Papers

The cosmological constant $\Lambda$, and its generalization as Dark Energy, makes up roughly 70% of the present-epoch universe and has been part of the dominant $\Lambda$CDM cosmological paradigm for more than a quarter of a century. It has been put on trial by recent measurements of galaxy clustering, Type Ia supernovae, and the cosmic microwave background. In this Perspective we evaluate the strength of the evidence for a constant $\Lambda$, versus Dynamical Dark Energy (DDE) in the light of recent developments. We also assess what the future holds both for our Universe and our understanding of its most mysterious component.

Structured spatial data require quantum encodings that preserve geometric relations, expose measurable observables, and remain implementable on finite-depth hardware. This work introduces a quantum representation and circuit architecture for rigid-body transformations and specializes it to Denavit–Hartenberg kinematics of serial open-chain manipulators. Each translational contribution is factorized into a classical metric magnitude and a signed unit direction encoded by a single-qubit Bloch vector, while parameterized rotations reproduce the ordered propagation of frame directions. A selector register prepares probabilities proportional to the contribution magnitudes, and the reduced state of a designated readout qubit encodes their normalized weighted sum. The retained classical scale then reconstructs the metric end-effector position. Two additional readout qubits encode terminal-frame axes, providing a compact and geometrically interpretable pose interface. At the ideal expectation-value level, measured Pauli observables reproduce the corresponding classical kinematic quantities. Alternative circuit architectures realize the same representation with different tradeoffs in qubit count, circuit depth, controlled operations, and measurement requirements. Validation on a serial manipulator yields numerically negligible position and orientation reconstruction errors under ideal simulation. Finite-shot simulations, noisy executions, transpilation analysis, and a hardware demonstration further characterize statistical error, noise sensitivity, and implementation overhead without asserting computational advantage.

Energy transition decision-making is pervaded by deep uncertainties. Computational models are helpful in addressing such uncertainties, as they can give insight into techno-economic complexity. However, models alone are insufficient, as part of the uncertainties involve justice dilemmas.

We study superconductors coupled with $X$-wave magnets with $X=p,d,f,g,i$. They are essentially different between altermagnets with $X=d,g,i$ and odd-parity magnets $X=p,f$ due to the compatibility of the spin-singlet formation of the $s$-wave superconductor. The altermagnets and odd-parity magnets show rich superconducting phase diagrams depending on the strength of the magnetic order, the chemical potential and the ratio of the on-site and nearest-neighbor interactions. Especially, we find that the altermagnetic order stabilizes the chiral ($p_{x}+ip_{y}$)-wave superconductor, which is a class D topological superconductor hosting Majorana chiral edge states. It is characterized by the Chern number. Especially, there emerge two chiral edge modes in the $i$-wave altermagnet, which are characterized by the Chern number 2. On the other hand, the $p$ ($f$)-wave odd-parity magnetic order stabilizes the $p$ ($f$)-wave topological superconductor, which is a class DIII topological superconductor hosting Majorana flat bands. It is characterized by the winding number. Majorana flat bands are robust in the presence of the mixing with the $s$-wave superconductivity, which is inevitable for odd-parity magnets although the magnitude of the mixing is tiny.

We construct a complex spherical fusion category with cyclic Haagerup-Izumi fusion rules for every odd n >= 3, and deduce pseudo-unitary existence. The proof has four parts: explicit real coefficients and their quadratic identities; a contour calculation for a range of cubic Fourier coefficients; algebraic completion of all cubics; and categorical reconstruction. Matrix inversion supplies reflection, and an extension of the dimension-field automorphism supplies the positive-dimensional category.

