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Physics

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Monday 31 August

History and Philosophy of Physics

Foreknowledge and Free Will Revisited

Eliyahu Zvi Engelberg

The apparent incompatibility between foreknowledge and free will is traditionally formulated in terms of the implication of knowledge of a future event for the freedom of that event. This paper reexamines the problem using the notions of causal order and physical determination provided by modern physics. I consider measurements of two entangled particles at spacelike-separated events, where a measurement outcome is taken to be free if it is not determined by the previous history of the part of the universe accessible to it. Relativity allows the temporal order of the two measurements to be reversed between reference frames while preserving their causal independence. Quantum correlations nevertheless allow an observer at one measurement event to know the outcome at the other. I show that there is, therefore, a frame in which an observer possesses foreknowledge of a measurement outcome that remains free in this sense. The argument demonstrates that epistemic access to a future event need not be grounded in physical conditions that determine it.
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High Energy Physics (Phenomenology)

Quantum Simulation of Markovian and Non-Markovian Open Quantum Dynamics in Heavy-Ion Collisions

Doojin Kim and Balbeer Singh

We present a quantum computing framework for simulating open-quantum-system approaches based on Markovian and non-Markovian dynamics, which is relevant to heavy-ion collisions. To simulate the non-Markovian evolution on quantum computers, we introduce an auxiliary two-level pseudomode that carries the memory forward and couples to both the subsystem and the residual Markovian bath. We explicitly show that tracing out the pseudomode reproduces the non-Markovian evolution with the exact memory kernel. Moreover, in the relevant time scale hierarchy, the quantum circuit construction of the pseudomode smoothly converges to the Markovian limit. For a given bath memory kernel, our results demonstrate the feasibility of quantum simulations of both Markovian and non-Markovian dynamics, establishing a framework for future studies of hard probes such as jets, heavy quarks, and quarkonia in heavy-ion collisions.
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High Energy Physics (Theory)

Superfluid memory effect

Kristan Jensen, Alfredo Pérez and Stefan Prohazka

We identify a memory effect produced by phonon scattering in a superfluid: a localized scattering event generates a far-field pressure pulse with vanishing time integral but a nonzero first temporal moment, corresponding to a permanent shift in a prepotential for the far-field velocity. The effect is controlled by the soft factor for phonon emission, including corrections from nonlinear dispersion. In superfluid $^4$He, scattering macroscopic phonon wave packets produces a signal whose estimated magnitude may lie within experimental reach, thereby providing a laboratory analogue of electromagnetic and gravitational memory.
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Materials Science

Strain-Tunable Spin Relaxation in Germanium from First Principles

Lauren A. Tan, Shaelyn Iyer, Ivan Maliyov et al. (+2 more)

Germanium is a leading platform for semiconductor spin qubits and spintronics. Yet its electron and hole spin dynamics remain understood primarily through phenomenological models. Here, we predict electronic transport and spin relaxation in bulk Ge entirely from first principles, combining hybrid-functional band structures with fully relativistic electron-phonon ($e$-ph) interactions. Without empirical parameters, we predict carrier mobilities, velocity-field curves, and electron and hole spin relaxation times in close agreement with experiments over 100$-$400 K. By resolving spin-flip scattering by valley and phonon mode, we identify the microscopic mechanisms governing spin relaxation and show that spin and momentum relaxation, although both mediated by $e$-ph scattering, are controlled by distinct processes. We further show that compressive biaxial strain enhances the hole spin lifetime by up to two orders of magnitude at 5% strain, through strain-induced valence-band splitting and suppressed spin mixing. This mechanism is directly relevant to Ge-on-Si devices, where strain provides a practical route to engineering long-lived hole spins for quantum technologies.
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All authors Lauren A. Tan, Shaelyn Iyer, Ivan Maliyov, Jinsoo Park, Marco Bernardi

Quantum Physics

Efficient search for excitable zero-modes in constrained systems

Jean-Yves Desaules

Kinetically constrained systems, such as those representing Rydberg atom arrays in the blockade regime, have gathered considerable attention due to the presence of atypical eigenstates in their spectrum. The latter manifests itself through the presence of quantum many-body scars as well as unusually large zero-mode (ZM) subspaces which contain analytically tractable eigenstates with various entanglement scalings. In particular, some of the latter are excitable zero-modes (EZMs), meaning that they can be promoted to a non-zero energy for open boundary conditions. In this work, I present an efficient protocol for finding analytical expressions for translation-invariant EZMs in constrained systems, based on the eigendecomposition of the local unconstrained Hamiltonian. I demonstrate the power of this method on a decorated Rydberg chain. In that model, my protocol directly produces a continuous matrix-product-state manifold located entirely in the zero-energy eigenspace for periodic boundary conditions. The span of that manifold grows exponentially with the system, and for odd system sizes it covers the entire zero-momentum eigenspace with zero energy. I then show how the physical structure of the manifold, which is tied to the local eigenbasis, also allows one to derive analytical expressions for ZMs at non-zero momentum and for a polynomial number of exact scars at $E=\pm\sqrt{3}$.
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General Relativity and Quantum Cosmology

