Statistical Mechanics · Cross-listed from cs.LG
On the Statistical Mechanics of Attention
Jerry Yao-Chieh Hu, Yu-An Chen, Maojiang Su et al. (+1 more)
We revisit the statistical mechanics of
Transformer attention via modern Hopfield models. We present a free-energy formalism to characterize parameter regimes and critical thresholds for robust
attention inference. The resulting free-energy landscape incorporates randomness in query states and
attention weights.
Attention then emerges as the equation of motion of the corresponding statistical-mechanical system (i.e., modern Hopfield model) through the standard free-energy minimization principle. This allows us to identify first-order phase transitions in
attention between glassy and robust-inference phases. We further extend to attentions with
stochastic queries and keys. Together, our results provide a rigorous statistical-mechanics framework for characterizing phase structure and inference reliability across a family of
Transformer attention mechanisms.
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All authors Jerry Yao-Chieh Hu, Yu-An Chen, Maojiang Su, Han Liu
Statistical Mechanics · Cross-listed from cond-mat.mes-hall
Turning a superconducting diode into a Feynman ratchet to realize a nanoscale heat engine
Konstantinos Kontogeorgiou, İnanç Adagideli, Géraldine Haack et al. (+1 more)
Feynman's ratchet illustrates how work can be extracted from thermal fluctuations in the presence of two heat baths at different temperatures. While some experimental realizations of the ratchet effect have been studied, most lack miniaturization, which is important for some applications. Here, we propose a physical implementation of Feynman's ratchet based on Josephson junctions exhibiting the superconducting diode effect. This setup functions as a heat engine that generates work solely from a temperature gradient via thermal fluctuations. We analyze its output power and efficiency, and, through the Seebeck coefficient, identify the conditions under which the device operates in reverse, functioning instead as a Peltier cooler.
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All authors Konstantinos Kontogeorgiou, İnanç Adagideli, Géraldine Haack, Fabian Hassler
Statistical Mechanics · Cross-listed from quant-ph
Entanglement Sudden Death in Gapped Ground States
Robert Ferydouni, Thomas Jackson and Samuel O. Scalet
Spatial sudden death of
entanglement refers to the disappearance of
quantum correlations between subsystems after a certain distance called the
entanglement length. Specifically, given a density
matrix $\rho_{ABC}$ on a tripartite system $ABC$ with $B$ spatially separating $A$ and $C$, the
entanglement length is the distance $\ell(A,C)$ after which the reduced density
matrix $\rho_{AC}$, given by tracing out the $B$ subsystem, is separable. We show in the case of gapped ground states in any dimension that the
entanglement length is finite on finite subsystems. Restricting to one-dimensional systems, we prove that normal
matrix product states have a finite
entanglement length independent of $A$ and $C$, and that a finite pure state with such uniform
entanglement length has a
matrix product state representation with bond dimension independent of $A$ and $C$. Consequently, in one dimension,
entanglement length distinguishes
matrix product states from all other pure states.
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Statistical Mechanics · Cross-listed from physics.chem-ph
Solvent Fluctuations Enable Photoionization of Aqueous Nitrite Microdroplets
Brandon J. Wallace, Eric R. Heller, Alex Prophet et al. (+4 more)
Nitrite photochemistry in atmospheric aerosols and natural waters is a major source of hydroxyl radicals and reactive nitrogen oxides. Contrary to the prevailing view that in the environment aqueous nitrite photochemistry proceeds exclusively through photoexcitation followed by homolytic bond cleavage, we show that visible light directly ionizes aqueous nitrite in individual micron-sized droplets. Although the photoionization cross section is exceptionally small, this pathway is observable at the high
photon flux densities accessible in single-droplet experiments. Molecular simulations reveal that this is because photoionization absorption has an exceptionally long wavelength tail due to the large solvent reorganization energy in aqueous solutions. Kinetic modeling of an aqueous-phase reaction mechanism quantitatively accounts for the observed chemistry and predicts the formation of nitrate, hydroxyl radicals, and solvated electrons. The overlap of the predicted broad photoionization continuum with the visible solar spectrum further suggests that visible-light photoionization is an overlooked source of nitrogen oxides, solvated electrons, and oxidants in atmospheric aerosols, snowpack, and natural waters. Under dilute conditions, where dissolved oxygen is the main sink for solvated electrons, photoionization is expected to be the dominant photochemical loss pathway for nitrite.
