Quantum Gases
Mixed bubbles in a binary mixture of spin-1 Bose-Einstein condensates
Uyen Ngoc Le, Ha Phuong Uyen Mai, Hieu Binh Le et al. (+1 more)
In mean-field theory, the ground state of a two-component Bose-Einstein condensate (BEC) in a uniform system is either uniformly mixed or totally separated. Beyond-mean-field effects introduce an additional phase, the mixed-bubble state, in which the two components remain mixed within one of the separated domains. Here we show that a mixed-bubble state can emerge in a binary mixture of
spin-1 ${}^{7}{\rm{Li}}$ and ${}^{23}{\rm{Na}}$ BECs even within the mean-field framework. We further demonstrate the existence of a metastable uniformly-mixed state, which undergoes a transition to the mixed-bubble state triggered by a local perturbation.
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All authors Uyen Ngoc Le, Ha Phuong Uyen Mai, Hieu Binh Le, Hiroki Saito
Statistical Mechanics
Excursion-Resolved Thermodynamic Inference without Observing Reverse Transitions
Jie Gu
Experiments often detect only selected transitions, leaving the underlying state dynamics and dissipation hidden. We show that waiting-time distributions between directed visible events can reconstruct the boundary dynamics without observing the reverse of every detected transition. Under a simple source-target closure condition, they determine visible rates and the hidden excursions connecting observed states, yielding a rigorous lower bound on total
entropy production that improves the standard waiting-time estimate when reverse events are available. Remarkably, observing only a spanning directed cycle is sufficient to identify the full Markov generator, even when all reverse cycle edges and other microscopic transitions remain unseen.
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Other Condensed Matter
Exact analytic solutions of classical time crystals
Stavros Theodorakis and Athina Hadjizorzi
We present examples of classical time
crystals (in a parabolic potential for the position) that admit simple exact analytic solutions. The kinetic energy in these
crystals is piecewise parabolic as a function of speed and is minimised at nonzero values of the speed. The solutions are periodic, while the speed acquires definite periodic discontinuities. The solutions are stable along the branches where the action is lower. We also examine the classical time
crystal with quartic kinetic energy. We show how the quartic kinetic energy can be emulated by a piecewise parabolic one, leading to accurate and transparent solutions.
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Strongly Correlated Electrons
Tunability of the structural and magnetic transition in kagome material: PrIr$_3$B$_2$
Gayathri V, Irshad K A, Sathishkumar M et al. (+2 more)
We report the temperature and pressure tunability of an unusual structural transformation associated with a two-step metal-
insulator-metal (MIM) transition in the kagome
lattice compound PrIr$_3$B$_2$ using synchrotron X-ray powder diffraction. At ambient conditions of temperature and pressure, the monoclinic ($C2/m$) and the hexagonal ($P6/mmm$) phases coexist as twinned structure in the
crystal. As the temperature (pressure) is decreased (increased), PrIr$_3$B$_2$ converts fully to monoclinic structure at $T =$ 280 K (at ambient pressure) and $P =$ 1.2 GPa (at room temperature). Temperature dependence of the monoclinic structure at ambient pressure presents complex
evolution of
lattice parameters with weak but clearly discernable anomalies at \SI{\sim 250} {\K} and \SI{\sim 110} {\K}, which are correlated with the second MIM transition and the linear to nonlinear temperature-dependent resistivity crossover, respectively. These anomalies are likely due to some charge order state causing a partially gapped Fermi surface. The
magnetic phase diagram of PrIr$_3$B$_2$ is also investigated from anisotropic measurements. At 10 K, a superzone gap opens near the antiferromagnetic transition, which does not close even in the polarized state. From the tunability of the
crystal structure and
magnetic and electronic ground state, promising electronic orders are indicated in this kagome metallic magnet.
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All authors Gayathri V, Irshad K A, Sathishkumar M, Boby Joseph, S. Manni
Mesoscale and Nanoscale Physics
Spin Birefringence and Spin Polarized Transmission across p-wave Altermagnetic Heterostructure
Yong-Mei Zhang and Zhi-Ping Niu
This paper investigates electron transport properties across N/AM interface or N/AM/N heterojunction. Based on
Hamiltonians in the three regions, general wave functions are proposed and combined linear equations are constructed. Reflection and transmission coefficients as well as
spin polarizatioin of the altermagnet
heterostructure are obtained. When electron incident from normal metal to altermagnet, it is scattered and split into + branch and _ branch transmitting into altermagnet zone with separate refractive angles. Total internal reflection might happen to + branch. Critical angle of total reflection is determined by incident conditions and properties of AM material. In the
heterostructure case,
spin-up and
spin-down electrons transmitted with same propagation directions but different transmission probabilities. Transmission and polarization periodically change with length of the junction. Exchange field and
spin-splitting strength have pronounced effect on
spin-polarized transmittance while the effect of
spin-orbit coupling is quite small. Optimized system can be found by tuning parameters of the AM material. This study will lay the theoretical groundwork for experimental research on
spin-selective outputs and spintronic devices.