Evolution of Cosmic String Loops under Gravitational Backreaction

Lasse Gerblich, Richard A. Battye and E.P.S. Shellard

Nambu-Goto cosmic string loops generically develop cusps, points where the string momentarily reaches the speed of light. These cusps produce strong gravitational wave bursts with a characteristic strain spectrum $\tilde{h}(\omega)\propto (G\mu)\,\omega^{-4/3}$, making them prime targets for gravitational wave searches, where $\mu$ is the string mass per unit length. However, this picture is modified when one accounts for gravitational backreaction. Using a convenient gauge, we reformulate the Nambu-Goto equations of motion for a loop moving in its own dynamically sourced gravitational field, enabling the first continuous numerical evolution of loops under this backreaction. A key finding is that locally cusps survive backreaction. Nevertheless, the gravitational waveform calculated in this formalism is significantly modified, weakening the cusp burst and introducing a high-frequency cutoff at $f_c\propto(G\mu)^{-3/2}$. This suppression above $f_c$ reduces the expected signal-to-noise ratio in current and near-future detectors relative to unperturbed waveform predictions.
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Instrumentation and Methods for Astrophysics

Agentic research is oxymoronic

Natalie B. Hogg

The use of agentic large language models obviates human interpretation of scientific results, and will lead to substantial distrust in the literature.

Instrumentation and Methods for Astrophysics

Ad Astra White Paper: A Pitch for the Next 25 Years of NASA's Physics of the Cosmos Program

Eric Burns, Ivan Agullo, Igor Andreoni et al. (+7 more)

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.
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All authors Eric Burns, Ivan Agullo, Igor Andreoni, Catherine M. Deibel, Christopher L. Fryer, Natasha Latouf, M. Coleman Miller, Jillian C. Rastinejad, Breann N. Sitarski, Zorawar Wadiasingh

Quantum Physics

Bosonic codes from compact phase spaces

David Roberts, Aaron Slipper, Alireza Parhizkar et al. (+2 more)

We present the algebraic structure of bosonic quantum error-correcting codes on genus-two Riemann surfaces. We explicitly construct the code words as automorphic forms and analytically generate the full tower of code spaces at all weights. We prove a fundamental no-go theorem: for any genus greater than one, the stabilizer group is non-amenable, forcing a strictly positive spectral gap in the stabilizer Hamiltonian. Consequently, no normalizable quantum state can satisfy all stabilizer conditions. This sharply contrasts with standard Gottesman-Kitaev-Preskill (GKP) codes, where the amenability of the stabilizer group $\mathbb{Z}^2$ permits approximate code words with arbitrary precision.
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All authors David Roberts, Aaron Slipper, Alireza Parhizkar, Victor V. Albert, Mohammad Hafezi

Quantum Physics

Engineering multi-photon dissipation with a dc-voltage-biased Josephson junction

Marco Paradina, Ambroise Peugeot, Roberto Negrin et al. (+8 more)

Multi-photon dissipation – a key resource for bosonic qubits – is usually realized by parametrically pumping a Josephson coupler at the cost of spurious nonlinear terms. Here we instead engineer it using a dc-voltage-biased SQUID, such that these parasitic terms average out. We activate the conversion of one, two, or four photons of a high-Q mode into a single photon of a lossy mode. We characterize the two-photon dissipation by Wigner tomography, establishing dc-biased junctions as a resource for reservoir engineering and a viable route to cat-qubit stabilization.
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All authors Marco Paradina, Ambroise Peugeot, Roberto Negrin, Oscar Novat, Tristan Villain, Anil Murani, Jean-Loup Ville, Sébastien Jezouin, Raphaël Lescanne, Audrey Bienfait, Benjamin Huard

Instrumentation and Methods for Astrophysics

Slysh haloes: the waste heat of cold computing as a submillimetre technosignature

Michael Garrett

Searches for Dysonian waste heat have operated almost exclusively in the mid-infrared and are therefore sensitive primarily to technology radiating at 100-600K. We argue that mature, computation-dominated civilisations may instead dissipate much of their energy at far lower temperatures. The Landauer cost of irreversible computation scales linearly with temperature, while ambient temperatures at large circumstellar radii approach the 2.7K cosmic microwave background floor. Cold computation is therefore thermodynamically attractive and, because the required radiating area scales as T**-4, potentially conspicuous. These considerations predict a new object class, which we term the SLYSH HALO after the first advocate of cold Dysonian searches. A Slysh halo is a physically motivated partial Dyson swarm producing grey, line-free thermal emission from the cold outer regions of planetary systems. We show that such structures are energetically and materially plausible, and that M dwarfs provide especially favourable search targets. Archival far-infrared and submillimetre surveys of nearby stars (DEBRIS, DUNES and SONS) can in principle be reinterpreted to constrain cold circumstellar dissipation at approximately the 10**20 Watt level, several orders of magnitude below the waste-heat luminosities targeted by previous infrared searches. Additional opportunities are provided by archival observations from Planck and the JCMT, together with the reprocessing of interferometric data from facilities such as ALMA and NOEMA. We assemble six observational discriminants that separate engineered radiators from natural cold sources and outline a three-tier search programme. Even a null result would provide the first temperature-complete assessment of Dysonian technosignatures.
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High Energy Physics (Theory)

