I gave a talk titled "Building a Quantum Computer with QLDPC Codes" at Simons. This is an overview talk on the recent developments in QLDPC-based fault-tolerant architectures, with more emphasis on high-level ideas. Here is the recording: simons.berkeley.edu/talks/sunny-...

New paper with Ewin and John on learning local Lindbladians! arxiv.org/abs/2606.30358 As a special case, we also get structure learning of Hamiltonians from high-temperature Gibbs states, which was wide open before our work 🙂

I’m starting a blog! Here is the first post: ‘Round-robin CCZ is all you need’. sunnyzhiyanghe.github.io/blog/round-robin-ccz/ It shows a fun observation on CCZ gates, proved by Claude Opus 4.8 and verified in Lean by an auto-formalization model MerLean. The blog has the full story.

Five years of work in the making: manual marathon followed by an AI-assisted verification sprint. Thank you @phfaist.bsky.social for being a steadfast and attentive architect! Suggestions on where to go from here very welcome.

Error Correction Zoo@eczoo.bsky.social · 2mo ago

Big update: the EC Zoo is now a handbook. It spans codes, sphere packings, lattices, designs, groups, and phases of matter. Extensively checked, but not perfect—feedback very welcome: arxiv.org/abs/2606.11484

Extractors: smaller than the code, enable full logical processing, same error rate as memory, compatible with fixed connectivity. As promised, they turn quantum memories into quantum processors. arxiv.org/abs/2606.03507 Joint work with the wonderful John Blue, Harry Zhou, and Ike Chuang.

Full Extractors for Logical Processing in Hypergraph Product Codes

Quantum low-density parity-check (QLDPC) codes are promising candidates for practical low-overhead quantum memories. For large-scale fault-tolerant quantum computation, we further need logical process...

arxiv.org

I’m very happy to be able to talk about this new paper, which came out of my internship at IBM last summer - scirate.com/arxiv/2605.2... . It’s being posted just in time for my next IBM internship this summer - lots to work on!

Concatenating Algebraic Codes over High-Rate Quantum LDPC Codes

Different quantum error correction schemes trade off overhead, error suppression, and hardware connectivity. Code concatenation can relax these tradeoffs by using an outer code whose non-local connect...

scirate.com

Excited to share our paper arxiv.org/abs/2604.16209 on ultra-high-rate codes co-designed for atom arrays! We co-design qLDPC codes with rates around 1/2, showing that they can reach good logical error rates under a circuit-level noise model. This was a fun project with Chen, Nishad, Casey and Andi.

Towards Ultra-High-Rate Quantum Error Correction with Reconfigurable Atom Arrays

Quantum error correction is widely believed to be essential for large-scale quantum computation, but the required qubit overhead remains a central challenge. Quantum low-density parity-check codes can...

arxiv.org

Great program this year!

Dripto Debroy@dripto.bsky.social · 4mo ago

Accepted submissions for QEC26 are out: qec-conference.org/2026/accepte.... Congratulations! If you are attending QEC, a few reminders below:

Accepted submissions for QEC26 are out: qec-conference.org/2026/accepte.... Congratulations! If you are attending QEC, a few reminders below:

This is a good example of why you should be cautious when extrapolating to the low logical error rate regime arxiv.org/abs/2604.08358

I would bet against Q day by 2030, but I wouldn't bet against it at 10:1 odds. ~10% risk is unacceptably high here, so I'm very in favor of transitioning to quantum-safe cryptography by 2029: blog.google/innovation-a... Yes this means I 90% expect to be made fun of in 2030. Oh well.

Quantum frontiers may be closer than they appear

An overview of how Google is accelerating its timeline for post-quantum cryptography migration.

blog.google

Don't know what Quantum Youtube is, but 👍

Adam Wills@adamwills1.bsky.social · 5mo ago

🚨🚨🚨New paper alert🚨🚨🚨 scirate.com/arxiv/2603.0... We just made Quantum Youtube buffer much less. It was a joy as always to work with David, Rachel and Min-Hsiu.

Good old code surgery, now more parsimonious than ever. arxiv.org/abs/2603.05082 Joint work with amazing collaborators Andrew Yuan, Alex Cowtan, David Lin, and Dom Williamson.

Parsimonious Quantum Low-Density Parity-Check Code Surgery

Quantum code surgery offers a flexible, low-overhead framework for executing logical measurements within quantum error-correcting codes. It encompasses several fault-tolerant logical computation schem...

arxiv.org

Gave a talk recently at Coogee on constructing and analysing spacetime volumes of LDPC codes & surgeries thereof. Thanks to @sunnyhe.bsky.social @domwilliamson.bsky.social and Ted Yoder for the wonderful collaboration. www.youtube.com/watch?v=Lxzw...

Coogee '26 Talks - Alex Cowtan (Xanadu)

YouTube video by Quantum @ Sydney

youtube.com

Quantum code surgery: fast, addressable, parallel, (almost) constant space overhead, all at once on your favorite hypergraph product codes. arxiv.org/abs/2603.021...