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Superconductivity
Spectroscopic Evidence for Nontrivial Band Topology in Superconducting FeTe/MnTe Heterostructure
Shiwu Su, Yu Liang, Tongrui Li et al. (+14 more)
FeTe has long been regarded as a nonsuperconducting antiferromagnetic metal with trivial band
topology, but recent advances in stoichiometry control have begun to challenge this picture. Here we use higher-order epitaxy on zinc-blende MnTe to stabilize near-stoichiometric FeTe with strongly suppressed interstitial Fe and a superconducting transition onset near 13 K. Angle-resolved photoemission spectroscopy reveals markedly enhanced quasiparticle coherence, well-defined Fe-derived hole bands, and a nearly two-dimensional Dirac-cone-like state near the Fermi level. First-principles calculations identify an inversion between odd- and even-parity bands, yielding nontrivial $Z_2$
topology and a Dirac surface state consistent with experiment. These results elucidate the intrinsic electronic structure of stoichiometric superconducting FeTe and provide evidence for nontrivial band
topology, positioning FeTe/MnTe as a promising platform for exploring topological superconductivity.
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All authors Shiwu Su, Yu Liang, Tongrui Li, Zhen Wang, Yuzhe Wang, Xianglin Li, Sen Liao, Pengxu Ran, Jiexiong Sun, Shengtao Cui, Zhe Sun, Zhengtai Liu, Jishan Liu, Mao Ye, Jing Tao, Donglai Feng, Juan Jiang
Statistical Mechanics
Interdependent-Network Criticality without a Second Network: Cascading Collapse of the Joule-Coupled Insulator-Metal Transition in $VO_2$
Ouriel Gotesdyner, Michal Wasserman, Hodaya Kaster et al. (+5 more)
When driven by a large enough electric field or current, the insulating state of vanadium dioxide ($VO_2$) typically collapses abruptly into the metallic state (the
insulator-metal transition, IMT) following a brief incubation delay. These incubation delays, typically lasting microseconds or less, have been analyzed predominantly through macroscopic electro-thermal modeling, providing little statistical insight into the transition dynamics. Here, we investigate the electrically driven IMT in a two-dimensional $VO_2$
lattice and demonstrate that the material behaves as a complex, interdependent network despite being a single structural entity. Because metallic domains dissipate significantly more Joule heat than insulating regions, each switching event raises the Joule heating of the network, resulting in network dependency and triggering a cascading chain reaction. Combining time-resolved resistance measurements with a Joule-coupled resistor-network model and interdependent-network theory, we observe an abrupt (first-order) transition preceded by an anomalously long incubation plateau lasting thousands of seconds. During this metastable plateau, an effective branching factor of the switching activity approaches unity at criticality, and the plateau lifetime diverges with exponent $\zeta=1/2$; the order parameter scales with exponent $\beta=1/2$. These signatures coincide with those predicted for interdependent networks, indicating that dissipative Joule coupling alone can drive mixed-order catastrophic cascades in a single-network correlated-oxide system.
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All authors Ouriel Gotesdyner, Michal Wasserman, Hodaya Kaster, Yosi Abulafia, Avital Fried, Bnaya Gross, Shlomo Havlin, Amos Sharoni
Materials Science
Nature of the 175-180 cm$^{-1}$ Raman Feature in Altermagnetic $\alpha$-MnTe
Pankaj Bhardwaj, Rajib Sarkar, Naresh Shyaga et al. (+6 more)
The 175 cm$^{-1}$ Raman mode in $\alpha$-MnTe has long been assigned to the material's only
symmetry-allowed
phonon ($E_{2g}$), yet first-principles calculations consistently place this mode below 100 cm$^{-1}$. Recent works have offered three competing explanations for the discrepancy: a weak
symmetry-lowering ($D_{6h}\rightarrow D_{3h}$)
phonon, an electronic plasmon arising from intrinsic hole self-doping, or an extrinsic MnTe$_2$ impurity signature. Here we resolve this controversy using stoichiometry-controlled molecular beam epitaxy (MBE). We deliberately vary the fraction of pyrite-type MnTe$_2$ secondary phase relative to the $\alpha$-MnTe
matrix. Across this series, the 175 cm$^{-1}$ mode tracks the presence of MnTe$_2$ essentially one-to-one – present wherever MnTe$_2$ is detectable, absent in stoichiometric, single-phase $\alpha$-MnTe at nominal
LASER powers. When
LASER power is ramped up, an additional mode emerges in MnTe as well positioned close to $\approx$ 175 cm$^{-1}$; our detailed temperatures dependendent Raman analysis identifies the
LASER power scorched region close to a distorted MnTe phase, confirmed via transmission electron microscopy. This direct, growth-controlled correlation identifies the mode as an extrinsic MnTe$_2$ impurity signature or as a distorted MnTe feature, rather than an intrinsic
phonon or plasmon feature, providing a practical diagnostic for phase purity in MBE-grown $\alpha$-MnTe and clarifying which Raman features can be reliably attributed to the intrinsic altermagnetic phase.
