arXiv subjects

Balázs Dóra

Publications and source records attributed to Balázs Dóra.

At least 19 recordsLinked to original sources

arXiv2026

Robust Spin Universality Across a Ballistic-to-Diffusive Transport Crossover

Whether a full counting statistical distribution preserves its universality class across a coherent-to-incoherent crossover is a fundamental question in open quantum systems. We resolve this for the infinite-$U$ Hubbard chain, showing that local density dephasing changes transport exponents without destroying the underlying non-Gaussian M-Wright spin fluctuations. Utilizing the exact spin-charge composition law inherent to impenetrable dynamics, we track the charge sector from ballistic flow to diffusive hydrodynamics. This dissipative crossover shifts the characteristic spin-transfer width from $t^{1/4}$ to $t^{1/8}$. Despite this altered scaling time, the central spin characteristic functions uniformly collapse onto a singular M-Wright scaling function, what we confirm using analytics as well as numerics.

cond-mat.quant-gas↗

arXiv2026

Spin-Charge Subordination in the Infinite-$U$ $SU(N)$ Hubbard Chain

We obtain the exact full counting statistics of charge and flavor transport in the one-dimensional infinite-$U$ $SU(N)$ Hubbard model. The no-passing constraint freezes the ordered flavor sequence while the particle coordinates evolve as free spinless fermions. Consequently, charge transfer is governed by a free-fermion determinant, whereas flavor transfer is exactly subordinated to the number of particles crossing the observation cut. For an arbitrary traceless Cartan generator this yields an exact relation between the charge and flavor cumulants. The complete asymptotic flavor distribution is a universal non-Gaussian M-Wright law. Together, these results establish spin--charge subordination as a kinematic mechanism for anomalously slow internal-state transport in one-dimensional impenetrable quantum gases.

cond-mat.quant-gas↗

arXiv2026

Interaction-induced asymmetry in infinite-temperature dynamical correlations of hard-core anyons

We study dynamical correlations of interacting hard-core anyons on a one-dimensional lattice at infinite temperature. This is a setting in which the many-body spectrum is independent of the statistical phase $θ$, while dynamical correlators remain sensitive to $θ$ through nonlocal Jordan-Wigner strings. We compute single-particle Green's functions, spectral functions, and density-density correlators, thereby separating the effects of fractional statistics on one-body coherence from those on density transport in a maximally mixed ensemble. In the noninteracting case $V=0$, high-temperature averaging leads to inversion-symmetric Green's functions for all $θ$ despite the presence of anyonic strings. Finite nearest-neighbor interactions $V$ generate, however, a pronounced left-right asymmetry in the Green's functions for $0<θ<π$, with the strongest chirality appearing at intermediate couplings $V\sim J$ where interactions and hopping compete most effectively. In this regime, the Green's function decays exponentially in time with a statistical-angle-dependent decay rate. At strong coupling, the dynamics crosses over to an atomic-limit regime in which the dependence on $θ$ is reduced. Here, the Green's function decays universally as $t^{-1}$ and the corresponding spectral function displays a three-band structure. In contrast, density-density correlations are insensitive to statistics and recover the known infinite-temperature transport regimes of the XXZ chain, including ballistic, superdiffusive, and diffusive behaviors. These results identify dynamical correlation functions as direct probes of fractional statistics in high-entropy quantum systems.

cond-mat.str-el↗

arXiv2026

Emergent modular Luttinger liquid from spin-partitioned entanglement in the one-dimensional Hubbard model

We study the spin-partitioned entanglement Hamiltonian of the one-dimensional repulsive Hubbard model. By combining bosonization with exact diagonalization, we show that tracing out one spin species produces a modular Luttinger liquid, whose properties fundamentally differ from those of the physical system. While the modular spectrum is fully dispersionless and possesses a momentum-independent entanglement gap, its eigenstates exhibit algebraic correlations governed by a single effective Luttinger parameter equal to the geometric mean of the charge and spin Luttinger parameters. The resulting entanglement spectrum displays a universal branching hierarchy in excellent agreement with exact diagonalization. We further demonstrate that the modular ground state is nearly identical to that of the spinless Luttinger liquid. These results uncover a universal modular structure in interacting one-dimensional fermionic systems.

cond-mat.str-el↗

arXiv2026

Interaction enhanced altermagnet in the Hatsugai-Kohmoto model

We investigate the interplay between altermagnetic band structures and electronic correlations by focusing on the $d_{x^2-y^2}$ altermagnetic generalization of the Hatsugai-Kohmoto model. We find that with increasing interaction, a many-body Lifshitz transition takes place when doubly occupied regions disappear from the Fermi surface and almost all momentum states become fully spin polarized. This is termed interaction enhanced altermagnet. We find that the dynamical susceptibility, which possesses only transverse non-zero components for small wavevectors, develops a gap proportional to the interaction strength, and displays a sharp peak at a frequency increasing with the interaction. Above the Lifshitz transition, this peak moves to the lower gap edge and becomes log-divergent. The signal intensity increases with the interaction up until the Lifshitz transition and saturates afterwards. The static susceptibility remains unaffected by the correlations and altermagnetism reduces the static transverse response.

