Mesoscale and Nanoscale Physics
Charge-tunable Cooper-pair diode
Jon Ortuzar, Stefano Trivini, Leonard Edens et al. (+2 more)
Superconducting diodes, devices that allow Cooper-pair currents to flow more easily in one direction than the other, are set to become key building blocks for dissipationless electronics. Existing realizations, however, rely on
magnetic fields, ferromagnets, or complex
heterostructures that hinder integration and scalability. Here we demonstrate a diode effect for Cooper-pairs that arises solely from electron-electron interactions in nanoscale superconducting lead islands. When these islands are driven into the Coulomb blockade regime, Cooper-pair transport occurs through resonant charge states. By tuning the island's electrostatic environment, we controllably break particle-hole
symmetry and induce nonreciprocal supercurrents, thereby achieving a gate-switchable superconducting diode without any external
magnetic field. Our approach enables robust rectification of superconducting currents and microwave photoresponse, providing a scalable strategy to superconducting logic devices.
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All authors Jon Ortuzar, Stefano Trivini, Leonard Edens, F. Sebastian Bergeret, Jose Ignacio Pascual
Materials Science
Engineering photomagnetism in collinear van der Waals antiferromagnets
MengXing Na, Viktoriia Radovskaia, Dinar Khusyainov et al. (+14 more)
Achieving efficient ultrafast optical control of
antiferromagnetic spin dynamics is a central goal for next-generation high-speed THz spintronic and magnonic devices. Resonant optical pumping of
crystal-field-split d-d orbital multiplets in
magnetic TM ions directly modulates exchange and
spin-orbit interactions, inducing large-amplitude coherent
spin precession. However, such effects are limited to a handful of systems and there is no general strategy to enhance d-d photomagnetism in antiferromagnets. Here, we demonstrate the engineering of photomagnetism via TM-ion doping in collinear van der Waals antiferromagnets. In Mn$_{1-x}$Ni$_x$PS$_3$, small amounts of Ni$^{2+}$ activate a strong photomagnetic response while largely preserving the Néel ground state. Even 10% Ni boosts the response by more than an order of magnitude compared to pure MnPS$_3$, with resonant pumping of Ni$^{2+}$ d-d transitions driving large-amplitude coherent
spin precession and providing helicity-dependent phase control. Tuning the pump energy across the full Mn$_{1-x}$Ni$_x$PS$_3$ composition range shows that Ni excitations remain effective across competing Néel and zig-zag
antiferromagnetic states while supporting tunable-frequency coherent
spin precession. These results establish TM-ion doping as a versatile strategy to harness orbital multiplet excitations for ultrafast, low-dissipation
spin control in van der Waals antiferromagnets.
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All authors MengXing Na, Viktoriia Radovskaia, Dinar Khusyainov, Peter Kim, Kingshuk Mukhuti, Peter C.M. Christianen, Ekaterina Kochetkova, Anna Isaeva, Anne de Visser, Dimitar Pashov, Mark van Schilfgaarde, Edwin H.T. Teo, Apoorva Chaturvedi, Swagata Acharya, Theo Rasing, Alexey V. Kimel, Dmytro Afanasiev
Mesoscale and Nanoscale Physics
Deep learning statistical defect models on magnetic material dynamic and static properties
C. Eagan, M. Copus and E. Iacocca
The modeling of realistic
magnetic materials requires the inclusion of defects. Based on the pseudospectral Landau-Lifshitz description of magnetisation dynamics, we propose a statistical model that takes into account defects, specifically vacancies. This statistical model can be integrated with deep learning techniques that correlate defect thresholds with relevant physical observables. We develop a convolutional neural network and a physics-informed neural network combined with theory of functional connections to predict the dispersion relation given defect parameters and physical constraints. A two-branch convolutional neural network is developed to predict domain-wall widths depending on defects threshold, taking into account the spatial profile and domain-wall width separately to achieve a prediction. The proposed physics-informed approaches leverage deep-learning and achieve statistical predictions measured in physical units. This is a stepping stone towards the discovery of new materials and the determination of minimal defect thresholds required for desired dynamics, states, or topological textures.
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Statistical Mechanics
Integrability-breaking-induced Mpemba effect in spin chains
Adam J. McRoberts
We show that there are two distinct mechanisms that can cause the
symmetry-restoration Mpemba effect in
spin chains with weakly broken integrability, such that the asymptotic equilibration is diffusive, but the lifetime of anomalously fast
spin hydrodynamics at low temperature is parametrically large. In particular, we consider isotropic
spin chains quenched out of
equilibrium by suppressing the $z$-components, without inducing any net magnetisation. Initially, the restoration of isotropy is faster in hotter systems – because they have more phase space available to scramble their initial conditions – which may cause the equilibration curves to cross at early times in both integrable and non-integrable systems. At later times, however, the equilibration is effectively hydrodynamic, and the colder systems start to equilibrate faster as the lifetime over which they evince superdiffusive
spin hydrodynamics is parametrically larger – but only in non-integrable models. Depending on the details of the temperatures and the extent of the initial
symmetry-breaking, two isotropy-restoration curves may have a crossing at early time, late time, neither, or both.