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All authors Pankaj Bhardwaj, Rajib Sarkar, Naresh Shyaga, Subhransu Kumar Negi, Kartick Biswas, Susmita Jana, Pavan Nukala, B. R. K. Nanda, Dhavala Suri
Materials Science
Three-Dimensional Topology from Stacking-Controlled Umklapp Scattering in Large-Angle Twisted Graphite
Juncheng Li, Cong Chen and Wang Yao
Large-angle twisted
graphene lies beyond the local-stacking description of conventional moiré systems: inequivalent rotation centers define distinct commensurate interfaces whose low-energy interlayer hybridization is governed by intervalley Umklapp tunneling. For three-dimensional twisted graphite assembled from interfaces with different crystalline
symmetries, a
symmetry-constrained effective model reveals that competition between nonchiral and chiral tunneling produces one-ring and two-ring nodal-line phases and a $C_3$-protected higher-order topological
insulator in the presence of sublattice (chiral)
symmetry. The nodal rings carry integer winding numbers, allowing oppositely wound rings to annihilate into the gapped phase. We further examine how sublattice-
symmetry breaking modifies these phases. Density functional theory (DFT) and atomistic calculations for $21.8^\circ$ twisted graphite identify the
equilibrium structure as a higher-order topological
insulator, while compression drives it into a topological Weyl semimetal phase. These findings establish the stacking sequence of
symmetry-inequivalent interfaces as a means of engineering band
topology in three-dimensional twisted structures.
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Materials Science · Cross-listed from physics.chem-ph
A strategic roadmap for an atomistic machine-learning ecosystem
Jörg Behler, Michele Ceriotti, Cecilia Clementi et al. (+47 more)
Data-driven machine learning (ML) techniques have become an essential tool in many domains of science. Their application to atomistic simulations of matter is particularly widespread and impactful. This success is due largely to the existence of a well-developed and established physics-based modeling framework, ranging from first-principles electronic-structure calculations to molecular dynamics and statistical sampling, into which ML was integrated naturally to reshape long-standing trade-offs between accuracy, efficiency, and scale. Nevertheless, this integration raises both conceptual and practical challenges, from choosing between data-centric and physics-based modeling approaches to adapting established software stacks to modern hardware accelerators and ML libraries. As the field evolves rapidly, fueled in part by widespread enthusiasm but also by tangible impact, it seems appropriate to take a moment to consider the current state of the art and open challenges, and reflect on what can be done to better coordinate efforts across the community. With this goal in mind, several members of this community met in Lausanne in January 2026 at CECAM to discuss
algorithms, models, software and hardware infrastructure, and the most promising scientific applications that have become possible thanks to the use of artificial intelligence in atomic-scale simulations. This strategic roadmap paper summarizes the outcomes of these discussions, suggesting some long-term goals, and some concrete actions, to establish a healthy, sustainable and impactful atomistic ML ecosystem.
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All authors Jörg Behler, Michele Ceriotti, Cecilia Clementi, Gábor Csányi, Alin-Marin Elena, Aditi Krishnapriyan, Joseph W. Abbott, Fabio Affinito, Albert P. Bartók, Ilyes Batatia, Filippo Bigi, Florian N. Brünig, Yannick Calvino Alonso, Giuseppe Carleo, Aurélie Champagne, Stefan Chmiela, Marc L. Descoteaux, Ralf Drautz, Alexandra Farcas, Meng Gao, Rohit Goswami, Michael F. Herbst, Christian Holm, James R. Kermode, Alexander L. M. Knoll, Tobias Kreiman, Marcel F. Langer, Hoang-Thien Luu, Yury Lysogorskiy, Mihai-Cosmin Marinica, Rocco Meli, Klaus-Robert Müller, Frank Noé, Mohamadhosein Nosratjoo, Simon Olsson, Christoph Ortner, Aldo S. Pasos-Trejo, Anyang Peng, Eric Qu, Andrea Rizzi, Mariana Rossi, Bassem Sboui, Gregor N. C. Simm, Alexandre Tkatchenko, Jacopo Venturin, O. Anatole von Lilienfeld, William C. Witt, Brandon M. Wood, Tigany Zarrouk, Fabian Zills
Statistical Mechanics · Cross-listed from quant-ph
Engineered Dissipation for Thermal-State Tracking Across Quantum Criticality
Saikat Mistry, Dibyajyoti Sahu and Suhas Gangadharaiah
Engineering dissipation has emerged as a powerful strategy for controlling
quantum many-body dynamics, complementing purely coherent control for state preparation. However, finite-time driving across a
quantum critical point generates nonadiabatic excitations and coherences, and existing dissipation-engineering approaches have largely characterized how a fixed environment modifies critical dynamics rather than actively steering a system toward a prescribed thermal trajectory. Here we develop a Markovian dissipative framework for finite-time thermal-state tracking based on engineered population currents with non-negative transition rates, and apply it to the transverse-field Ising model driven across its
quantum critical point. Compared with
unitary dynamics and a natural thermal bath, the engineered dynamics strongly suppresses thermal excitation deviations and provides additional control over coherence damping through a free common current $Q_k$, while exhibiting a substantially steeper residual scaling, $\delta n_{\mathrm{ex}}^{\mathrm{th}}\sim(v/v_{\mathrm{ch}})^2$, than the Kibble–Zurek behavior recovered for
unitary evolution. These results point toward engineered dissipation as a route for controlling thermal-state preparation in driven
quantum critical systems.
