Organisation des séminaires et calendrier

Abstract: I will present examples of Limit Shapes – the most probable macroscopic shape
with sharp boundaries separating frozen and fluctuating regions – which arise
in a variety of classical and quantum systems. I will explain a special role
played by analytic functions defining Riemann surface whose topology can be
changed abruptly across phase transitions. Most of the examples are based on
free fermionic models, however recently we studied a notable exception from
this rule – the Polytropic Gas with a power-law equation of state. The hydrodynamic
approach to Emptiness Formation Probability in Politropic Gas will be discussed.

[1] J. Pallister, D.M. Gangardt and A. Abanov, « Limit shape phase transitions: a merger of arctic circles »,
J. Phys. A 55, 304001, 2022

[2] James S. Pallister, Samuel H. Pickering, Dimitri M. Gangardt and Alexander G. Abanov, « Phase transitions in full counting statistics of free fermions and directed polymers », Phys. Rev. Research 7, L022008, 2025

[3] Alexander G. Abanov, Dimitri M. Gangardt, « Emptiness instanton in quantum polytropic gas », SciPost Phys. 18, 122, 2025

TBA

Abstract: In this talk I shall review the work done in the past few years, inspired by a previously unnoticed observation by Tsirelson [1]: the Wigner negativity of some states of a single harmonic oscillator can be certified by measuring only one observable (say, position) at one among a set of suitable times. This is somewhat surprising, as it is common knowledge that the evolution of a harmonic oscillator is identical to the classical one in the Heisenberg representation. 

We improved the characterization of the original protocol for continuous variables and extended it to discrete variables [2,3], the latter case leading to the first experimental implementation [4]. We also modified the protocol to detect entanglement: for continuous variables, it gives an entanglement witness that is free of false positives [5]; for discrete variable, we reported the first witness that detects the GHZ state of N spins using only measurements of the total angular momentum [6,7]. On a more foundational level, the task being operational, it can be phrased in the language of generalized probabilistic theories: contrary to what happens for Bell inequalities, here quantum theory can always reach the maximal score [8]

References:

[1] B. Tsirelson, https://arxiv.org/abs/quant-ph/0611147

[2] L.H. Zaw et al., Phys. Rev. A 106, 032222 (2022) https://arxiv.org/abs/2204.10498

[3] L.H. Zaw, V.S., npj Quantum Information 11, 152 (2025) https://arxiv.org/abs/2411.03132

[4] A. Vartjees et al., Newton 1, 100017 (2025) https://arxiv.org/abs/2410.07641

[5] P. Jayachandran et al., Phys. Rev. Lett. 130, 160201 (2023) https://arxiv.org/abs/2210.10357

[6] K.-N. Huynh-Vu et al., Phys. Rev. A 109, 042402 (2024) https://arxiv.org/abs/2311.00806

[7] J. Chen et al., Phys. Rev. A 110, 062408 (2024) https://arxiv.org/abs/2410.07641

[8] L.H. Zaw et al. Phys. Rev. Lett. 134, 190201 (2025) https://arxiv.org/abs/2401.16147

TBA