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Materials Science
Bias in Universal Machine-Learned Interatomic Potentials and its Effects on Fine-Tuning
Nicolas Wong and Julia H. Yang
Universal machine learned interatomic potentials (uMLIPs) embody a growing area of interest due to their transferability across the periodic table, displaying an error of about 0.6 kcal/mol against the Matbench Discovery test set. However, we show that achieving more accurate predictions on out-of-domain tasks requires fine-tuning. Additionally, we investigate the existence and influence of model biases in molecular dynamics (MD) by examining two approaches for data generation: from multiple MD trajectories in parallel, which we call naive fine-tuning, and from a single MD trajectory with fine-tuning after set intervals, which we call periodic fine-tuning. Our results find that naive fine-tuning generates constrained
datasets that fail to represent MD simulations, and thus downstream fine-tuned models fail during extrapolation. In contrast, periodic fine-tuning yields models which are more generalizable and accurate, producing low-error dynamics. These findings indicate the role of uMLIP bias in fine-tuning, and highlights the need for multiple fine-tuning steps. Lastly, we relate unphysical behavior to principal component space, and quantify extrapolations through Q-residual analysis, which are useful as a proxy for epistemic uncertainty for larger simulations.
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Materials Science
Intertwined Swirling Polarization States in BaTiO$_3$ with Embedded BaZrO$_3$ Nanoregions
R. Machado, F. Di Rino, M. Sepliarsky et al. (+1 more)
Ferroelectric materials embedded with dielectric inclusions offer a unique platform for exploring novel topological polar textures. Using first-principles-based atomistic simulations, we investigate the polarization behavior of a BaTiO$_3$
matrix containing segregated BaZrO$_3$ nanoregions. We demonstrate that the polar texture in three-dimensionally ordered arrays of dielectric inclusions is governed by their size and spacing, revealing three distinct regimes. At large separations, the nanocomposite exhibits bulk-like BaTiO3 phase transitions, while at smaller spacings, interconnected swirling polarization patterns give rise to
vortex supercrystal states. We analyze the stabilization mechanisms of these states and show that each regime is characterized by distinct switching behavior. Furthermore, we find that nanocomposites with randomly distributed dielectric inclusions exhibit swirling polarization textures, giving rise to an amorphous network of entangled
vortices. Our findings provide new insights into the physics of relaxor ferroelectrics, are consistent with recent experimental observations, and open up new possibilities for designing materials with emergent topological functionalities.
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All authors R. Machado, F. Di Rino, M. Sepliarsky, M. G. Stachiotti
Statistical Mechanics
Bridge Scaling in Conditioned Henyey-Greenstein Random Walks
Claude Zeller
We study fixed-length bridge paths – half-space excursions that start and end at a planar boundary – for three-dimensional random walks with Henyey-Greenstein scattering angles and exponentially distributed step lengths, using Monte Carlo simulation over asymmetry parameter g from 0 to 0.95 and path lengths from 4 to 200 steps. The key structural feature is that the walk evolves on a two-dimensional Markovian state space (depth, direction cosine) rather than the scalar depth coordinate alone. Four anomalies with respect to classical Brownian-excursion theory are reported. The mean amplitude scales super-diffusively, as path length to a power of 0.57–0.58 for isotropic scattering, nine standard deviations above the Brownian prediction of 0.5, with no sign of convergence out to 200 steps. The
diffusion coefficient scales as the transport mean free path to the power 0.415 rather than the predicted 1.0. The midpoint depth distribution is Rayleigh rather than half-normal, consistent with a two-dimensional Bessel process. The bridge-conditioned mean direction cosine converges to minus two-thirds at the final step, independently of the asymmetry parameter and initial direction – the classical Milne result anchored by the H-function moment identity. All anomalies are attributed to the two-dimensional state-space structure. The two anomalous exponents sum to approximately unity, suggesting a common
geometric origin. Whether this constitutes a permanent universality-class shift or an anomalously slow crossover to Brownian-excursion behaviour remains the primary open question.
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Mesoscale and Nanoscale Physics
Geometry of Contact Terms in Linear Response: Applications to Elasticity
Ian Osborne, Gustavo Monteiro and Barry Bradlyn
Employing the Kubo linear response formalism to calculate the elasticity of anisotropic systems has been shown to yield odd elastic
moduli. For
Hamiltonian systems, this result seems to be contradictory as it would violate energy conservation. To resolve this discrepancy, we examine the predictions of
quantum linear response in the context of our expectation from classical elasticity theory. Our framework reveals that the geometry of the space of strain perturbations introduces correction factors to the correspondence between the Kubo formula and the elastic
moduli which resolves the contradiction. We use a two-dimensional gas of electrons in a
magnetic field as a pedagogical example. We use generalized f-sum rules to demonstrate how contact terms may reveal themselves in experimental measurements. Finally, we discuss the implications of our results for interpreting more general linear response functions.