LUX-ZEPLIN has recently revealed a single nuclear recoil event compatible with a recoil energy of $E_R\simeq248\,\mathrm{keV}$, in a region with a small expected background. Interpreting this as a signature of dark matter, we compute the posterior probability distribution of the parameters of the dark matter scattering off xenon nuclei. We retain the exact two-body kinematics for an arbitrary mass splitting between the incoming and outgoing dark-sector states, thus encompassing both elastic and inelastic scatterings. The data select non-trivial, disconnected regions of this distribution, which correspond to physically distinct endothermic and exothermic regimes, in which the observed recoil is generated either close to a kinematic threshold or through the release of dark-sector mass energy. We determine the recoil spectra preferred by the observed data and show how the absence of accompanying events at lower recoil energies sharply constrains the viable parameter space. We find a kinematically tuned region of endothermic WIMP-like models at high mass for generic couplings, as well as exothermic models ranging from sub-GeV to heavy dark matter with sizable mass splittings. Elastic dark matter scatterings require instead momentum-suppressed and/or nuclear-spin-dependent non-relativistic interactions.

Many quantum sensors infer parameters from continuously emitted fields, yet in the presence of unmonitored loss, it is difficult to determine how much critical enhancement survives in the accessible output. In this work, we calculate the full frequency-resolved output quantum Fisher information (QFI) of a stationary vacuum-seeded optical parametric oscillator for cavity-detuning estimation. We show that, for any fixed nonzero unmonitored loss, the QFI of correlated sideband pairs grows quadratically with the mean intracavity photon number near threshold, but only within a spectral window that narrows inversely with that number; consequently, the spectrum-integrated output QFI rate scales asymptotically only linearly. We identify a far-detuned, near-threshold regime in which the monitored output alone asymptotically approaches the loss-imposed upper bound on the joint cavity-output QFI. We further determine the operating points that maximize the output QFI rate per intracavity photon and introduce a frequency-resolved homodyne strategy that maximizes the Fisher information obtainable from a single record. Our results establish an operational connection between critical enhancement and metrological information accessible in the output field, while providing concrete guidance for the design and readout of dissipative parametric sensors.

We investigate how neutrino-mass constraints from cosmology depend on the assumed thermal history of the universe. Photon injection after neutrino decoupling would decrease the neutrino abundance inferred from the temperature of the cosmic microwave background (CMB), potentially loosening the upper limit on their masses. We first evaluate how the cosmological neutrino-mass bound is altered by the decay of massive particles into photons and dark radiation after Big Bang nucleosynthesis. To test the robustness of this constraint more generally, we also assess the impact of varying the temperature of the cosmic neutrino background without assuming a specific physical mechanism. We perform MCMC analyses of both frameworks with primary CMB observations from Planck, CMB lensing measurements from Planck and ACT, and baryon acoustic oscillation data from DESI. For the degenerate mass ordering, the $95\%$ credible limit tightens from $\sum m_\nu<0.0691$ eV in a standard thermal history to $\sum m_\nu<0.0652$ eV if the massive particles decay only into photons, while the injection of dark radiation in addition to photons slightly relaxes this limit to $\sum m_\nu<0.0710$ eV. The same pattern holds for the normal and inverted orderings, and the decay scenario shifts the bound on the sum of the neutrino masses by at most $0.004$ eV for fixed mass splittings. Allowing model-agnostic changes in the neutrino-to-photon ratio yields a $95\%$ credible limit of $\sum m_\nu<0.0724$ eV for the degenerate ordering, indicating that the stringency of our neutrino-mass bounds is not driven by constraints on the decay scenario. We find that the neutrino temperature and the sum of the neutrino masses are positively correlated, which implies that reducing the pre-recombination radiation density will only worsen the emerging tension between cosmological bounds on the neutrino masses and the measured mass splittings.

