Statistical Mechanics
Strongly-connected percolation on directed lattices
M. E. J. Newman, P. Grassberger and R. M. Ziff
We study percolation on
lattices with directed bonds, focusing on the behavior of strongly-connected percolation clusters – clusters in which every site is reachable from every other along a directed path. We consider the two-dimensional square
lattice and various globally isotropic arrangements of the directions of the bonds. Performing simulations using a range of algorithmic approaches, we calculate high-precision values for critical exponents, fractal dimensions, crossing probabilities, and percolation thresholds for bond percolation with each bond arrangement. We find that the critical behavior is in a distinctly different universality class from that of traditional undirected percolation, but that all bond arrangements appear to fall in the same universality class.
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Statistical Mechanics · Cross-listed from quant-ph
A Kernel-Based Density of States Estimator for Quantum Computing
Julio Cesar Siqueira Rocha
The density of states (DoS) encodes the thermodynamic and spectral properties of
quantum many-body systems, yet its reconstruction becomes intractable for
Hilbert spaces too large to diagonalize. Classically, the kernel
polynomial method (KPM) addresses this by combining
stochastic trace estimation with a smoothing kernel. Here we show that the Rodeo
algorithm—one of the simplest
eigenvalue-location protocols for near-term
quantum hardware—provides a direct
quantum analogue of this approach. Averaging the Rodeo response over Haar-random input states yields the DoS convolved with a spectral kernel fixed entirely by the distribution of
evolution times: the random states play the role of
stochastic trace estimation, and the temporal sampling distribution that of the damping kernel. The construction requires only the standard single-ancilla
circuit, and
quantum typicality suppresses the statistical error as the
Hilbert-space dimension grows. We derive the
estimator and its uncertainties, establish an explicit dictionary between signal-processing window functions and
quantum reconstruction kernels, and validate the method on the one-dimensional transverse-field Ising and
spin-1 models.
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Mesoscale and Nanoscale Physics
A.-F. Kalo, E. A. Rodríguez-Mena, J. C. Abadillo-Uriel et al. (+2 more)
Unstrained bulk germanium is a particularly attractive material for
circuit quantum electrodynamics with
spins (
spin-cQED). We show, through systematic modeling and comparison with state-of-the-art strained germanium
heterostructures, that hole
spins in bulk germanium double
quantum dots readily reach the strong-coupling regime with superconducting microwave resonators, achieving
spin-
photon coupling strengths $g_s/2\pi\gtrsim100$\,MHz. This enhancement originates from large
spin-orbit interactions beyond the perturbative regime. In addition, the coupling is much less sensitive to the orientation of the applied
magnetic field, which shall ease operation and limit the impact of device-to-device variability. Our results establish bulk germanium as a compelling platform for scalable
spin-cQED.
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All authors A.-F. Kalo, E. A. Rodríguez-Mena, J. C. Abadillo-Uriel, M. Filippone, Y.-M. Niquet
Strongly Correlated Electrons
Chiral Magnons: Mechanisms and Research Progress
Wanxing Lin, Hanchen Deng, Bao-Tian Wang et al. (+1 more)
Chiral magnons are distinctive collective
spin excitations in
magnetic ordered systems, whose dispersion relations break momentum-inversion
symmetry, $\omega(\boldsymbol{k}) \neq \omega(-\boldsymbol{k})$, resulting in essential non-reciprocal
spin-wave propagation. This built-in directionality provides new opportunities for
spin information transfer, thermal-
spin interconversion, and low-dissipation non-reciprocal microwave devices, which complement but differ from topological magnonics. In recent years, the proposal and rapid development of altermagnetism have broadened the physical origin and research framework of
chiral magnons, making them a research frontier in condensed matter physics. This review presents a unified framework for
chiral magnons, covering
symmetry-breaking mechanisms, material implementation, experimental characterization, transport response, and many-body non-Hermitian dynamics, and evaluates routes toward room-temperature and device-related platforms. The discussion is based on
symmetry analysis, model
Hamiltonians, and
spin-wave theory, combined with first-principles calculations as well as recent spectroscopic (e.g., inelastic and polarized
neutron scattering, Brillouin light scattering) and transport measurements. This review further summarizes bulk-gap and Berry-
curvature induced
chiral magnon edge states, the enhancement of non-reciprocity via
chiral spin pumping and cavity-
magnon hybrids, as well as non-Hermitian features arising from multiparticle damping and gain-loss competition. This review provides a comprehensive reference for elucidating the underlying mechanisms of
chiral magnons, advancing the synthesis and experimental characterization of novel materials, and also guiding the design of next-generation non-reciprocal magnonic devices.