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Materials Science
Operando Charge Carrier Dynamics by Intensity-Modulated Photoluminescence: From Perovskite Thin Films to Solar Cells
Constantin Bach, Dong Won Kim, Yitian Du et al. (+2 more)
The charge-carrier lifetime in halide perovskites often varies by orders of magnitude with the injection level, complicating the analysis of conventional time-resolved photoluminescence and comparisons of reported lifetimes. We use intensity-modulated photoluminescence spectroscopy (IMPLS) as a frequency-domain alternative. Carried out under operating conditions, it yields the lifetime at a specific injection level, e.g., one-sun-equivalent illumination. On thin films, IMPLS and steady-state photoluminescence yield comparable lifetimes. For perovskite/transport-layer stacks, the IMPLS response becomes more complex. A dedicated transfer function disentangles charge transfer from interface recombination and predicts an upper limit on the charge-carrier lifetime in the solar
cell. In devices, electrical methods such as intensity-modulated photovoltage spectroscopy (IMVS) often fail to measure the lifetime due to capacitive effects. IMPLS shows not only the same two characteristic frequencies as IMVS, but also a third one, thereby resolving the lifetime itself.
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All authors Constantin Bach, Dong Won Kim, Yitian Du, Yana Vaynzof, Carsten Deibel
Materials Science · Cross-listed from physics.chem-ph
An atom-based machine-learned dipole-moment model and application to conjugated systems
Yuansheng Zhao, Tamio Yamazaki, Ryohei Hosoya et al. (+2 more)
We introduce a method for predicting the dipole moments of molecular systems by systematically decomposing the total dipole moment into the sum of atomic contributions using the wavefunction from density-functional-theory calculations, and then use graph neutral networks to predict this effective atomic dipole moment from input atomic structure. It is demonstrated that the dipole moments and dielectric function can be accurately predicted even for complicated conjugated systems where the previous bond-based model [Phys. Rev. B 110, 165159] fails. The inference cost of our model scales linearly with the number of atoms and is about 3 times faster compared with Born-effective-charge-based schemes, but shows similar or better accuracy for dielectric function at terahertz range.
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All authors Yuansheng Zhao, Tamio Yamazaki, Ryohei Hosoya, Yu-ichiro Matsushita, Shinji Tsuneyuki
Statistical Mechanics
Reference-Measure Freedom of the Effective Hamiltonian: From Stochastic Thermodynamics to the Macroscopic Limit
Ryuichi Okamoto
The effective
Hamiltonian (EH), also referred to as the potential of mean force or free-energy landscape, is widely used to describe
equilibrium properties and slow dynamics in chemical and soft-matter systems. However, the conventional EH has been argued to be ill-defined because it does not transform as a scalar under coordinate transformations. We identify an implicit change of reference measure (gauge), rather than the coordinate transformation itself, as the origin of this apparent problem. We formulate the EH as a scalar relative to a chosen gauge and derive the intrinsic, gauge-independent Fokker–Planck equation (FPE) on the
manifold of slow variables. The conventional EH and the
diffusion-dependent EH introduced in a Riemannian formulation, together with their corresponding FPEs, are thus different gauge representations of the same
equilibrium measure and intrinsic
stochastic dynamics. We further demonstrate that the gauge choice has an operational meaning: different restraint protocols select different reference measures. In the macroscopic limit, the leading EH becomes gauge independent within a class of subleading gauges and is determined by the large-deviation rate function. In the same limit, the
stochastic dynamics reduces to gauge-independent deterministic dynamics.
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Strongly Correlated Electrons
Eigenstate thermalization at the edge of the many-body spectrum
Arnav Pushkar, Pranay Patil, Soumya Bera et al. (+2 more)
It is well-known that thermalization breaks down in presence of an extensive number of
symmetries or conservation laws that are mutually compatible or commuting with each other. We ask here how an extensive number of mutually incompatible local
symmetries govern eigenstate thermalization (ETH). We will investigate this through models within the class of bond-dependent $\mathbb{Z}_2$-symmetric
quantum spin-$\frac{1}{2}$
Hamiltonians that naturally admit this structure. This leads to exponentially large degeneracies in the spectrum governed by the incompatible
symmetry structure. Here, using spectral diagnostics, we show that non-integrability can survive despite extensively many conserved quantities when they are incompatible. Furthermore, we show that ETH behavior persists deep into the many-body spectral edge due to this structure. In other words, incompatible local
symmetries enable a mechanism to obtain enough thermodynamic
entropy at low excitation energy densities to make ETH operational or predictive near the ground state.