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Materials Science
Endohedral Derivatives of the Recently Synthesized Two-Dimensional Fullerene Networks: Electronic and Optical Insights from First-Principles Calculations
Marcelo L. Pereira Junior, Raphael M. Tromer, Luiz A. Ribeiro Junior et al. (+1 more)
The quasi-hexagonal phase of the two-dimensional fullerene network (qHPC$_{60}$), recently synthesized, has emerged as a stable carbon-based material with distinct structural and electronic features. In this work, we employed density functional theory (DFT) calculations to investigate the electronic and optical properties of its endohedral derivatives. The encapsulation of nitrogen, cerium, and strontium atoms inside fullerene cages was systematically analyzed at different concentrations. Our results show that encapsulation preserves the semiconducting backbone of pristine qHPC$_{60}$ while introducing localized electronic states that alter the bandgap and enable new transition channels. Nitrogen encapsulation produces intragap states with potential relevance for discrete optical emission, whereas cerium and strontium generate intraband states near the conduction edge. These modifications induce a red shift of the absorption onset into the visible spectrum, accompanied by enhanced refractive and absorptive responses. The robustness of the electronic structure under reduced concentrations indicates that the fully encapsulated limit adequately represents the system. Overall, the findings highlight
impurity-endowed qHPC$_{60}$ as a promising platform for optoelectronic and light-harvesting applications.
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All authors Marcelo L. Pereira Junior, Raphael M. Tromer, Luiz A. Ribeiro Junior, Douglas S. Galvao
Mesoscale and Nanoscale Physics
Spin-polarized transport in copper-oxide atomic junctions revealed by anomalous shot-noise behavior in presence of the Kondo effect
Marcel Strohmeier, Samanwita Biswas, Wolfgang Belzig et al. (+2 more)
Noise measurements provide a valuable tool for revealing
spin polarization effects in the electronic transport through
quantum coherent conductors. We present an extension of the Landauer description of shot noise to include energy-dependent transmission functions and apply it to explore local
magnetic correlations in air-oxidized copper contacts, for which first-principle studies have predicted the emergence of
ferromagnetic ground states, attributing certain atomic configurations with
spin filtering capabilities. By means of low-temperature transport measurements, we provide comprehensive experimental evidence, including hysteretic magnetoresistance and zero-bias anomalies (ZBAs) attributed to the Kondo effect, for the presence of local magnetism. The analysis of the anomalous shot noise in the presence of ZBAs allows us to determine the
spin polarization of the current which may reach even full polarization, confirming the
spin-filtering capability of copper
oxide atomic contacts.
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All authors Marcel Strohmeier, Samanwita Biswas, Wolfgang Belzig, Regina Hoffmann-Vogel, Elke Scheer
Materials Science
ALD Oxidant as A Tuning Knob for Memory Window Expansion in Ferroelectric FETs for Vertical NAND Applications
Ranie Jeyakumar, Prasanna Venkatesan, Lance Fernandes et al. (+12 more)
Dielectric inserts are widely used to expand the
memory window (MW) in ferroelectric FETs (FeFETs) for vertical NAND applications, with prior efforts focused primarily on material selection and stack positioning. Here, we demonstrate that the ALD oxidant used for the Al2O3 interlayer serves as a process-level tuning knob for MW engineering. H2O-grown Al2O3 yields a significantly larger MW (7-8 V) compared to O3 (4 V) for both gate-injection (12/3) and tunnel dielectric (8/3/8) configurations. While the tunnel dielectric (8/3/8) stack maintains robust retention up to 1e4s at 125C despite the larger MW, the gate-injection (12/3) configuration exhibits pronounced retention degradation for the H2O case. The enhanced MW is attributed to higher interlayer leakage associated with H2O-based ALD. These results establish oxidant choice as a key process parameter for co-optimizing MW and retention in ferroelectric NAND technologies.
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All authors Ranie Jeyakumar, Prasanna Venkatesan, Lance Fernandes, Salma Soliman, Priyankka Ravikumar, Taeyoung Song, Chengyang Zhang, Woohyun Hwang, Kwangyou Seo, Suhwan Lim, Wanki Kim, Daewon Ha, Shimeng Yu, Suman Datta, Asif Khan
Mesoscale and Nanoscale Physics
A unifying framework for sum rules and bounds on optical, thermoelectric and thermal transport from quantum geometry
M. Nabil Y. Lhachemi and Jennifer Cano
We present a
geometric formulation of optical, thermoelectric, and thermal linear response in clean, zero temperature band
insulators based on a single object: a generalized time-dependent
quantum geometric tensor (g-tQGT) built from correlations of projected particle and heat polarization operators. Within this framework, the AC transport tensors admit compact expressions that make their
geometric content explicit. The response splits into a Berry
curvature contribution that remains finite in the DC limit and a frequency correction governed by the
quantum metric, implying geometry driven effects even in topologically trivial
insulators. At equal times, the g-tQGT recovers the usual integrated QGT and yields energy-weighted thermal analogs whose antisymmetric parts are fixed by orbital and heat magnetization. Importantly, in the thermal channel, a thermal
quantum geometric tensor is obtained. Casting the theory in a
Hilbert-Schmidt inner product form yields a bound on the trace of the thermal QGT, an uncertainty relation on the projected polarization operators and a purely
geometric upper bound on the finite-time accumulated response. The latter is used in the optical channel to derive a
geometric upper bound on the electric current. Finally, time derivatives of the g-tQGT are used to generate a hierarchy of generalized thermoelectric and thermal sum rules, and bounds on these sum rules are obtained. These bounds are used to find inequalities between different physical objects such as the optical mass, susceptibility functions and magnetizations.