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All authors Wanxing Lin, Hanchen Deng, Bao-Tian Wang, Dao-Xin Yao
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Non-Hermitian entropy production from fluctuation theorems
Vasco Cavina, Frank Ernesto Quintela Rodríguez and Donato Farina
We develop a first-principles thermodynamic framework for non-Hermitian dynamics based on a post-selected version of the fluctuation
theorem. This allows us to identify a quantity that remains positive throughout the non-Hermitian
evolution and can be interpreted as the
entropy production of the post-selected dynamics. We relate this quantity to previously proposed notions of non-Hermitian
entropy and derive an associated second law. Furthermore, we establish a connection with information-theoretic quantities, in particular the Petz-Rényi divergences, and leverage this connection to derive upper and lower bounds. Finally, we decompose the
entropy production into incoherent and coherent contributions, identifying distinctive features of the coherent term in the vicinity of exceptional points. We illustrate our results using a paradigmatic model of non-Hermitian
evolution based on a two-level system.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Numerical Modeling of Quasiparticle-Induced Dissipation in Fluxonium Qubits
Kate Azar, Max Hays and Kyle Serniak
Nonequilibrium quasiparticles (QPs) generated by stray infrared and ionizing radiation can limit the performance of superconducting
quantum processors and present challenges for
quantum error correction schemes. Models of QP-induced energy relaxation commonly assume that the characteristic energy of the QPs and the
qubit transition energy are both small relative to the superconducting gap. Under these assumptions, certain
qubits such as the fluxonium would exhibit protection against QP-induced dissipation at specific bias points. Here, we show that this is not necessarily the case, numerically analyzing the predicted rate of QP-induced dissipation in fluxonium
qubits for different QP energy distributions and for QPs created via
photon-assisted tunneling processes. We find that accounting for small numerical factors, existing theoretical models predict sensitivity to QP-induced errors at bias points previously thought to be protected. We find that inclusion of asymmetry in the superconducting gap energy across the junction can reintroduce suppression of QP-induced relaxation, as expected. Additionally, for QPs created by
photon-assisted tunneling, we predict that $T_1$ protection will only occur for a specific energy of pair-breaking radiation. This understanding of fluxonium sensitivity to QP-induced dissipation informs the development of fluxonium-based processors and future QP-mitigation strategies.
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Materials Science
Organizing Principles for Moiré Quantum Matter
Qiaoling Xu, Yifan Gao, Tao Zhang et al. (+16 more)
Moiré flat bands in van der Waals
bilayers are usually discussed through a small set of mechanisms associated with the $\Gamma$ and $K$ valleys of hexagonal
crystals, and more recently with $M$-valleys systems. Here we show that this view is incomplete. The momentum-space location and effective local orbital character of the monolayer's band edge, in conjunction with the moiré
symmetry and the
symmetry representations of the resulting bands, provide a general set of organizing variables for the emergent low-energy moiré
Hamiltonian. Applying fully relaxed first-principles calculations, band unfolding and
symmetry-representation analysis to more than 600 commensurate twisted
bilayers spanning all 2D
lattice classes, we identify several routes to moiré
quantum matter beyond the conventional single-orbital paradigm. The resulting flat bands realize trigonal, honeycomb, square, checkerboard and kagome-like Hubbard models with single-orbital, multi-orbital and multi-site
Hilbert spaces;
spin-orbit-coupled multi-orbital flat bands exhibit
symmetry-indicated
topology beyond the conventional $K$-valley setting; and nonsymmorphic moiré
symmetries enforce semimetallic flat-band connectivity. Analogous quasi-one-dimensional flat-band structures are found in $M$-valley hexagonal systems and $X$-valley square or rectangular systems resulting from emergent momentum-space nonsymmorphic
symmetries. Separately, coupled multi-valley
manifolds with kagome-like connectivity are identified in several systems whose parent band edges lie at non-high-
symmetry points. These results establish a valley-orbital-
symmetry framework for connecting parent-material electronic structure to emergent moiré
Hamiltonians relevant to correlated, topological and
symmetry-enforced moiré phases.
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All authors Qiaoling Xu, Yifan Gao, Tao Zhang, Ammon Fischer, Yi Jiang, Hanqi Pi, Zike Fan, Dongdong An, Kun Zhou, Yingjian Li, Yongqing Li, Yuhao Fu, Lei Wang, Lijun Zhang, B. Andrei Bernevig, Dante M. Kennes, Enge Wang, Angel Rubio, Lede Xian
Strongly Correlated Electrons · Cross-listed from quant-ph
Resolving Structure in Prethermal Floquet Dynamics with Precision Quantum Computation
Eyal Leviatan, Tasneem Watad, Roy Perry et al. (+38 more)
Periodically driven interacting
quantum many-body systems can exhibit long-lived prethermal dynamics, where local observables retain coherent structure even as
entanglement and operator complexity grow. Accessing this regime at the system sizes and times needed to determine physical properties of the prethermal state remains a central challenge: state-of-the-art classical methods become unreliable, while noise in
quantum hardware degrades observable expectation values. Here we overcome these limitations for a Floquet Ising magnet realized on a heavy-hex
lattice. Using the advanced error mitigation software QESEM on an IBM Heron r3 superconducting
quantum processor, we measure magnetization dynamics with percent-level precision and resolve long-lived subharmonic prethermal oscillations in systems of up to 74
qubits. These experiments reach regimes for which leading tensor-network simulations fail to converge, while sparse Pauli-path simulations remain strongly truncation dependent despite extensive computations on advanced GPUs and the Fugaku supercomputer. Leveraging this
quantum-accessible regime, we extend finite-size scaling to larger systems and find an unexpectedly slow decrease of the oscillation amplitude with system size, providing strong evidence that this oscillatory response persists in the thermodynamic limit of heavy-hex ladders. A hierarchy of mitigation and validation tests, including unbiased error mitigation, agreement between independent mitigation
estimators, noise-model validation on the superconducting hardware, and cross-platform corroboration at selected Floquet cycles on Quantinuum System Model H2 and Quantinuum Helios trapped-ion hardware, supports the reliability of these findings. Our work establishes error-mitigated
quantum processors as quantitative scientific instruments for discovering new physics in non-
equilibrium quantum matter.