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All authors Arnav Pushkar, Pranay Patil, Soumya Bera, Masaki Tezuka, Sumiran Pujari
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Quantum-echo Markov process for combinatorial optimization
Tatsuhiko Shirai
We introduce a
quantum-echo Markov process for combinatorial optimization.
Quantum dynamics based on
quantum annealing (QA) or the
quantum approximate optimization
algorithm (QAOA) is used to engineer the transition kernel. Increasing the annealing time in QA or the number of layers in QAOA enables transitions to explore distant configurations while suppressing large energy changes. The Hamming-space delocalization originates from operator spreading, whereas the energy-space localization arises from a dynamically generated correlation. For optimization, we propose
quantum-echo local optimization with and without greedy descent. We find that its performance is governed by the interplay between Hamming-space nonlocality and energy-space locality, and that excessive energy-space localization can degrade optimization performance. Incorporating greedy descent substantially improves the performance, highlighting the complementary roles of
quantum dynamics for exploration and greedy descent for exploitation. These results establish
quantum-echo dynamics as a framework for engineering structured transition kernels and provide a route to using finite-resource
quantum many-body dynamics as a computational primitive for iterative optimization.
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Materials Science
First-Principles Study of Two-Dimensional CeN: Interplay between Structural Stability, Electronic Structure, and Magnetism
Jose Mario Galicia Hernandez, Jose Jorge Rios Ramirez, Gregorio Hernandez Cocoletzi et al. (+1 more)
In this work, the structural stability, and the electronic and
magnetic properties of a novel CeN monolayer derived from the (111) surface of bulk rock salt CeN are investigated using first-principles calculations. Dimensional reduction produces substantial changes in the local atomic environment, decreasing the Ce-N coordination from sixfold in the bulk to threefold in the monolayer and shortening the Ce-N bond length, while preserving an essentially planar hexagonal structure. Moreover, the electronic and
magnetic properties are significantly modified, which may be useful for practical applications. Both ferromagnetic (FM) and antiferromagnetic (AFM) configurations were investigated and found to be strongly bound, with the FM state slightly lower in energy. The
magnetic moments are predominantly localized on the Ce atoms and mainly originated from the Ce 4f states. The electronic structure also exhibits a pronounced dependence on
magnetic ordering, highlighting the connection between localized 4f states and the
spin-dependent electronic properties of the system. In addition, the calculated elastic properties confirm the mechanical stability of the monolayer, while
phonon calculations support its dynamical stability. Ab initio molecular dynamics simulations further indicate that the two-dimensional structure preserves its integrity under finite-temperature conditions. Overall, these results demonstrate that dimensional reduction significantly modifies the structural, electronic, and
magnetic behavior of CeN without compromising the stability of the resulting two-dimensional
lattice. The combination of structural robustness, localized Ce 4f magnetism, and
spin-dependent electronic properties make the CeN monolayer an interesting system for further exploration in two-dimensional magnetism and
spin-dependent applications.
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All authors Jose Mario Galicia Hernandez, Jose Jorge Rios Ramirez, Gregorio Hernandez Cocoletzi, Juan Francisco Rivas Silva
Strongly Correlated Electrons · Cross-listed from quant-ph
Optical studies of negative g-factor dopants in an antiferromagnet: Nd:GdVO$_4$
Lachlan W. Cronin, Masaya Hiraishi, Luke S. Trainor et al. (+1 more)
Neodymium-doped gadolinium vanadate (Nd:GdVO$_4$) is a popular
laser material at room temperature. It has received limited
attention for
quantum technologies because of the linebroadening effects of disordered gadolinium
spins in the host. Here we investigate the optical properties at temperatures below the 2.5 K Néel temperature, revealing narrow optical transitions. We demonstrate that rare earth ions in
magnetic hosts give us a new way of observing the signs of
magnetic g-factors. The interplay between the exchange and Zeeman interactions means that we see clear evidence of negative g-factors. These results provide a detailed spectroscopic foundation for Nd:GdVO$_4$ and expand the understanding of its candidacy as a material for hybrid
quantum systems.