Coarse-grained models for loop quantum gravity and their renormalization

Mehdi Assanioussi and Martin Zeiß

We introduce a family of effective theories and use them to define a specific type of coarse-grained models for canonical loop quantum gravity. Each effective theory is characterized by two parameters and it consists mainly of a Hilbert space of coarse states and an effective Hamiltonian operator. The construction of the coarse Hilbert spaces relies on a systematic coarse-graining procedure for spin network states. The effective Hamiltonians are then obtained from an analysis of the interplay between this coarse-graining procedure and the action of various Hamiltonian operators defined in loop quantum gravity. Finally, we provide a prescription for implementing the Hamiltonian non-perturbative renormalization framework for the coarse-grained models, and we explicitly write down the renormalization flow equations. The aim of this work is to build an arena for studying the emergence of the continuum limit and the derivation of phenomenological models in the context of canonical loop quantum gravity.
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High Energy Physics (Theory)

The large $N$ vector model with angular velocity

Justin R. David and Srijan Kumar

We study the free energy of a critical vector model at large $N$ on $S^{1}\times S^{2}$ with an angular velocity $\hat\mu$ without the singlet constraint. We study the model for which the large $N$ dynamics is controlled by the uniform saddle point of the auxiliary field arising in the Hubbard-Stratanovich transformation. The leading high-temperature behaviour is determined analytically both as an expansion about $\hat\mu r=0$ and $\hat\mu^{2}r^{2}=1$ where $r$ is the radius of the sphere. We supplement the analytic results with a numerical analysis that agrees with both the analytical expansions in their respective regimes and smoothly interpolates between them. The leading high-temperature contribution to the free energy develops a pole at $\hat\mu^{2}r^{2}=1$, in agreement with expectations from the thermal effective field theory. Its residue coincides with that of the massless free theory. Sub-leading terms, however, exhibit non-analytic dependence on the angular velocity and distinguish the critical fixed-point result from the free theory answer. The residue at the pole can also be obtained by placing the model on the pp-wave geometry. We show that the residue agrees with that obtained from the direct computation. The free energy of the model connects the non-trivial fixed point of the $O(N)$ model at $\hat\mu r=0$ to its free fixed point at $\hat\mu^2r^2=1$.
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Instrumentation and Methods for Astrophysics

The Analysis, not the Aperture: End-to-End Transformer Reconstruction for Imaging Atmospheric Cherenkov Telescopes

Elli Jobst, Lea Heckmann, Lukas Heinrich et al. (+1 more)

Imaging Atmospheric Cherenkov Telescopes (IACTs) detect very-high-energy gamma rays by imaging the nanosecond Cherenkov flash of the air shower they initiate in the Earth's atmosphere. For four decades the first steps of IACT event reconstruction have been essentially unchanged, relying on a heavy parameterisation and dimensionality reduction of the recorded images. This is reasonable when the image is bright, but discards important information when only a few tens of Cherenkov photons are recorded, which is a primary reason why small telescopes perform poorly at sub-TeV energies. We show that this limitation is a property of the analysis rather than of the hardware. We simulate a deliberately simple and idealised compact telescope and treat each event as a short movie that is passed directly to a video vision transformer with a factorised spatio-temporal encoder. A single composite network with a gradient-normalised multi-task loss performs gamma/hadron classification, energy regression and arrival-direction regression at once. This is the first application of a video vision transformer to IACT data. We compare it against an optimised standard analysis on the same dataset. The transformer lowers the energy threshold by a factor of three, from 0.22 to 0.07 TeV, and reconstructs arrival directions down to 0.05 TeV. At 0.2 TeV it increases the effective collection area by a factor of three, and raises the gamma/hadron separation power from an area under the receiver operating characteristic curve of 0.80 to 0.91. At 0.05 TeV, where the standard analysis retains almost nothing, that area grows by nearly two orders of magnitude. These results show promising new opportunities for compact and affordable telescopes operating at sub-TeV energies, paving the way for a broader exploration of time-domain astrophysics.
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All authors Elli Jobst, Lea Heckmann, Lukas Heinrich, David Paneque

Mathematical Physics

Exactly flat bands beyond the chiral limit in Bistritzer–MacDonald Hamiltonians

Zhen Huang and Kevin D. Stubbs

The chiral limit of the Bistritzer–MacDonald model for twisted bilayer graphene has exactly flat bands at magic angles. We show that exact flatness can persist beyond the chiral limit with nonchiral tunnelling potentials in the usual symmetry class. We construct a family of nonchiral tunnelling potentials for which the Hamiltonian has at least two zero-energy states at every Bloch momentum and for every real value of the nonchiral coupling. This gives a family of counterexamples to Open Problem~3 of Zworski's survey \cite{ZworskiSurvey}. Conversely, we prove that every admissible potential with this property belongs to this family, thereby obtaining a complete characterization. By contrast, we show that the standard BM model, namely, BM Hamiltonians with first harmonic tunnelling potentials, does not admit exactly flat bands at the magic angle except possibly at a discrete set of nonchiral coupling strengths, with no finite accumulation point. To prove this, we introduce an explicit invertibility criterion. The criterion requires the projected perturbation to have a nonzero scalar coefficient at some Bloch momentum, obstructing exact flatness for general nonchiral tunnelling. A local Taylor expansion argument verifies the criterion for the standard BM potentials. For the family constructed above, however, the projected perturbation vanishes at every Bloch momentum, so the invertibility criterion fails.
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Optics