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Quantum Gases · Cross-listed from quant-ph
Digital dissipative state preparation for frustration-free gapless quantum systems
Johannes Feldmeier, Yu-Jie Liu, Mikhail D. Lukin et al. (+1 more)
Preparing algebraically correlated ground states of
quantum many-body systems is an important, yet challenging task for
quantum simulation. We introduce a protocol that employs local projective measurements and
unitary feedback for frustration-free gapless systems. Our approach prepares a priori unknown ground states in time that scales polynomially with system size. We analytically show the performance our protocol for the dynamics of a single-particle; we argue the same mechanism generalizes to many-body systems based on the physics of quasiparticles. Our theory predicts that a transient cooling dynamics directly reveals the system's universal critical properties. In particular, the state preparation time is linear in the inverse of the finite-size gap (up to log correction) when the system's dynamical critical exponent is larger or equal the effective spatial dimension explored by the quasiparticles. We verify these predictions in numerical simulations of
ferromagnetic Heisenberg models in one- and two dimensions, a Fredkin
spin chain, and a two-dimensional model of resonating valence bond states. Our protocol stabilizes gapless many-body ground states fully digitally without requiring analog rotations, enabling access to high-fidelity states beyond conventional adiabatic approaches in near-term experiments.
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All authors Johannes Feldmeier, Yu-Jie Liu, Mikhail D. Lukin, Soonwon Choi
Strongly Correlated Electrons
Classical Kitaev model in a magnetic field
Paul A. McClarty, Roderich Moessner, Karlo Penc et al. (+1 more)
Motivated by experiments on
spin-orbit coupled magnets with Kitaev exchange in
magnetic fields, we present an analysis of the classical Kitaev honeycomb model in the presence of a
magnetic field. We show that there is a
spin liquid regime that exists within a finite window of fields from zero up to a finite threshold before transitioning into the polarized paramagnet. We uncover constraints that
spins need to satisfy in the ground state and show that they determine the exact limiting zero temperature behavior of the heat capacity and
magnetic susceptibility within the
spin liquid as a function of field. When the field is finite, both the two-point
spin and the quadrupolar correlations are short-ranged, in contrast to the zero-field case. We rationalize an effective mass for the quadrupolar correlations in terms of a coarse-grained theory with fluctuating effective charge degrees of freedom. Finally, we show that weak site-dilution does not change the magnetization within the
spin liquid – a kind of "perfect" compensation of the site dilution.
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All authors Paul A. McClarty, Roderich Moessner, Karlo Penc, Jeffrey G. Rau
Mesoscale and Nanoscale Physics
Plasmon-driven electron-hole pair formation in a non-equilibrium Fermi liquid
Rishi Acharya, Eli Gerber, Nina Bielinski et al. (+13 more)
Collective modes in
Fermi liquids are usually regarded as dissipation channels that relax electronic excitations through Landau damping. Whether such modes can instead mediate the formation of correlated electronic states under non-
equilibrium conditions remains an open question. Here, we show that under optical photo-doping, a bulk plasmon can drive correlated inter-band transfer within a transient electronic continuum. Using time- and angle-resolved photoemission spectroscopy (Tr-ARPES) on EuCd$_2$As$_2$ supported by electronic structure calculations, we observe that at high excitation density, plasmons transfer energy from a weakly dispersing bulk band into unoccupied surface states. This bulk-to-surface redistribution stabilizes a long-lived, energy-localized spectral feature consistent with a Mahan
exciton. Our results reveal a non-
equilibrium regime of
Fermi-
liquid physics in which collective modes do not merely dissipate energy, but also stabilize correlated bound states.