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All authors Lachlan W. Cronin, Masaya Hiraishi, Luke S. Trainor, Jevon J. Longdell
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Surface quantum response of plasmonic heterodimers: revealing the hidden nonlocality
Ida Juliane Bundgaard, Christos Mystilidis, Frederik Wulff Christensen et al. (+7 more)
We probe the
quantum response of plasmonic heterodimers with extended (plane waves) and localized (point dipoles and electron beams) sources. Implementing the surface-response formalism based on Feibelman parameters, we explore nanosphere heterodimers where one particle is characterized by electron spill-in, while the other by spill-out. We identify situations where the two
quantum surface corrections that act in opposite spectral-shift directions can cancel out, producing mesoscopic spectra that do not differ from the predictions of the local-response approximation. This picture changes dramatically once localized sources are implemented, allowing one to selectively probe the
quantum response of the particles independently. Such probing occurs in terms of higher-order modes in the case of electron beams, or for the complete modal landscape in the case of point dipole sources. This description offers a new insight into the mechanisms governing light–matter interactions in extreme plasmonic architectures, and opens new perspectives for the understanding and tailoring of plasmonic–
quantum emitter architectures.
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All authors Ida Juliane Bundgaard, Christos Mystilidis, Frederik Wulff Christensen, Lorenz Huber, P. Elli Stamatopoulou, Carsten Rockstuhl, P. A. D. Gonçalves, Ulrich Hohenester, N. Asger Mortensen, Christos Tserkezis
Strongly Correlated Electrons
Quantum quenches of scar states in the Affleck-Kennedy-Lieb-Tasaki model via Clifford augmented tensor network simulation
Azar C. Nakhl, Ben Harper, Muhammad Usman et al. (+1 more)
Clifford augmented methods have emerged as a powerful technique to simulate
quantum circuits and many-body systems by exploiting the stabiliser structure found in said systems, whilst additionally enabling one to readily quantify the non-stabilizerness (i.e.\ magic) present. In this work, we utilise a qudit Clifford augmented simulation method to probe the presence of magic in the Affleck-Kennedy-Lieb-Tasaki (AKLT) model, finding that its ground state and scar states are highly magical as quantified by their Stabiliser Rényi
Entropy (SRE). Nevertheless, owing to its low
entanglement structure, these states are still readily expressible as a Clifford augmented
Matrix Product State with low bond-dimension and moreover may be time-evolved using the Clifford augmented time-dependent variational principle (TDVP)
algorithm. We utilise Clifford augmented TDVP to study the string order dynamics in the scar states of the AKLT model after a quench within the Haldane phase to the anti-ferromagnetic Heisenberg
Hamiltonian. We observe that there is a decay of string order following the quench, which is more pronounced with increasing bimagnon number. This finding highlights the sensitivity of string order in the AKLT scar states to
symmetry-preserving quenches, even when the initial and final
Hamiltonians belong to the same topological phase.
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All authors Azar C. Nakhl, Ben Harper, Muhammad Usman, Thomas Quella
Materials Science
Defect Dynamics and Isomer Quenching in $^{229}$Th:CaF$_2$ Crystals
Ming Guan, Michael Bartokos, Kjeld Beeks et al. (+16 more)
Thorium-229 doped calcium fluoride ($^{229}$Th:CaF$_2$) is a leading candidate for a solid-state nuclear clock, owing to the unusually low energy of the $^{229}$Th isomer transition at 8.3557\,eV and the very high banggap of CaF$_2$ around 12\,eV. Here we report a temperature-dependent study of $^{229}$Th:CaF$_2$ luminescence, covering radioluminescence, photoluminescence, thermoluminescence, and afterglow. Using synchrotron x-ray excitation together with a cryo-
vacuum system, we resolve the thermal quenching of the self-trapped
exciton (STE) scintillation into its triplet and singlet components, identify eleven thermoluminescence glow peaks together with their associated emission bands, and separate the temperature-dependent components that make up the long-lived afterglow. The trap depths obtained in this way are closely correlated with the temperature dependence of x-ray-induced isomer quenching, including the enhanced isomer yield near \SI{-60}{\celsius} and the minimum near \SI{-80}{\celsius}, supporting the carrier-trapping picture in which trapped carriers are unavailable to quench the
nucleus. Taken together, these results connect the optical and nuclear observables of $^{229}$Th:CaF$_2$ through a unified picture of electron defects and Th-related traps, while providing a comprehensive characterization of the material relevant to solid-state nuclear clock operation.
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All authors Ming Guan, Michael Bartokos, Kjeld Beeks, Takahiro Hiraki, Shinji Kitao, Takahiko Masuda, Nobumoto Nagasawa, Koichi Okai, Ryoichiro Ogake, Martin Pimon, Noboru Sasao, Fabian Schaden, Thorsten Schumm, Makoto Seto, Kenji Tamasaku, Sayuri Takatori, Yoshitaka Yoda, Akihiro Yoshimi, Koji Yoshimura
Mesoscale and Nanoscale Physics
Optical observation of interlayer spin correlation
Akiyoshi Park, Pranshoo Upadhyay, Andrey Grankin et al. (+16 more)
Spin correlations govern numerous collective behaviors of
quantum materials, underpinning exotic phenomena such as unconventional superconductivity and topological magnetism. In layered materials, the interlayer
spin correlation is important because it characterizes the
magnetic ground state and determines
spin transport across the interface. Yet interlayer
spin correlations have remained hard to measure directly, leaving one of the most basic quantities of two-dimensional magnetism out of experimental reach. Here we provide the first direct optical probe of interlayer
spin correlations, using two-
magnon Raman scattering in the van der Waals antiferromagnet (AFM) CrSBr, in remarkable agreement with a microscopic
spin-wave model without any fitting parameter. Moreover, the two-
magnon channel switches on only in the AFM state and vanishes when a
magnetic field takes the
crystal to a ferromagnetic state. We furthermore establish an
exciton-mediated variant of the technique, where tuning the
laser near the
exciton resonance enhances the signal roughly tenfold due to the
exciton's large oscillator strength.
