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 Winter Semester

During the 2024 winter semester, the seminar generally takes place on Mondays at 11:30 in the Erwin Schrödinger lecture room (Boltzmanngasse 5, 5th floor). Occasionally, there might be additional seminars out of schedule, or seminars given online, as announced here.

Ilya Kull (University of Vienna)

Methods for certifying the presence of a spectral gap in frustration-free spin systems
Abstract: I will first give a pedagogical overview of the existing methods to certify spectral gaps of frustration-free spin systems (Knabe and co., Martingale), and will then proceed to present our recently developed method.

(date/time/location: 14.10.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)

Adrian Franco Rubio (University of Vienna)

Defects and gauging for matrix product states with matrix product unitary symmetries
Abstract: Gauging, or the promotion of a global symmetry to a local symmetry, plays a fundamental role in many areas of physics, from high energy theory to topological phases of matter. Tensor network states, and in particular 1d matrix product states, provide a nice framework where the gauging of global symmetries has been developed for unitary onsite symmetries and certain matrix product operator groups. In this talk, we review this formalism and present a potential extension to states with matrix product unitary group symmetries, based on a defect construction that mimics the onsite formalism and can be of interest on its own.

(date/time/location: 21.10.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)

Shuhei Oyama (University of Vienna)

1+1d SPT phases with fusion category symmetry: interface modes and non-abelian Thouless pump
Abstract: Fusion category symmetry is the most general finite symmetry in 1+1 dimensional systems. We investigated gapped phases defined on a lattice with fusion category symmetry using the technique of matrix product states, focusing on the following aspects:
1. SPT invariants
2. Bulk-boundary correspondence/Thouless pump
3. Classification of a parametrized family of general gapped phases
In my talk, I will first review the basics of topological phases, and then I would like to mainly explain topic 1.
This talk is based on a joint work arXiv:2408.15960 with Kansei Inamura.

(date/time/location: 28.10.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)

Refik Mansuroglu (University of Vienna)

Preparation of matrix-product states with quantum circuits
Abstract: I discuss several ways of preparing matrix-product states (MPS) on a quantum computer with local gates. MPS provide an efficient classical representation of ground states of gapped local Hamiltonians and are of versatile use in studying quantum many-body physics. As a resource for quantum computation, they define a class of promising initial states, in particular for the simulation of non-equilibrium dynamics. I compare natural circuit implementations that are apparent from the MPS structure with more elaborate techniques enabling state preparation with circuits of logarithmic and in some cases even constant depth. I close with an outlook to hardware-oriented state preparation methods that strive to find optimal circuits tailored to a given MPS and the available gate set.

(date/time/location: 04.11.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)

David Blanik (University of Vienna)

Dualities from Gauging
Abstract: Dualities are a powerful tool in statistical mechanics and quantum phase transitions, often simplifying complex models by relating them to more tractable ones, thus revealing deep insights into low-energy dynamics, phase transitions, and critical behavior. A prominent example is the Kennedy-Tasaki (KT) transformation, which connects the Z2xZ2 symmetry-protected topological (SPT) phase in spin-1 chains to its symmetry-broken (SSB) counterpart. Recent research has explored generalized approaches to such transformations using the concept of gauging and in this talk I will discuss how our recent classification of SPT and SSB phase behaviors under gauging facilitates the construction of novel dualities across diverse phases and symmetry groups. These new dualities offer a systematic framework to understand and classify phases, enriching our understanding of quantum phase transitions and critical phenomena.

(date/time/location: 11.11.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)

Paul Brehmer (University of Vienna)

Topology Protects Chiral Edge Currents in Stochastic Systems
Abstract: I present a recent publication by Tang et al. [1] which finds interesting connections between topology, non-Hermitian physics and stochastic systems. Based on two-dimensional stochastic networks, both numerical and analytical approaches are used to show the emergence of chiral edge currents in the configuration space as well as non-Hermitian features driven by out-of-equilibrium cycles at the microscopic scale. As an application, we focus on a biochemical oscillator where a global clock arises from macroscopic time scales of the underlying edge currents.

[1] E. Tang, J. Agudo-Canalejo, and R. Golestanian, Phys. Rev. X 11, 031015 (2021).

(date/time/location: 18.11.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)

Christian Schilling (Arnold Sommerfeld Centre for Theoretical Physics, LMU Munich)

Quantum Information Perspective on the Ground State Problem: What is Electron Correlation?
Abstract: Describing strongly interacting electrons is one of the crucial challenges of modern quantum physics. A comprehensive solution to this electron correlation problem would simultaneously exploit both the pairwise interaction and its spatial decay. By taking a quantum information perspective, we explain how this structure of realistic Hamiltonians gives rise to two conceptually different notions of correlation and entanglement. The first one describes correlations between orbitals while the second one refers more to the particle picture. We illustrate those two concepts of orbital and particle correlation and present measures thereof. Our results for different molecular systems reveal that the total correlation between molecular orbitals is mainly classical, raising questions about the general significance of entanglement in chemical bonding. Finally, we also speculate on a promising relation between orbital and particle correlation and explain why this may replace the obscure but widely used concept of static and dynamic correlation.

(date/time/location: 16.12.2024, 11:30, Boltzmanngasse 5/Strudlhofgasse 4, 5th floor, Erwin Schrödinger lecture hall)