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All authors Brandon J. Wallace, Eric R. Heller, Alex Prophet, Pranav Ballapuram, Ashok Ajoy, David T. Limmer, Kevin R. Wilson
Statistical Mechanics
Mutual linearity from classical response theory
Timur Aslyamov and Massimiliano Esposito
We unify known mutual-linearity relations for Markov jump processes and chemical reaction networks within a common framework based on classical finite-response theory. In a Markov jump process, an exact finite-response identity shows that all stationary probability changes share a common factor when the rates of one edge change. Eliminating this factor gives the relations between probabilities, observables, and currents, even far from
equilibrium. We also explain how the same argument applies when one coefficient of a linear system changes and recovers the known relations in Laplace space and between stationary complex activities in chemical reaction networks.
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Statistical Mechanics · Cross-listed from hep-th
Out-of-time-order hydrodynamics and scrambling
Marta Bucca, Akash Jain, Márk Mezei et al. (+1 more)
Hydrodynamics as an effective field theory (EFT) has been immensely successful for predicting the behaviour of time-ordered correlation functions in the long-time, large-distance regime. In this paper, we analyse the predictions of hydrodynamics for scrambling as probed by out-of-time order correlators (OTOCs). To do so, we consider an all-derivative order generalisation of the Schwinger-Keldysh EFT of hydrodynamics extended to a four-fold time contour required to capture OTOCs. A crucial ingredient of the construction is a local SL(2,R)
symmetry, which has previously been suggested as a mechanism for scrambling. We also derive this exact EFT from the microscopic formulation of the maximally chaotic low-temperature limit of the SYK
lattice, thereby determining all transport coefficients for this model. As a novel application, we compute the OTOC of energy currents, find that its exponential growth saturates the chaos bound, and match it to expectations based on a shockwave (or scramblon) effective description. Our work shows that the universality of hydrodynamics degrees of freedom extends beyond traditional time-ordered correlators to more complex observables such as OTOCs.
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All authors Marta Bucca, Akash Jain, Márk Mezei, Alexey Milekhin
Statistical Mechanics · Cross-listed from math.PR
Iterated Graph Systems (III): Alexander-Orbach conjecture on hierarchical lattices
Ziyu Neroli
Can the Alexander-Orbach
conjecture hold on hierarchical
lattices? We construct Gromov-Hausdorff-Prokhorov scaling limits of critical percolation clusters on hierarchical
lattices in the chemical metric and determine the typical spectral dimensions of the associated
diffusions. These dimensions are dense in $(1,2)$; however, outside a narrow region in dimension space, we prove that the Alexander-Orbach
conjecture fails on every hierarchical
lattice under consideration.
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Statistical Mechanics · Cross-listed from cond-mat.soft
Self-phoresis on a one-dimensional periodic domain
Leah Anderson and David S. Dean
We study the spontaneous motion and collective dynamics of self-phoretic particles on a one-dimensional periodic domain. The particles act as localized chemical sources (of a particle-dependent strength) of a field and the particles themselves respond to the gradients of the field they generate (with a particle-dependent phoretic mobility). The chemical field itself diffuses and evaporates. For a single particle, we derive the exact threshold for spontaneous propulsion and establish the emergence of stable constant-velocity states near onset through a supercritical pitchfork bifurcation. We then consider an active source coupled to a non-emitting tracer and determine the conditions for slipping and stable phase-locked motion. For two mutually coupled sources, the stationary antipodal configuration can lose stability through either a pitchfork or a Hopf bifurcation, depending on the relative source strengths and phoretic mobilities. We determine the competing instability thresholds and compare them with direct numerical simulations of the coupled particle-field equations. Beyond onset, the resulting translating and oscillatory states provide qualitative counterparts to modes of motion observed experimentally for camphor disks in annular water channels. These results connect the onset of individual propulsion, tracer entrainment, and collective motion within a common analytically tractable framework.