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All authors Rishi Acharya, Eli Gerber, Nina Bielinski, Hannah E. Aguirre, Younsik Kim, Camille Bernal-Choban, Gaurav Tenkila, Suhas Sheikh, Pranav Mahaadev, Faren Hoveyda-Marashi, Subhajit Roychowdhury, Chandra Shekhar, Claudia Felser, Peter Abbamonte, Benjamin J. Wieder, Fahad Mahmood
Strongly Correlated Electrons
Symmetric localization of $\nu_{\text{tot}}=4/3$ fractional topological insulator edges
Yang-Zhi Chou and Sankar Das Sarma
Motivated by the recent twisted MoTe$_2$ experiment [arXiv:2601.18508], we develop a disordered interacting edge theory of a fractional topological
insulator at $\nu_{\text{tot}}=4/3$, consisting of two time-reversal-conjugated $\nu=2/3$ fractional
quantum Hall states. For an $S_z$-conserving edge, we uncover three distinct phases with two possible conductance values per edge in the long-edge limit: $\frac{2}{3}\frac{e^2}{h}$ and $\frac{4}{3}\frac{e^2}{h}$. In the presence of $S_z$-changing perturbations (e.g., Rashba
spin-orbit coupling), an interaction-induced insulating edge state can emerge without breaking time-reversal or charge-conservation
symmetry, corresponding to the absence of a topologically protected edge state. We show an exact mapping (with a special choice of parameters) to a noninteracting fermionic theory exhibiting Anderson localization, and the weak-coupling phase diagrams are also constructed, showing that symmetric localization can emerge regardless of other $S_z$-conserving perturbations. Our results showcase an explicit, experimentally relevant example that the edge-state two-terminal transport can yield false-negative results in identifying the $\nu_{\text{tot}}=4/3$ fractional topological
insulators.
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Quantum Gases
Stability of flat-band Bose-Einstein condensation from the geometry of compact localized states
Kukka-Emilia Huhtinen
We consider Bose-Einstein condensation in flat-band models from a real-space perspective. Using a basis of compact localized states, we reformulate the minimization of the mean-field energy as a Euclidian geometry problem. Within Bogoliubov theory, we show that flat-band models where the solutions to this problem are frameworks consisting of triangles with nonzero area are promising for condensation, whereas for instance square frameworks indicate condensation in a single mode is impossible. When restricting the analysis to Bloch states, this approach can be related to a necessary condition for a non-vanishing
quantum distance. This work provides a new perspective on how condensation in flat bands is destabilized, and offers principles for the construction of models where flat-band Bose-Einstein condensation is possible.
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Strongly Correlated Electrons · Cross-listed from math.QA
On the structure of categorical duality operators
Corey Jones and Xinping Yang
We systematically study categorical duality operators on
spin (and anyon) chains with respect to an internal fusion category
symmetry C. We parameterize duality operators on the quasi-local
algebra in terms of data dependent on the associated
quantum cellular automata (QCA) on the symmetric subalgebra $B$. In particular, a QCA $\alpha$ on $B$ defines an invertible C-C bimodule category $M_{\alpha}$, and the duality operators extending $\alpha$ form a simplex, with extreme points in bijective correspondence with the simple object of $M_{\alpha}$. Then we consider the structure of external
symmetries generated by a family of duality operators, and show that if the UV models are all defined on tensor product
Hilbert spaces, these categories necessarily flow to weakly integral fusion categories in the IR.
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Materials Science
Nanoscale imaging of spin textures with locally varying altermagnetic response in $\alpha$-Fe$_2$O$_3$
R. Yamamoto, S. Mayr, A. Hariki et al. (+20 more)
Altermagnetism is a recently identified
magnetic state in which time-reversal
symmetry is broken despite a collinear compensated
spin structure. The response of altermagnets is determined not only by their $d$-, $g$-, or $i$-wave
spin order, but also the orientation of their Néel vector $\mathbf{L}$. Therefore, accessing a response that fundamentally depends on the orientation of $\mathbf{L}$, such as the anomalous
Hall effect, remains experimentally challenging in particular at the nanoscale. Here, we harness nano-spectroscopic X-ray
magnetic circular dichroism (XMCD) to investigate nanoscale modulated altermagnetic responses in $\alpha$-Fe$_2$O$_3$ (Hematite). By performing spectroscopy across the temperature-induced $\mathbf{L}$-reorientation Morin transition, we observe the on-and-off switching of XMCD, in agreement with our theoretical calculations. Although the bulk XMCD vanishes below the Morin temperature, we confirm the reorientation of $\mathbf{L}$ by harnessing polarization-independent X-ray absorption spectroscopy. Moreover, we observe a finite XMCD signal in nanoscale domain walls with locally modulated Néel vectors, while the surrounding domains exhibit no XMCD. At room temperature, we instead identify altermagnetic meron
spin textures that exhibit XMCD in their planar regions but no XMCD in their nanoscopic cores. Our results establish a pathway to harness complex
spin textures with nanoscale functionalities in a broader class of altermagnets with various $\mathbf{L}$-orientations and using light, earth-abundant elements.
