Program > Contributed Seminars

Ameye Orjan

Title: Exploring Floquet Engineering and Parametric Instability in N-Coupled Kerr Oscillators: A Pump Photon Approach

Abstract :  Non-equilibrium many-body systems manifest across multiple physics disciplines. Typically, the problem touches on describing the stationary behaviour of complex models of coupled nonlinear oscillators. In my talk, I will discuss our recently developed framework for describing many-body out-of-equilibrium stationary states, in both the quantum and classical limits. In our approach, we address the shortcomings of the rotating-wave approximation (RWA) for periodically driven oscillators. Specifically, combining the canonical quantum description with the RWA yields incorrect results for finite detuning. Consequently, the standard RWA description breaks the quantum-to-classical limit [1]. To address this, we introduce an alternative operator basis that reconciles the RWA with off-resonant driving. We demonstrate our approach for single nonlinear oscillators and extend it to more complex many-body networks. More specifically, we explore the steady-state topologies and phase diagrams of so-called Kerr Parametric Oscillator (KPO) networks. It has been shown that systems of coupled KPOs can be used as Ising machines holding potential for neuromorphic computations. I will present a novel approach that complements existing methodologies, enabling a comprehensive understanding of the emergence of phase transitions within systems involving many-coupled KPOs [2]. Our findings give insight into how to operate KPO networks as Ising chains and networks.

[1] K. Seibold, O. Ameye, and O. Zilberberg, Floquet engineering counting pump photons, (in preparation). [2] O. Ameye, A. Eichler, and O. Zilberberg, Mapping the parametric instability of N-coupled Kerr Parametric Oscillators, (in preparation).

Apolinario Gabriel

Title: Statistical modeling of bifractal statistics with a superposition of characteristic functionals 

Abstract :  We study an ensemble of random fields, each with statistics described by a general characteristic functional. Intermittency is produced by letting the typical length scale of these fields be a random variable. This ensemble decomposition approach [Wilczek, New J. Phys. 18, 125009 (2016)] allows for an analytically tractable approximation to turbulent statistics. We build bifractal statistics by choosing an appropriate distribution for the random length scale. As a result, the velocity statistics are Gaussian, but increment and velocity gradient moments are bifractal. Skewness, a hallmark of turbulent fields, is obtained by truncating a Taylor-expanded cumulant generating functional, a useful approximation to non-Gaussian fields.

Bernard Maximilien

Title: Anomalous scaling of heterogeneous interfaces: a new picture from sample to sample fluctuations (In collaboration with P. Le Doussal, A. Rosso and C. Texier)

Abstract :  We study a discrete model of an heterogeneous elastic line with internal disorder, submitted to thermal fluctuations. The monomers are connected through random springs with independent and identically distributed elastic constants drawn from $p(k)\sim k^{\mu-1}$ for $k\to0$. When $\mu>1$, the scaling of the standard Edwards-Wilkinson model is recovered. When $\mu<1$, the elastic line exhibits an anomalous scaling of the type observed in many growth models and experiments. Here we derive and use the exact expression for the exact probability distribution of the line shape at equilibrium, as well as the spectral properties of the matrix containing the random couplings,to fully characterize the sample to sample fluctuations. Our results lead to novel scaling predictions that partially disagree with previous works, but which are corroborated by numerical simulations. We also provide a novel interpretation of the anomalous scaling in terms of the abrupt jumps in the line's shape that dominate the average value of the observable.

Berti Anna

Title: The physics of ferromagnetic Bose-Einstein condensate mixtures.

Abstract :  Bose-Einstein condensates (BEC) of ultracold atoms have proven to be a promising platform for the realization of analog models. While the analogy is typically exploited in the gravitational context, coherently coupled two-component BEC mixtures behave analogously to a spin chain, showing a para-to-ferromagnetic quantum phase transition (QPT) driven by interactions. The unique combination of superfluidity and ferromagnetic character, the absence of decoherence and dissipation and the impressive experimental control on these systems, make them an ideal platform to study the nature of magnetic elementary excitations, out-of-equilibrium spin dynamics, QPT in lower dimensionality, metastability and more.

[1] Cominotti, Berti, et al, PRX 13 (2), 021037 (2023) [2] Zenesini et al, Nature Phys., 1-6 (2024).