We confront a class of dark-energy equations of state emerging from group field theory (GFT) quantum gravity with DESI Data Release 2 baryon acoustic oscillations and Pantheon+ type-Ia supernovae. We introduce sampling parametrisations that replace microscopic initial-condition parameters by combinations more directly measured by background probes. The GFT solutions separate into logarithmic, power-law and oscillatory branches, determined by the microscopic interaction parameter $m$. The logarithmic branch is constrained to lie extremely close to a cosmological constant, while the power-law branch permits a small phantom deviation. Without perturbative-theory priors, oscillatory solutions can reproduce the mild preference of the distance data for a dip in $w(z)$ near $z\simeq0.5$–$1$. Profile-likelihood constraints favour $m\sim-2$ and $m\sim-5$ from BAO and supernovae, shifting towards $m\sim-3.5$ when CMB information is included. Conservative perturbative priors strongly suppress these deviations from $\Lambda$CDM. The quantum-gravity scale $z_q$, related to the average number of quantum gravity atoms, remains unconstrained, although its role in the time evolution makes higher-redshift observations a promising route to probing it. We further find that strong projection effects highlight the importance of performing likelihood profiling alongside our marginal posterior constraints. Our results provide a first direct test of GFT-motivated dynamical dark energy and demonstrate the potential for cosmological observations to inform quantum-gravity model building.

Laser-plasma accelerators have demonstrated the ability to produce ultrashort relativistic electron bunches with peak currents suitable for compact light sources, ultrafast diffraction, and strong-field studies. However, their performance critically depends on preserving the longitudinal phase-space density of the beam as it exits the plasma accelerator. Here, we report the first direct observation of a previously unresolved process in which a highly charged electron bunch undergoes significant longitudinal expansion and progressively loses electrons during extraction from a laser-driven wakefield accelerator, a phenomenon we refer to as electron shedding. Using femtosecond relativistic electron microscopy, we tracked the evolution of the beam far beyond the accelerator exit and observed the bunch stretching over many plasma wavelengths before shedding electrons during propagation. Particle-in-cell simulations reproduce the observed behavior and reveal that it originates from a combination of effects when a high-charge-density beam exits the accelerator. These dynamics redistribute energy from the beam head into a low-energy tail, thereby reducing the useful peak charge density and ultimately decreasing the efficiency of the laser-plasma accelerator. Our results provide new insight into beam extraction and phase-space evolution in laser plasma accelerators and highlight the importance of controlling these collective effects for future applications.

The ultraviolet continuum from a high-redshift accreting black hole is routinely used to infer its mass. GN-z11 offers a sharp test of whether that inference is secure. A thin-disk fit to its continuum gives an Eddington mass of $M_{\rm E}=1.12\times10^{7}\,\Msun$, an order of magnitude above the $\log(\Mbh/\Msun)=6.2\pm0.3$ inferred from broad N~iv. We show that this apparent tension is not imposed by the ultraviolet slope alone. We derive a closed-form criterion comparing the radius where observed photons are produced with the radius where a supercritical flow departs from efficient solution. For GN-z11, the criterion places the supercritical transition inside the ultraviolet-emitting region. Composite disks retaining the outer solution confirm this numerically, requiring $\Mdot_{\rm out}=3.1$–$4.4\,\Msun\,\mathrm{yr^{-1}}$ and placing $\Rsph=(1.2$–$1.8)\times10^{3}\,\rg$ inside $\Ruv=(2.6$–$2.9)\times10^{3}\,\rg$. Replacing the inner $\sim10^{3}\rg$ by a supercritical flow shifts the fitted slope by only $\Delta\betaUV=+0.08$ to $+0.11$, comparable to uncertainties from standard spectral modelling. Reversing the radial ordering requires the effective transition to move outward by a factor $1.7$–$2.1$. Within our composite models, the measured slope constrains black-hole mass only to around $10^{6}\,\Msun$, an order of magnitude below the continuum Eddington mass. Continuum Eddington masses should therefore be treated as model-dependent bounds that assume global thin-disk efficiency. The same hierarchy appears in three additional JWST sources under the disk-dominated interpretation, where separation masses are only $4$–$6$% of continuum Eddington masses. This distinction can substantially weaken the seed-mass and early-growth demands inferred from ultraviolet continua at cosmic dawn for the first massive black holes.