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All authors R. Yamamoto, S. Mayr, A. Hariki, S. Finizio, K. Sakurai, E. Weschke, K. Litzius, M. T. Birch, L. A. Turnbull, E. Zhakina, M. Di Pietro Martínez, J. Reuteler, F. Schulz, M. Weigand, J. Raabe, G. Schütz, S. S. P. K. Arekapudi, O. Hellwig, W. H. Campos, L. Šmejkal, J. Kuneš, C. Donnelly, S. Wintz
Statistical Mechanics · Cross-listed from math-ph
Intertwining Markov Processes via Matrix Product Operators
Rouven Frassek, Jan de Gier, Jimin Li et al. (+1 more)
Duality transformations reveal unexpected equivalences between seemingly distinct models. We introduce an out-of-
equilibrium generalisation of
matrix product operators to implement duality transformations in one-dimensional boundary-driven Markov processes on
lattices. In contrast to local dualities associated with generalised
symmetries, here the duality operator intertwines two Markov processes via generalised exchange relations and realises the out-of-
equilibrium duality globally. We construct these operators exactly for the symmetric simple exclusion process with distinct out-of-
equilibrium boundaries. In this case, out-of-
equilibrium boundaries are dual to
equilibrium boundaries satisfying Liggett's condition, implying that the Gibbs-Boltzmann measure captures out-of-
equilibrium physics when leveraging the duality operator. We illustrate this principle through physical applications.
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All authors Rouven Frassek, Jan de Gier, Jimin Li, Frank Verstraete
Statistical Mechanics · Cross-listed from quant-ph
Qubit reset beyond the Born-Markov approximation: optimal driving to overcome polaron formation
Carlos Ortega-Taberner, Eoin O'Neill and Paul Eastham
Qubits are typically reset into a known state by coupling them to a low-temperature environment. When treated in the Born-Markov approximation such couplings produce exponential relaxation to
equilibrium, giving high reset fidelities limited only by temperature. We investigate
qubit reset beyond this approximation, using numerically exact tensor network methods and the time-dependent variational principle, focussing on a
spin-
boson model describing a transmon
qubit coupled to a resistor. Beyond the Born-Markov approximation the reset fidelity becomes limited by the buildup of system-environment correlations which corresponds to the formation of a polaron. We implement numerical optimal control to find time-dependent
qubit Hamiltonians which overcome this limitation by steering the dynamics of the correlated system-environment state. The optimal controls becomes more effective when the environment is filtered to span a smaller spectral range, and remain effective when the multilevel nature of the transmon is considered. A related paper [C. Ortega-Taberner, E. O'Neill and P. R. Eastham, arXiv:XXXX.XXXX] addresses the complementary case of control via a time-dependent system-environment coupling. Our results show how limitations on reset speed and fidelity can be overcome, and how time-dependent driving can steer system-environment correlations and reverse polaron formation.
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Statistical Mechanics · Cross-listed from quant-ph
Quantum control of the environment in open quantum systems enables rapid qubit reset
Carlos Ortega-Taberner, Eoin O'Neill and Paul Eastham
Qubit reset is crucial in
quantum technology and is typically achieved by coupling the
qubit to a dissipative environment. However, the achievable speed and fidelity are limited by
qubit-environment
entanglement. We use exact tensor-network simulations and a time-dependent variational approach to investigate these effects for transmon
qubits with a time-dependent system-environment coupling. We show that they are due to the formation of a polaron state and how this can be reversed using a time-dependent coupling. Coupling protocols are identified which achieve reset with an excited-state population of $10^{-6}$ in $10$ ns. A related paper [C. Ortega-Taberner, E. O'Neill and P. R. Eastham, arXiv:XXXX.XXXX] addresses the complementary case of control via a time-dependent
Hamiltonian. Our work shows how the dynamics of the environment of an open
quantum system can be controlled to design effective
quantum processes in non-Markovian systems.
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Soft Condensed Matter
Synthetic design of force-responsive hydrogels with ring-forming catch bonds
Wout Laeremans and Wouter G. Ellenbroek
Catch bonds are interactions whose lifetimes increase under mechanical load, a counterintuitive behaviour that underlies diverse biological processes. Translating this mechanism to synthetic materials offers the potential to create systems that are compliant at low stress but stiffen under applied force, with applications ranging from impact-responsive materials to dynamic tissue scaffolds. However, engineering materials with tunable, force-dependent interactions remains challenging, and existing conceptual designs are limited. Here, we present a minimal synthetic framework for catch bond behaviour in dynamic hydrogels, based on reversible ring-forming
polymers. Using coarse-grained molecular dynamics simulations, we show that hydrogels with such a chemistry undergo fewer bond-breaking reactions as the stress increases and can even display a non-monotonic dependence of the strain rate on the applied stress. Our results highlight the potential of reversible ring formation as a versatile platform for designing mechanically adaptive materials with tunable durability and responsiveness.
