arXiv subjects

Andreas Bauer

Publications and source records attributed to Andreas Bauer.

At least 19 recordsLinked to original sources

arXiv2026

The Institutional Window: Occupation- and Jurisdiction-Specific Calibration of Liability Signaling for Preserved Human Fallback Capability

Problem definition. When generative AI produces expert artifacts clients cannot distinguish from a competent provider's, the classical cost-based quality signal collapses and only outcome-contingent commitments can separate types. Such a commitment certifies an endogenous, perishable asset: the human fallback capability a firm builds by keeping staff engaged with cases the AI handles, eroding otherwise. Prior work is silent on where that mechanism holds. We ask where, across occupations and liability institutions, it remains informative. Methodology/results. We introduce an institutional wedge between the liability cap a firm posts and the retained exposure that carries information, generated by four legal primitives: the cost rule, the enforceability of penalty clauses, the displacement of private liability by state liability or pooled indemnity, and mandatory limits on contractual liability. The wedge compresses the separating type space into a signaling window, bounded above by solvency and the penalty doctrine and below where standard-terms control voids caps beneath a threshold. We calibrate five occupations and seven jurisdictions on published evidence. In common-law agreed-damages channels the provability gross-up is unavailable whenever verifiability falls below 1/m, turning a contracting problem into an operational one. Verifiability investment widens the window where the ceiling binds but narrows it where the cap floor binds. In an agent-based market, within the tested policy class, every empty-window cell converges to zero engagement and skill collapse. Managerial implications. Liability institutions are a workforce-capability instrument, not merely a risk-allocation device. Firms should target the binding margin in each jurisdiction; cap floors and pooled indemnity each suppress the signal sustaining fallback capacity.

econ.TH↗

arXiv2026

The Fallback as Signal: Preserved Human Skill, Liability, and Competence Signaling in Credence-Good Markets under Improving AI

Firms that deploy improving but imperfect AI must decide how much to keep human workers engaged. Engagement lowers current output yet builds the fallback skill the firm needs when AI fails. We ask what that fallback skill signals to two audiences at once: mobile workers, who sort across firms on the skill trajectory a job builds, and clients, who cannot observe skill in a credence-good market and must infer competence. We embed the engagement-skill dynamics of Singh et al. (2026) in a signaling game and add a liability commitment. Because a more-skilled provider fails less often precisely in the states where AI is down, the expected cost of a liability pledge is decreasing in fallback skill. This restores Spence-Mirrlees single crossing on a type that is endogenous - built, not drawn - and yields a separating equilibrium in which liability certifies preserved human competence that no artifact can certify once AI writes as well as the expert. We characterize the least-cost separating pledge schedule, show that client stakes shift engagement toward or away from the least-skilled worker depending on the size of the pledge, and derive a stakes threshold above which building skill dominates free-riding on a rival's training - reversing the asymmetric-specialization result of the underlying labor model. Two boundaries close the market from both sides: small tickets cannot fund enforcement, and large tickets exceed the provider's solvency. An agent-based version of the market reproduces the analytical thresholds under noisy beliefs, learning-by-record and worker churn.

econ.TH↗

arXiv2026

Finding diagonal logical gates in CSS codes and circuits

Finding efficient schemes for non-Clifford logic or magic state preparation is one of the central challenges on the way to fault-tolerant quantum computation. Many of the proposed schemes rely on diagonal non-Clifford logical gates acting on CSS codes in space or decorating CSS-type syndrome-extraction circuits in spacetime. Here we propose and implement efficient algorithms to find all (spacetime) logical gates of a given CSS code (circuit) composed from a prescribed set of ansatz gates. Depending on the choice of ansatz gates, this means finding transversal gates, more general locality-preserving logical circuits, folding gates, or similar. While we focus on qubit diagonal gates in the Clifford hierarchy, we also discuss the generalization to arbitrary diagonal non-hierarchy gates, certain non-diagonal gates, as well as prime and composite-dimensional qudits. Our method works by rephrasing code-space preserving gates as the kernel of the ``pullback'' of the $X$ check matrix onto phase functions, which maps between finite abelian 2-groups. We implement a fast ``filtration'' method to find this kernel. The runtime for finding fault-tolerant logical gates in a qLDPC code with $O(n)$ qubits or a circuit with $O(n)$ gates in a naive dense implementation is $O(n^3)$, with potential for improvement making use of sparsity.