In this work, we investigate the finite-bias charge current, shot noise, and Fano factor in an Aharonov-Bohm interferometer composed of two parallel quantum dots, each side-coupled to a topological superconducting nanowire represented by an effective Kitaev chain hosting Majorana bound states at its ends. The transport properties are calculated using the nonequilibrium Green's function formalism within the equation-of-motion approach. Our results show that coupling to the Majorana bound states significantly modifies the interference pattern, producing distinctive signatures in the current, shot noise, and Fano factor. These signatures are particularly pronounced at the half-flux condition, where destructive interference suppresses the conventional transport background and enhances the visibility of Majorana-assisted transport. These findings demonstrate that finite-bias shot-noise spectroscopy provides a sensitive indirect probe of Majorana bound states in hybrid superconducting-nanowire interferometers.

Thermal conduction can act as a heating mechanism for cool-core clusters, yet the same transport must erode any temperature discontinuity it crosses. Ophiuchus permits both effects to be tested in the same atmosphere. Its temperature rises from about $1$ keV in the innermost core to $9$ keV at $r\sim30$ kpc, making conductive heating especially favorable, while two sharply resolved cold fronts independently constrain the same transport. \textcolor{black}{We construct a steady radial energy balance from deprojected Chandra density and temperature profiles, with XRISM-based limits on turbulent heating and a subsonic inflow contribution.} Closing the balance with conduction requires only sub-Spitzer coefficients — \Ftwentyfive\ at 25 kpc and \Finner\ and \Fouter\ at the inner and outer cold fronts — so conduction can energetically supply the missing heat. Yet the same coefficients, applied normal to the cold-front surfaces, would broaden the fronts to their observed width limits within \Tinner\ and \Touter\ Myr, short compared to the characteristic sloshing timescales that generate and sustain such interfaces. For a representative 200 Myr residence time, the radial conductivity demanded by the energy balance exceeds the cross-front conductivity permitted by front survival by roughly a factor of three, with the required anisotropy exceeding unity in 99.9% and 98.8% of accepted models. The result leaves two broad regimes. Thermal conduction is either subdominant in Ophiuchus or contributes substantially but is strongly anisotropic, with heat transport suppressed across the cold fronts relative to the radial direction. Together they disfavor locally isotropic conduction as a dominant heating mechanism in cool cores generally.

The radio/X-ray/black-hole-mass Fundamental Plane (FP) is widely used to estimate masses of accreting intermediate-mass black hole (IMBH) candidates. Its inverse use is justified only when radio luminosity traces a compact jet core and X-rays arise from the same sub-Eddington hard-state accretion flow. We formulate an accretion-state validity criterion for inverse-FP masses using verified BH X-ray binary radio/X-ray tracks as the empirical reference. Using 424 detections from 21 BHXBs and candidates, we find that both standard and curved tracks are present and the luminosity at which radio/X-ray behavior changes is source dependent. A low X-ray Eddington ratio is therefore not, by itself, sufficient to establish inverse-FP validity. Within a scale-invariant jet/hot-flow framework, track steepening reduces the effective mass leverage of the inversion, while at much lower accretion rates uncertainties in the dominant emission mechanism and compact-core production can invalidate the underlying FP assumptions altogether. We apply the criterion to representative IMBH-relevant systems without fitting a new plane. NGC 4395 is low-Eddington but compact-radio deficient: its VLA-scale and VLBI jet-base luminosities imply formal inverse-FP mass underestimates of about 1.0 and more than 2.8 dex if the deficit is misread as a mass signal. Globular-cluster X-ray populations in NGC 1399 and NGC 4472 are source-identity limited: 71% and 67% lie below $L_{\rm Edd}(10\,M_\odot)$, and the high-luminosity tail alone does not identify an IMBH accretor. The radio non-detection of the $\omega$ Centauri IMBH candidate constrains gas supply, accretion efficiency, and compact-core production rather than excluding the black hole. The resulting test defines which SKA/ngVLA-era radio cores can be converted into FP masses, and which instead constrain gas supply, source identity, or compact-core production.

