@domwilliamson.bsky.social
Topological phases of matter and fault-tolerant quantum computing at The University of Sydney.
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...
19.02.2026 13:15 — 👍 5 🔁 1 💬 0 📌 0
New work out today with a killer app for our recent fast and fault tolerant logical measurement procedure on quantum codes. Here we apply it to higher-form Clifford gates to prepare many logical magic states in parallel in constant time.
arxiv.org/abs/2601.22939
I had a great time hosting TOPO2025 this week in Sydney. thanks to all the speakers and our sponsors: sites.google.com/view/topowor...
14.11.2025 11:59 — 👍 6 🔁 0 💬 0 📌 0
We are offering 4 PhD scholarships in #physics and #astronomy topics @sydney.edu.au
Including:
* FRBs with @manishacaleb.bsky.social
* Quantum critical points with @domwilliamson.bsky.social
* Nanostructured materials with @boriskuhlmey.bsky.social
www.sydney.edu.au/scholarships...
⚛️ 🔭 ☄️ 🧪
Come and join us: we have 2x Postdoctoral Research Associate positions available at SMRI. Mathematicians of all areas are encouraged to apply (pure, applied, statistics). Please share with your network #MathSky
Closing December 3
usyd.wd105.myworkdayjobs.com/en-GB/USYD_E...
Some cool related works
scirate.com/arxiv/2410.1...
scirate.com/arxiv/2510.0...
scirate.com/arxiv/2510.0...
Thanks again to the quantum surgeons, Alex, Sunny, and Ted!
17.10.2025 05:36 — 👍 2 🔁 0 💬 1 📌 0Finally, we introduce a general upper bound on the fault tolerance of any logical measurement scheme in terms of the spacetime region of the code that is addressed by the measurement procedure.
Our results point to a tradeoff between overhead and addressability for fault-tolerant quantum logic.
We demonstrate an equivalence between block reading and homomorphic measurement, and characterize when this equivalence can preserve fault tolerance.
17.10.2025 05:36 — 👍 1 🔁 0 💬 1 📌 0
In the extreme limit of measuring a single logical operator, this scheme reduces to regular lattice surgery with a time overhead that scales with the code distance.
17.10.2025 05:36 — 👍 1 🔁 0 💬 1 📌 0
We go on to study partial block reading We characterize the space and time overhead depending on the properties of the subcode being measured.
17.10.2025 05:36 — 👍 1 🔁 0 💬 1 📌 0
Here is what block reading looks like on a pair of surface codes.
17.10.2025 05:36 — 👍 1 🔁 0 💬 1 📌 0Block reading is a simple class of hypergraph surgeries that measure transversal logical operators. These measure logicals across copies of a code block in parallel, in constant time and linear qubit overhead. This doesn’t require the code to be single-shot, similar to algorithmic fault tolerance.
17.10.2025 05:36 — 👍 1 🔁 0 💬 1 📌 0
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
This was also fun to listen to.
15.10.2025 00:43 — 👍 4 🔁 0 💬 0 📌 0Quantum low density parity check!
15.10.2025 00:41 — 👍 2 🔁 0 💬 0 📌 0That was fun.
14.10.2025 21:46 — 👍 14 🔁 0 💬 3 📌 0
Very happy that I was scheduled to present first today. Talk about a hard act to follow…
14.10.2025 16:27 — 👍 22 🔁 0 💬 1 📌 1Also see related work with similar results plus a bunch of other cool stuff about random input Layer Codes arxiv.org/abs/2510.06659
13.10.2025 01:46 — 👍 2 🔁 0 💬 0 📌 0
Applying this decoder to a family of Layer Codes reveals a strong form of partial self-correction where a growing number of encoded qubits are protected for an exponentially long time in the linear system size, up to a scale that is exponential in the inverse temperature.
& here is the correction:
The concatenated matching decoder involves rounds of minimum-weight perfect-matching on coupled surface code layers, combined with a decoder for an input Quantum Tanner Code.
13.10.2025 01:46 — 👍 1 🔁 0 💬 1 📌 0
How do you correct this error in a Layer Code?
In new work arxiv.org/abs/2510.09218 we introduce a concatenated matching decoder and show that Layer Codes assisted by this decoder are partially self-correcting quantum memories at finite temperature!
Layer Codes are partially self-correcting: arxiv.org/abs/2510.09218
13.10.2025 01:31 — 👍 1 🔁 0 💬 0 📌 0
Floquet codes fit neatly onto the heavy-hex lattice. In new work out today, we show that making full use of all the heavy-hex qubits allows us to fit two floquet codes at once. We also describe transversal gates and low-depth adaptive circuits to switch to the color code.
arxiv.org/abs/2510.05225
📢 Come be my colleague: the School of Computer Science at 🇦🇺 #USyd is hiring!
Multiple tenure-track-equivalent positions across the board (including theory!), but with a specific focus on Cybersecurity and Trustworthy Digital Systems, and ML/AI.
⏰ Dec 1
usyd.wd105.myworkdayjobs.com/en-GB/USYD_E...
Gauging versus dualities: equivalent up to constant depth quantum circuits. arxiv.org/abs/2509.22051
29.09.2025 07:29 — 👍 14 🔁 3 💬 1 📌 0
There and back again… a gauging nexus between topological and fracton phases
Join us on a journey through the gauging nexus between topological and fracton phases. In this work we show how to pass through a web of dualities between topological, symmetry-protected, and fractonic phases of quantum matter, and back again.
arxiv.org/abs/2509.19440
Layer codes may not be self-correcting in the strict sense but that isn’t the end of the story. Stay tuned!
23.09.2025 06:39 — 👍 3 🔁 0 💬 0 📌 1
Another fantastic paper by Noédyn Baspin on arxiv today.
Introducing the free energy barrier for quantum codes and using it to destroy our dreams of a self-correcting quantum memory in 3D based on existing codes.
scirate.com/arxiv/2509.1...
The spiders and snakes really made it feel like home.
06.07.2025 08:34 — 👍 2 🔁 0 💬 0 📌 0
