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Joschka Roffe

@qec.codes

546 followers 585 following 53 posts

Quantum Error Correction | Quantum Software Lab | University of Edinburgh Homepage: roffe.eu

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Joschka Roffe @qec.codes · 08/06/2026

Back in Santa Barbara this week for #QEC2026. Looking forward to meeting colleagues, old and new, and hearing about the latest and greatest in QEC!

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Joschka Roffe @qec.codes · 01/06/2026

🚨Registration deadline today! TartanQEC Workshop 24-26 June. Poster submissions remain open until end-of-day (AOE). Sign up now 👇 qec.codes/tartan2026

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Joschka Roffe @qec.codes · 04/02/2026

Great day back in Durham visiting @durhamqlm.bsky.social to give a seminar on QEC and our recent work at Quantum Software Lab. Also fun to discuss the fault-tolerance of the Welsh towname Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch w/ @ifanghughes.bsky.social @tobifranzen.bsky.social

Opening slide of my presentation on Quantum Error Correction at Durham Uninversity. Slide features a picture of the Durham student union and Kingsgate bridge, famously designed by legendary North Eastern arcitect Ove Arup and considered to be one of the world's finest examples of brutalist architecture.

A slide from my presentation comparing surface codes to QLDPC codes. Background: surface codes are a leading approach to QEC, favoured for their local connectivity and straightforward ability to scale to arbitrary distance. However, from a coding theory perspective, they are far from optimal codes, owing to the fact that only a single logical qubit is encoded per patch. In practice, it is estimated that ~1000 qubits will be required per logical qubit in a surface code architecture, making them much less efficient than classical LDPC codes (of the type used in 5G and WiFi) where encoding ratios can be as low as 2-to-1. Quantum LDPC are modelled on classical codes, and it is has been shown (through simulation) that they code achieve encoding densities as low as 50-to-1 (some 20x improvement than surface codes). The tradeoff is that QLDPC codes are much less structured than surface codes, requiring long-range interactions between qubits. The QLDPC Tanner graph shown on the slide depicts a naive layout that I usefully refer to as the "spaghetti connectivity".

Language is redundant by design. The town of Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch in Anglesey Wales is probably the best error corrected placename in the world!

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Joschka Roffe @qec.codes · 12/08/2025

James Mills introducing Logical Accreditation to #QEC2025 at @yaleqi.bsky.social See our recent preprint here: arxiv.org/abs/2508.05523

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Joschka Roffe @qec.codes · 14/04/2025

Happy World Quantum Day! I'm excited to announce that I will be starting a new group dedicated to quantum error correction (QEC) at The University of Edinburgh Quantum Software Lab, funded by an EPSRC Quantum Technology Career Acceleration Fellowship!

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Joschka Roffe @qec.codes · 21/11/2024

Remember: the surface code threshold is not the breakeven point (for finite-size codes).

This image shows a threshold plot. The breakeven line is superimposed. I am explaining the difference.

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Joschka Roffe @qec.codes · 21/11/2024

PSA: The Tanner graph representation is the best way of depicting surface codes.

Image displays two representations of a QEC protocol. The first uses the traditional circuit notation and the second a Tanner graph notation similar to that used for classical LDPC codes.

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Joschka Roffe @qec.codes · 21/11/2024

I've enjoyed teaching students at Edinburgh University about QEC this term. Here I am introducing the famous [[9,1,3]] Shor code.

The circuit for the [[9,1,3]] Shor code. This QEC protocol is constructed by concatenating the 3-qubit phase-flip repetition code with the 3-qubit bit-flip repetition code.

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