introduces quantum Hamiltonian embeddings, a supervised learning framework that encodes a classical training dataset into a single effective, parameterized Hamiltonian. Training optimizes the parameters of this data-dependent Hamiltonian, and its approximate ground state defines the classification rule. The authors describe efficient gradient estimation and generalization guarantees, and demonstrate the framework at scale on IBM Heron processors using a standard benchmark dataset.
Riccardo Molteni, Minjun Jeon, Paolo Braccia et al.
In briefFast Thouless pumping with local counterdiabatic driving
SummaryThe paper studies how to speed up topological Thouless pumping in the Rice-Mele model without exciting the system. Exact counterdiabatic correction terms are non-local in many-body systems, so the authors first use a variational method that gives accurate nearest-neighbor approximations for noninteracting fermions. For an interacting spinful chain, that approach fails, and they propose a local ansatz with 14 coefficients based on interaction-energy-resolved currents. The ansatz keeps the pumping quantized at cycle times of 2/t and 1/t, with per-site accuracy that does not degrade between 8- and 12-site rings.
In briefCorrelated decoding loses surface code distance below threshold
SummaryCorrelated decoding improves surface-code matching and clustering decoders by reweighting one subgraph based on the other's correction. The paper shows that standard reweighting can make correlated decoders fail on fault configurations of size (d-1)/2 that a distance-d code should correct, weakening error suppression well below threshold. Regularizing the reweighting rule restores the nominal distance scaling and a clear advantage for correlated decoding.
C\'esar Hernando de la Fuente, Joonas Majaniemi, Evert van Nieuwenburg et al.
In briefHigh-accuracy local decoding for fast transversal Clifford circuits
SummaryThis paper benchmarks the Iterative Redecode Scheme (IRS) on fast transversal Clifford circuits, using local decoders that exchange messages instead of decoding a global hypergraph. On a deep random Clifford benchmark and in three-block GHZ preparation, IRS reports lower logical failure rates than the ghost protocol and logical observable matching. The error rates saturate after a few iterations, so iteration caps cost negligible accuracy.
Mark Webber, Simanraj Sadana, Matthew A. Lane et al.
In briefCapacities of bosonic Gaussian channels assisted by PPT-preserving operations
SummaryThis paper determines the exact quantum communication and entanglement-distribution capacities of three bosonic channels: thermal loss, thermal amplification, and additive Gaussian noise, assisted by operations that completely preserve positive partial transpose (PPT). These operations are stronger than LOCC but cannot generate distillable entanglement on their own. For thermal loss, the unconstrained capacity matches the PLOB bound in the non-entanglement-breaking regime, and the upper bounds are also attained for the other two channels. The results are extended to energy-constrained communication.
WhyExact PPT-assisted capacities for three bosonic Gaussian channels, including energy constraints, attaining the PLOB bound; strong theoretical proofs with broad relevance.
In briefGeneral Master Equation for Two Accelerated Detectors: Steady States and Entanglement
SummaryThe paper derives a general master equation for two co-located, uniformly accelerated two-level detectors weakly coupled to scalar fields in Minkowski vacuum, keeping coherent and dissipative terms for arbitrary orientations, field masses, and dimensions. For equal orientations and coupling to massless fields in four dimensions, it finds stationary states and their entanglement. Symmetric coupling gives concurrence that depends on acceleration, while rotating-wave coupling gives concurrence independent of acceleration.
In briefPhase-sensitive quantum-state texture during thermalization of a Dzyaloshinskii-Moriya Heisenberg dimer
SummaryThis paper studies quantum-state texture as an anisotropic spin-1/2 Heisenberg dimer with a longitudinal field and Dzyaloshinskii-Moriya interaction relaxes toward thermal equilibrium. The authors build a global weak-coupling Lindblad equation from local couplings to a bosonic bath and examine the limits of the secular approximation. They find that the DM coupling changes both the modulus and phase of single-excitation coherence, and that texture behaves differently from coherence magnitude and purity during heating and cooling.
Onofre Rojas, Zhirayr Adamyan, Fadwa Benabdallah et al.
In briefPrimer on quantum optimal control techniques
SummaryThese are detailed lecture notes from a Ph.D. course on quantum control taught at Seoul National University's Department of Chemistry in 2014, partly also taught at Friedrich Schiller University Jena. The notes focus on quantum optimal control and quantum optimal control algorithms based on gradient and extended gradient methods.