cond-mat.str-el↗

arXiv2026

Mimicry of chaos and $k$-design in higher order OTOCs of Luttinger liquids

Out-of-time-order correlators (OTOCs) provide a fundamental metric for quantum chaos, but capturing the fine structure of information scrambling requires exploring their higher-order generalizations. Here, we systematically investigate the sequence of higher-order OTOCs in a Luttinger liquid and its lattice realization, the XXZ Heisenberg chain. Using bosonization and numerics, we extract the full temporal dynamics of the first three OTOCs, revealing that they rapidly erase memory of the initial state, and quickly saturate to their steady state values. Strikingly, we show that calculating the late time saturation values for the entire sequence of higher-order OTOCs maps exactly onto determining the partition function of a non-Hermitian Harper model. Through this mapping, we demonstrate that for moderately strong interactions, the steady-state OTOCs become parametrically small up to the seventh order, mimicking higher $k$-design. Our results reveal that Luttinger liquids exhibit an unexpectedly profound degree of apparent scrambling when viewed through the lens of higher-order OTOCs.

cond-mat.str-el↗

arXiv2026

Dynamic scaling and Family-Vicsek universality in the Hubbard model at infinite temperature

We study Family-Vicsek scaling of charge, spin, and energy fluctuations in the one-dimensional Hubbard model at infinite temperature. Using a quantum generating function approach, we compute time-dependent cumulants of transferred conserved quantities and analyze how the corresponding roughness depends on subsystem size and time. We start by focusing on a single interface at half the chain and determine the transport exponents. Then we turn to fluctuations of a small finite interval and study the Family-Vicsek universality of fluctuations over an extended timescale. We find that the long-time scaling behavior is controlled by integrability. In the free limit, charge, spin, and energy all display ballistic transport. In the interacting integrable Hubbard chain, charge and spin cross over to a KPZ scaling regime, while the energy sector remains ballistic. Once integrability is broken by a next-nearest-neighbor density interaction, the long-time dynamics becomes diffusive in all sectors. In every case we also observe a short-time microscopic regime with apparently universal ballistic growth before the hydrodynamic scaling window sets in. The Family-Vicsek setup allows us to determine the growth, the saturation as well as the dynamical exponents.

cond-mat.str-el↗

arXiv2026

Two-parameter Family-Vicsek scaling in a dissipative XXZ spin chain

Family-Vicsek (FV) scaling provides an understanding for the growth and finite-size saturation of fluctuations in classical systems. Here, we extend the FV roughness to transferred segment magnetization after quantum quenches in a dissipative XXZ spin chain with homogeneous gain and loss, starting from a nonequilibrium steady state with finite magnetization. In the non-interacting limit, we derive a closed-form expression for the roughness in the presence of dissipation. It displays two-parameter FV scaling and smoothly interpolates between the clean ballistic behavior and the dissipation dominated scalings. For interacting chains, tensor-network simulations show that the non-dissipative ballistic growth at finite magnetization is robust, whereas the full Lindblad evolution is generically controlled by the dissipative relaxation time and exhibits a dissipation-dominated collapse.

quant-ph↗

arXiv2026

Nonstabilizerness generation in a multiparticle quantum walk

We investigate the generation of non-stabilizerness, or magic, in a multi-particle quantum walk by analyzing the time evolution of the stabilizer Rényi entropy $M_2$. Our study considers both single- and two-particle quantum walks in the framework of the XXZ Heisenberg model with varying interaction strengths. We demonstrate that the spread of magic follows the light-cone structure dictated by the system's dynamics, with distinct behaviors emerging in the easy-plane ($Δ< 1$) and easy-axis ($Δ> 1$) regimes. For $Δ< 1$, magic generation is primarily governed by single-particle dynamics, while for $Δ> 1$, doublon propagation dominates, resulting in a significantly slower growth of $M_2$. Furthermore, the magic exhibits logarithmic growth in time for both one and two-particle dynamics. Additionally, by examining the Pauli spectrum, we show that the statistical distribution of level spacings exhibits Poissonian behavior, independent of interaction strength or particle number. Our results shed light on the role of interactions on magic generation in a many-body system.