Integrated Microwave Photonics: From Material Platforms to Systems-on-Chip

Jiejun Zhang and Jianping Yao

In this paper, recent advances in integrated microwave photonics (IMWP) are reviewed, including material platforms, integration technologies, and system functionalities. Emerging opportunities and future perspectives are discussed. Silicon (Si) and silicon nitride (SiN) provide dense routing, programmable filtering, and low-loss delay; indium phosphide (InP) supplies optical gain, light generation, and high-speed photodetection; thin-film lithium niobate (TFLN) offers linear and broadband electro-optic conversion; and photonic integration is emerging as a practical path to synergize complementary capabilities. Recent work shows a marked shift from isolated modulators, filters, and delay lines toward chip- and module-level systems, ranging from signal processing engines, real-time spectrum sensing, to full-spectrum wireless links, fiber-wireless conversion, silicon beamforming, integrated radar, programmable processors, and photonic convolution engines with on-chip sources and detectors. As these demonstrations become more mature and complete, the key questions move beyond bandwidth and efficiency toward system integration, microwave packaging, calibration stability, analog link performance, and application-level validation.
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Astrophysics of Galaxies

The impact of hot mode accretion and angular momentum conservation on metallicity gradients of galactic discs

Jennifer K.S. Friske, Filippo Fraternali and Gabriele Pezzulli

The hot circumgalactic medium (CGM) of a galaxy inevitably rotates more slowly than the cold gas in the disc it surrounds, due to a higher pressure support against gravity. If it accretes vertically onto the disc, angular momentum conservation leads to radial flows, advection of metals inwards and the steepening of a metallicity gradient. The observed gradient hence carries information on the kinematics of the accreting gas. Previous models built on this premise parametrised the angular momentum mismatch as a simple function of radius, constant in time, rather than derived from the properties of the CGM itself. Here, we present a semi-analytic chemical evolution model of a galaxy with a cosmologically motivated evolution, a self-consistent and time-evolving potential and an isothermal rotating CGM. The model includes inside-out formation and the radial flows induced both by the deepening of the potential well (acting on gas and stars) and by accretion, following their combined effect on the gas-phase metallicity gradient over cosmic time. We use a Bayesian framework to fit simultaneously the structural properties and metallicity gradient of a galaxy, inferring both the required inside-out growth and the CGM temperature needed to drive the required radial flows and abundance gradient. Fitting our model to the Milky Way, we find a mild preference for a subvirial corona ($T_\mathrm{CGM}/T_{200}=0.82^{+0.44}_{-0.38}$), in mild tension with observations, and we discuss possible resolutions. The predicted CGM rotation velocity lies between ~100-160 km/s at the present time and is substantially lower at earlier epochs. We further recover an evolution of the gradient over the past ~8Gyr consistent with observations. Our approach is not restricted to the Milky Way and can be directly applied to external galaxies, offering a new handle to constrain hot mode accretion onto galactic discs.
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Fluid Dynamics

Numerical simulation of a two-frequency-driven superlattice Faraday-wave pattern

Debashis Panda, Nicolas Périnet, Abdullah M. Abdal et al. (+6 more)

The formation of a superlattice pattern in two-frequency-driven Faraday waves discovered and named SSS-I by Arbell & Fineberg (1998, 2002) is investigated by means of Direct Numerical Simulations (DNS) of the full three-dimensional Navier–Stokes equations with a free surface. Two simulations with distinct quasi-hexagonal initial conditions run at a forcing amplitude $25\%$ above the Faraday-wave onset followed quite different routes, but both led eventually to the same superlattice pattern after around 250 forcing periods. This regime is inaccessible to the approximations of weak nonlinearity or viscosity. The standing-wave pattern contain rows of patches, alternating in time between hills and lakes that are connected by a long skeleton resembing the backbone of DNA strands. The patches and skeleton of the pattern can be related to its spatial Fourier decomposition, which combines hexagonal modes with a spatially and temporally subharmonic mode. One of the transition routes passes through several fairly long-lived transients including different hexagonal patterns and another superlattice pattern; the other passes only through erratic and disordered states. After another 100 periods, the pattern became unstable and was succeeded by a dynamic version of SSS-I in which the superlattice is modulated and drifts in the direction of the backbone, while preserving its basic shape. Convergence to SSS-I states both experimentally in a large geometry and numerically from two different initial conditions and in a minimal geometry demonstrates the robustness of the SSS-I pattern.
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All authors Debashis Panda, Nicolas Périnet, Abdullah M. Abdal, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Damir Juric, Omar K. Matar, Laurette S. Tuckerman

