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L. Canet

Publications and source records attributed to L. Canet.

10 recordsLinked to original sources
arXiv2026

Crossing over universal scaling laws in two-dimensional driven dissipative condensates

In low dimensional systems, fluctuations are enhanced and prevent the spontaneous breaking of continuous symmetries. As a result, spatial and temporal correlation functions decay at large distances and long times. A well established example is given by two-dimensional bosonic condensates at equilibrium, which do not display long-range order of the coherence but algebraic decay belonging to the Berezinski-Kosterlitz-Thouless universality class. In contrast, the universal behaviors of non-equilibrium bosonic condensates are more diverse and many open questions remain. Here, we explore the spatio-temporal coherence properties of two-dimensional driven-dissipative polariton condensates in semiconductor optical microcavities. By tuning microscopic parameters, we observe a cross-over between two scaling laws that we attribute to the Edwards-Wilkinson (EW) and the Kardar-Parisi-Zhang (KPZ) universality classes. We demonstrate the collapse of the measured first-order correlations onto the EW and KPZ universal scaling functions and obtain critical exponents, well matching the values predicted theoretically. Our results highlight the intrinsic non-equilibrium nature of polariton condensates and establish them as a platform of choice for controlled exploration of the two-dimensional KPZ universality class.

cond-mat.quant-gas↗
arXiv2026

Comment on "Observation of Kardar--Parisi--Zhang universal scaling in two dimensions"

In their paper published in Science 392, 221 (2026), Widmann and collaborators reported interferometry experiments to explore the emission coherence decay of a two-dimensional polariton condensate generated in an array of coupled resonators. The authors claim evidence of Kardar--Parisi--Zhang (KPZ) universal scaling in the measured spatio-temporal coherence decay. We argue in the following that the data were not properly analyzed. We re-analyze the experimental data acquired both with the square and the triangular lattices for various values of the excitation power. Instead of stretched exponential decays, in the space (time) windows considered in the paper we find that the measured $|g^{(1)}(\delta {\bf r}, \delta t)|$ at $\delta t=0$ ($|\delta {\bf r}| $ close to $0$) rather show Gaussian (exponential) decay for all excitation powers. As a result, using as temporal and spatial exponents $\beta=0.5$ and $\chi=1$, the data for all pump powers are found to collapse onto a single curve, which is not the KPZ scaling function. In particular, we show that the data collapse onto the KPZ scaling function presented in the paper is an artifact stemming from incorrect data normalization. We thus conclude that the main claim of the paper is not justified as the spatio-temporal decays of the coherence over the space-time windows analyzed in the paper are not well described by the KPZ universal behavior.

cond-mat.quant-gas↗
arXiv2020

The nonperturbative functional renormalization group and its applications

The renormalization group plays an essential role in many areas of physics, both conceptually and as a practical tool to determine the long-distance low-energy properties of many systems on the one hand and on the other hand search for viable ultraviolet completions in fundamental physics. It provides us with a natural framework to study theoretical models where degrees of freedom are correlated over long distances and that may exhibit very distinct behavior on different energy scales. The nonperturbative functional renormalization-group (FRG) approach is a modern implementation of Wilson's RG, which allows one to set up nonperturbative approximation schemes that go beyond the standard perturbative RG approaches. The FRG is based on an exact functional flow equation of a coarse-grained effective action (or Gibbs free energy in the language of statistical mechanics). We review the main approximation schemes that are commonly used to solve this flow equation and discuss applications in equilibrium and out-of-equilibrium statistical physics, quantum many-particle systems, high-energy physics and quantum gravity.

cond-mat.stat-mech↗
arXiv2007

Universality classes of the Kardar-Parisi-Zhang equation

We re-examine mode-coupling theory for the Kardar-Parisi-Zhang (KPZ) equation in the strong coupling limit and show that there exists two branches of solutions. One branch (or universality class) only exists for dimensionalities $d<d_c=2$ and is similar to that found by a variety of analytic approaches, including replica symmetry breaking and Flory-Imry-Ma arguments. The second branch exists up to $d_c=4$ and gives values for the dynamical exponent $z$ similar to those of numerical studies for $d\ge2$.

cond-mat.stat-mech↗
arXiv2007

Single-site approximation for reaction-diffusion processes

We consider the branching and annihilating random walk $A\to 2A$ and $2A\to 0$ with reaction rates $σ$ and $λ$, respectively, and hopping rate $D$, and study the phase diagram in the $(λ/D,σ/D)$ plane. According to standard mean-field theory, this system is in an active state for all $σ/D>0$, and perturbative renormalization suggests that this mean-field result is valid for $d >2$; however, nonperturbative renormalization predicts that for all $d$ there is a phase transition line to an absorbing state in the $(λ/D,σ/D)$ plane. We show here that a simple single-site approximation reproduces with minimal effort the nonperturbative phase diagram both qualitatively and quantitatively for all dimensions $d>2$. We expect the approach to be useful for other reaction-diffusion processes involving absorbing state transitions.

cond-mat.stat-mech↗
arXiv2005

Non-perturbative fixed point in a non-equilibrium phase transition

We apply the non-perturbative renormalization group method to a class of out-of-equilibrium phase transitions (usually called ``parity conserving'' or, more properly, ``generalized voter'' class) which is out of the reach of perturbative approaches. We show the existence of a genuinely non-perturbative fixed point, i.e. a critical point which does not seem to be Gaussian in any dimension.

cond-mat.stat-mech↗
arXiv2004

What can be learnt from the nonperturbative renormalization group?

We point out some limits of the perturbative renormalization group used in statistical mechanics both at and out of equilibrium. We argue that the non perturbative renormalization group formalism is a promising candidate to overcome some of them. We present some results recently obtained in the literature that substantiate our claims. We finally list some open issues for which this formalism could be useful and also review some of its drawbacks.

cond-mat.stat-mech↗
arXiv2004

Quantitative Phase Diagrams of Branching and Annihilating Random Walks

We demonstrate the full power of nonperturbative renormalisation group methods for nonequilibrium situations by calculating the quantitative phase diagrams of simple branching and annihilating random walks and checking these results against careful numerical simulations. Specifically, we show, for the 2A->0, A -> 2A case, that an absorbing phase transition exists in dimensions d=1 to 6, and argue that mean field theory is restored not in d=3, as suggested by previous analyses, but only in the limit d -> $\infty$.

cond-mat.stat-mech↗
arXiv2003

Optimization of the derivative expansion in the nonperturbative renormalization group

We study the optimization of nonperturbative renormalization group equations truncated both in fields and derivatives. On the example of the Ising model in three dimensions, we show that the Principle of Minimal Sensitivity can be unambiguously implemented at order $\partial^2$ of the derivative expansion. This approach allows us to select optimized cut-off functions and to improve the accuracy of the critical exponents $ν$ and $η$. The convergence of the field expansion is also analyzed. We show in particular that its optimization does not coincide with optimization of the accuracy of the critical exponents.

hep-th↗