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Statistical Mechanics · Cross-listed from q-fin.ST
Asymmetric $q$-Gaussian Distributions from Tsallis Maximum Entropy
Francesco Cesarone, Massimiliano Corradini, Nicolò Giunta et al. (+1 more)
Within the framework of non-extensive statistical mechanics, $q$-Gaussian distributions arise as maximum-
entropy solutions of Tsallis
entropy under suitable escort moment constraints. Although widely used in physics, biology, geology, finance, and related fields, standard $q$-Gaussians are intrinsically symmetric and cannot capture asymmetric fluctuations often observed in empirical data. We ask whether asymmetry can arise from the Tsallis maximum-
entropy principle without externally skewing or joining distributions. We show that this is achieved by retaining the Tsallis
entropy and imposing a global escort mean together with distinct downside and upside escort semi-variances. The key step is to reformulate the problem of maximum Tsallis
entropy in terms of the escort density. The nonlinear escort constraints then become affine, while maximizing Tsallis
entropy becomes equivalent to maximizing a strictly concave functional over a convex feasible set. Consequently, any admissible stationary solution is the unique global maximizer of the corresponding variational problem. The finite-sample approximation properties of the proposed asymmetric $q$-Gaussian are studied through Monte Carlo experiments using synthetic data generated from Azzalini skew-Student distributions. Compared with the classical symmetric $q$-Gaussian, the asymmetric specification systematically provides a closer approximation to synthetic asymmetric heavy-tailed distributions. Finally, we fit the model to return series from major equity indices, a commodity, and cryptocurrencies, and compare its in-sample goodness of fit with that of a symmetric $q$-Gaussian. The results show that the asymmetric model offers a closer in-sample description of unconditional return distributions, most clearly in the tails.
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All authors Francesco Cesarone, Massimiliano Corradini, Nicolò Giunta, Serena Rocci
Statistical Mechanics · Cross-listed from cond-mat.soft
Solubility of poorly soluble species in bulk and nanopores from grand-canonical Wang-Landau sampling
Russell Kajouri, Adyant Agrawal, Philipp Stärk et al. (+2 more)
Poorly soluble species can have mean populations below one in small systems such as nanopores. In this regime, the grand-potential minimum, which identifies the most probable particle number, differs from the ensemble-averaged solute loading. We use grand-canonical Wang-Landau sampling (GCWLS) to calculate the density of states $\Omega(N_\mathrm{A}, N_\mathrm{B})$ for a binary Lennard-Jones mixture of solute B in solvent A, both in bulk and in slit pores. One set of GCWLS simulations gives ensemble averages over a range of chemical potentials, whereas conventional grand-canonical Monte Carlo (GCMC) simulation requires a separate simulation at each state point. Independent GCMC simulations confirm the GCWLS ensemble averages. The solvent number distribution is nearly Gaussian, whereas the dilute solute distribution is skewed and Poisson-like. The most probable solute number therefore lies below the ensemble-averaged loading $\langle N_\mathrm{B}\rangle$ and is zero whenever $\langle N_\mathrm{B}\rangle<1$. Reading the solute loading from the grand-potential minimum underestimates it and can falsely indicate that no solute is present. Defining the oversolubility as $\mathcal{O}_\mathrm{B}=x_\mathrm{B}^{\mathrm{conf}}/x_\mathrm{B}^{\mathrm{bulk}}$, where $x_\mathrm{B}$ is the solute mole fraction, we find $\mathcal{O}_\mathrm{B}\approx12$ in a pore of 3.5 particle diameters width when both wall interactions are repulsive. Adding wall-solute attraction moderately raises it to $\approx13$, whereas wall-solvent attraction lowers it to $\approx3.4$. This comparison shows that the wall-solvent interaction controls most of the enhancement. As the pore widens, $\mathcal{O}_\mathrm{B}$ decreases toward unity. In bulk and in nanopores alike, the solubility of poorly soluble species should be obtained from ensemble averages rather than from grand-potential minima.
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All authors Russell Kajouri, Adyant Agrawal, Philipp Stärk, Alexander Schlaich, Christian Holm
Statistical Mechanics · Cross-listed from cond-mat.soft
Activity-Induced Structural and Dynamical Heterogeneity in Colloidal Gels
Santu Nath, Sudipta Mandal and Smarajit Karmakar
Active gels are intrinsically non-
equilibrium materials whose structural and dynamical heterogeneity emerges from the interplay of attractive interactions, thermal fluctuations, and self-propulsion. We investigate a model active gel, simulated using large-scale Brownian dynamics simulations, to explore the effects of temperature $T$, active force strength $f_0$, persistence timescale $\tau_p$, and active particle concentration $\rho_a$. We characterize the structure of the evolving gel network through morphological analysis, while dynamical changes are quantified by the relaxation timescale and dynamical heterogeneity (DH). We show that an optimal choice of activity parameters yields a percolating gel network with faster gelation and larger voids and clusters, enhancing mechanical stability. Conversely, the structural relaxation timescale and DH decrease with increasing activity, indicating enhanced particle rearrangements and reduced spatial correlations of mobile and immobile regions. An effective temperature ($T_\text{eff}$) framework for colloidal gels maps structural quantities and relaxation timescales in an active gel onto those of a passive gel. More interestingly, the growth of DH with increasing swim force can also be described by the same effective-temperature framework, in stark contrast to observations in active glasses. Our findings show that, in colloidal gels, temperature and active force compete, giving rise to similar structural ordering and, consequently, similar DH at the same $T_\text{eff}$. These findings highlight the crucial role of structural ordering in governing DH in active colloidal gels, as compared to active glasses.