quant-ph↗

arXiv2026

The Last Costly Signal: How Generative AI Collapses Competence Signaling and Why Liability Sustains Markets for Expert Services

Generative artificial intelligence has reduced the cost of producing convincing artifacts of expertise-reports, analyses, proposals-to nearly zero. Signaling theory predicts that signals whose content rests on production cost lose it when production becomes cheap. We formalize this for expert services, a class of credence goods, by modeling AI as a compression of the discernible headroom between what machines produce at negligible cost and what buyers can distinguish. Below a critical headroom no separating equilibrium in production-side signals exists; the market pools, high-competence providers earn no premium, and those with outside options exit-Akerlof's lemons dynamic. An outcome-contingent signal-a warranty backed by damages D with ex-post verifiability phi-restores full separation at any level of AI capability whenever phi*D >= v, the value of a solved problem, under four preconditions stated explicitly and priced in turn: no seller-side private information beyond type; verifiable collectible retention behind the promise; no buyer influence on outcome or claim; negligible enforcement deadweight. Expected liability cost depends on whether the problem is solved, not on production costs. A further proposition shows that provenance certification priced as a type-independent stamp (e.g., C2PA) cannot restore full separation, while a verified commitment to forgo the AI frontier re-imposes the pre-AI artifact cost function. Two results endogenize contract institutions: civil-procedure costs set a minimum ticket size v_min below which the modeled court-enforced warranty cannot sustain separation; under liability insurance the signal-effective quantity is the retained, collectible exposure. We state falsification conditions and propose a preregistered conjoint experiment with German-speaking B2B decision-makers; the estimand is willingness to pay in excess of the promise's actuarial value.

econ.TH↗

arXiv2026

Cyclotron mass-selective de Haas-van Alphen measurements using temperature modulation

We present a temperature-modulated de Haas-van Alphen measurement technique that allows selective addressing of quantum oscillations with different effective masses $m^{\ast}$ using a non-monotonic amplitude evolution with temperature and magnetic field, governed by the temperature derivative of the Lifshitz-Kosevich factor. The technique relies on harmonic modulation of the sample temperature and phase-sensitive detection of quantum oscillations in the voltage induced in a pick-up coil. We use a set of frequencies with strong Zeeman-driven harmonic content in the compensated topological semimetal MoSi$_{2}$ as a natural linear mass comb ranging from 1$m^{\ast}$ to 13$m^{\ast}$ to demonstrate the tunability of the mass-dependent quantum oscillation amplitudes experimentally. The technique allows to reliably isolate weak contributions of heavy orbits that are inaccessible in conventional de Haas-van Alphen frequency spectra because their frequency peaks overlap with much stronger frequency peaks of lighter orbits.

cond-mat.str-el↗

arXiv2026

Magnetoelastic effects in the metallic frustrated antiferromagnet CrB$_2$

Hexagonal chromium diboride CrB$_2$ is a metallic frustrated antiferromagnet with a N\'{e}el temperature $T_N \sim$ 88 K. In CrB$_2$, Cr 3$d$ electrons not only give rise to localized magnetic moments but also contribute to metallic conduction. We perform ultrasound velocity measurements on a single crystal of hexagonal CrB$_2$ to determine its elastic properties. The temperature dependence of the $ab$-plane shear elastic modulus exhibits Curie-type softening upon cooling from $\sim$120 K down to $T_N$. This behavior is interpreted as a precursor to a symmetry-lowering lattice distortion at $T_N$, indicating that magnetic frustration is relieved via transverse magnetoelastic coupling. In addition, the $a$-axis and $c$-axis compressive elastic moduli show unusual softness and their suppression upon cooling, which are naturally explained by Fermi-surface nesting and its suppression upon cooling. The present results suggest that, in CrB$_2$, longitudinal magnetoelastic coupling suppresses Fermi-surface nesting and enhances frustrated exchange interactions, while transverse magnetoelastic coupling plays a key role in relieving the frustration.