Incorporating dynamical fermions is a central challenge for diffusion samplers of lattice gauge theories. We propose an analytic pseudofermion sampler based on continuous Hasenbusch transport as a component for gauge diffusion. The construction uses shifted linear solves and a finite-path correction, requiring neither explicit fermion determinant evaluation nor a learned pseudofermion model. We demonstrate the coupling in the two-flavour Schwinger model without neural networks, obtaining corrected physical observables compatible with independent references. We also show why accurate covariance transport can leave large weight fluctuations, tracing them to the backward transition density. This analysis leads to a correction based on the Wilson operator trace that reduces log-weight variance without changing the generated fields or increasing the number of Dirac operator applications. The predicted improvement is verified on previously unused gauge backgrounds. These results provide an analytic option for incorporating fermions in gauge diffusion and a guide to controlling its correction weights.

Despite their promise as structural and electronic analogs to cuprates, nickelate thin films consistently exhibit broadened superconducting transitions in many experiments that remain poorly understood. Local measurements are ideal for revealing the presence of defects or competing phases, which may cause this transition broadening through a phase-separation. Here, we use scanning SQUID microscopy to investigate local superfluid density and magnetic texture of optimally doped $\mathrm{Nd}_{1-x}\mathrm{Eu}_{x}\mathrm{NiO}_{2}$ (NENO) (x=0.25) grown via molecular beam epitaxy. We observed a weakly-magnetic texture coexisting with superconductivity. Spatially resolved susceptibility imaging reveals a highly non-uniform superconducting state, characterized by a robust stripe-like enhancement pattern appearing near the phase transition. By resolving the mesoscopic landscape of electronic and magnetic inhomogeneities, these findings suggest that a competing magnetic phase is a primary contributor to the unusually broad superconducting transitions of these optimally doped NENO samples. Understanding the uncovered superconducting enhancement may provide a path to raising superconducting temperatures in these materials.

We propose a Landau-analysis-inspired strategy for directly computing the symbol of integrals that evaluate to multiple polylogarithms in twisted cohomology. The central idea is to identify all ways in which singular hypersurfaces, twisted hypersurfaces, and integration boundaries can interact when external parameters are varied, giving rise to logarithmic or algebraic branch points. By tracking how an integral is modified when analytically continued around each of its branch points, we can recursively construct its symbol. We illustrate this approach by outlining an efficient algorithm for computing the symbol of finite integrals over twisted hyperplane arrangements, when they are expanded around special values of the twist parameter. This algorithm can be used to compute the (transcendental) integrands of cosmological correlators in conformally coupled theories to any order in the twist expansion.

Doping a quantum spin liquid is expected to produce a superconductor. We show that for the Dirac spin liquid on the kagome lattice the doped charge orders first. The charge is carried by a chargon doublet whose two gauge components are degenerate on the square and triangular lattices, and the kagome lattice, as the line graph of the honeycomb lattice, splits them. One component disperses and condenses in four valleys. The other has flat lowest bands and stays empty over a window in the bare mass whose width, $(\sqrt6-1)t$, follows from the band structure alone. Within that window, in the mean-field chargon theory constructed from the projective symmetry group of the spin liquid, the doped state forms charge and loop-current crystals with the electromagnetic U(1) unbroken and no superconductivity. Pairing requires a gapped descendant of the spin liquid as the parent and then takes the form of a pair-density wave, with no uniform $d+id$ channel at leading order and none at any order for the crystals at the $M$ point. The predicted charge order is odd under the twofold rotation and has no cubic invariant, which distinguishes it from the charge order of the kagome metals.

We are in an era of unprecedented spectroscopic data availability, with surveys such as APOGEE, GALAH, and DESI observing millions of stars. However, data are heterogeneous and to date, efforts to exploit synergies between surveys have been limited. In particular, there is a lack of principled methods that combine spectroscopic data from different surveys to improve inference of physical parameters. In this work we present a new method, MUSHY, for spectroscopic data fusion. MUSHY is an amortized Bayesian inference method, using a rectified flow model with multimodal inputs to learn a posterior distribution over physical parameters. Using synthetic spectra generated via ATLAS12/SYNTHE, including realistic instrumental effects and noise, we demonstrate that MUSHY can precisely infer physical parameters with well-calibrated posteriors from any combination of surveys, with multimodal inputs providing stronger constraints on the posterior than single-survey data alone. This work paves the way for principled combination of spectroscopic data from heterogeneous sources.