Constant-Time Surgery on 2D Hypergraph Product Codes with Near-Constant Space Overhead

Generalized code surgery is a versatile and low-overhead technique for performing fault-tolerant computation on quantum low-density parity-check (qLDPC) codes. In many settings, surgery exhibits pract...

arxiv.org

Excited to share our perspective article, written with Maddie Cain and Misha Lukin, on designing low-overhead fault-tolerant architectures: rdcu.be/eVTiB. The landscape is rapidly evolving, and excited to see where the field goes next!

Opportunities in full-stack design of low-overhead fault-tolerant quantum computation

Nature Computational Science - Quantum error correction is vital for scalable quantum computing, but it incurs high resource overheads. This Perspective outlines recent breakthroughs and explores...

rdcu.be

Fault-tolerant logical measurement just got a lot faster! In new work, we show that code surgeries based on hypergraphs, rather than graphs, allow fast and parallel fault-tolerant logical measurements with low qubit overhead (without requiring the code to be single-shot). arxiv.org/abs/2510.14895

Quantum code surgery, but get them for constant time a piece if you run many of them. arxiv.org/abs/2510.14895 Joint work with Alex Cowtan, Dom Williamson and Ted Yoder.

Fast and fault-tolerant logical measurements: Auxiliary hypergraphs and transversal surgery

Quantum code surgery is a promising technique to perform fault-tolerant computation on quantum low-density parity-check codes. Recent developments have significantly reduced the space overhead of surg...

arxiv.org

Have you heard of high-density parity-check codes before? Anyways, layer codes with random HDPC input codes have provable and numerical partial self-correction properties. arxiv.org/abs/2510.06659 Joint work with Shouzhen Gu, Libor Caha, Shin Ho Choe, Aleksander Kubica, and Eugene Tang.

Layer codes as partially self-correcting quantum memories

We investigate layer codes, a family of three-dimensional stabilizer codes that can achieve optimal scaling of code parameters and a polynomial energy barrier, as candidates for self-correcting quantu...

arxiv.org

Check it out: permutation unitaries in the 3rd level of the Clifford hierarchy whose inverses escape any fixed, finite level of the hierarchy. arxiv.org/abs/2510.04993 Joint work with Luke Robitaille and Xinyu (Norah) Tan.

Characterization of permutation gates in the third level of the Clifford hierarchy

The Clifford hierarchy is a fundamental structure in quantum computation whose mathematical properties are not fully understood. In this work, we characterize permutation gates -- unitaries which perm...

arxiv.org

Can ChatGPT help with research? Maybe not yet for finding new results, but it can certainly speed up some tedious tasks. An example about quantum Tanner codes #qLDPC Working with qudits (d=5) lets you use nice local codes [4,2,3]_5. Then the idea is simply to enumerate small groups and (1/4)

Peter Shor receives a small gift on the 30th anniversary of his QEC paper at #QEC2025.

Very exciting announcement, the next Quantum Error Correction conference QEC26 will be hosted by Google 7-12 June 2026 in Santa Barbara. See you there! @dripto.bsky.social @mattmcewen.bsky.social

Fault-tolerance is, at its core, a combinatorial study. arxiv.org/abs/2508.08246

Composable Quantum Fault-Tolerance

Proving threshold theorems for fault-tolerant quantum computation is a burdensome endeavor with many moving parts that come together in relatively formulaic but lengthy ways. It is difficult and rare ...

arxiv.org

The QIP 2026 call for papers is out! QIP 2026 will be held in Riga, Latvia from January 24–30, 2026. See you there! qip2026.lu.lv

In May I gave a talk at Simons about our recent work on extractors architectures, which is a surgery-powered proposal to perform universal Pauli-based computation on any QLDPC codes, with reasonable overheads. arxiv.org/abs/2503.10390 The talk recording is here: www.youtube.com/watch?v=L6cDAbaW2Zs

Extractors: Building a Quantum Computer with QLDPC Codes

YouTube video by Simons Institute for the Theory of Computing

youtube.com

Our paper on logical magic state distillation was just published in Nature! www.nature.com/articles/s41...

New preprint out!! scirate.com/arxiv/2507.0... Here, we follow up our previous work by constructing the first asymptotically good quantum codes to have transversally addressable non-Clifford gates.

Asymptotically Good Quantum Codes with Addressable and Transversal Non-Clifford Gates

Constructing quantum codes with good parameters and useful transversal gates is a central problem in quantum error correction. In this paper, we continue our work in arXiv:2502.01864 and construct the...

scirate.com

Raymond Laflamme 1960-2025. A great scientist, renowned for his pioneering contributions to quantum error correction. A great leader, founding director of the Institute for Quantum Computing. A great colleague and teacher whose legacy continues to inspire us. uwaterloo.ca/institute-fo...

IQC and Waterloo mourn the loss of Raymond Laflamme | Institute for Quantum Computing | University of Waterloo

Raymond Laflamme, a trailblazer in quantum information processing and pioneer of the Institute for Quantum Computing (IQC) at the University of Waterloo, died on June 19 after a lengthy battle with ca...

uwaterloo.ca