arXiv subjects

Alessio Franchi

Publications and source records attributed to Alessio Franchi.

15 recordsLinked to original sources

arXiv2024

Wild Berry image dataset collected in Finnish forests and peatlands using drones

Berry picking has long-standing traditions in Finland, yet it is challenging and can potentially be dangerous. The integration of drones equipped with advanced imaging techniques represents a transformative leap forward, optimising harvests and promising sustainable practices. We propose WildBe, the first image dataset of wild berries captured in peatlands and under the canopy of Finnish forests using drones. Unlike previous and related datasets, WildBe includes new varieties of berries, such as bilberries, cloudberries, lingonberries, and crowberries, captured under severe light variations and in cluttered environments. WildBe features 3,516 images, including a total of 18,468 annotated bounding boxes. We carry out a comprehensive analysis of WildBe using six popular object detectors, assessing their effectiveness in berry detection across different forest regions and camera types. WildBe is publicly available on HuggingFace at https://huggingface.co/datasets/FBK-TeV/WildBe.

cs.CV↗

arXiv2023

Liouvillian gap and out-of-equilibrium dynamics of a sunburst Kitaev ring: from local to uniform dissipation

We consider an open quantum system composed of a $(1+1)$-dimensional Kitaev ring coupled with the environment via $n$ particle-loss dissipators in a \textit{sunburst} geometry. We describe the out-of-equilibrium dynamics of the whole apparatus in terms of Lindblad master equations and focus on the scaling behavior of the Liovillian gap $\Delta_\lambda$ with the system size $L$. We unveil different regimes, which depend primarily on the number of dissipation sources considered in the large-size limit and the dissipation strength $w$, which may be either fixed or attenuated to zero as $w\sim1/L$. In the second part, we develop a dynamic Finite-Size Scaling framework close to Continuous Quantum Transitions to monitor the time evolution of the critical correlations and the entanglement entropy, emphasizing the role of $\Delta_\lambda$ in this regime.

cond-mat.stat-mech↗

arXiv2022

Chiral critical behavior of 3D lattice fermionic models with quartic interactions

We study the critical behavior of the three-dimensional (3D) Gross-Neveu (GN) model with $N_f$ Dirac fermionic flavors and quartic interactions, at the chiral ${\mathbb Z}_2$ transition in the massless ${\mathbb Z}_2$-symmetric limit. For this purpose, we consider a lattice GN model with staggered Kogut-Susskind fermions and a scalar field coupled to the scalar bilinear fermionic operator, which effectively realizes the attractive four-fermion interaction. We perform Monte Carlo (MC) simulations for $N_f=4,8,12,16$. By means of finite-size scaling analyses of the numerical data, we obtain estimates of the critical exponents that are compared with the large-$N_f$ predictions obtained using the continuum GN field theory. We observe a substantial agreement. This confirms that lattice GN models with staggered fermions provide a nonpertubative realization of the GN quantum field theory, even though the lattice interactions explicitly break the flavor ${\rm U}(N_f)\otimes {\rm U}(N_f)$ symmetry of the GN field theory, which is only recovered in the critical limit.

hep-lat↗

arXiv2022

Quantum critical behaviors and decoherence of weakly coupled quantum Ising models within an isolated global system

We discuss the quantum dynamics of an isolated composite system consisting of weakly interacting many-body subsystems. We focus on one of the subsystems, S, and study the dependence of its quantum correlations and decoherence rate on the state of the weakly-coupled complementary part E, which represents the environment. As a theoretical laboratory, we consider a composite system made of two stacked quantum Ising chains, locally and homogeneously weakly coupled. One of the chains is identified with the subsystem S under scrutiny, and the other one with the environment E. We investigate the behavior of S at equilibrium, when the global system is in its ground state, and under out-of-equilibrium conditions, when the global system evolves unitarily after a soft quench of the coupling between S and E. When S develops quantum critical correlations in the weak-coupling regime, the associated scaling behavior crucially depends on the quantum state of E whether it is characterized by short-range correlations (analogous to those characterizing disordered phases in closed systems), algebraically decaying correlations (typical of critical systems), or long-range correlations (typical of magnetized ordered phases). In particular, different scaling behaviors, depending on the state of E, are observed for the decoherence of the subsystem S, as demonstrated by the different power-law divergences of the decoherence susceptibility that quantifies the sensitivity of the coherence to the interaction with E.

cond-mat.stat-mech↗

arXiv2022

Decoherence and energy flow in the sunburst quantum Ising model

We study the post-quench unitary dynamics of a quantum sunburst spin model, composed of a transverse-field quantum Ising ring which is suddenly coupled to a set of independent external qubits along the longitudinal direction, in a way to respect a residual translation invariance and the Ising $\mathbb{Z}_2$ symmetry. Starting from the different equilibrium quantum phases of the system, we characterize the decoherence and the energy storage in the external qubits, which may be interpreted as a probing apparatus for the inner Ising ring. Our results show that, in proximity of the quantum transitions of the Ising ring, either first-order or continuous, it is possible to put forward dynamic FSS frameworks which unveil peculiar scaling regimes, depending on the way in which the large-size limit is taken: either by fixing the number $n$ of probing qubits, or their interspace distance $b$. In any case, the dependence of the various observables on $n$ can be reabsorbed into a redefinition of the quench parameter by a $\sqrt{n}$ prefactor. We also address the role of a nearest-neighbor coupling between the external qubits.

