Aiman Al-Eryani, Ruhr-University Bochum, Germany

 

Title: Diagrammatic bosonization and aspects of criticality in parquet approaches

 

Abstract: We demonstrate, using the recent single-boson exchange (SBE) reformulation of the parquet equations, how the diagrammatics of parquet approaches can be faithfully mapped onto purely bosonic diagrammatics of a conventional (s-wave) order-parameter. We show how this mapping can be used to study the critical properties of parquet approaches. Revisiting a conjecture of Bickers and Scalapino, we show that, at finite temperatures, the parquet approximation yields critical exponents equivalent to those of a self-consistent version of the large-N resummation of the order-parameter theory. We discuss the role of the electron self-energy and crossing symmetry in enforcing the Hohenberg–Mermin–Wagner theorem.

 

 

 

Jan Budich, Technical University of Dresden, Germany

 

Title: Obstructions to Quantum State Preparation: From Topology to Computational Complexity

 

Abstract: The complexity of the quantum many-body problem is well known to be fully reflected in the generally hard task of quantum state preparation. In this talk, we discuss the critical slowdown of disipative state preparation protocols due to two fundamental obstructions: topological quantum phase transitions and the computational complexity of combinatorial problems the solution to which is encoded in the targeted quantum many-body state. Specifically, we relate the complexity of a given obstruction directly to the finite size scaling of the dissipative dynamics. Finally, we discuss implications on realizing or simulating state preparation protocols both on classical and quantum devices.

 

 

Wayne Jordan Chetcuti, LPMMC, Université Grenoble Alpes

 

Title: Interferometric probe for the zeros of the many-body wavefunction

 

Abstract: Nodal surfaces of the many-body wavefunction encode fundamental information about particle statistics and interactions, playing a central role in determining the properties of correlated quantum systems. Despite their importance for many-body dynamics and quantum phases of matter, precise statements about their structure are difficult to formulate, and they remain challenging to characterize and access experimentally. I will present exact results for the nodal structure of repulsive two-component fermionic wavefunctions confined on one-dimensional ring geometries, obtained from the Bethe Ansatz solution, and show how these features can be probed in ultracold-atom experiments. Distinguishing between symmetry-dictated nodes, enforced by particle statistics, and  non-symmetry-dictated nodes arising from interactions, I will demonstrate how the spin degrees of freedom modify the nodal geometry, leading to cusp-like structures in the many-body wavefunction. I will then show that nodal surfaces give rise to sharp dislocations in interference fringes in  a self-heterodyne interferometric protocol. These results establish nodal structures as experimentally measurable objects and provide a route to their identification through interferometric measurements  without requiring full reconstruction of the many-body  wavefunction.

 

 

 

Nicolas Dupuis, LPTMC, CNRS and Sorbonne Université

 

Title: Finite-temperature phase diagram of the one-dimensional disordered Bose gas 

 

Abstract: We determine the finite-temperature phase diagram of a one-dimensional disordered Bose gas using bosonization and the nonperturbative functional renormalization group (RG). We discuss two different scenarios, based on distinct truncations of the effective action. In the first scenario, the Bose glass is destabilized at any finite temperature, giving rise to a normal fluid. Nevertheless, one can identify a low-temperature glassy regime, where disorder plays an important role on intermediate length and time scales. In the second scenario, below a temperature Tc, the RG flow exhibits a singularity at a finite value of the RG momentum scale. We propose that this singularity signals a lack of thermalization and the existence of a many-body localized phase for T<Tc

 

 

 

Rafael Flores-Calderón, Technical University of Munich, Germany

 

Title: Spontaneous breaking of a continuous symmetry at a non-conformal quantum critical point in one dimension

 

Abstract: In this work, we present evidence for the spontaneous breaking of a continuous symmetry in a nearest-neighbour interacting spin-1 chain tuned to a quantum critical point at T=0 between two XY quasi-long-range order phases differing by the spontaneous breaking of a $\mathbb{Z}_2$ symmetry. Our matrix product state results reveal that the quantum phase transition has an anomalous dimension of $\eta \simeq 1$ together with the dynamical critical exponent $z\simeq 3/2$, known from the Kardar-Parisi-Zhang universality class in one dimension. We perform a perturbative renormalization group calculation about the upper critical dimension $d_c=2$ which we could close at second loop order. We find an interacting fixed point with critical exponents distinct from the Ising ones. Together, our findings suggest the nature of the fixed point to be non-perturbative. We propose a field theory that we believe to improve the quantitative results.

  

 

Loïc Herviou,  LPMMC, CNRS and Université Grenoble Alpes 

 

Title: Tensor network simulations of 2+1D CFT: the Fuzzy sphere

 

Abstract: The study of conformal field theories (CFTs) in 2+1 dimensions represents a significant challenge in theoretical physics due to their strong coupling nature and the lack of exact solutions. In this talk, I will present recent advancements in numerical simulations of these CFTs using tensor network methods combined with the fuzzy sphere regularization technique. This approach provides a powerful framework for non-perturbative studies of 2+1D CFTs, enabling (a somewhat) precise extraction of conformal data. The fuzzy sphere regularization involves constructing quantum systems on a spherical geometry with a non-commutative structure, which serves as an ultraviolet regulator while maintaining the full SO(3) rotational symmetry of the sphere. This construction is based on the well-known Integer quantum Hall physics and the physics of quantum Hall ferromagnets. After a brief introduction of tensor networks, I will discuss the strength and limitations of this method through the examples of the Ising and O(N) CFTs. If time allows, I will also discuss its generalization to non-unitary CFTs or to boundary CFTs (BCFTs) using a fuzzy hemisphere.

 

 

Cécile Repellin, LPMMC, CNRS and Université Grenoble Alpes 

 

Title: Signatures of fractional quantum Hall states in few-body systems

 

Abstract: Realizing strongly correlated topological phases of ultracold gases is a central goal for quantum gas experiments. Due to the difficulty in preparing these phases, ongoing experiments are focusing on ensembles of few atoms, and the preparation of a fractional quantum Hall state of two bosonic atoms has been achieved. Beyond their preparation, the characterization of these few-body states poses a unique challenge due to their small system size. I will discuss which signatures can be used, and show that hallmark fingerprints of fractional quantum Hall phases, such as a quantized Hall conductivity, or chiral edge modes, can be extracted in few-particle systems through local density measurements.