Fontaine Quentin

Title: Exploring Universal Scaling Laws In Two-Dimensional Polariton Condensates

Abstract :  Revealing universal behaviors in different systems is a hallmark of statistical physics. In this context, the Kardar-Parisi-Zhang (KPZ) [1] equation is a paradigmatic example of universality out of equilibrium. This equation describes the critical roughening of stochastically growing interfaces in classical systems. The spatial and temporal correlation functions of the height profile exhibit scalings, with critical exponents specific to the KPZ universality class and depending only on dimensionality. While KPZ physics has been thoroughly studied in one-dimensional (1D) systems, an experimental platform is still missing for its exploration in two dimensions (2D). Interestingly, theoretical predictions show that the phase of polariton condensates behaves as an interface, whose spatio-temporal evolution is described by the KPZ equation [2]. Since the phase is a compact variable, the physics is enriched by the possible emergence of spatial and spatio-temporal vortices. Recent experiments have demonstrated that the coherence of 1D polariton condensates show spatiotemporal decay characteristic of the KPZ universality class. [3]. In this talk, we report optical interferometry experiments on extended 2D polariton condensates generated in lattices of coupled microcavities. We retrieve the spatio-temporal decay of the first order coherence |g(1)|. Close to condensation threshold, the |g(1)| temporal decay can be nicely fitted by a stretched exponential using the characteristic KPZ growth exponent 2β ≃ 0.48. At higher powers, the coherence dynamics evolves into an exponential decay. We will discuss the overall measured spatio-temporal coherence behavior in the KPZ phase as well as the role of vortices in the departure from this phase at higher powers, in accordance with theoretical predictions [4, 5].

[1] M. Kardar, G. Parisi, Y.-C. Zhang. Phys. Rev. Lett., 56:889–892, 1986. [2] L. He, L. M. Sieberer, E. Altman, S. Diehl. Phys. Rev. B, 92:155307, 2015. [3] Q. Fontaine, et al, Nature, 608(7924):687–691, 2022. [4] Q. Mei, K. Ji, M. Wouters. Phys. Rev. B, 103(4):045302, 202. [5] K. Deligiannis, Q. Fontaine, D. Squizzato, M. Richard, S. Ravets, J. Bloch, A. Minguzzi, L. Canet, Phys. Rev. Res., 4:043207, 2022.

Jin Tony

Title: KPZ physics in single-particle, classical or quantum system under monitoring or dephasing.

Abstract :  I will present some of the recent results concerning the dynamical fluctuations of single, classical or quantum, particle subject to external monitoring or dephasing. Exploiting analogies with KPZ physics, I will show that these systems have non trivial scaling of their fluctuations and can exhibit phase transition in dimensions higher than 1.

Mu Sen

Title: Kardar-Parisi-Zhang Physics in the Density Fluctuations of Localized Two-Dimensional Wave Packets

Abstract :  We identify the key features of Kardar-Parisi-Zhang universality class in the fluctuations of the wave density logarithm, in a two-dimensional Anderson localized wave packet. In our numerical analysis, the fluctuations are found to exhibit an algebraic scaling with distance characterized by an exponent of 1/3, and a Tracy-Widom probability distribution of the fluctuations. Additionally, within a directed polymer picture of KPZ physics, we identify the dominant contribution of a directed path to the wave packet density and find that its transverse fluctuations are characterized by a roughness exponent 2/3. Leveraging on this connection with KPZ physics, we verify that an Anderson localized wave packet in 2D exhibits a stretched-exponential correction to its well-known exponential localization.

Pisegna Giulia

Title: Emergent polar order in non-reciprocally coupled conserved densities

Abstract :  In a stochastic field theory for two species of particle densities with non-reciprocal interactions, polar order emerges spontaneously in the form of traveling waves. We build the equation of motion for a suitable polar order parameter to show that its dynamics differs strikingly from existing field theories for flocking. Stability analysis of the ordered state shows that the theory developed up to linear terms in deviations from perfect order is robust under spontaneous fluctuations at every d. When non-linearities are included, the fluctuations remarkably follow a noisy Burgers equation driven by non-reciprocity. Using a Renormalization Group approach, we confirm that our theory falls in the Burgers/KPZ universality class, hence validating robust long-range order properties.

Tierz Miguel

Title: Random matrix description of the Loschmidt echo of spin chains and dynamical quantum phase transitions.

Abstract :  We will explain the random matrix formulation of the Loschmidt echo for several spin chain and fermionic models. This will help us discover new dynamical quantum phase transitions. The XX spin chain case produces three primary outcomes. Firstly, a third-order phase transition occurs at a rescaled critical time, which we determine. Secondly, this third-order phase transition persists away from the thermodynamic limit. For values below the critical point, the difference between the thermodynamic limit and a finite chain decreases exponentially as the system size increases. This is based on the joint work David Pérez-García, Leonardo Santilli, and Miguel Tierz, Quantum 8, 1271 (2024), other works involving D. Pérez-García and/or L. Santilli, and work in progress.

Vercesi Francesco

Title: Scaling regimes of the phase turbulence in the complex Ginzburg-Landau equation

Abstract :  We study the phase turbulence of the one-dimensional complex Ginzburg-Landau equation, in which the defect-free chaotic dynamics of the order parameter maps to a phase equation well approximated by the Kuramoto-Sivashinsky model. In this regime, the behaviour of the large wavelength modes belongs to the Kardar-Parisi-Zhang universality class [1]. We present numerical evidence of the existence of an additional scale-invariant regime, with dynamical scaling exponent z=1, emerging at scales which are intermediate between the microscopic, intrinsic to the modulational instability, and the macroscopic ones. We argue that this new regime is a signature of the universality class corresponding to the inviscid limit of the Kardar-Parisi-Zhang equation [2].

[1] D. Roy and R. Pandit, Phys. Rev. E 101, (2020). [2] C. Fontaine, F. Vercesi, M. Brachet, and L. Canet, Phys. Rev. Lett. 131, (2023).