Magnon-pair Raman spectroscopy thus opens a direct optical window into interlayer
spin correlations in van der Waals magnets, extendable to twisted bilayers and proximity-coupled
heterostructures.
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All authors Akiyoshi Park, Pranshoo Upadhyay, Andrey Grankin, Emil Viñas Boström, Mahdi Ghafariasl, Hassan Alnatah, Masoud Mohammadi-Arzanagh, Gautam Nambiar, Beini Gao, Alireza Alvandi, Sakthi Rajmano Madhan Kumar, Ghadah Alshalan, Isaac Sherwood, Mahmoud Jalali Mehrabad, You Zhou, Arun Ramanathan, Xavier Roy, Angel Rubio, Mohammad Hafezi
Disordered Systems and Neural Networks
Synchronous Monte Carlo method and its application to a mean-field spin glass model
Yoshiyuki Kabashima
Standard Markov chain Monte Carlo methods update variables one at a time to satisfy detailed balance, which prevents them from fully exploiting massively parallel hardware such as graphics processing units (GPUs). We study a Monte Carlo method for systems with pairwise interactions in which all variables are updated simultaneously, made possible by auxiliary Gaussian fields introduced through the Gaussian integral identity. The method satisfies detailed balance and is therefore guaranteed to converge to the canonical distribution. For mean-field
spin glasses, its dynamics can be analyzed exactly by dynamical mean-field theory (DMFT). Applying the method and the DMFT to the random orthogonal model, which exhibits a random first-order transition, we find that the fluctuation-dissipation
theorem (FDT) is clearly violated below the dynamical transition temperature, and that the relation between response and correlation takes the two-slope form of a generalized FDT, with simulations and theory in quantitative agreement.
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Materials Science
Polymorph-Tunable Spin Texture and Excitonic Structures in Monolayer WSi2P4
Xianbo Chenwei, Yu Zhou, Ke Wu et al. (+6 more)
Two-dimensional
semiconductors that simultaneously possess a direct band gap and strong
spin-orbit coupling (SOC) are highly attractive for
quantum optoelectronics. Using first-principles GW plus Bethe-Salpeter equation (GW-BSE) calculations, we show that monolayer WSi2P4-an experimentally accessible member of the MSi2X4 family-hosts a direct K-valley gap together with strong SOC. Its three competing polymorphs (alpha, beta and gamma) are all direct-gap
semiconductors and are kinetically locked behind 1.3 eV migration barriers. The sigma_h mirror plane of the D3h of alpha and gamma phases enforces a persistent
spin texture across the Brillouin zone, weakly modulated near gamma by interband SOC mixing, whereas the polar beta phase (C3v) exhibits Rashba
spin splitting. SOC splits the doubly-degenerate lowest bright
exciton into dark states and splits the original absorption peak into two peaks (A and B), whose relative brightness is governed by the K-valley conduction-band splitting. alpha-WSi2P4 displays the brightest Peak A because a tiny band crossing of opposite-
spin branches can open a
spin-allowed radiative channel. These results establish the MSi2P4 family as a phase-tunable platform for the cooperative engineering of
spin texture, band splitting, and excitonic brightness within a single material system.
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All authors Xianbo Chenwei, Yu Zhou, Ke Wu, Gaofeng Xu, Ruixue Li, Yuan Li, Yabei Wu, Shaowen Xu, Fanhao Jia
Strongly Correlated Electrons
Sign problem and criticality in world-line quantum Monte Carlo methods
Rubem Mondaini and Richard T. Scalettar
Discussions of the sign problem usually focus on its role as the primary limitation of the applicability of
quantum Monte Carlo methods for reliably solving
quantum many-body models. Its behavior as a function of spatial
lattice size, doping, temperature, and interaction strengths has been carefully characterized within the determinant
quantum Monte Carlo
algorithm. Here, we consider the much less well-explored question of the temperature- and size-dependence of the sign problem in the world-line
quantum Monte Carlo method. We review how, in this
algorithm, even sampling the partition function of free
fermions yields a sign problem, which we connect to non-analytic behavior in the corresponding reference model, hard-core
bosons on a
lattice. The latter exhibits a finite-temperature Kosterlitz-Thouless phase transition in 2D, and we show how this non-analytic behavior is imprinted on the average sign of the weights for the corresponding free
fermion 2D tight-binding model. Our results thus show how phase-transition information can remain encoded in the sign problem even after direct sign sampling becomes impractical.