cond-mat.stat-mech↗

arXiv2022

Color-flavor reflection in the continuum limit of two-dimensional lattice gauge theories with scalar fields

We address the interplay between local and global symmetries in determining the continuum limit of two-dimensional lattice scalar theories characterized by $SO(N_c)$ gauge symmetry and non-Abelian $O(N_f)$ global invariance. We argue that, when a quartic interaction is present, the continuum limit of these model corresponds in some cases to the gauged non-linear $\sigma$ model field theory associated with the real Grassmannian manifold $SO(N_f)/(SO(N_c)\times SO(N_f-N_c)$), which is characterized by the invariance under the color-flavor reflection $N_c\leftrightarrow N_f-N_c$. Monte Carlo simulations and Finite-Size Scaling analyses, performed for $N_f=7$ and several values of $N_c$, confirm the emergence of the color-flavor reflection symmetry in the scaling limit, and support the identification of the continuum limit.

hep-lat↗

arXiv2022

Quantum many-body spin rings coupled to ancillary spins: The sunburst quantum Ising model

We study the ground-state properties of a quantum "sunburst model", composed of a quantum Ising spin-ring in a transverse field, symmetrically coupled to a set of ancillary isolated qubits, to maintain a residual translation invariance and also a $\mathbb{Z}_2$ symmetry. The large-size limit is taken in two different ways: either by keeping the distance between any two neighboring ancillary qubits fixed, or by fixing their number while increasing the ring size. Substantially different regimes emerge, depending on the various Hamiltonian parameters: for small energy scale $\delta$ of the ancillary subsystem and small ring-qubits interaction $\kappa$, we observe rapid and nonanalytic changes in proximity of the quantum transitions of the Ising ring, both first-order and continuous, which can be carefully controlled by exploiting renormalization-group and finite-size scaling frameworks. Smoother behaviors are instead observed when keeping $\delta>0$ fixed and in the Ising disordered phase. The effect of an increasing number $n$ of ancillary spins turns out to scale proportionally to $\sqrt{n}$ for sufficiently large values of $n$.

cond-mat.stat-mech↗

arXiv2022

Critical crossover phenomena driven by symmetry-breaking defects at quantum transitions

We study the effects of symmetry-breaking defects at continuous quantum transitions (CQTs), which may arise from localized external fields coupled to the order-parameter operator. The problem is addressed within renormalization-group (RG) and finite-size scaling frameworks. We consider the paradigmatic one-dimensional quantum Ising models at their CQT, in the presence of defects which break the global ${\mathbb Z}_2$ symmetry. We show that such defects can give rise to notable critical crossover regimes where the ground-state properties experience substantial and rapid changes, from symmetric conditions to symmetry-breaking boundaries. An effective characterization of these crossover phenomena driven by defects is achieved by analyzing the ground-state fidelity associated with small changes of the defect strength. Within the critical crossover regime, the fidelity susceptibility shows a power-law divergence when increasing the system size, related to the RG dimension of the defect strength; in contrast, outside the critical defect regime, it remains finite. We support the RG scaling arguments with numerical results.

cond-mat.stat-mech↗

arXiv2021

Continuum limit of two-dimensional multiflavor scalar gauge theories

We address the interplay between local and global symmetries by analyzing the continuum limit of two-dimensional multicomponent scalar lattice gauge theories, endowed by non-Abelian local and global invariance. These theories are asymptotically free. By exploiting Monte Carlo simulations and finite-size scaling techniques, we provide numerical results concerning the universal behavior of such models in the critical regime. Our results support the conjecture that two-dimensional multiflavor scalar models have the same continuum limit as the $\sigma$-models associated with symmetric spaces that have the same global symmetry.

hep-lat↗

arXiv2021

Phase diagram and Higgs phases of 3D lattice SU(Nc) gauge theories with multiparameter scalar potentials

We consider three-dimensional lattice SU(Nc) gauge theories with degenerate multicomponent (Nf>1) complex scalar fields that transform under the fundamental representation of the gauge SU(Nc) group and of the global U(Nf) invariance group, interacting with the most general quartic potential compatible with the global (flavor) and gauge (color) symmetries. We investigate the phase diagrams, identifying the low-temperature Higgs phases and their global and gauge symmetries, and the critical behaviors along the different transition lines. In particular, we address the role of the quartic scalar potential, which determines the Higgs phases and the corresponding symmetry-breaking patterns. Our study is based on the analysis of the minimum-energy configurations and on numerical Monte Carlo simulations. Moreover, we investigate whether some of the transitions observed in the lattice model can be related to the behavior of the renormalization-group flow of the continuum field theory with the same symmetries and field content around its stable charged fixed points. For Nc=2, numerical results are consistent with the existence of charged critical behaviors for Nf > Nf*, with 20 < Nf* < 40.