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All authors Eyal Leviatan, Tasneem Watad, Roy Perry, Lukas Broers, Mohammed Zuhair Mullath, Ori Alberton, Itai Arad, Yosi Atia, Eyal Bairey, Shaul Barkan, Matan Ben Dov, Asaf Berkovitch, Ewout van den Berg, Itsik Cohen, Omri Golan, Ilya Gurwich, Avieli Haber, Barak A. Katzir, Oded Kenneth, Roei Levi, Yotam Y. Lifshitz, Yaron Lukovsky, Ron Melcer, Adiel Meyer, Boris Muratov, Aviad Panahi, Gili Schul, Tali Shnaider, Maor Shutman, Alireza Seif, Tomonori Shirakawa, Asif Sinay, Vincent P. Su, Hayk Tepanyan, Omri Trebitch, Assaf Zubida, Dorit Aharonov, Hrant Gharibyan, Abhinav Kandala, Seiji Yunoki, Netanel H. Lindner
Strongly Correlated Electrons
Momentum-Selective Two-Component Excitations in Electron-Doped Mott Insulators
Zeyu Han, Can Cui, Jia-Xin Zhang et al. (+1 more)
Experimental studies reveal a striking asymmetry in low-energy single-particle excitations between electron- and hole-doped cuprates. Electron-doped cuprates display a nontrivial dichotomy:
Fermi-
liquid-like behavior (suggesting weaker electronic correlations) coexists with correlation-driven features typical of hole-doped systems. This dual nature challenges a unified description within a doped Mott
insulator framework. The present work addresses this issue by establishing that the ground-state wave function of the $t$-$t'$-$J$ model generically possesses a two-component structure, comprising a coherent quasiparticle and an incoherent composite component. The kinetic energy arises from both the intrinsic propagation of the coherent quasiparticle and the resonance between these components. Using variational Monte Carlo at the level of a single hole, we show that for hole doping ($t'<0$), this resonance between components dominates and concentrates in the nodal region at low energies. This emergent propagation induced by resonance can be physically interpreted as originating from the recombination of fractionalized degrees of freedom, which drives various phenomena associated with strong correlations. Conversely, for electron doping ($t'>0$), the coherent quasiparticle propagation, which exhibits conventional properties of a
Fermi liquid, is selectively enhanced in the antinodal region at low energies. This produces a separation in momentum space for systems with electron doping: the antinodal spectral weight at low energies is governed by the coherent quasiparticle, fundamentally differing from the nodal region, which remains dominated by the incoherent composite component. Motivated by such a structure and guided by experimental observations, we propose a phenomenological Green's function at finite doping, yielding spectral features consistent with experiments.
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All authors Zeyu Han, Can Cui, Jia-Xin Zhang, Zheng-Yu Weng
Soft Condensed Matter
Controlling Turbulent Flows in Compressible Active Liquid Crystals
Dimitrios Krommydas, Paarth Gulati, Aparna Baskaran et al. (+1 more)
Motivated by experiments on light-patterned, quasi-2D active suspensions that exhibit large density variations, we develop a continuum theory of compressible active nematics–suspensions of apolar rods whose orientation is invariant under $\pi$ rotations. Under spatially patterned activity, the extensile isotropic active pressure expels material from high-activity regions and accumulates it in low-activity ones; an exactly solvable scalar reduction shows that the resulting density contrast is governed by a single dimensionless parameter, linear in the compressibility. Using compressibility as a tuning knob, we then steer active
turbulence from high- to low-activity regions and, at sharp activity interfaces, stabilize an analytically tractable dynamical steady state: a one-dimensional chain of
vortices held by soft, activity-induced confinement. Our results establish compressibility as a control parameter for density variations and turbulent flow in active nematic suspensions.