cond-mat.str-el↗

arXiv2026

High-threshold decoding of non-Pauli codes for 2D universality

Topological codes have many desirable properties that allow fault-tolerant quantum computation with relatively low overhead. A core challenge for these codes, however, is to achieve a low-overhead universal gate set with limited connectivity. In this work, we explore a non-Pauli stabilizer code that can be used to complete a universal gate set on topological toric and surface codes in strictly two dimensions. Fault-tolerant syndrome extraction for the non-Pauli code requires mid-circuit $X$ corrections, a key difference to conventional Pauli codes. We construct and benchmark a just-in-time (JIT) matching decoder to reliably decide these corrections. Under a phenomenological error model with equally likely physical and measurement errors, we find a high threshold of $\approx 2.5\,\%$, close to the $\approx 2.9\,\%$ of a decoder with access to the full syndrome history. We also perform a finite-size scaling analysis to estimate how the logical error rate scales below threshold and verify an exponential suppression in both physical error rate and in the system size. A second global decoding step for $Z$ errors is required and the non-Clifford gates in the circuit reduce the threshold from $\approx 2.9\,\%$ to $\approx 1.8\,\%$ with a naive decoder. We show how $Z$ decoding can be improved using knowledge of the $X$ corrections, pushing the threshold to $\approx 2.2\,\%$. Our results suggest non-Clifford logic in 2D codes could perform comparably to 2D quantum memory. Our formalism for efficient benchmarking and decoding directly generalizes to a broader family of CSS codes whose $X$ stabilizers are twisted by diagonal Clifford operators, and spacetime versions thereof, defined by CSS-like circuits enriched by $CCZ$, $CS$, and $T$ gates.

quant-ph↗

arXiv2026

Non-reciprocal spin excitations across the skyrmion-paramagnetic phase transition in MnSi

The magnetic excitations of the skyrmion lattice in MnSi comprise a multitude of individual modes, which are non-reciprocal and thereby propagate unidirectionally. We report inelastic neutron scattering experiments for temperatures near and above the skyrmion-paramagnetic phase transition in the chiral magnet MnSi tracking the evolution from the skyrmion lattice towards the high-temperature paramagnetic state. Within the resolution of the triple-axis measurements the excitations vary smoothly across the skyrmion-paramagnetic boundary, and, the quasi-elastic paramagnetic signal under applied field retains the non-reciprocal character seen in the skyrmion phase even far above the critical temperature. Using a resolution-convolution our results are consistent with linear spin-wave theory.

cond-mat.str-el↗

arXiv2026

Quadratic tensors as a unification of Clifford, Gaussian, and free-fermion physics

Certain families of quantum mechanical models can be described and solved efficiently on a classical computer, including qubit or qudit Clifford circuits and stabilizer codes, free-boson or free-fermion models, and certain rotor and GKP codes. We show that all of these families can be described as instances of the same algebraic structure, namely quadratic functions over abelian groups, or more generally over (super) Hopf algebras. Different kinds of degrees of freedom correspond to different "elementary" abelian groups or Hopf algebras: $\mathbb{Z}_2$ for qubits, $\mathbb{Z}_d$ for qudits, $\mathbb{R}$ for continuous variables, both $\mathbb{Z}$ and $\mathbb{R}/\mathbb{Z}$ for rotors, and a super Hopf algebra $\mathcal F$ for fermionic modes. Objects such as states, operators, superoperators, or projection-operator valued measures, etc, are tensors. For the solvable models above, these tensors are quadratic tensors based on quadratic functions. Quadratic tensors with $n$ degrees of freedom are fully specified by only $O(n^2)$ coefficients. Tensor networks of quadratic tensors can be contracted efficiently on the level of these coefficients, using an operation reminiscent of the Schur complement. Our formalism naturally includes models with mixed degrees of freedom, such as qudits of different dimensions. We also use quadratic functions to define generalized stabilizer codes and Clifford gates for arbitrary abelian groups. Finally, we give a generalization from quadratic (or 2nd order) to $i$th order tensors, which are specified by $O(n^i)$ coefficients but cannot be contracted efficiently in general.

quant-ph↗

arXiv2025

Development of a Modular Optically Detected Magnetic Resonance Setup for Optical Experiments in a Variable Temperature Insert

