News Archive

We show new interesting states in the one-dimensional Bose gas can be engineered with cyclic interaction changes. These states resemble canonical Fermi seas, but they have fractional occupancy and feature puzzling correlation functions.

A. Bastianello, Y. Zeng, S. Dhar, Z. Wang, X. Yu, M. Horvath, G. E. Astrakharchik, Y. Guo, H.C. Nägerl, M. Landini, Phys. Rev. Lett. 136, 230402 (2026).

Check out the press release for the general public here!

Special thanks to the experimental group, which managed to create fractional Fermi seas in the lab: arXiv:2602.17657! 

Conventionally, a free-falling object increases its velocity with time. If it moves in a viscous medium, it reaches a stationary velocity.

However, in ultracold quantum gases, impurities accelerated in a continuum medium can experience periodic Bloch oscillations even in the absence of a lattice: previously this phenomenon was understood only for single impurities at zero temperature.

In this preprint, we consider the two-component integrable Yang-Gaudin model and develop a generalized-hydrodynamic theory of Bloch oscillations for a finite density of impurities embedded in a homogeneous interacting background, which we show to persist superimposed to a drift due to the acceleration of the center of mass.

S. Scopa, P. Zechmann, M. Knap, J. De Nardis, A. Bastianello, arXiv:2605.18957 (2026)

We hope our findings can inspire future experiments in ultracold gases, where Bloch oscillations in the absence of a lattice have been so far observed only in the dilute impurity regime.

At large scales, many diverse processes obey the law of large numbers. Whenever many weakly correlated variables contribute to the same quantity, the latter are expected to have Gaussian typical fluctuations.

However, there are exceptions to this common scenario!

In this preprint, we investigate the typical fluctuations of the integrated spin-current in the XXZ quantum spin chain in the so-called easy axis regime. Using ballistic macroscopic fluctuation theory, we analytically show the emergence of a "nested-Gaussian" distribution, previously only numerically observed.

Takato Yoshimura, Žiga Krajnik, Alvise Bastianello, Enej Ilievski, arXiv:2602.24242 (2026)

Besides the already interesting axial-regime, we hope this approach will help further understanding the even more intriguing isotropic regime, which has an intimate, but not fully disclosed, connection with the KPZ universality class.

The Pauli exclusion principle is a cornerstone of quantum physics: in the ground state, fermions occupy the lowest-energy levels forming a Fermi sea. In one-dimension, when interactions are deeply linked to statistics, even interacting bosons feature emergent Fermi seas universally described by the Tomonaga-Luttinger liquid approach. In these partner preprints, we show that generalizations of Fermi seas with a fractional occupancy can be realized in ultracold bosons out of equilibrium!

In this theoretical preprint, we show how fractional Fermi seas can be realized through cyclic changes in the interactions in the 1d Bose gas. Correlation functions in these states feature a new form of criticality, beyond the Tomonaga-Luttinger liquid

Exotic critical states as fractional Fermi seas in the one-dimensional Bose gas, A. Bastianello, Y. Zeng, S. Dhar, Z. Wang, X. Yu, M. Horvath, G. E. Astrakharchik, Y. Guo, H.-C. Nägerl, M. Landini, arXiv:2602.17656 (2026)

As a cherry on top, fractional Fermi seas are realized in practice in ultracold Cesium atoms, and they imprint Friedel oscillations in the one-body correlation function

Realization of fractional Fermi seas, Y. Zeng, A. Bastianello, S. Dhar, Z. Wang, X. Yu, M. Horvath, G. E. Astrakharchik, Y. Guo, H.-C. Nägerl, M. Landini, arXiv:2602.17657 (2026)

Correlation functions lie at the core of our understanding of many-body phenomena, and in particular unequal-time correlations detect the emergence of hydrodynamics. In contrast with general systems following the Fick law, which behave diffusively, integrable models show ballistic behavior in correlation functions.

In a new preprint, we observe ballistic correlation functions in a photonic platform whose dynamics is well-described by the Nonlinear Schroedinger equation, and compare observations with predictions from GHD.

E. Charnay, A. Escoubet, F. Copie, S. Randoux, T. Bonnemain, A. Bastianello, P. Suret, arXiv:2601.21085 (2026)

A special thanks goes to Elias Charnay who collected such great experimental data!

Together with Stefano Scopa (ENS) and Andrea De Luca (ENS), I co-organized a conference targeting quantum many-body systems out of equilibrium.

Gathering experts in analytical theory, numerical and computational methods, and experimental platforms, Threefold Quantum fostered direct exchange and dialogue between communities that often interact only indirectly.

I am truly grateful for the large international participation in the event and for the enthusiasm of the participants!

Conference Website

I co-organized a conference on the hydrodynamics of integrable models together with Friedrich Hübner (ENS Paris), Alessandra Iacobucci (Université Paris Dauphine-PSL), Ronan Memin (ENS Paris), Stefano Olla (Université Paris Dauphine-PSL).

This focused workshop aimed to bring together researchers from physics and mathematics to foster genuine cross-fertilization through intensive, thematically organized sessions.

Conference website

Our joint experimental-theoretical work on Observation of a generalized Gibbs ensemble in photonics is now published  A. Bastianello, A. Tikan, F. Copie, S. RandouxPhys. Rev. A 113, 013514 (2026).

The referral process helped us to substantially improve the presentation. We hope this work will help connect the scientific communities working on non-linear classical media and quantum many-body systems, both experimentally and theoretically, by showing the deep analogies between the two.

My work on quantum engines in collaboration with Alberto Brollo and Adolfo Del Campo recently appeared in Nature Communications. In particular, thank to Alberto Brollo as the young driving force in this project!

Under minimal assumptions, we show that additional conservation laws are beneficial to the efficiency of Otto cycles where the working matter follows prethermal phases of matter, compared to canonical prethermalization, provided the external baths have negative temperatures.

Our work also been selected for an outreach summary on the webpage of the Donostia International Physics Center - EHU (link)

I am thrilled to share I have been awarded the ERC Starting Grant for my project "Nonergodic Hydrodynamics in quantum systems" NonErgHydro!

I am immensely grateful to ERC for its generous funding and to all collaborators and friends who supported my research. 

After many efforts, we managed to excite and observe Bethe strings in a one-dimensional ultracold gas of attractive Cesium atoms! Check it out on arXiv.

The experiment has been performed by the group led by H.C. Nägerl at University of Innsbruck. I am specially thankful to Milena Horvath and Sudipta Dhar, for the exceptional quality of experimental data, and for the long hours on Zoom spent teaching me about the experiment. 

Generalized Gibbs Ensembles (GGE) are non-thermal stationary states featured by integrable models: this concept originated in quantum physics, but it describes emergent statistical properties of integrable classical partial differential equations (PDE) as well!

A. Bastianello, A. Tikan, F. Copie, S. Randoux, P. Suret, arXiv:2503.16526

This experiment observes the emergence of the GGE in a photonic platform, well described by the defocusing Non-Linear Schroedinger equation. Within the "soliton gas" framework, relaxation of NLS has been framed within "integrable turbulence": we show that the ending point of integrable turbulence is nothing but the GGE.

Many more analogies between quantum and classical concepts and experiments will come: stay tuned!