quant-ph↗

arXiv2025

Nonstabilizerness in open XXZ spin chains: Universal scaling and dynamics

Magic, or nonstabilizerness, is a crucial quantum resource, yet its dynamics in open quantum systems remain largely unexplored. We investigate magic in the open XXZ spin chain under either boundary gain and loss, or bulk dephasing using the stabilizer Rényi entropy $M_2$. To enable scalable simulations of large systems, we develop a novel, highly efficient algorithm for computing $M_2$ within the matrix product states formalism while maintaining constant bond dimension--an advancement over existing methods. For boundary driving, we uncover universal scaling laws, $M_2(t) \sim t^{1/z}$, linked to the dynamical exponent $z$ for several distinct universality classes. We also disentangle classical and quantum contributions to magic by introducing a mean-field approximation for magic, thus emphasizing the prominent role of quantum critical fluctuations in nonstabilizerness. For bulk dephasing, dissipation can transiently enhance magic before suppressing it, and drive it to a nontrivial steady-state value. These findings position magic as a powerful diagnostic tool for probing universality and dynamics in open quantum systems.

quant-ph↗

arXiv2025

Non-stabilizerness as a Diagnostic of Criticality and Exceptional Points in Non-Hermitian Spin Chains

We investigate non-stabilizerness, also known as ``magic,'' to understand criticality and exceptional points in non-Hermitian quantum many-body systems. Our focus is on parity-time ($\mathcal{PT}$) symmetric spin chains, specifically the non-Hermitian transverse-field Ising and XX models. We calculate stabilizer Rényi entropies in their ground states using non-Hermitian matrix product state methods. Our findings show that magic exhibits unique and model-specific signs of phase transitions. In the Ising chain, it peaks along the regular Hermitian-like critical line but disappears across exceptional points. In contrast, in the XX chain, it reaches its maximum at the exceptional line where $\mathcal{PT}$ symmetry is broken. Finite-size scaling reveals that these effects become more pronounced with larger systems, highlighting non-stabilizerness as a sensitive marker for both quantum criticality and non-Hermitian spectral degeneracies. We also investigate magic in momentum space for the XX model analytically and find that is reaches a minimum around exceptional points. Our results indicate that magic takes extremal values at the exceptional points and serves as a valuable tool for examining complexity, criticality, and symmetry breaking in non-Hermitian quantum matter.

quant-ph↗

arXiv2025

Anomalous Quantum Relaxation in the Infinite Temperature Hubbard Chain

The self-energy encodes the fundamental lifetime of quasiparticle excitations. In one dimension, it is known to display anomalous behavior at zero temperature for interacting fermions, reflecting the breakdown of Fermi-liquid theory. Here we show that the self-energy is also anomalous in the infinite temperature Hubbard chain, where thermal fluctuations are maximal. Focusing on the second order ring diagram, we find that the imaginary part of the self-energy diverges non-perturbatively: as a power law with exponent $-1/3$ near half filling, and logarithmically away from it. These divergences imply anomalous temporal relaxation of Green's functions, confirmed by infinite temperature tensor-network simulations. Our results demonstrate that anomalous relaxation and the breakdown of perturbation theory survive even at maximal entropy, which can be observed in cold-atom experiments probing the Hubbard chain at high temperatures.

cond-mat.str-el↗

arXiv2025

Quantum Coherence in a Maximally Hot Hubbard Chain

We present a detailed study of the real-time dynamics and spectral properties of the one-dimensional fermionic Hubbard model at infinite temperature. Using tensor network simulations in Liouville space, we compute the single-particle Green's function and analyze its dynamics across a broad range of interaction strengths. To complement the time-domain approach, we develop a high-resolution Chebyshev expansion method within the density matrix formalism, enabling direct access to spectral functions in the frequency domain. In the non-interacting limit, we derive exact analytical expressions for the Green's function, providing a benchmark for our numerical methods. As interactions are introduced, we observe a transition in the spectral function from a sharp peak at the free dispersion to a broadened two-band structure associated with hole and doublon excitations. These features are well captured by a Hubbard-I mean-field approximation, even at intermediate coupling. At infinite interaction strength ($U = \infty$), we exploit a determinant representation of the Green's function to access both real-time and spectral properties. In this regime, the system retains a sharp, cosine-like momentum dispersion in frequency space, while the dynamics display nontrivial light-cone spreading with sub-ballistic scaling. Our results demonstrate that strong correlations and nontrivial quantum coherence can persist even at infinite temperature.

cond-mat.str-el↗

arXiv2025

Hot but Coherent: Doublons at Infinite Temperature in the Hubbard chain

We investigate the spectral properties and the dynamics of doublons in the one-dimensional Hubbard model at infinite temperature. Using a Chebyshev expansion approach formulated in the superfermionic representation, we compute the momentum- and frequency-resolved doublon spectral function across a wide range of interaction strengths $U$ and in the presence of an external electric field. Increasing the interaction, the spectrum gradually splits into separate bands associated with two-hole and two-particle excitations. Despite the presence of strong correlations, we find that doublons retain their coherence and undergo long-lived Bloch oscillations, as well as rich quantum walk dynamics characterized by light-cone spreadings at strong coupling, which we analyze through the time-and space-resolved Green's function.