We developed an optically detected magnetic resonance (ODMR) setup designed for compatibility with a widely used, commercially available helium bath cryostat equipped with a variable temperature insert. The optical path extends nearly two meters, spanning the full length of the cryostat insert, enabling excitation of the nitrogen-vacancy (NV) centers and detection of the resulting fluorescence from outside the cryostat. The setup preserves optical alignment and beam quality along this extended path allowing integration into existing cryogenic systems without significant modifications. We demonstrate the setup's performance by measuring the temperature dependence of the resonance signal and its behavior under small applied magnetic fields, as well as the magnetic transition of a SrRuO$_3$ sample, thereby showcasing the feasibility of NV magnetometry on a sample in constrained cryogenic environments.

physics.ins-det↗

arXiv2025

Reflections on the Reproducibility of Commercial LLM Performance in Empirical Software Engineering Studies

Large Language Models have gained remarkable interest in industry and academia. The increasing interest in LLMs in academia is also reflected in the number of publications on this topic over the last years. For instance, alone 78 of the around 425 publications at ICSE 2024 performed experiments with LLMs. Conducting empirical studies with LLMs remains challenging and raises questions on how to achieve reproducible results, for both researchers and practitioners. One important step towards excelling in empirical research on LLM and their application is to first understand to what extent current research results are eventually reproducible and what factors may impede reproducibility. This investigation is within the scope of our work. We contribute an analysis of the reproducibility of LLM-centric studies, provide insights into the factors impeding reproducibility, and discuss suggestions on how to improve the current state. In particular, we studied the 85 articles describing LLM-centric studies, published at ICSE 2024 and ASE 2024. Of the 85 articles, 18 provided research artefacts and used OpenAI models. We attempted to replicate those 18 studies. Of the 18 studies, only five were sufficiently complete and executable. For none of the five studies, we were able to fully reproduce the results. Two studies seemed to be partially reproducible, and three studies did not seem to be reproducible. Our results highlight not only the need for stricter research artefact evaluations but also for more robust study designs to ensure the reproducible value of future publications.

cs.SE↗

arXiv2025

Real-space observation of the low-temperature Skyrmion lattice in Cu2OSeO3(100) single crystal

Cu2OSeO3 is a skyrmion host material in which two distinct thermodynamically stable skyrmion phases were identified. We report magnetic force microscopy imaging of the low-temperature magnetic phases in bulk Cu2OSeO3(100) single crystal. Tuning the external magnetic field over the various phase transition at a temperature of 10 K, we observe the formation of helical, conical, tilted conical and skyrmion lattice domains in real space.

cond-mat.mes-hall↗

arXiv2025

Quo Vadis, Code Review? Exploring the Future of Code Review

Context: Code review has long been a core practice in collaborative software engineering. As automation becomes increasingly embedded in development workflows, the role and functioning of code review are subject to change. Objective: This study explores how professional developers anticipate the evolution of code review and identifies emerging tensions reflected in these expectations. Method: We conducted a cross-sectional survey with 100 developers across five software-driven companies. The survey captured estimates of current review time and reviewed artifacts, as well as anticipated changes over a five-year horizon. Open-ended questions invited reflections on the future of code review. Quantitative responses were analyzed descriptively, and open-ended responses were independently coded by multiple researchers using thematic analysis to identify recurring patterns in participant responses. Results: Practitioners expect code review to remain essential, anticipating stable or increased time investment and a broader range of reviewed artifacts over the next five years. In open-ended responses, many participants explicitly referenced AI and large language models (LLMs), describing increasing automation in both code authoring and reviewing, including scenarios in which automated systems operate in both roles. Conclusion: Our analysis suggests emerging tensions concerning understanding, accountability, and trust in automation-mediated code review. These tensions provide early empirical signals of socio-technical challenges and position code review as a concrete setting for examining the implications of LLM integration in collaborative software engineering.

cs.SE↗

arXiv2025

Graphical Calculus for Fermionic Tensors

We introduce a graphical calculus, consisting of a set of fermionic tensors with tensor-network equations, which can be used to perform various computations in fermionic many-body physics purely diagrammatically. The indices of our tensors primarily correspond to fermionic modes, but also include qubits and fixed odd-parity states. Our graphical calculus extends the ZX calculus for systems involving qubits. We apply the calculus in order to represent various objects, operations, and computations in physics, including fermionic Gaussian states, the partial trace of Majorana modes, purification protocols, fermionization and bosonization maps, and the construction of fermionic codes.