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Statistical Mechanics · Cross-listed from quant-ph
Ergotropy from energetic coherence and the third law of thermodynamics
O. S. Yáñez-Soria, G. Guarnieri, B. Çakmak et al. (+1 more)
We study the ergotropy and the thermodynamic potentials of a
qubit battery charged by repeated interactions with clusters of thermal ancillas,
qubits or oscillators, through a composite system-bath coupling that generates steady-state coherence in the energy basis. A single parameter encoding the bath
quantum statistics yields the coherence and ergotropy in closed form for any cluster size. For large clusters, the ergotropy becomes independent of the bath statistics and, at optimal couplings, reaches a universal fraction of the
equilibrium internal energy of the
qubit at the bath temperature. Since the charged state has no population inversion, all extractable work comes from coherence. The ergotropy is flat at low temperatures. We trace this plateau to the third law, and show that the ergotropy is proportional to the
equilibrium enthalpy of the
qubit, whose slope vanishes with the heat capacity. For a battery composed of multiple
qubits, the coherence grows exponentially with the number of
qubits while the ergotropy grows linearly, both remaining a nearly constant fraction of their respective maxima. The charged state is a non-
equilibrium steady state with finite
entropy at zero temperature, sustained by the work of switching the collisional interaction on and off. The cost is nonzero whenever the parallel coupling is nonzero, and, unlike the ergotropy, it depends on the bath statistics.
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All authors O. S. Yáñez-Soria, G. Guarnieri, B. Çakmak, R. Román-Ancheyta
Materials Science
Dense and porous phase transition study of SEI formation using phase-field method
Joonyeob Jeon, Lukas Kobbing, Tejs Vegge et al. (+3 more)
The solid electrolyte interphase (SEI) is essential for the long-term stability of batteries because it influences the reactions between the electrode and electrolyte. Despite previous studies, the SEI
evolution from dense to porous phases remains incompletely understood. Here, we investigate the SoC-dependent
evolution of the SEI using a phase-field framework under open-
circuit conditions. Spatially correlated noise is introduced to describe
stochastic transport perturbations, and the dense-to-porous transition time is evaluated from the
evolution of interface roughness arising from the competition between noise-induced transport and surface relaxation. The simulations reveal three distinct roughness
evolution regimes. The predicted transition time generally increases from approximately one month at 20% SoC to more than seven months at 80% SoC, with a pronounced change between 55% and 60%. This change corresponds to the graphite SoC-OCV relation, which controls the interfacial Li0 radical concentration through the Nernst condition. Under dynamic SoC conditions caused by irreversible capacity loss, the transition behavior changes as the SoC evolves during storage. These results show that the SoC-OCV relation is central to determining SEI phase stability and the dense-to-porous transition time under open-
circuit storage.
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All authors Joonyeob Jeon, Lukas Kobbing, Tejs Vegge, Jin Hyun Chang, Birger Horstmann, Ivano Eligio Castelli
Materials Science · Cross-listed from math.AP
Magnetic Stabilization of the Greenhill Instability and Hysteretic Switching in Slender Rods
Vivekanand Dabade, Likhit Ganedi, Mohd Tahseen et al. (+1 more)
In a bulk ferromagnet,
magnetic energy is six orders of magnitude weaker than elastic energy. Slenderness removes this disparity. In a thin ferromagnetic rod, the two energies scale differently with aspect ratio, and an ordinary nickel wire deforms nonlinearly even under modest remote fields. We develop a three-dimensional variational theory of a ferromagnetic Kirchhoff rod under
gravity and
magnetic loading and study it through bifurcation analysis, computation, and experiment. A uniform field can stabilize a vertical rod against buckling under its own weight, the classical Greenhill instability. We give sharp criteria for clamped and pinned supports in terms of an Airy-type principal
eigenvalue, and give a fine description of the character of the bifurcation landscape, which has qualitatively different features than its non-
magnetic counterpart. When subject to the field generated by a permanent magnet, we identify a rich bifurcation landscape as the magnet is rotated quasistatically along a circle of radius slightly larger than the rest length of the rod. We prove that instability occurs only through a planar mode and that each snap is a nondegenerate saddle-node. We also locate the two folds that produce hysteresis. Experiments on $50\,\mu$m nickel wires confirm the Greenhill threshold, restabilization at ~$30$ mT for both clamped and pinned supports, as well as the salient features of the hysteresis loop such as switching angles, width, and geometry of folds accurately. Our analysis and experiments offer principled design rules for field-stabilized filaments and remotely switched bistable actuators. Our analysis also offers a well-conditioned numerical method is valid near the switching events, where the direct numerical minimization is strongly ill-conditioned.
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All authors Vivekanand Dabade, Likhit Ganedi, Mohd Tahseen, Raghavendra Venkatraman