cond-mat.stat-mech↗

arXiv2021

Three-dimensional lattice SU($N_c$) gauge theories with multiflavor scalar fields in the adjoint representation

We consider three-dimensional lattice SU($N_c$) gauge theories with multiflavor ($N_f>1$) scalar fields in the adjoint representation. We investigate their phase diagram, identify the different Higgs phases with their gauge-symmetry pattern, and determine the nature of the transition lines. In particular, we study the role played by the quartic scalar potential and by the gauge-group representation in determining the Higgs phases and the global and gauge symmetry-breaking patterns characterizing the different transitions. The general arguments are confirmed by numerical analyses of Monte Carlo results for two representative models that are expected to have qualitatively different phase diagrams and Higgs phases. We consider the model with $N_c = 3$, $N_f=2$ and with $N_c=2$, $N_f= 4$. This second case is interesting phenomenologically to describe some features of cuprate superconductors.

hep-lat↗

arXiv2021

Two-dimensional lattice SU($N_c$) gauge theories with multiflavor adjoint scalar fields

We consider two-dimensional lattice SU($N_c$) gauge theories with $N_f$ real scalar fields transforming in the adjoint representation of the gauge group and with a global O($N_f$) invariance. Focusing on systems with $N_f\ge 3$, we study their zero-temperature limit, to understand under which conditions a continuum limit exists, and to investigate the nature of the associated quantum field theory. Extending previous analyses, we address the role that the gauge-group representation and the quartic scalar potential play in determining the nature of the continuum limit (when it exists). Our results further corroborate the conjecture that the continuum limit of two-dimensional lattice gauge models with multiflavor scalar fields, when it exists, is associated with a $\sigma$ model defined on a symmetric space that has the same global symmetry as the lattice model.

hep-lat↗

arXiv2020

Berezinskii-Kosterlitz-Thouless transitions in two-dimensional lattice SO($N_c$) gauge theories with two scalar flavors

We study the phase diagram and critical behavior of a two-dimensional lattice SO($N_c$) gauge theory ($N_c \ge 3$) with two scalar flavors, obtained by partially gauging a maximally O($2N_c$) symmetric scalar model. The model is invariant under local SO($N_c$) and global O(2) transformations. We show that, for any $N_c \ge 3$, it undergoes finite-temperature Berezinskii-Kosterlitz-Thouless (BKT) transitions, associated with the global Abelian O(2) symmetry. The transition separates a high-temperature disordered phase from a low-temperature spin-wave phase where correlations decay algebraically (quasi-long range order). The critical properties at the finite-temperature BKT transition and in the low-temperature spin-wave phase are determined by means of a finite-size scaling analysis of Monte Carlo data.

hep-lat↗

arXiv2020

Asymptotic low-temperature critical behavior of two-dimensional multiflavor lattice SO(Nc) gauge theories

We address the interplay between global and local gauge nonabelian symmetries in lattice gauge theories with multicomponent scalar fields. We consider two-dimensional lattice scalar nonabelian gauge theories with a local SO(Nc) (Nc >= 3) and a global O(Nf) invariance, obtained by partially gauging a maximally O(Nf x Nc)-symmetric multicomponent scalar model. Correspondingly, the scalar fields belong to the coset S(Nf Nc-1)/SO(Nc), where S(N) is the N-dimensional sphere. In agreement with the Mermin-Wagner theorem, these lattice SO(Nc) gauge models with Nf >= 3 do not have finite-temperature transitions related to the breaking of the global nonabelian O(Nf) symmetry. However, in the zero-temperature limit they show a critical behavior characterized by a correlation length that increases exponentially with the inverse temperature, similarly to nonlinear O(N) sigma models. Their universal features are investigated by numerical finite-size scaling methods. The results show that the asymptotic low-temperature behavior belongs to the universality class of the two-dimensional RP(Nf-1) model.

hep-lat↗

arXiv2020

Asymptotic low-temperature behavior of two-dimensional RP$^{N-1}$ models

We investigate the low-temperature behavior of two-dimensional (2D) RP$^{N-1}$ models, characterized by a global O($N$) symmetry and a local ${\mathbb Z}_2$ symmetry. For $N=3$ we perform large-scale simulations of four different 2D lattice models: two standard lattice models and two different constrained models. We also consider a constrained mixed O(3)-RP$^2$ model for values of the parameters such that vector correlations are always disordered. We find that all these models show the same finite-size scaling (FSS) behavior, and therefore belong to the same universality class. However, these FSS curves differ from those computed in the 2D O(3) $\sigma$ model, suggesting the existence of a distinct 2D RP$^2$ universality class. We also performed simulations for $N=4$, and the corresponding FSS results also support the existence of an RP$^3$ universality class, different from the O(4) one.

cond-mat.stat-mech↗