quant-ph↗

arXiv2025

Planar fault-tolerant circuits for non-Clifford gates on the 2D color code

We introduce a family of scalable planar fault-tolerant circuits that implement logical non-Clifford operations on a 2D color code, such as a logical $T$ gate or a logical non-Pauli measurement that prepares a magic $|T\rangle$ state. The circuits are relatively simple, consisting only of physical $T$ gates, $CX$ gates, and few-qubit measurements. They can be implemented with an array of qubits on a 2D chip with nearest-neighbor couplings, and no wire crossings. The construction is based on a spacetime path integral representation of a non-Abelian 2+1D topological phase, which is related to the 3D color code. We turn the path integral into a circuit by expressing it as a spacetime $ZX$ tensor network, and then traversing it in some chosen time direction. We describe in detail how fault tolerance is achieved using a "just-in-time" decoding strategy, for which we repurpose and extend state-of-the-art color-code matching decoders.

quant-ph↗

arXiv2025

Easy-plane ferromagnetism in single-crystal ErB$_{2}$ at low temperatures

We report a study of single crystals of the hexagonal rare-earth diboride ErB$_{2}$ prepared by means of the self-adjusted flux travelling-solvent floating-zone technique. Measurements of the magnetization, ac susceptibility, specific heat, and electrical resistivity consistently establish ferromagnetic order of the Er$^{3+}$ moments below a second-order phase transition at $T_{c} = 14$~K and a very strong easy-plane anisotropy. Curie--Weiss fits of the ac susceptibility are characteristic of ferromagnetic coupling within the easy hexagonal basal plane, and antiferromagnetic coupling along $\langle001\rangle$. Under magnetic field within the basal plane the magnetization is reminiscent of a soft ferromagnet that is polarized in fields above a few tenth of a Tesla, vanishing hysteresis and negligible in-plane anisotropy. Under field along $\langle001\rangle$, typical hard-axis behavior is observed with the magnetization increasing only weakly up to a spin-flip transition at $\mu_{0}H_{c} = 12$~T. The easy-plane anisotropy emerges below a crossover temperature $T_{x} \approx 50$~K , i.e. a broad paramagnetic temperature range above $T_{c}$ is governed by strongly anisotropic magnetic fluctuations.

cond-mat.str-el↗

arXiv2025

Fermi surface and magnetic breakdown in PdGa

We study the electronic structure of the chiral semimetal PdGa by means of the de Haas-van Alphen and Shubnikov-de Haas effect. We find that the Fermi surface of PdGa comprises multiple pockets split by spin-orbit coupling. We compare our experimental findings with the band structure calculated ab initio. We demonstrate that the quantum oscillation spectra can be fully understood by considering nodal plane degeneracies at the Brillouin zone boundary and magnetic breakdown between individual Fermi surface pockets. Expanding traditional analysis methods, we explicitly calculate magnetic breakdown frequencies and cyclotron masses while taking into account that extremal breakdown trajectories may reside away from the planes of the single-band orbits. We further analyze high-frequency contributions arising from breakdown trajectories involving multiple revolutions around the Fermi surface which are distinct from conventional harmonic frequencies. Our results highlight the existence of gaps induced by spin-orbit coupling throughout the band structure of PdGa, the relevance of nodal planes on the Brillouin zone boundary, and the necessity for a comprehensive analysis of magnetic breakdown.

cond-mat.str-el↗

arXiv2025

Shaking and pushing skyrmions: Formation of a non-equilibrium phase with zero critical current

In three-dimensional chiral magnets, skyrmions are line-like objects oriented parallel to the applied magnetic field. The efficient coupling of magnetic skyrmion lattices to spin currents and magnetic fields permits their dynamical manipulation. Here, we explore the dynamics of skyrmion lattices when slowly oscillating the field direction by up to a few degrees on millisecond timescales while simultaneously pushing the skyrmion lattice by electric currents. The field oscillations induce a shaking of the orientation of the skyrmion lines, leading to a phase where the critical depinning current for translational motion vanishes. We measure the transverse susceptibility of MnSi to track various depinning phase transitions induced by currents, oscillating fields, or combinations thereof. An effective slip--stick model for the bending and motion of the skyrmion lines in the presence of disorder explains main features of the experiment and predicts the existence of several dynamical skyrmion lattice phases under shaking and pushing representing new phases of matter far from thermal equilibrium.

cond-mat.str-el↗