We present the first application of neural-network-based baryon acoustic oscillation (BAO) reconstruction to real galaxy survey data, restoring the acoustic signature damped by nonlinear structure growth. {NERV} (Neural-network Enhanced Reconstruction of the UniVerse) augments standard reconstruction with a convolutional neural network trained on cubic $N$-body simulations, and explicitly accounts for realistic observational effects including the curved-sky geometry, the redshift-dependent selection function, and finite survey boundaries, by tessellating the survey volume into local patches. We validate the method on the MultiDark-Patchy mock catalogs, recovering unbiased BAO dilation parameters. Applied to the BOSS DR12 galaxy sample, NERV improves the precision of the BAO distance measurements significantly. These results establish neural reconstruction as a practical component of BAO analyses for ongoing surveys such as DESI, with the potential to substantially tighten constraints on the cosmic expansion history and the nature of dark energy.

Heavy-quarkonium hadroproduction at the LHC can access kinematic configurations in which the partonic center-of-mass energy is much larger than the quarkonium mass and transverse momentum. Fixed-order predictions may become unstable in this regime because large logarithms of the collision energy are not resummed. Extending high-energy factorization beyond leading logarithms requires process-dependent impact factors at next-to-leading order (NLO). We report the first complete NLO BFKL impact factors, with exact heavy-quark-mass dependence, for the production of the NRQCD states ${}^1S_0^{[1]}$, ${}^1S_0^{[8]}$, and ${}^3S_1^{[8]}$. The real-emission calculation is combined with the previously known virtual corrections through a local subtraction procedure. Soft singularities cancel, initial-state collinear poles are absorbed into the parton distributions, and rapidity divergences are removed by BFKL factorization. These results provide the ingredients needed for full-NLL studies of forward quarkonium and of quarkonium-associated production with a large rapidity separation.

Spiral spin liquids are magnetic states whose classical ground-state manifold consists of planar incommensurate spin spirals with wave vectors lying on a continuous ring or surface in reciprocal space. The resulting subextensive degeneracy suppresses magnetic long-range order and gives rise to liquid-like behavior. Despite numerous material realizations and theoretical investigations, the structure of low-temperature spin configurations of spin-isotropic Heisenberg spiral spin liquids has remained poorly understood. Here, we classify and characterize the classical topological defects supported by these systems. We uncover a rich family of vortex types involving concerted windings of spin directions, spiral-plane normals, and wave-vector orientations, yielding a $\mathbb{Z} \times \mathbb{Z}_2$ classification. Remarkably, the elementary defects are half-vortices carrying fractional $2\pi$ windings in both spin and momentum space and obey fusion rules resembling to those of Ising anyons. Large-scale classical simulations of a square-lattice spiral spin liquid reveal that these vortices are dense in the spiral-spin-liquid regime, and bind tightly below an order-by-disorder phase transition, eventually fusing to vacuum.

Coherent and efficient light-matter interfaces between an atom and a single mode of the electromagnetic field are essential for quantum technologies. Traditionally, these systems employ optical cavities or waveguides to isolate a specific mode of light, but a more recent approach is to engineer antennas from ordered configurations of trapped ultracold atoms that exhibit controllable and directed scattering. In this work, we propose a method to engineer an antenna from the center-of-mass wavefunction of a single atom, which can produce directed emission and thereby exhibit strong coupling to a target mode of light in free space. We predict that the resulting single-atom cooperativity can be comparable to the current state of the art in optical cavity and waveguide QED experiments. Building on this approach, we show that a wavepacket antenna becomes a single-atom mirror in the linear response regime. We study the modified dipole-dipole interactions and band structure of chains of such emitters, which can exhibit sub- and superradiance at spacings much larger than the wavelength of the light. Extending our approach to multi-level atoms, we propose a method to achieve arbitrary spatial scattering from a single atom, including uni-directional spontaneous emission. Finally, we elucidate how our approach can enhance cooperative scattering in conventional arrays of tightly trapped atoms.