Cosmology and Nongalactic Astrophysics

SPT-3G D1: Quadratic-Estimator CMB Lensing Reconstruction and Cosmology

Y. Omori, W. L. K. Wu, Y. Nakato et al. (+92 more)

We present a map of the cosmic microwave background (CMB) lensing potential reconstructed from observations taken during the 2019 and 2020 seasons with the third-generation camera on the South Pole Telescope (SPT), covering the $1500\,{\rm deg}^{2}$ SPT-3G Main field, referred to as the SPT-3G D1 dataset. From the multi-frequency temperature and polarization data, we reconstruct the CMB lensing field using a quadratic estimator that jointly accounts for the $T$, $E$, and $B$ fields and their covariance. The resulting lensing map is dominated by polarization information for $L \lesssim 600$ and provides the highest signal-to-noise measurement per mode reported to date. With nuisance parameters fixed to their best-fit values, we measure a lensing amplitude consistent with unity at $2\%$ precision relative to the $\Lambda$CDM model that best fits the combined Planck, ACT DR6, and SPT-3G D1 $TT/TE/EE$ likelihoods (${\rm CMB}_{\rm SPA}$). We further measure the structure-growth parameter $\sigma_{8}\Omega_{\rm m}^{0.25}$ to be $0.6046\pm0.0096$ from the SPT-3G D1 lensing spectrum alone and $0.6020\pm0.0084$ when combined with ACT DR6 and Planck PR4 CMB lensing. By further combining this with ${\rm CMB}_{\rm SPA}$ and the latest DESI DR2 BAO data, we obtain $\sum m_{\nu} < 0.072\,\mathrm{eV}$ (95% C.L.) when allowing the neutrino mass to vary within $\Lambda$CDM. Compared with previous work, the better agreement of our measurement with DESI DR2 BAO yields both this relaxed upper bound and reduced ($\mathord{\sim}2\sigma$) preferences for nonzero spatial curvature and for deviations of $(w_0,w_a)$ from the $\Lambda$CDM expectation. When we combine CMB lensing with the DES Y3 3$\times$2pt analysis, we obtain $S_{8}=0.811\pm0.011$, corresponding to a $1.4\%$ constraint on the late-time clustering amplitude. This precision is competitive with that obtained from the primary CMB within $\Lambda$CDM.
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All authors Y. Omori, W. L. K. Wu, Y. Nakato, F. Bianchini, L. Balkenhol, C. Daley, W. Quan, E. Anderes, A. J. Anderson, B. Ansarinejad, M. Archipley, D. R. Barron, P. S. Barry, K. Benabed, A. N. Bender, B. A. Benson, L. E. Bleem, S. Bocquet, F. R. Bouchet, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, J. Carron, C. L. Chang, P. M. Chichura, A. Chokshi, T.-L. Chou, A. Coerver, T. M. Crawford, T. de Haan, K. R. Dibert, M. A. Dobbs, M. Doohan, D. Dutcher, C. Feng, K. R. Ferguson, N. C. Ferree, K. Fichman, A. Foster, S. Galli, A. E. Gambrel, A. K. Gao, F. Ge, F. Guidi, S. Guns, N. W. Halverson, E. Hivon, G. P. Holder, W. L. Holzapfel, J. C. Hood, A. Hryciuk, N. Huang, T. Jhaveri, F. Kéruzoré, A. R. Khalife, L. Knox, K. Kornoelje, C.-L. Kuo, K. Levy, Y. Li, A. E. Lowitz, C. Lu, G. P. Lynch, T. J. Maccarone, A. S. Maniyar, E. S. Martsen, F. Menanteau, M. Millea, J. Montgomery, T. Natoli, A. Ouellette, Z. Pan, P. Paschos, K. A. Phadke, A. W. Pollak, K. Prabhu, M. Rahimi, A. Rahlin, C. L. Reichardt, M. Rouble, J. E. Ruhl, A. C. Silva Oliveira, A. Simpson, J. A. Sobrin, A. A. Stark, J. Stephen, C. Tandoi, C. Trendafilova, J. D. Vieira, A. G. Vieregg, A. Vitrier, Y. Wan, N. Whitehorn, M. R. Young, J. A. Zebrowski

Instrumentation and Detectors

FPGA-based TDC for SiPM Timing and Amplitude Measurements

Lucas Finazzi, Felipe Soriano, Leandro Gagliardi et al. (+1 more)

Silicon photomultipliers (SiPMs) are widely used in photon-counting applications, such as positron emission tomography or particle physics, where precise timestamps and photoelectron number information are both required. In this work, a Time-to-Digital Converter with amplitude measurement capabilities was designed using an Artix-7 XC7A35T FPGA. For amplitude measurements, the internal xADC of the FPGA was chosen over other alternatives for simplicity. This design has two channels and can operate in timestamp-only mode or timestamp + amplitude mode. In turn, channels can be operated independently or in coincidence. The Integral Non-Linearity and Differential Non-Linearity of the design were studied, along with its time resolution, which is $(19 \pm 1)$ ps. Using a CAEN DT5810 pulse emulator, the design was tested further in timing-only mode, timing + amplitude mode and in coincidence mode to showcase its performance when using Poisson distributed SiPM-like pulses of various amplitudes.
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All authors Lucas Finazzi, Felipe Soriano, Leandro Gagliardi, Federico Golmar