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All authors Dimitrios Krommydas, Paarth Gulati, Aparna Baskaran, M. Cristina Marchetti
Statistical Mechanics
Effective Field Theory of Operator Scrambling from Strong-to-Weak Symmetry Breaking
Bai-Lin Cheng, Shao-Kai Jian and Zhi-Cheng Yang
Operator scrambling is commonly diagnosed by the growth of out-of-time-ordered correlators (OTOCs), yet a general
symmetry principle underlying their effective dynamics has remained elusive. For Brownian or short-time-correlated large-$N$ Majorana systems, we develop a
symmetry-based effective field theory for operator scrambling, organized by a strong-to-weak U(1)
symmetry breaking in operator space. The key observation is that, in the noninteracting
fermion limit, the four-fold Keldysh contour representation of an OTOC admits an emergent strong U(1)
symmetry in a doubled
Hilbert-space description, even when the original system has no ordinary conserved quantity. The associated slow mode is the phase of the strong-charge creation operator, whose conjugate density is identified with the local operator size. Generic interactions explicitly break the strong
symmetry and generate a mass term at lowest order for the would-be Goldstone mode, thereby converting diffusive operator spreading into chaotic growth. We further show that higher-order
symmetry breaking terms are tightly constrained by an emergent duality that combines time reversal with contour permutation. This duality fixes the effective action up to quadratic order in the response field, relates the multiplicative noise strength directly to the Lyapunov exponent, and makes the positivity of the Lyapunov exponent a consequence of convergence of the real-time path integral. The resulting OTOC dynamics is governed by a noisy FKPP equation, which captures within a unified framework the early-time exponential growth, ballistic propagation, nonlinear saturation, and
stochastic front broadening of operator scrambling. We verify this construction in a Brownian SYK chain, where a direct saddle-point expansion reproduces the
symmetry-based effective action. Our results reveal a
symmetry origin of operator-size hydrodynamics and scrambling.
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Statistical Mechanics · Cross-listed from quant-ph
Efficient computation of real-time correlators using Pauli Propagation
Alexander F. Kemper, Raghav G. Jha, Arnab Bachhar et al. (+3 more)
Pauli propagation has shown promise for classically simulating
quantum dynamics by evolving observables directly in the Heisenberg picture. In this work, we investigate its use for computing real-time two-point time-ordered correlators in one- and two-dimensional
quantum systems. One major limitation of Pauli propagation is the rapid growth in the number of Pauli strings beyond short times. We overcome this limitation by combining accurate short-time Pauli-propagation data with time extension methods based on a positivity condition and the observation that the dynamics are often dominated by a small number of characteristic frequencies. This combined approach extends correlation functions far beyond the directly accessible time window while avoiding the exponential proliferation of Pauli operators. We demonstrate that the resulting correlators retain the relevant dynamical and spectral information. Our results broaden the regime in which classical methods can reliably probe the real-time dynamics of interacting
quantum many-body systems.
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All authors Alexander F. Kemper, Raghav G. Jha, Arnab Bachhar, Goksu C. Toga, Mariano Guerrero Perez, Nicholas J. Mayhall
Statistical Mechanics · Cross-listed from hep-th
OPE = QNM
Paolo Arnaudo, Cristoforo Iossa, Robin Karlsson et al. (+1 more)
At microscopic scales the linear response of thermal states of large-$N$ CFTs is governed by a thermal operator product expansion (OPE), while at large scales response is governed by collective excitations known as quasinormal modes (QNM). We show that the OPE and QNM representations of the retarded correlator in mixed time and spatial momentum coordinates have an overlapping region of convergence in the complex time plane, giving a map between OPE and QNM data. We show that large-overtone QNM asymptotics are related to OPE singularities, while low-overtone QNM data appear in analytic continuation from short to large times. Using this approach we obtain new analytic results for QNM asymptotics, and numerically obtain low-overtone QNMs from OPE data for the Schwarzschild-AdS$_5$ black brane. We further show that the OPE spectrum is intimately related to QNM data through a set of sum rules which we derive in Mellin space. Finally, using the lightcone OPE, we argue that stress tensor correlators at large spatial momentum thermalise slower as the conformal
collider bounds approach saturation. This work points to a new thermal bootstrap programme where OPE and QNM data constrain each other.
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All authors Paolo Arnaudo, Cristoforo Iossa, Robin Karlsson, Benjamin Withers
Statistical Mechanics · Cross-listed from hep-lat
TempLat: a versatile C++ engine for lattice field theories
Adrien Florio and Franz R. Sattler
We present TempLat, a C++ framework for
lattice field theory simulations in arbitrary dimensions. Its symbolic
language, built on expression templates, translates mathematical expressions almost verbatim into C++ while compiling to highly optimized kernels, in contexts ranging from classical-statistical to Monte Carlo simulations. TempLat is performance-portable: building on Kokkos, it supports large CPU clusters, as well as NVIDIA and AMD GPUs. Its abstraction of hardware into a device concept makes TempLat extensible to future architectures. We demonstrate excellent strong and weak scaling on both CPUs and GPUs. We also present ParaFaFT, a standalone parallel discrete
Fourier transform library supporting arbitrary dimensions on all of the above hardware, and
benchmark its scaling. Both are open source and available on GitHub, and power a new release of CosmoLattice, a widely used early-universe simulation library now available on GPUs.
