Location:
Kurt Gödel lecture hall
Faculty of Physics, Strudlhofgasse 4/Boltzmanngasse 5, ground floor

In this special seminar, two speakers will each give a 30-minute talk:

Alexander Jahn (Freie Universität Berlin)
Universal fault-tolerant logic with heterogeneous holographic codes

Abstract:
The study of holographic bulk-boundary dualities has led to the construction of novel quantum error correcting codes. Although these codes have shed new light on conceptual aspects of these dualities, they have widely been believed to lack a crucial feature of practical quantum error correction: The ability to support universal fault-tolerant quantum logic. In this work, we introduce a new class of holographic codes that realize this feature. These heterogeneous holographic codes are constructed by combining two seed codes in a tensor network on an alternating hyperbolic tiling. We show how this construction generalizes previous strategies for fault tolerance in tree-type concatenated codes, allowing one to implement non-Clifford gates fault-tolerantly on the holographic boundary. We also demonstrate that these codes allow for high erasure thresholds under a suitable heterogeneous combination of specific seed codes. Compared to previous concatenated codes, heterogeneous holographic codes achieve large overhead savings in physical qubits, e.g. a 21.8% reduction for a two-layer Steane/quantum Reed-Muller combination. Unlike standard concatenated codes, we establish that the new codes can encode more than a single logical qubit per code block by applying "black hole'' deformations with tunable rate and distance, while possessing fully addressable, universal fault-tolerant gate sets. Therefore, our work strengthens the case for the utility of holographic quantum codes for practical quantum computing.
[arXiv:2504.10386]

Dimitris Saraidaris (Freie Universität Berlin)
Searching for emergent spacetime in spin glasses

Abstract:
Recent work on algebraic formulations of holographic dualities in terms of large N algebras has revealed a deep connection between the properties of the associated spectral functions and the emergence of a semiclassical spacetime. One of the main lessons is that, for a radial direction to emerge, the spectral function has to exhibit non-compact support. Furthermore, there exist conjectures upon a possible duality between complex gravitational configurations and glassy systems. The goal of this work is to combine these ideas by studying many-body quantum-mechanical systems and assess in which parameter regimes they could potentially be holographic. Thus, we compute the spectral functions of three many-body systems with quenched disorder, the SYK model, the p-spin model and the SU(M) Heisenberg chain in the large N limit and present results in different parameter regimes. Our main finding is that in the quantum spin glass phase of the SU(M) Heisenberg model, the spectral function develops an exponential tail, similar to the large q limit of SYK, while for the rest of the spin glass phase, compact support. In addition, we demonstrate the presence of an exponential tail in the spectral function for all cases without compact support and conformal symmetry.
[authors: Dimitris Saraidaris and Leo Shaposhnik]

Hosts:
Norbert Schuch & Refik Mansuroglu

You are welcome to join this talk without prior registration.

This talk is part of the Quantum Information and Quantum Many-Body Physics seminar. For information on further talks in this series, please visit our seminar page.