Disordered Systems and Neural Networks · Cross-listed from math.PR

Colorful Exponential Random Graph Models

Bhaswar B. Bhattacharya, Pierfrancesco Dionigi, Ankan Ganguly et al. (+1 more)

In this paper, we initiate the study of colored exponential random graph models (ERGMs), a class of exponential-family models for networks with multiple types of edge relations. Using the framework of probability graphons, we first derive a variational representation for the limiting free energy, whose maximizers determine the asymptotic structure of typical samples from the model. Then we identify several general families of colored ERGMs exhibiting replica symmetry, where the variational problem has constant maximizers and the model asymptotically concentrates on product colorings with independent edges. For general colored ERGMs, we derive Euler-Lagrange fixed-point equations for the variational maximizers, which in turn yield a general high-temperature uniqueness criterion. In the complementary zero-temperature regime, we establish a two-level selection principle: the leading energy term determines the ground states, while the lower-order energy terms, combined with entropy, act as a tie-breaker to determine the asymptotic zero-temperature structure of the model. We illustrate this principle through the induced wedge and rainbow triangle ERGMs. Both models have natural interpretations in multitype networks, and their zero-temperature limits exhibit interesting structures that connect to well-known results in extremal combinatorics. We further establish finite-temperature symmetry breaking for both these models and complement the rigorous results with numerical experiments.
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All authors Bhaswar B. Bhattacharya, Pierfrancesco Dionigi, Ankan Ganguly, Giulio Zucal

General Relativity and Quantum Cosmology

Asymptotic Gravitational Radiation of Photon Rockets with $\Lambda$: Point, String, and Sheet Sources

Francisco Fernández-Álvarez and José M. M. Senovilla

We study the existence of gravitational radiation at infinity for pure-radiation Robinson-Trautman metrics with one spacelike Killing vector and a cosmological constant $\Lambda$ of arbitrary sign. These metrics describe "photon rockets" with point, string, and sheet sources moving through spacetime while emitting null radiation. For $\Lambda\neq 0$, we use criteria for the existence of gravitational radiation based on the asymptotic super-Poynting vector. For point sources, we extend to $\Lambda\neq 0$ the known $\Lambda=0$ result that the Kinnersley rocket is the only rocket without gravitational radiation. However, for string and sheet sources, new possibilities without gravitational radiation arise. For $\Lambda>0$, we show that the vanishing of the canonical asymptotic super-Poynting vector—computed with respect to the unit normal to scri—exactly characterizes the absence of radiation. On the other hand, for $\Lambda<0$, we show that the appropriate criterion is the vanishing of the components normal to scri of the asymptotic super-Poynting vectors associated with any unit timelike vector tangent to scri or, equivalently, the proportionality between the Cotton-York tensor and the holographic stress tensor at scri. In particular, we provide explicit examples of metrics for which the Cotton-York and holographic stress tensors commute, yet gravitational radiation is present because the two tensors are not proportional. We also determine the principal null directions (PNDs) of the rescaled Weyl tensor at scri for both signs of $\Lambda$ and relate their geometry relative to the normal to scri to the tensorial criteria for gravitational radiation.
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Superconductivity

Microwave-Induced Optomagnetism in High-Temperature Superconductors

Anoop Dhillon, Amir Borji and Hamed Majedi

We report the first experimental observation of a steady-state, microwave-driven inverse Faraday effect in a high-temperature superconductor. Circularly polarized microwave radiation generates a helicity-dependent response in an epitaxial $\mathrm{YBa_2Cu_3O_{7-\delta}}$ film, detected using homodyne Hall transport. The optomagnetic response emerges exclusively below $T_c$, vanishes in the normal state, and exhibits no power-dependent counterpart under linearly polarized excitation. The effective optomagnetic conversion reaches $1.75\,\mathrm{T}/(\mathrm{W\,cm^{-2}})$, surpassing optical benchmarks by several orders of magnitude. At higher microwave powers, the signal collapses when the self-generated field exceeds $B_{c1}$, marking the onset of a vortex phase-slip regime, and subsequently re-emerges at mode-locked vortex-washboard harmonics. These results establish steady-state microwave optomagnetism as a route to contactless, non-inductive magnetic control and nonequilibrium vortex spectroscopy in superconducting quantum systems.
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High Energy Physics (Phenomenology)

From Threshold Crossing to Wave-function Renormalization: Defining the Pion Mott Temperature in a Magnetic Field

Sidney S. Avancini, Maximo Coppola, Dyana C. Duarte et al. (+3 more)