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Superconductivity
Probing nonlocal superconducting fluctuations with covariance noise magnetometry
Gustav Romare, Ilya Esterlis, Shimon Kolkowitz et al. (+1 more)
The nonlocal superconducting fluctuation corrections to the conductivity tensor $\sigma_{ij}(\mathbf{q},\omega)$ are calculated within the time-dependent Ginzburg-Landau framework, and their observable consequences for
quantum noise magnetometry are worked out. For a single nitrogen-vacancy (NV) sensor we obtain the relaxation rate $1/T_1$ as a function of temperature, sample-sensor distance, and probe frequency, identifying the scales at which the nonlocality and the dynamics of the pair fluctuations cut off the critical enhancement near $T_c$. For two-sensor covariance magnetometry we show that the two-point field correlator develops additional spatial structure whose range directly measures the fluctuation correlation length $\xi(T)$. We further analyze two channels that accompany the paraconductivity: the Maki-Thompson correction to the
spin susceptibility, and the fluctuation diamagnetism. Finally, we solve exactly, to all orders in a dc electric field and at all wave vectors, for the nonequilibrium current noise of the fluctuating film: the noise decouples from the nonlinear paraconductivity, violating the fluctuation-dissipation
theorem by universal factors at criticality and acquiring a bias-induced spatial anisotropy directly measurable by covariance magnetometry. The results are connected to a recent experiment measuring current noise near a thin film of BSCCO.
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All authors Gustav Romare, Ilya Esterlis, Shimon Kolkowitz, Alex Levchenko
Superconductivity
Stripe-tuned superconductivity in single-flavor metals with nontrivial quantum geometry
Yi-Ting Tu, Yang-Zhi Chou, Yi Huang et al. (+1 more)
We study how the interplay between nontrivial
quantum geometry and an applied stripe potential affects superconductivity in a two-dimensional single-
flavor metal. Assuming a weak contact attractive interaction and focusing on the lowest subband in the presence of a strong stripe potential, we analytically derive two possible pairing states in the quasi-one-dimensional limit. In addition to the conventional longitudinal $p_y$-wave order (with the stripes along the $y$ direction), we find that an exotic transverse $p_x$-wave order can be stabilized. The competition between these two orders is controlled by the electron density of each stripe and the Berry-
curvature-dressed interaction. Notably, the transverse $p_x$ wave order develops a nodal line at $k_x=0$, while the longitudinal $p_y$ order is fully gapped. We discuss the possible experimental probes distinguishing these orders. Our results establish a way of controlling the pairing
symmetry through a stripe potential, predicting superconductivity with nontrivial
quantum geometry.
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All authors Yi-Ting Tu, Yang-Zhi Chou, Yi Huang, Sankar Das Sarma
Materials Science
A flexible kinetic Monte Carlo framework for GaN molecular beam epitaxy with adaptive on-the-fly barrier evaluation
Sajid Ali, Norbert Krause and Carla Verdi
We present a
lattice-based kinetic Monte Carlo (KMC) framework for simulating GaN(0001) growth by molecular beam epitaxy. The framework captures the key microscopic processes governing epitaxial growth, including temperature-dependent surface
diffusion, flux-driven deposition, Ehrlich–Schwoebel (ES) step-edge barriers, Ostwald ripening, and species-specific desorption, within a scalable architecture that enables systematic exploration of experimentally relevant growth conditions. In addition to predefined activation-energy catalogs, the framework supports adaptive on-the-fly barrier evaluation using machine-learned interatomic potentials. When previously unencountered local atomic configurations arise, activation barriers are computed via nudged elastic band, potential energy scans, or Brønsted–Evans–Polanyi methods, and cached for reuse. Predefined-barrier simulations reproduce compact triangular island formation, and further capture Ostwald ripening during growth interruptions and ES barrier-induced multilayer nucleation. At elevated temperatures, desorption drives an island “walking” regime, in which N–Ga exchange generates weakly bound Ga adatoms (AdGa) at trailing edges; preferential desorption of AdGa leads to asymmetric edge retreat and net island translation. Our KMC framework provides a flexible platform for predictive simulations of GaN epitaxy at the atomic scale and, more broadly, non-
equilibrium growth of compound
semiconductors.
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Strongly Correlated Electrons
Anyon Condensation In Symmetry-Enriched Topological Phases: $G$-Grading of Multifusion Categories
Nianrui Fu, Siyuan Wang, Yu Zhao et al. (+1 more)
Although anyon condensation is a standard mechanism for relating topological orders, anyon condensation in
symmetry-enriched topological (SET) phases is more intricate because the condensate must also be compatible with the global
symmetry. We study
symmetry-preserving anyon condensation in SET phases described by the enlarged Hu-Geer-Wu (HGW) string-net model with multifusion-category input data. We show that a $G$-preserving condensation is characterized by a compatible grading of the input multifusion category, and that this grading constructs the multifusion-category input of the child SET phase. To make this construction concrete, we consider the case where the relevant data come from a finite group extension $E$ of $G$ by $N$: an $E$-graded fusion category induces a $G$-SET input by passing to the quotient
symmetry $G$, and the resulting input naturally carries a compatible $N$-grading that implements the further condensation inside the SET phase while preserving $G$. We illustrate the construction using three
quantum-double examples: the trivial extension $\mathbb{Z}_2\times\mathbb{Z}_2$, the non-Abelian semidirect product $S_3$, and the nontrivial central extension $\mathbb{Z}_4$. The $\mathbb{Z}_4$ example further shows that
symmetry fractionalized anyons do not obstruct
symmetry-preserving condensation once the condensate is treated as a physical coherent state.