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Soft Condensed Matter
Three phases of odd robotic active matter
Fan Bo, Shiqi Liu, Zenghong He et al. (+8 more)
Nonreciprocal interactions in active matter are known to generate exotic mechanical behaviors such as odd elasticity and odd viscosity. However, these phenomena have largely been studied in isolation, raising a fundamental question: Is there a single system that embodies these distinct regimes of odd matter and can transition between phases, establishing a unified phase diagram for nonreciprocal active matter? To address this, we introduce a tunable robotic active matter platform, the Magnetomechanically Augmented Spinning roBotic (MASBot) collective, in which particle-level control of chirality, activity, and pairwise interactions enables access to distinct phases of odd matter. By continuously increasing repulsive forces relative to attractive and transverse forces, we experimentally map a transition from an odd elastic
crystal to an odd viscous
liquid, and then to a
chiral active gas. We find that this latter phase forms a non-space-filling, nonreciprocal active gas stabilized by long-range hydrodynamic attractive forces, whose statistical signatures are consistent with those of a two-dimensional self-gravitating point
vortex gas. Within these phases, adjusting spinning frequency and introducing spatially patterned activity allows us to fine-tune odd mechanical responses and tailor power spectra. Further polar and rotational
symmetry breaking at the particle scale leads to novel emergent states such as phase separation and collective translation. Together, our system provides a fundamental experimental testbed for nonequilibrium physics and establishes a blueprint for treating robotic swarms as programmable states of matter, enabling functions that range from resilient structures to adaptive swarm reconfiguration.
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All authors Fan Bo, Shiqi Liu, Zenghong He, Wyatt Joyce, Gregor Leech, Kiet Tran, Keilan Ramirez, Nicholas Boechler, Nicholas Gravish, Hongbo Zhao, Tzer Han Tan
Superconductivity
Critical behavior of the thermal phase transition of U(1) lattice gauge systems
Greta Sophie Reese and Ludwig Mathey
We model the phase transition of a
superconductor as a U(1)
lattice gauge system, and determine its critical behavior. For this, we perform Monte Carlo simulations, treating the order parameter field and the gauge field on equal footing, without additional approximations. As the defining correlation function, we determine the order parameter correlation function including a gauge string, thus achieving a gauge-invariant characterization of the long-range behavior explicitly. We obtain a critical exponent $\beta$ that is consistent with the exponent of the U(1) transition of neutral
bosons, i.e. of Bose-Einstein condensation. We further extract the anomalous dimension $\eta$ for our parameter sets which is significantly smaller than the U(1) anomalous dimension. We determine the critical behavior of the heat capacity, which displays a temperature depends consistent with an XY transition. These results clarify the universality class of the phase transition of this system.
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Materials Science
Direct Laser Writing of Ferromagnetic Nickel Utilizing the Principle of Sensitized Triplet-Triplet Annihilation Upconversion
Kristin E. J. Kühl, Katharina Rediger, Nikhita Khera et al. (+5 more)
Direct
laser writing of
ferromagnetic microstructures is of great interest for sensing and data storage in compact three-dimensional architectures. However, reliable direct
laser writing of metallic and even more so
ferromagnetic materials remains a major challenge. Here, we present a novel photoresist suitable to direct
laser write
ferromagnetic nickel based on sensitized triplet-triplet annihilation upconversion. By combining an in-situ photochemical deoxygenation process with a sensitized triplet-triplet annihilation upconversion process as well as a photoreduction of Ni2+ ions, the deposition of metallic nickel is enabled under ambient conditions. Using this approach, nickel structures are fabricated as a proof of concept. Scanning electron microscopy and EDX analysis confirm the spatially confined deposition of nickel, while
magnetic characterization by vibrating sample magnetometry and scanning NV magnetometry demonstrate the
ferromagnetic nature of the printed structures. This work presents a major step forward in extending the possibilities of direct
laser writing to metallic and
ferromagnetic materials.
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All authors Kristin E. J. Kühl, Katharina Rediger, Nikhita Khera, Ephraim Spindler, Gereon Niedner-Schatteburg, Elke Neu, Mathias Weiler, Georg von Freymann
Materials Science
A systematic study of single molecule metallocenes with 4d and 3d transition metal atoms
Daniela Herrera-Molina, Kushantha P. K. Withanage, Jesus N. Pedroza-Montero et al. (+3 more)
The realization of
spin-based devices remains one of the central goals of spintronics research. Single-molecule magnets (SMMs) constitute an important class of nanoscale
magnetic systems with significant potential for spintronic applications, where individual molecules can serve as fundamental building blocks of functional devices. In this work, we systematically investigate a family of 4d and 3d transition-metal metallocenes using first-principles density functional theory. Among the seven 4d metallocenes considered, only Mo and Rh metallocenes undergo Jahn Teller distortions and exhibit uniaxial anisotropy with energy barriers of approximately 20 K. Similarly, among the 3d metallocenes studied in this work, only Cr and Co metallocenes undergo Jahn Teller distortions and display uniaxial anisotropy, although with smaller barriers below 10 K. All remaining metallocenes exhibit easy-plane anisotropy. We find that the
magnetic anisotropy energy does not increase monotonically with the number of d electrons; instead, it is governed primarily by the orbital ordering of the transition-metal d states. Our calculations further show that the Jahn Teller distortion induces transverse anisotropy, leading to zero-field magnetization tunneling across the energy barrier, with the weakest tunneling rate for Mo metallocene. For the Mo metallocene, the
magnetic anisotropy energy increases to approximately 60 K in cationic charge states, although the
magnetic anisotropy changes from uniaxial to easy-plane. In this work, we also investigate the influence of ligand size on the structural stability of metallocenes and establish practical guidelines for constructing reliable molecular models for first-principles studies. Finally, we also propose that metallocenes with easy-plane anisotropy could serve as
magnetic sensing elements, highlighting their potential beyond
memory applications.