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Statistical Mechanics · Cross-listed from cond-mat.str-el
Scalable Quantum Monte Carlo for Shannon-Rényi Entropy: An Experiment-visitable Probe of Quantum Phases and Criticality
Dong-Xu Liu, Zhe Wang, Zenan Liu Yi-Ming Ding et al. (+1 more)
The Shannon-Rényi (SR)
entropy characterizes the probability distribution of many-body wave functions in a chosen basis and is directly accessible from single-shot measurement snapshots in cold-atom experiments, yet its theoretical evaluation in interacting systems carries exponential cost. Here we construct a field-theoretic spacetime
manifold for the SR
entropy in which $q$ replicas are glued at the imaginary-time boundaries, recasting it as a ratio of generalized partition functions amenable to large-scale
quantum Monte Carlo simulation. On this basis we develop a reweight-annealing framework with two complementary strategies: a virtual-parameter scheme interpolating between unglued and fully glued limits via binomial-weighted partial gluing, and a real-parameter scheme using a physical coupling constant as the annealing variable within
stochastic series expansion. Both reduce the computational cost from exponential to
polynomial. Most importantly, we establish for the first time a finite-size scaling theory for the SR
entropy near a
quantum critical point, $S_q=a(g)L^2+S_q^0\left((g-g_c)L^{1/\nu}\right)$; data collapse of its first derivative yields the correlation-length exponent $\nu$ for both the O(3) and Ising universality classes, realized in the
spin-$\frac{1}{2}$ columnar dimerized Heisenberg model and the bilayer Heisenberg-Ising model. The same simulations extract the Goldstone-mode count $N_G=2$ and the $Z_2$ ground-state degeneracy $\ln 2$ from subleading terms. These results elevate the SR
entropy to a standalone, order-parameter-free diagnostic of
quantum criticality with the same scaling status as the
entanglement entropy, and close the loop between theory and
quantum simulation by enabling quantitative benchmarking of experimental snapshots from state-of-the-art
quantum simulators.
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All authors Dong-Xu Liu, Zhe Wang, Zenan Liu Yi-Ming Ding, Zheng Yan
Statistical Mechanics · Cross-listed from cond-mat.soft
Thermal softening of the yield stress in glasses with different stability
Tianze Wan and Ludovic Berthier
The yielding of amorphous solids has been extensively studied in the athermal limit, but the influence of thermal fluctuations is much less understood, in particular for glasses of different stability. Using molecular dynamics simulations of a model glass where the swap Monte Carlo
algorithm can be employed, we study the yield stress at finite temperature and shear rate, both in steady flow and at shear start-up, over a broad range of glass stability. Thermal fluctuations soften both the dynamic yield stress in steady state and the start-up yield stress. In all cases, the temperature dependence is compatible with the $T^{2/3}$ law expected for thermally activated yielding near a saddle-node instability, with no systematic dependence of the exponent on stability or shear rate. Extrapolations to zero temperature recover the athermal yield stresses. The amplitude of the softening at start-up, by contrast, depends strongly on stability: highly stable glasses are much less sensitive to temperature than poorly annealed ones. A description of yielding at finite temperature must therefore account explicitly for the stability of the glass.
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Statistical Mechanics · Cross-listed from cond-mat.soft
Derjaguin-corrected Kelvin equation for finite open slits
Alexandr Malijevský
We formulate a Derjaguin-corrected Kelvin equation for phase transitions in finite open slits. In such pores, capillary condensation is modified by the finite wall length because the condensed phase is bounded by two terminal menisci pinned at the slit ends. Starting from the macroscopic generalized Kelvin equation, we introduce a scaling approximation which replaces the implicit edge-contact-angle condition by a closed analytic expression while preserving the exact limiting behaviours. We then incorporate mesoscopic wetting-layer contributions into the finite-slit free-energy balance. The single-wall contribution naturally separates into a planar Derjaguin term and a residual finite-length correction controlled by the competition between the wall length $H$ and the parallel correlation length $\xi_\parallel$. The resulting equation reduces to the standard Derjaguin-Kelvin equation for infinitely long slits and to the macroscopic finite-slit Kelvin equation when adsorbed layers are absent. Explicit forms are derived for long-ranged dispersion forces and for short-ranged forces. The theory is tested using classical density functional theory for finite slits with attractive Lennard-Jones walls and hard walls, corresponding respectively to capillary condensation and its drying analogue, capillary evaporation. The Derjaguin-corrected theory substantially improves on the purely macroscopic prediction, capturing both the correct infinite-slit limit and the observed dependence on wall length. For the short-ranged hard-wall system, the agreement with DFT remains nearly quantitative even for very narrow slits.