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All authors Nianrui Fu, Siyuan Wang, Yu Zhao, Yidun Wan
Other Condensed Matter · Cross-listed from quant-ph
Pulse engineering via projection of response functions at infinite nonlinear order
Lia Kley and Ludwig Mathey
Optimal control problems arise in a wide range of scientific disciplines, but the corresponding optimization
algorithms often display a strong dependence on hyperparameters that significantly influence performance and convergence. For the optimal implementation of
quantum algorithms, these challenges are further amplified by high-dimensional control landscapes and the need for high-fidelity operations. Here, we propose an
algorithm for optimal control problems in
quantum computing to efficiently generate high-fidelity control protocols for multi-
qubit systems in a hyperparameter and gradient free manner. The method, referred to as Pulse Engineering via Projection of response functions at infinite nonlinear order (PEPRino), leverages the framework of response theory to navigate the control landscape to find high-fidelity implementations. This is achieved by determining the control landscape via response functions to infinite order, efficiently evaluated by resummation in terms of the first and second order response function. To demonstrate the approach, we apply it to
quantum systems consisting of two and three
qubits for the optimal implementation of the
Quantum Fourier Transform (QFT). We
benchmark the proposed
algorithm against the Chopped Random Basis (CRAB)
algorithm utilizing the Nelder-Mead method, focusing on the 2-
qubit scenario. The results indicate faster convergence regarding iteration steps and computational time, highlighting the advantages of our approach.
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Statistical Mechanics
Fluctuation theorems for autonomous work in the quantum regime
Xiu-Hua Zhao and H. T. Quan
Fluctuation
theorems for work provide universal constraints on nonequilibrium fluctuations, yet their
quantum generalizations often rely on externally prescribed classical driving protocols. While for classical systems, fluctuation
theorems have been extended to autonomous work, where the dynamics of the work source is subject to the backaction of the system, their generalization to the
quantum regime is constrained by the uncertainty principle. Here, we extend fluctuation
theorems for autonomous work from the classical regime to the
quantum regime. By performing successive projective measurements over the work source and the system, we derive Jarzynski-type and Crooks-type fluctuation
theorems for autonomous inclusive work from initial mixed thermal states. These relations are analogous to fluctuation
theorems for autonomous work in the classical regime and explicitly incorporate the fluctuations of the work source. However,
quantum noncommutativity prevents a consistent reduction to the nonautonomous counterparts, even in the limit of a large work source and correspondingly negligible backaction. By contrast, under the exclusive work definition, the nonautonomous limit is recovered when the measured observable of the work source commutes with its bare
Hamiltonian and the backaction of the system on the work source is negligible. Our results are illustrated with the Dicke model, where a single-mode radiation field and an ensemble of two-level atoms act as the system of interest and the work source, respectively.
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Materials Science
Growth and characterization of planar hexagonal Ge on CdS
Andrea Besana, Veronica Regazzoni, Marco Faverzani et al. (+13 more)
Hexagonal group-IV
semiconductors have attracted increasing interest owing to their unconventional electronic and optical properties compared to the cubic diamond phase. However, the stabilization of these metastable allotropes in planar
heterostructures remains a major challenge. In this work, we demonstrate the epitaxial growth of planar hexagonal germanium on non-basal $m$-plane CdS substrates by low-energy
plasma-enhanced chemical vapor deposition. The role of growth temperature in the formation and stabilization of the hexagonal phase is investigated. X-ray diffraction, scanning transmission electron microscopy, and polarization-resolved Raman spectroscopy reveal the formation of epitaxial hexagonal germanium with the expected
crystal symmetry. In particular, the Raman response exhibits the characteristic polarization selection rules of the E$_\text{2g}$
phonon mode of hexagonal Ge. Conversely, photoluminescence spectroscopy does not reveal any Ge-related emission feature. Combined transmission electron microscopy observations and atomistic modeling show that strain relaxation is governed by a limited set of dislocation mechanisms, which efficiently relieve most of the mismatch strain within a few nanometers from the interface and can involve localized cubic stacking insertions. At greater distances from the interface, the progressive loss of hexagonal order is increasingly dominated by stacking-fault disorder, particularly I3-type defects. These results establish CdS as a promising template for the planar stabilization of hexagonal Ge and provide insight into the defect mechanisms governing strain relaxation in metastable group-IV
heterostructures.