We investigate the dissociation of the neutral pion in hot magnetized quark matter within the two-flavor Nambu–Jona-Lasinio model. At zero magnetic field, the Mott temperature is conventionally determined by $m_{\pi^0}(T_{\rm Mott})=2M(T_{\rm Mott})$, above which a real pole ceases to exist. At finite magnetic field, Landau quantization replaces this single threshold by a hierarchy of quark–antiquark continua and generates multiple solutions of the pion pole equation, rendering a direct threshold-crossing criterion ambiguous since a real pion solution below the lowest nominal threshold always exists. We therefore propose to define the magnetic Mott temperature through the inflection point of the pion wave-function renormalization factor $Z_{\pi^0}(T,eB)$ of that lowest pole, corresponding to the fastest loss of its spectral function strength. The prescription reproduces the conventional Mott temperature as $eB\to 0$ and tracks the chiral pseudocritical temperature for both constant and magnetic-field-dependent couplings. Our results characterize pion dissociation in a magnetic field as a spectral crossover rather than a simple threshold crossing.
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All authors Sidney S. Avancini, Maximo Coppola, Dyana C. Duarte, Ricardo L. S. Farias, Norberto N. Scoccola, William R. Tavares

Instrumentation and Detectors

Development and characterization of a wingless ICPC HPGe detector with thin amorphous-Ge contacts

S. A. Panamaldeniya, K. M. Dong and D. M. Mei

High-purity germanium (HPGe) detectors with thin amorphous-germanium (a-Ge) contacts can provide bipolar charge blocking and surface passivation while minimizing contact-related inactive thickness. We report the fabrication and characterization of a p-type inverted coaxial point-contact (ICPC) HPGe detector using thin a-Ge contacts in a wingless geometry that avoids the protective wing structure used in our previous prototype. The detector was fabricated from a USD-grown, zone-refined HPGe crystal and has a mass of 20.0~g. At 77~K, it exhibited picoampere-scale leakage current and an operational depletion voltage of approximately 440~V. Gamma-ray spectroscopy yielded energy resolutions of 1.75~keV FWHM at 59.5~keV and 3.19~keV FWHM at 662~keV. The calibrated charge-injection method gave an absolute capacitance of 0.496~pF, with an estimated method-level relative uncertainty of 6–8%, consistent with the 0.488~pF value obtained from electrostatic modeling with SolidStateDetectors.jl. With a $^{241}$Am source positioned inside the detector bore, the detector showed a source-correlated excess current and a broad degraded-alpha continuum centered near 3558~keV, demonstrating sensitivity to near-surface interactions. Because the source encapsulation, intervening materials, and near-surface charge-collection response were not independently characterized, the continuum is not used to infer a unique dead-layer thickness or energy-loss mechanism. The principal result is successful fabrication and stable sub-pF operation of a 20-g wingless thin-contact ICPC prototype.
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Quantum Physics

"Train classical, deploy quantum" requires rethinking generalization

Snehal Raj, Natansh Mathur and Alejandro Perdomo-Ortiz

Generative models have become central across science and industry, from image and text synthesis to the design of molecules and materials. Quantum generative models are considered one of the most promising applications for quantum computers, since a quantum circuit naturally produces samples from the distribution it encodes, and for suitable circuits that distribution is believed to be hard for any classical computer to reproduce. A leading strategy trains these models on a classical computer and reserves the quantum device for generating samples at deployment. This is possible when the training loss can be evaluated on a classical computer. A prime example is the maximum mean discrepancy (MMD$^2$), a moment-matching loss that compares the model and the data through their Pauli-$Z$ correlations. Research so far has asked whether such models can be trained and whether their sampling is hard; whether minimizing such an objective yields a model that generalizes, rather than one that merely reproduces the training statistics, remains poorly understood. We benchmark thirteen quantum and classical generative models by direct sampling on two application-inspired datasets: first a cardinality-constrained dataset at up to $30$ qubits and second a dataset of genomic single-nucleotide variants, whose valid set is the observed data. Models that converge the loss to the same value differ widely in how much of the unseen valid set they cover. These results indicate that a converged moment-matching loss is not a reliable measure of generalization, and that a train-classical, deploy-quantum workflow has to measure generalization by sampling the trained model, a step that at the sizes of interest is believed to require the quantum device.
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Quantum Gases

Static-Field Shielding of Bosonic Molecules: Evaporation to Degeneracy and Self-Bound Droplets

Jongheum Jung, Laura Futamura, Matteo Ciardi et al. (+5 more)

