SEMINARS

Our group seminar features talks on current research topics from the field of Quantum Information and Quantum Many-Body Physics, and in particular Tensor Networks, given both by group members and by external guest speakers.

If you are interested in receiving seminar announcements, please send an informal e-mail to schuch-office.quantum[at]univie.ac.at to be added to our mailing list.

For info on past seminars click here.

2024 Summer Semester

During the 2024 summer semester, the seminar generally takes place on Tuesdays at 11:30 in the seminar room on the 5th floor (Strudlhofgasse 4, room nr. 3510). Occasionally, there might be additional seminars out of schedule, or seminars given online, as announced here.

Adrián Franco Rubio (Max Planck Institute for Quantum Optics, Garching)

Gaussian tensor networks, conformal field theories, and analogue quantum simulation - An overview of my recent research
Abstract: I will introduce three research projects I have been working on. The first one involves the study of the expressive power of Gaussian fermionic tensor networks, and leads to the proof that, in 1d, they cannot approximate Gaussian critical systems with polynomial bond dimension. The second project revolves around families of ansatz wavefunctions for spin chains defined by virtual conformal field theories on a torus, which can be interpreted as matrix product states of infinite bond dimension. The last project involves the study of the impact of extensive errors in analogue quantum simulation for thermodynamic limit problems, and the search for a rigorous framework to define quantum advantage in this setting.
Based on arXiv:2204.02478, 2212.04924 and ongoing research.

(date/time/location: 05.03.2024, 11:30, Strudlhofgasse 4, 5th floor, seminar room/Kleiner Seminarraum, room no. 3510)

Jose Garre Rubio (University of Vienna)

Emergent (2+1)D topological orders from iterative (1+1)D gauging
Abstract: Gauging involves introducing new degrees of freedom, known as gauge fields, to localize an existing global symmetry. It is known that, following this process, the gauge fields exhibit a dual global symmetry. Subsequently, one can gauge this emergent global symmetry by creating new gauge fields that once again exhibit a global symmetry. We investigate this iterative process, wherein new degrees of freedom are created and entangled with the previous ones through local symmetries. We focus on gauging spin chains with Abelian group symmetries and arranging the new spins on a 2D lattice. The local symmetries of the emergent 2D state, which are modified by the concatenation of the following gauging maps surprisingly correspond to the stabilizer terms of the $XZZX$-code generalized to any Abelian group. We encode our construction in the family of tensor network states that we dub "projected entangled pair emergent states" (PEPES). Utilizing this representation and considering the local symmetries as stabilizer Hamiltonian terms, we establish a connection between the condensable anyons at the boundary and the quantum phase of the initial symmetric state before the gauging process.

(date/time/location: 12.03.2024, 11:30, Strudlhofgasse 4, 5th floor, seminar room/Kleiner Seminarraum, room no. 3510)

David Blanik (University of Vienna)

SPT and SSB Phases under Gauging
Abstract: It has been well established that gauging maps implement a duality between VecG and RepG symmetric (1+1)D systems. For abelian G, both cases correspond to global group symmetries and ground states can be classified into SPT (symmetry protected topological/trivial) phases and/or SSB (spontaneous symmetry breaking) phases. In ongoing work with Norbert Schuch and José Garre Rubio we use MPS (matrix product states) to investigate how these phases behave under gauging. I will give an introduction to our method and discuss preliminary results.

(date/time/location: 19.03.2024, 11:30, Strudlhofgasse 4, 5th floor, seminar room/Kleiner Seminarraum, room no. 3510)

Ilya Kull (University of Vienna)

Certified algorithms for equilibrium states of local quantum Hamiltonians
Abstract: I will talk about this recent paper [1] by Fawzi, Fawzi & Scalet. The paper describes a complete hierarchy of convex optimization problems that gives both upper and lower bounds on expectation values of local observables in thermal states of local Hamiltonians.

[1] arxiv.org/abs/2311.18706

(date/time/location: 09.04.2024, 11:30, Strudlhofgasse 4, 5th floor, seminar room/Kleiner Seminarraum, room no. 3510)

Lilith Zschetzsche (University of Vienna)

Simulating coupled classical oscillators using Hamiltonian simulation - proof of BQP-completeness
Abstract: I will give an introduction to the simulation of exponentially large networks of classical oscillators using Hamiltonian simulation, based on the paper [1] by Babbush et al.. When the displacements and momenta of the oscillators are encoded in a wave function, the time evolution simulating the classical dynamics of a sparse network can be efficiently computed on a quantum computer. The kinetic energy of a subset of harmonic oscillators can be obtained by measurement on the wave function. Based on that, a BQP-complete problem can be constructed.

[1] R. Babbush et al., "Exponential quantum speedup in simulating coupled classical oscillators", Phys. Rev. X (2023), https://doi.org/10.1103/PhysRevX.13.041041

(date/time/location: 23.04.2024, 11:30, Strudlhofgasse 4, 5th floor, seminar room/Kleiner Seminarraum, room no. 3510)