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All authors Andrea Besana, Veronica Regazzoni, Marco Faverzani, Fabrizio Rovaris, Emiliano Bonera, Sonia Freddi, Elisa Brugaletta, Mohamed Zaghloul, Fabio Pezzoli, Francesco Montalenti, Monica Bollani, Daniel Chrastina, Anna Marzegalli, Antonio M. Mio, Emilio Scalise, Giovanni Isella
Strongly Correlated Electrons
Sign-optimized Quantum Monte Carlo
Julius S. Herz, Robin Schäfer, Matías G. Gonzalez et al. (+1 more)
The sign problem breaks the
polynomial scaling of
Quantum Monte Carlo methods. We alleviate it by rotation of the local basis of the
Hilbert space, such that the phase of off-diagonal
matrix elements of the rotated
Hamiltonian is minimized. These minima coincide with optima of the average sign. We
benchmark our method for frustrated Heisenberg antiferromagnets in one dimension and on the two-dimensional maple-leaf
lattice. Our approach reveals more efficient bases with improved sign in a large part of the parameter space for all models considered, enabling us to reach lower temperatures, on par with state-of-the-art numerical linked cluster expansions which we directly compare to.
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All authors Julius S. Herz, Robin Schäfer, Matías G. Gonzalez, David J. Luitz
Mesoscale and Nanoscale Physics
Skew scattering induced contribution to orbital Hall response
Dayana Joy, Vivek Pandey, Rhonald Burgos Atencia et al. (+1 more)
Our study provides the disorder-induced contribution to the orbital
Hall conductivity in three-dimensional Weyl semimetals with broken time-reversal
symmetry. Using the
quantum kinetic approach, we analyse the impact of side-jump and skew scattering contributions to the system. The dependence of the orbital
Hall conductivity on both disorder potential and the
Fermi energy is explicitly demonstrated. Furthermore, we demonstrate that the higher-order disorder contribution, especially from the third power of disorder potential, dominates the orbital
Hall conductivity under an oscillating electric field in a time-reversal
symmetry broken Weyl semimetal, suppressing other scattering mechanisms, including the side jump contributions. We can enhance the extrinsic orbital
Hall conductivity by tuning the strength of the disorder potential, applied energy, and choosing the system with appropriate Weyl node separation. Finally, our results are supported by numerical estimations and highlight potential experimental relevance for advancing orbitronics device technologies.
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All authors Dayana Joy, Vivek Pandey, Rhonald Burgos Atencia, Pankaj Bhalla
Statistical Mechanics · Cross-listed from q-bio.PE
From Local Payoffs to Global Instabilities: A Spectral Cartography of Spatiotemporal Chaos in Canonical 2x2 Evolutionary Games
Ozgur Aydogmus
We develop a motif-based framework for spatiotemporal chaos in spatial evolutionary games and use it to map the dynamical phase diagram in the payoff plane. Using Boolean linearization of the imitate-the-best rule, we derive analytical instability thresholds for local motifs including invaders, cooperative pairs, stripe interfaces, and cooperative cores. These thresholds are obtained from payoff balance at contested motif interfaces and recover classical invasion thresholds of spatial evolutionary games, which emerge here as boundaries of the chaotic phase. Combining the Derrida slope with the asymptotic Hamming distance, we obtain a four-region cartography: ordered, transient-chaotic, sustained-chaotic, and subcritical-chaotic dynamics. The phase diagram is organized by density-dependent motif selection: different initial cooperator densities activate different instability mechanisms, yet a small set of motif-instability lines consistently bounds the sustained-chaos region across densities. This cartography reveals a subcritical chaotic phase (Derrida slope $s<1$ but asymptotic Hamming distance $d_\infty>0$), where infinitesimal perturbations decay while finite-amplitude perturbations sustain chaos. The motif-based framework is anchored by an exact
benchmark: for homogeneous backgrounds, the Boolean Jacobian yields an exact correspondence between the Derrida slope and spectral radius, linking damage spreading to deterministic instability.
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Strongly Correlated Electrons · Cross-listed from hep-th
Krylov complexity and spectral density of BMN matrix model
Dibakar Roychowdhury
We use Krylov complexity as a typical diagnostic of
quantum many body dynamics in the context of BMN
matrix model at large mass gap. We calculate several physical entities, for example, the moments and return amplitudes at large mass deformation. We calculate them for both spread complexity of states as well as Krylov growth of operators in the
matrix model. We propose a general expression for the moments at any given order $n$. We also discuss orthogonal
polynomials for spread as well as operator Krylov complexity. In the context of the Krylov operator growth we further compute the spectral function and the density of states. A careful analysis of the spectral function near the resonance reveals various IR divergences in addition to the physical collective modes. These collective modes appear to be exceptionally stable due to large mass gap. On the other hand, the UV of the theory appears to be extremely damped due to higher scattering rates. We carefully diagnose these IR divergences near resonance which reveals that these collective modes are in fact non-propagating and should be thought of as
diffusion modes or relaxation modes with infinite relaxation time. We also calculate the Krylov variance and Krylov
entropy for the
matrix model and in particular at early time. The linear early time growth of the Krylov
entropy confirms the onset of
quantum chaos in the
matrix model at large mass gap.