The strong, tunable dipolar interactions of ultracold molecules make them a powerful platform for quantum many-body physics, but reaching degeneracy by evaporative cooling requires suppressing inelastic collisions. Microwave collisional shielding has enabled the preparation of degenerate Fermi gases and Bose-Einstein condensates of polar molecules, whereas static electric field shielding has been limited to fermionic species, which are less prone to inelastic loss. We demonstrate static-field Förster shielding of bosonic $^{23}$Na$^{87}$Rb molecules, suppressing two-body loss by up to four orders of magnitude. Within a bound-state-free electric-field window, three-body loss is also strongly suppressed, enabling efficient evaporation. Evaporating with an efficiency of 2.09(9), we increase the phase-space density of the gas by two orders of magnitude, reaching degeneracy with 7200(1000) molecules. We observe self-bound droplets at the end of evaporation over a wide range of field strengths, emerging from either degenerate or non-degenerate parent gases. We perform Path Integral Monte Carlo simulations, which suggest that the observed droplets are filamentary in nature, and find good agreement with the experimentally observed droplet formation temperatures. Our results establish Förster shielding as a single-field route to prepare degenerate gases and self-bound droplets of bosonic polar molecules.
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All authors Jongheum Jung, Laura Futamura, Matteo Ciardi, Jason Rosenberg, Youssef Aziz Alaoui, Yukai Lu, Thomas Pohl, Waseem S. Bakr

Statistical Mechanics

Overcoming critical slowing down in frustrated spin systems by learned multiscale sampling

Gabriele Bandini, Giulio Biroli, Patrick Charbonneau et al. (+1 more)

Cluster algorithms, such as the Swendsen–Wang and Wolff methods, are among the most successful MCMC methods for mitigating critical slowing down in statistical systems. These constructive cluster algorithms, however, fail in the presence of even extremely weak frustration. Here, we sidestep this fundamental limitation by learning rather than constructing the relevant clusters. Specifically, we use the wavelet conditional renormalization group (WCRG) sampling method to learn the probability distribution of collective fluctuations of a frustrated two-dimensional soft-spin model. Configurations are then generated recursively from coarse to fine scales by sampling conditional wavelet distributions. The WCRG method reproduces the main statistical properties of the system across different phases, including the local-field distribution and the structure factor. At an Ising-like critical point, the conditional dynamics remains decorrelated within $\mathcal{O}(1)$ sweeps at each scale, yielding an overall sampling complexity of $\mathcal{O}(\log_2 L)$, thus making WCRG much more efficient than standard local MCMC methods. These results show that learned multiscale sampling can overcome critical slowing down in frustrated systems for which conventional cluster algorithms fail. By assessing the sampling accuracy of different observables, we also clarify the main tradeoff of the WCRG method: the accuracy of the fast sampling scheme depends on the expressiveness of the energy-based model used to estimate the wavelet conditional distributions.
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All authors Gabriele Bandini, Giulio Biroli, Patrick Charbonneau, Andrea Gambassi

Quantum Physics

Unconditional Certified Randomness without Structure

Andrea Coladangelo, Dakshita Khurana, Saachi Mutreja et al. (+3 more)

We obtain a certified randomness protocol in the quantum random oracle model. The protocol is non-interactive and publicly verifiable with a classical verifier, and is based on Yamakawa and Zhandry's proof of quantumness [JACM'24]. We prove unconditional security of this protocol against adversaries making subexponentially-many adaptive quantum queries to the random oracle. Prior work on certified randomness relative to a random oracle additionally assumed the Aaronson–Ambainis conjecture or proved security only against low query-depth adversaries.
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All authors Andrea Coladangelo, Dakshita Khurana, Saachi Mutreja, Bhaskar Roberts, Joseph Slote, Avishay Tal

Solar and Stellar Astrophysics

Accretion Rates and Thermohaline Convection in Polluted White Dwarfs

J. R. Fuentes, Matias Castro-Tapia, Jim Fuller et al. (+1 more)

The atmospheres of polluted white dwarfs have information about the composition of disrupted planetary material. However, interpreting the observed abundances requires a quantitative description of the mixing processes that transport such material through their envelopes. The accretion of metal-rich debris drives thermohaline convection in the star's radiative zone. Previous studies have modeled this form of turbulence as an enhanced diffusive process, often inferring mass accretion rates $\dot{M}_{\rm acc}$ that exceed X-ray constraints. We develop a time-dependent model that treats thermohaline mixing as a propagating front whose evolution is coupled self-consistently to the surface abundance of heavy elements. We perform hydrodynamical simulations which demonstrate that thermohaline mixing drives the composition gradient towards values slightly above marginal thermohaline stability. Using this condition, we derive analytic solutions for the mixed layer depth $h$ and surface abundance $X_{\rm surf}$, finding that both scale as $t^{1/2}$ at early times, transitioning to $h \propto t^{4/27}$ and $X_{\rm surf} \propto t^{10/27}$ at later times. Without gravitational settling, the thermohaline front never reaches a steady state, while including settling leads to an equilibrium surface abundance $X_{\rm surf, eq} \propto \dot{M}_{\rm acc}^{30/43}$. Applied to G 29–38, our model matches the observed heavy-element abundance for $\dot{M}_{\rm acc} \sim 1\times 10^{10}$–$2\times 10^{10}~\mathrm{g~s^{-1}}$, comparable to previous findings using stellar evolution codes. These rates exceed the X-ray estimate by about an order of magnitude, which may point to a partially suppressed X-ray luminosity from the accretion boundary layer. We present a practical prescription for inferring accretion rates directly from the observed surface abundance and stellar parameters of other polluted white dwarfs.
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All authors J. R. Fuentes, Matias Castro-Tapia, Jim Fuller, Marcus King