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All authors Daniela Herrera-Molina, Kushantha P. K. Withanage, Jesus N. Pedroza-Montero, Pardeep Kaur, Mark. R. Pederson, M. F. Islam
Quantum Gases · Cross-listed from hep-th
Equilibrium Partition Function of Non-Relativistic CFTs in Harmonic Trap
Eunwoo Lee
We investigate the
equilibrium partition function of non-relativistic conformal field theories in harmonic quantization. We first analyze the hydrodynamic regime and show that, at leading order, the partition function exhibits a universal structure determined by the equation of state: the logarithm of the partition function develops simple poles in $\omega^2-\Omega_a^2$, where $\omega$ is the harmonic trapping frequency and $\Omega_a$ are angular velocities acting as chemical potentials for angular momentum. The corresponding residue is determined by a single-variable function of $\mu/T$, with $\mu$ the particle-number chemical potential and $T$ the temperature. We then study the large-angular-momentum limit $\Omega_a\to\omega$. In this regime centrifugal effects nearly cancel the trapping potential, and the logarithm of the partition function again exhibits simple poles in $\omega^2-\Omega_a^2$, but with a less universal residue depending separately on $\mu/T$ and $\omega/T$. As explicit examples we analyze superfluid systems realizable in cold-atom experiments, in particular
fermions at unitarity confined in a harmonic trap.
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Statistical Mechanics
Non-equilibrium generalized Langevin equation for multi-dimensional observables
Benjamin J. A. Héry, Lucas Tepper, Andrea Guljas et al. (+4 more)
The Mori-Zwanzig formalism is a powerful theoretical framework for deriving equations of motion for coarse-grained observables in the form of generalized Langevin equations (GLEs) involving
evolution and projection operators. Using a time-dependent many-body
Hamiltonian and a multi-dimensional Mori projection operator, we derive a non-
equilibrium Mori GLE for a multi-dimensional observable of interest $\vec{A}$ that consists of a Markovian force, a running integral over time of a non-Markovian friction force, and an orthogonal force that is often interpreted as a random force. We study the structure of the derived GLE in three limiting cases: when the components of $\vec{A}$ are uncorrelated, when the
Hamiltonian is time-independent and thus the system is at
equilibrium, and when both conditions are simultaneously satisfied. We highlight the presence of a contribution to the Markovian force that takes the form of an instantaneous friction force which only vanishes when the components of $\vec{A}$ are uncorrelated. Our non-Markovian framework is an important step towards the systematic modeling of the coupled kinetics of coarse-grained reaction coordinates in biological complex systems, exemplified for the coupled intra- and inter-
protein folding during fibril formation of the human islet amyloid polypeptide (IAPP).
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All authors Benjamin J. A. Héry, Lucas Tepper, Andrea Guljas, Artem Pavlov, Beate Koksch, Cecilia Clementi, Roland R. Netz
Mesoscale and Nanoscale Physics
Higher-harmonic acoustic control of laser-dressed quantum-dot states at sub-Rabi frequencies
Mateusz Kuniej, Paweł Machnikowski and Michał Gawełczyk
Acoustic control and coupling of
quantum systems via
phonons can enable miniaturized on-chip
quantum devices. Optically active
quantum dots (QDs) are essential for such platforms, yet they have long lacked direct acoustic transitions between charge states. The recently proposed hybrid acousto-optical swing-up scheme introduces such high-fidelity transitions but, as typical for coherent control, requires driving fields matching the transition energy and has been proposed for sub-THz
phonon frequencies, limiting practical implementations. Here, we overcome this limitation by exploiting higher-harmonic-assisted processes arising from strain-induced modulation of the optical transition energy. This parametric modulation of the optically dressed splitting produces multi-
phonon-like resonances when a harmonic of the mechanical modulation matches the generalized Rabi frequency. An effective model reveals a hierarchy of harmonic couplings, while our
geometric interpretation shows how modulated dressed splitting enables even harmonics that are otherwise
symmetry-forbidden. We predict faithful state preparation with an acoustic frequency being only a fraction of the splitting, specifically 42 GHz for a 0.341 THz splitting, bridging accessible acoustic frequencies and THz energy scales. This establishes control principles that separate optical energy delivery from coherent acoustic control. A non-Markovian calculation of
phonon-induced decoherence indicates high state-preparation fidelities comparable to one-
phonon and all-optical schemes. Since the same interaction structure arises for a quantized acoustic field, our results provide a foundation for multi-
phonon processes in QD-phononic-resonator systems, including
entanglement, state transfer, and optical preparation of nonclassical mechanical states.
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