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Materials Science
A General Model of Interfacial Chemical Equilibrium in Phase-Field Method
Yanzhou Ji and Long-Qing Chen
We report a new approach to interfacial
equilibria among multiple solution phases in the phase-field method. It employs auxiliary non-conserved variables to describe the composition differences among different phases, and their temporal
evolution is driven by the differences among different chemical diffusional potentials. It is reduced to the Wheeler-Boettinger-McFadden (WBM) model of equal interfacial chemical compositions and to the Kim-Kim-Suzuki (KKS) model of equal interfacial chemical
diffusion potentials as two limiting cases. It can directly incorporate thermodynamic databases without any further approximations and simplifications. It is generally applicable to a wide range of problems involving composition
evolution and chemical
equilibria, including processes such as interdiffusion between two ordered phases not sharing any common composition range, which would pose difficulty to the existing treatments using WBM and KKS models.
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Statistical Mechanics
Control of morphology and topology in a lattice model of branching morphogenesis
Christian Hanauer, Frank Jülicher and Efe Ilker
We present a
lattice model for morphogen-controlled branching morphogenesis which combines ideas and concepts from non-
equilibrium physics and developmental biology. In this model, the
stochastic occupation dynamics of
cells is coupled with signaling molecules (morphogens) produced by the
cells. We investigate growth patterns governed by morphogen concentration gradients, spanning regimes ranging from the
diffusion-limited aggregation limit to the
stochastic surface growth (Eden model) limit. Moreover, we introduce control over
topology by a local operator and study growth, degrowth, and steady-state dynamics of branched patterns. The
topology-preserving steady-state clusters exhibit a power-law scaling of radius of gyration with cluster size, yielding the exponents $0.68\pm0.01$ in square
lattice and $0.67\pm 0.01$ in hexagonal
lattice.
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Statistical Mechanics · Cross-listed from physics.soc-ph
Extreme outbreaks in non-Markovian epidemics on complex networks
Ami Taitelbaum and Michael Assaf
Extreme epidemic risk is controlled by the right tail of the outbreak-size distribution, but this distribution is generally unknown for non-Markovian spreading on networks. Here we determine this distribution by mapping non-Markovian SIR dynamics to an effective Markovian description. We show that arbitrary infection and recovery time statistics can be incorporated through a single edge transmissibility, yielding an effective Markovian process that reproduces the full outbreak-size statistics. For weakly heterogeneous networks, the reduction yields a universal well-mixed semiclassical theory governed by the bond-percolation reproductive number. Outbreak statistics across diverse waiting-time distributions and
topologies collapse onto one predictive curve. For highly heterogeneous and empirical networks, the corresponding effective Markovian dynamics on the network captures the complete distribution. Our results provide a direct route from measured waiting-time distributions to quantitative predictions of network-level extreme-outbreak risk.
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Materials Science
Quantum oscillation fingerprints of altermagnetism in hole-doped RuO2
Yuchi Yang and Yusheng Hou
Altermagnetism, characterized by its ferromagnetism-like
spin-splitting band structure and antiferromagnetism-like
magnetic order, has garnered considerable
attention recently. Although hole doping may promote magnetism in the debated altermagnet candidate RuO2, the
evolution of its electronic and
magnetic properties under hole doping remains poorly understood. Based on first-principles calculations, we employ
quantum oscillations to study hole-doped RuO2. We find that hole doping can enhance
spin splitting and reconstruct the
Fermi surface in RuO2, which is revealed by the angle-dependent
quantum oscillation frequency. By tracking a pair of closed
Fermi-surface pockets, we identify a meaningful correlation between the
magnetic moment of Ru and a
quantum-oscillation-based signature of
spin splitting. This correlation follows a quasi-linear trend over a broad doping range, which can be captured by a minimal two-dimensional d-wave altermagnetic model. In addition, the hole-doped RuO2 exhibits a transition from a nonmagnetic to an altermagnetic state via an intermediate state. The quasi-linear correlation through
quantum oscillation and the distinct
quantum oscillation frequency of the stable altermagnetic state can serve as useful signatures for identifying the altermagnetic state in RuO2. Our results provide a comprehensive framework for understanding hole-doped RuO2, offering new insights into altermagnetic transitions and their identification.
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Statistical Mechanics · Cross-listed from physics.comp-ph
Reframing the coupling force of adaptive resolution simulation in terms of the Liouville-type hierarchy for open systems
Julian F. Hille and Rupert Klein
In this work, we present a novel perspective on the coupling force employed to compensate the interface artifacts prevalent in adaptive resolution simulations (AdResS) of open many-particle systems. We show that a substantial part of this "thermodynamic force" can be framed in terms of the theoretical model of the Liouville-type hierarchy for open systems. The correspondence is made explicit for the case of a simple atomistic fluid, for which a one-dimensional integral expression is derived. This enables the analysis for dependencies of the thermodynamic force on important simulation parameters, which is taken to inspire both simplifications for the numerical calculation of the thermodynamic force and new criteria for its validation that are adequate to the interfacial nature of the problem. The theoretical claims are then verified in a simulation study of the atomistic supercritical Lennard-Jones fluid at different thermodynamic states.
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