We investigate dark-matter-induced neutron disappearance as an interpretation of the high-energy nuclear recoil event reported by LUX-ZEPLIN. An incoming dark matter (DM) particle annihilates a bound neutron into an invisible scalar, leaving a recoiling daughter nucleus. For each accessible daughter state, two-body kinematics fixes the recoil energy in the zero-velocity limit, producing a line spectrum broadened by halo velocities. We identify parameter regions for benchmark DM masses of 5 and 50 GeV that can account for the event near 248 keV without producing events at lower energy. We examine collider constraints in an illustrative ultraviolet completion and recast Borexino data to constrain accompanying nuclear de-excitation signals. More generally, the DM-induced neutron disappearance provides a framework for interpreting localized nuclear recoil excesses in future direct-detection experiments.

Next-generation gravitational-wave observatories like Cosmic Explorer will provide an unprecedented opportunity to probe the cosmological stochastic gravitational-wave background, providing insight into the early Universe that is inaccessible with other means. We investigate the prospects for measuring a Gaussian cosmological gravitational-wave background in Cosmic Explorer in the presence of a distinguishable, non-Gaussian foreground of binary black hole mergers, using a Bayesian search that simultaneously fits binary black hole and background parameters. We successfully recover a Gaussian cosmological background with a signal-to-noise ratio of 5 in one day of simulated data in Cosmic Explorer without contamination from unresolved signals or data exclusion. However, when introducing waveform systematic errors to our analysis, our inference on the stochastic background parameters becomes biased and can falsely infer the presence of a background when there is none. The bias is driven by signal mismatches at low frequencies (<20 Hz), especially when the recovery waveform is missing physical effects included in the injected signals. While we propose a metric for diagnosing if measurements will be strongly biased by waveform systematics, our results suggest improvements in waveform modeling or other mitigation techniques will be required to accurately recover a primordial stochastic gravitational-wave background in next-generation detectors.

We identify the spatial projection of a conserved string charge density with a bit-thread flow. This correspondence gives bit threads a string worldsheet description and allows us to compute black hole entropy from the maximal entropy flux of a worldsheet-derived current. We first reproduce the BTZ entropy and then extend the construction to the ten-dimensional F1-NS5-P and D1-D5-P systems. Under Type IIB S-duality, the F1 current maps to the D1 current. Although the local currents, metrics, and flow norms change, the maximal physical flux remains unchanged and gives the same entropy. This provides a nontrivial check of the correspondence. Finally, we propose a D1-D5 boundary-matching conjecture. In the coarse-grained picture, each string-charge line defines an entropy-carrying tube. The boundary CFT entanglement entropy and the bulk black hole entropy both fix the product of the number of tubes and the maximum entropy carried by each tube. For a fixed tube discretization, they assign the same capacity to each tube. They therefore describe the same conserved maximal entropy flux, providing an information-flow interpretation of the equality between entanglement entropy and black hole entropy.

