Fri, 17 Oct 2025
12:00
L3

Multi-Entropy Measures for Topologically Ordered Phases in (2+1) Dimensions

Shinsei Ryu
(Princeton)
Abstract

 

Entanglement entropy has long served as a key diagnostic of topological order in (2+1) dimensions. In particular, the topological entanglement entropy captures a universal quantity (the total quantum dimension) of the underlying topological order. However, this information alone does not uniquely determine which topological order is realized, indicating the need for more refined probes. In this talk, I will present a family of quantities formulated as multi-entropy measures, including examples such as reflected entropy and the modular commutator. Unlike the conventional bipartite setting of topological entanglement entropy, these multi-entropy measures are defined for tripartite partitions of the Hilbert space and capture genuinely multipartite entanglement. I will discuss how these measures encode additional universal data characterizing topologically ordered ground states.

In the Short Story above, we asked Josh what he would be if he weren't a mathematician and Josh says he'd have liked to have been a musician. In Tom Lehrer's case it really was true and mathematics became part of his musical routine. This song is about plagiarism in maths. Many of you might know it. And even if you don't, you might recognise it.

Lehrer gave up music in the early 70s to concentrate on teaching maths. He died earlier this year at the age of 97.

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What's everyone like round here? Do they have fun? 

Films about people who also do maths.

The Monty Hall Problem with Becky Crossley. Blew a few minds on social media. There's a longer version with the maths here.

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