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Statistical Mechanics · Cross-listed from quant-ph
Finite-time quantum equilibration from local correlations
Piotr Ćwikliński
An isolated
quantum system evolves reversibly, yet a small subsystem can lose nearly all information about its initial state. Conserved quantities may retain some of this information, depending on how strongly they overlap with local observables. Here we consider a subsystem in an arbitrary initial state coupled to a maximally mixed bath. We show that the worst-input mean-square equilibration error, maximised over window origins, is bounded from above and below by the mean square of a complete local autocorrelation, with the stationary part subtracted. A correlation record over a finite interval therefore controls the equilibration error in every interval of the same length. The result allows arbitrary degeneracies of energies and gaps. We apply it to two static
Hamiltonian families. For fixed
spin subsystems in the one-particle sector of a bounded-range periodic clock, fixed-accuracy thermalisation is guaranteed on windows that grow only slightly faster than linearly with system size, despite exponentially small positive energies. A random commuting model with logarithmic interaction range retains an extensive set of conserved observables. Its expected mean-square error is bounded by a finite-size term and an inverse-time term. The inverse-time dependence is unavoidable because of the initial transient. These examples show how local relaxation can coexist with exact conservation laws and a finely spaced spectrum.
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Statistical Mechanics
Universal Boolean Computation in Negatively Coupled Circle Map Lattices
Priyanka D. Bhoyar and Prashant M. Gade
We investigate the computational capabilities of a one-dimensional
lattice of negatively coupled circle maps in its traveling wave regime. We interpret propagating waves as information carriers and exploit their interactions to implement Boolean logic. The logical states are encoded by the propagation direction of the traveling waves, while the presence or absence of a wave at a designated output location represents the logical output. Using controlled wave collisions, we demonstrate the realization of NAND and NOR gates along with other basic gates. Since NAND and NOR operations are functionally complete, the results establish that the traveling wave regime of the negatively coupled circle-map
lattice supports universal Boolean computation in principle. The demonstrated logical operations remain valid over a finite range of the coupling strength \epsilon and map parameter \omega, indicating robustness of the computational scheme to parameter variations. Our results therefore demonstrate that computational functionality can emerge from the collective nonlinear dynamics of a coupled map
lattice, providing a con- nection between the dynamical properties of traveling wave states and collision based information processing.
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Statistical Mechanics · Cross-listed from cond-mat.soft
Length-scale dependence of collective time reparameterization in swap dynamics
Massimo Pica Ciamarra
Swap Monte Carlo dramatically accelerates the equilibration of deeply supercooled
liquids while preserving the
equilibrium Boltzmann distribution. Recent work has argued that swap and other accelerated
algorithms act by reparameterizing time: different dynamics follow the same slow relaxation process, but with different clocks. Here we test this idea in a continuously polydisperse glass former. We confirm that mean collective overlaps satisfy an approximate time reparameterization, in agreement with earlier results. However, the associated clock depends systematically on the collective probe length and on the relaxation stage. Thus the observed collective collapse does not define a unique, observable-independent material time. Over the numerically accessible $\alpha$-relaxation regime, swap changes not only the rate of relaxation, but also its length-scale dependence. The resulting collective reparameterization is therefore only approximate and does not establish an exact dynamical equivalence between swap and reference relaxation.
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Statistical Mechanics · Cross-listed from quant-ph
Permanent Thermodynamic Mpemba Inversion from Quantum-Jump Feedback
Jincheng Lu and Chen Wang
We show that a common
quantum-jump feedback protocol can permanently reverse the nonequilibrium free-energy ordering of two prescribed initial states while preserving their Gibbs
equilibrium. The construction exploits collective compensation between monitored channels: their feedback corrections cancel at
equilibrium but remain active during relaxation. This balance preserves free-energy monotonicity while allowing the relaxation modes to be reshaped. We prove that eliminating the complete slow-sector contribution of the initially higher-free-energy state, while retaining it for the comparison state, produces distinct asymptotic decay exponents. Their free-energy ratio then vanishes at long times, guaranteeing a permanent thermodynamic
quantum Mpemba inversion under the same controlled dynamics. A thermal qutrit realizes the mechanism through coherence interference and exhibits distinct detection thresholds for spectral selection and exact slow-sector cancellation under feedback retuning.
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