While quantum interactive proof systems using at least three messages can achieve perfect completeness, as shown by Kitaev and Watrous (STOC 2000), whether perfect completeness is achievable for one- and two-message quantum proof systems has remained open. For the one-message case, whether $\sf QMA$ can achieve perfect completeness was posed as an open problem in Watrous (FOCS 2000) and Aharonov and Naveh (2002); for the two-message case, the corresponding problems were (implicitly) posed in Jain, Upadhyay, and Watrous~(FOCS 2009) and Kobayashi, Le Gall, and Nishimura (SICOMP, 2019). In this work, we establish that ${\sf QIP}(2)$, ${\rm qq}\text{-}{\sf QAM}$, $\sf QAM$, and $\sf QMA$ can achieve perfect completeness. Here ${\rm qq}\text{-}{\sf QAM}$ denotes the class of promise problems admitting two-message quantum-public-coin quantum interactive proof systems in which the verifier's only message consists of half-EPR pairs. Our main technical contributions are the follows: 1. For $\sf QMA$ (and directly for $\sf QAM$), an exactly constructible block-encoded matrix whose kernel certifies yes instances, constructed from the acceptance operator induced by the verification circuit. This also yields an alternative proof of ${\sf QCMA}={\sf QCMA}_1$. 2. For ${\sf QIP}(2)$ (and implicitly ${\rm qq}\text{-}{\sf QAM}$), a new turn-halving transformation that preserves completeness and ensures that the resulting proof system retains at least two messages, provided that the terminal state before the final measurement is efficiently preparable.

We develop a decision tree classifier that recovers 3D magnetic field geometry from synthetic polarization and position angle maps of a magnetized, turbulent field. We test the classifier for a series of geometries: Uniform, Wavy, Helical, and Hourglass. The classifier is calibrated across a range of Alfvénic Mach numbers and injected Stokes Q,U noise levels for each geometry. Our models show the median and skewness of the polarization fraction, as well as the position angle circular variance, vary systematically with both geometry and the Alfvénic Mach number. We find that the 3D geometry can be isolated by using a variety of polarization and position angle metrics to break degeneracies. The classifier recovers most geometries well for sub-Alfvénic cases (Alfvénic Mach Number < 1). For Alfvénic Mach Number > 1, polarization and position angle statistics converge across all geometries and the classifier fails to recover the magnetic field structure.

Quantum error correcting (QEC) plays a crucial role in protecting quantum information against decoherence and enabling scalable, reliable quantum computing. One of the most realistic and ubiquitous sources of noise affecting quantum hardware today is generalized amplitude-damping (GAD) noise. Conventional, deterministic QEC codes struggle to correct for GAD noise because of their inherent structure, leading to fidelity losses that scale linearly with the damping strength. In this work, we introduce the framework of probabilistic approximate quantum error correction (PAQEC), that combines the flexibility of approximate QEC with the potential of post-selected recovery, enabling high-fidelity, resource-efficient error correction. We construct a five-qubit permutation-invariant code that, under probabilistic recovery, achieves a fidelity loss quadratic in the damping strength, thus outperforming existing QEC codes. Formulating PAQEC as an optimization problem, we present a numerical technique based on Charnes-Cooper and semidefinite programming to identify the optimal recovery map for any PAQEC code. Our results establish PAQEC as a powerful tool for developing resource-efficient, high-fidelity quantum codes tailored to realistic noise, with promising implications for near-term quantum devices and future fault-tolerant architectures.

Reflection high-energy electron diffraction (RHEED) provides rich information about evolving surfaces during thin-film growth, but non-automated, operator-dependent alignment and fragmented analysis workflows limit its potential in fully autonomous synthesis. Here, we present an open-source hardware and software toolkit that makes RHEED control and quantitative analysis accessible to operators and artificial intelligence (AI) agents. Demonstrated on a pulsed laser deposition system, the toolkit provides programmable electron-optics control, automated beam alignment and rocking-curve acquisition, and a training-free method for crystallographic azimuthal alignment. The auto RHEED application extracts structural and growth-related observables through shared graphical and programmatic interfaces, including a Model Context Protocol (MCP) server. An agent-driven demonstration shows how natural-language requests can guide the selection, configuration, and execution of quantitative analyses. An extensible adapter interface streamlines the incorporation of community-developed methods for AI analysis and RHEED simulation as they emerge, supported by Markdown implementation guides designed for AI coding agents. These capabilities support complementary descriptions of surface evolution through physical measurements and learned image representations while providing a practical route for incorporating new computational methods. Together, these tools reduce barriers to automated and agentic RHEED measurements and establish a foundation for future agentic control of thin-film synthesis guided by the evolving surface.