Events calendar

Magnetic quivers and their Coulomb branches provide a framework for studying the Higgs branch of theories with eight supercharges, including those without a known Lagrangian description. In particular, they capture the foliation structure of the Higgs branch, which encodes the sequence of spontaneous symmetry-breaking phenomena in the theory. Each elementary step in this process corresponds to an isolated symplectic singularity. We employ the fission–decay algorithm to classify all magnetic quivers whose Coulomb branches exhibit such isolated singularities.

Résumé/abstract: In the last few years, quantifying the complexity of quantum states has found applications in many fields, including quantum information and computing, quantum dynamics in many-body systems, and black hole physics. Among these measures, the spread complexity roughly quantifies the size of the space of states visited along quantum dynamics. It is obtained through Krylov space methods, which consist of projecting the evolution of a state onto one-dimensional dynamics. In this talk, I will discuss the evolution of the spread complexity after a local quantum quench in conformal field theories (CFT). Interestingly, this quantity depends on the central charge of the considered theory. I will also show that, to get rid of all the non-universal contributions in the leading time behaviour, it is convenient to study another Krylov space quantity, the K-entropy, an entropy measure defined for pure states without the need for a bipartition. These results support the usefulness of the Krylov space methods to study quantum dynamics.

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

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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

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