cond-mat.str-el↗

arXiv2025

Localized states and skin effect around non-Hermitian impurities in tight-binding models

We use the generalized Bloch theorem formalism of Alase {\it et al.} [{\it Phys. Rev. Lett.} {\bf 117} 076804 (2016)] to analyze simple one-dimensional tight-binding lattice systems connected by Hermitian bonds (all with the same hopping parameter $t$), but containing one bond impurity which can be either Hermitian or non-Hermitian. We calculate the band structure, the bulk-boundary correspondence indicator ($D_L(ε)$) and analyze the eigenvalues of the lattice translation operator ($z$), for each eigenstate. From the $z$ values the generalized Brillouin zone can be reconstructed. If the impurity is Hermitian (and $\mathcal{PT}$-symmetric), we find a parameter regime in which two localized edge states separate from the tight-binding band. We then simulate a non-Hermitian impurity by keeping hopping in one direction of the bond impurity the same as the rest of the tight-binding system, and varying only its reciprocal. Again, we find a region with localized edge states, but in this case the energy eigenvalues are purely imaginary. We also find that in this case the two zero energy eigenvectors coalesce, hence this system is an exceptional line. We then perform an interpolative scan between the above two scenarios and find that there is an intermediate region exhibiting a non-Hermitian skin effect. In this region a macroscopic fraction of states acquire complex energy eigenvalues and exhibit localization towards the impurity. Our numerical results are supported by a detailed analysis of the solutions of the boundary/impurity equation.

cond-mat.mes-hall↗

arXiv2025

Infinite temperature spin dynamics in the asymmetric Hatsugai-Kohmoto model

We focus on the infinite temperature dynamical spin structure factor of the asymmetric Hatsugai-Kohmoto model, the relative of the asymmetric Hubbard model. It is characterized by distinct single particle energies for the two spin species, which interact with each other through a contact interaction in momentum space. We evaluate its spin structure factor exactly and follow the evolution of its excitation spectrum for all fillings and interactions, identify signatures of the Mott transition and fingerprints of the asymmetric hoppings. The longitudinal spin structure factor exhibits sound like and interaction induced gapped excitations, whose number gets doubled in the presence of hopping asymmetry. The transverse response displays the competition of interaction and asymmetry induced gaps and results in a quadratic excitation branch at their transition. The complete asymmetric case features momentum-independent dynamical structure factor, characteristic to transitions involving a flat band.

cond-mat.str-el↗

arXiv2025

Dynamic scaling and Family-Vicsek universality in $SU(N)$ quantum spin chains

The Family-Vicsek scaling is a fundamental framework for understanding surface growth in non-equilibrium classical systems, providing a universal description of temporal surface roughness evolution. While universal scaling laws are well established in quantum systems, the applicability of Family-Vicsek scaling in quantum many-body dynamics remains largely unexplored. Motivated by this, we investigate the infinite-temperature dynamics of one-dimensional $SU(N)$ spin chains, focusing on the well-known $SU(2)$ XXZ model and the $SU(3)$ Izergin-Korepin model. We compute the quantum analogue of classical surface roughness using the second cumulant of spin fluctuations and demonstrate universal scaling with respect to time and subsystem size. By systematically breaking global $SU(N)$ symmetry and integrability, we identify distinct transport regimes characterized by the dynamical exponent $z$: (i) ballistic transport with $z=1$, (ii) superdiffusive transport with the Kardar-Parisi-Zhang exponent $z=3/2$, and (iii) diffusive transport with the Edwards-Wilkinson exponent $z=2$. Notably, breaking integrability always drives the system into the diffusive regime. Our results demonstrate that Family-Vicsek scaling extends beyond classical systems, holding universally across quantum many-body models with $SU(N)$ symmetry.

cond-mat.str-el↗

arXiv2025

Slow approach to adiabaticity in many-body non-Hermitian systems: the Hatano-Nelson Model

We explore the near adiabatic dynamics in a non-Hermitian quantum many-body system by investigating a finite-time ramp of the imaginary vector potential in the interacting Hatano-Nelson model. The excess energy, the Loschmidt echo, and the density imbalance are analyzed using bosonization and exact diagonalization. The energy becomes complex valued, despite the instantaneous Hamiltonian having the same real spectrum throughout. The adiabatic limit is approached very slowly through damped oscillations. The decay scales with $τ^{-1}$ with $τ$ the ramp duration, while the oscillation period is $2L/v$ with $v$ the Fermi velocity and $L$ the system length. Yet, without the need for auxiliary controls, a shortcut to adiabaticity is found for ramp times commensurate with the period. Our work highlights the intricate interplay of adiabaticity and non-Hermitian many-body physics.

quant-ph↗