In briefMeasurement-efficient method for estimating correlated energies of photodynamic materials
SummaryThe paper presents a measurement-efficient estimator for correlated energy differences in quantum chemistry, tested on an H2DBB–Ru model derived from a Ru-functionalized hafnium metal-organic framework for radiodynamic and photodynamic therapies. It combines a quantum-prepared target state with sparse multiconfiguration references and recovers ground-state corrections using magnitude-only compute-uncompute measurements. Analytical estimates predict 1.6 mHa precision with a few hundred shots. Emulator and trapped-ion experiments on Quantinuum Helios validate the approach up to (10,10) active space.
Connor Lenihan, Kripa Panchagnula, Luca Erhart et al.
In briefMatching ground-state sampling in penalty-based and constrained quantum annealing
SummaryQuantum annealing usually samples degenerate ground states unevenly, and this bias depends on how the driver Hamiltonian couples those states near the end of annealing. The paper compares the penalty method and constrained quantum annealing (CQA) for combinatorial problems with a cardinality constraint, using simulations on random graph bipartitioning and degenerate perturbation theory. For sufficiently large penalties and long annealing times, the conditional ground-state distribution of penalty-based annealing approaches that of CQA. The authors attribute this convergence to a correspondence between the effective Hamiltonians of the two methods.
In briefA solvable obstructed seam on a lattice Klein bottle, and how register choice affects toric codes
SummaryThe paper studies a frustrated seam formed by reflection-gluing Wen's plaquette model on a closed lattice Klein bottle. Its seam operators reduce to free Majorana rings, and bulk stabilizers restrict the allowed sectors, yielding exact ground energies, gaps and degeneracies. It contrasts this with consistent toric-code realizations using an edge register, which preserves anyon labels, and a Hadamard-dressed site register, which has colour-dependent seam transport.
In briefLower bounds on tunneling between two magnetic wells at large separation
SummaryThe paper studies tunneling between two identical, smooth, compactly supported potential wells in a constant perpendicular magnetic field, letting the well separation tend to infinity. For small positive field strength, it proves lower bounds on the hopping coefficient and the splitting of the two lowest eigenvalues, outside a set of separations of density zero. The bounds take an exponential form with a quadratic term in the separation plus a correction of order d to the power 1+δ. The proof uses the explicit Landau resolvent kernel and a complex analytic estimate for logarithmic averages, and assumes no radial or reflection symmetry.
Charles L. Fefferman, Say-Yeon Kwon, Jacob Shapiro et al.
In briefNon-Markovian exceptional points and information backflow via a Heisenberg reaction-coordinate method
SummaryThis paper studies exceptional points (EPs) in open quantum systems using a Heisenberg-equation approach based on the reaction-coordinate formalism, yielding exact analytical dynamics. The method is shown to simplify analysis compared with master equations. The authors examine non-Markovian revivals in systems with second and higher-order EPs, finding that EPs do not generally mark the onset of revivals, and they derive bounds on the number of revivals and enhanced asymptotic relaxation near higher-order EPs. They also study non-Markovian EPs with engineered reservoirs and show how these can control the rate of irreversible information loss.
Daniel Holst, Gianmichele Blasi, Shishir Khandelwal
In briefBeyond Fidelity: Fixing Errors When Generating Photonic Seed States
SummaryLinear optical quantum computing often requires probabilistically generating small dual-rail entangled states, called seed states. This paper develops a framework that separates how physically distinct errors affect the output state in linear-optical state generation. Using it, the authors identify seed state generators where destructive many-photon interference stops detector loss and noise from causing false heralding events, which suppresses errors.
Sara Bartolucci, Patrick Birchall, Jacob Bulmer et al.
In briefLocal measurement theory for quantum cellular automata: building spatially extended measurements from local operations
SummaryThe paper develops a local measurement theory for quantum cellular automata, describing measurements with localized completely positive maps organized into non-adaptive protocols. Each protocol induces an effective measurement on the initial time slice whose support is bounded by the automaton's causal structure. As an example, a two-step protocol for a one-dimensional nearest-neighbour qubit automaton realizes a Bell-basis projective measurement on two neighbouring sites for suitable parameters, and deforms continuously away from that point.
Tommaso Brambilla, Alessandro Tosini, Paolo Perinotti
