James Wootton

Next week I am hoping for a paper with an algorithm that helps me to proofread bluesky posts, but I think that might be QMA hard.

And then another end-to-end architecture, this time looking at how the best way to use qLDPC codes for the one big application we all know about: breaking current crypto systems. The team at Iceberg Quantum show that it can be done with less that 100k physical qubits.

arxiv.org/abs/2602.11457

Two great papers on the arXiv today!

One has a title echoing that of Kitaev's "Fault-tolerant quantum computation by anyons" almost 30 years ago. Finally Anasuya Lyons and @benbrown.bsky.social shown how to make it work from encoding to decoding.

arxiv.org/abs/2602.11258

We've studied iterative strategies for finding ground states

We use the ground state of an easy Hamiltonian to `warm start' finding the ground states for some harder Hamiltonians

We derive gradient guarantees that (as for adiabatic methods) depend on the gap and a few other natural properties

🧵👇

Did you know you can simulate quantum states with Pauli and Majorana propagation?

In short: High-temperature states are provably and practically sparse, and we can use imaginary time evolution to get there starting from the infinite-temperature state.

scirate.com/arxiv/2602.0...

If we are comparing to 1st century Galilean miracle workers, perhaps Majoranas are more like Shimon bar Yochai: Spends years naked in a cave, but expected to suddenly emerge with superpowers.

How do we figure out the circuit required to prepare a given state, and what's the best circuit? With help from MPS, these guys get it down to logarithmic depth.
arxiv.org/abs/2602.02698

Weight-four parity checks with silicon spin qubits Recent advances in coherent spin shuttling have made sparse semiconductor spin qubit arrays an appealing solid-state platform to realize quantum processors. The dynamic and long-range connectivity ena...

Spin qubits have finally reached the point where superconducting qubits were 10 years ago!
arxiv.org/abs/2601.23267

Banishing 512 might be easier.

I have 1024 followers!

Nobody else follow me now. I like powers of 2.

Realizing Repeated Quantum Error Correction in a Distance-Three Surface Code Quantum computers hold the promise of solving computational problems which are intractable using conventional methods. For fault-tolerant operation quantum computers must correct errors occurring due ...

No, distance 3
arxiv.org/abs/2112.03708

It's a 17 qubit rotated surface code.

Logical qubits encoded in the fusion space of non-Abelian anyons in a generalized surface code.

Not the most efficient way to build a quantum computer, but definitely the coolest!

Quantinuum and co show how it's done on one of their H2 devices.

arxiv.org/abs/2601.20956

The background did indeed highlight the experience

Yesterday I did two things:

* Wrote a self-indulgent blog post reflecting on the last 10 years in which I went crazy and started doing quantum games.
* Held a surface code in my hand.

Here I share both with you, the denizens of blue sky

open.substack.com/pub/mothquan...

Today we get the computer scientists' view on the transition into fault-tolerance.

There will indeed be a whole lot of classical computing involved in getting early fault-tolerance running, and the better it is, the more quantum we can use.

arxiv.org/abs/2601.20247

Yeah, that would be an interesting and novel test. Especially now that @andreasateth.bsky.social at ETH has finally provided us some loophole free Bell tests.

Always nice to see that quantum foundations have survived the wave of capitalism that has swept through quantum.

Today Hausmann and Renner from ETH show that quantum states are more than just a few probability distributions in a trenchcoat.

arxiv.org/abs/2601.18872

In terms of the 'early fault tolerance' naming debate. This seems a bit more on the NISQ with FTQC sprinkles side, but could also help out in the early days of full FTQC.

bsky.app/profile/deco...

I got out of the habit of posting half-baked thoughts about papers when Twitter died, But I think I should bring it back!

This paper combines error mitigation inside QEC to cancel leading logical errors and effectively giving a distance boost.

arxiv.org/abs/2601.18384

Sketch of quantum warfare utilising various quantum technology systems

"We are a group of quantum scientists who oppose the ongoing militarization of our societies and the use of quantum research for military purposes."
disarmquantum.com
Manifesto:
arxiv.org/abs/2601.14282

Here's just one example:
"Quantum technology for military applications"
doi.org/10.1140/epjq...

Quantum computing wouldn't be where it is today without the cryptographic applications of Shor's algorithm. We've been militarized for 30 years, and just pretending otherwise. But I definitely support finding ways to fill up QPUs with more inspirational applications.

Yes, I agree that this approach will definitely be a thing on the journey to fault-tolerance. But it should should it's own term, and "partially fault-tolerant" seems good to me.

That's a definition I can get behind!

Is there clear taxonomy that I don't know about. For the noble purpose of avoiding misleading press releases, there probably should be!

To me these seem pretty different. One is about finding and correcting all the errors, and so is proper FTQC. Even if it is early days.

The other is more about detecting and avoiding errors, and probably paying a sampling overhead to ignore them once you find them. So still a form of mitigation.

The other is to have elements of QC interleaved into NISQ. So maybe you have a low distance code mostly (or entirely) doing the job of error correction. Maybe you use a distillation style process to give you a high quality initial state to kick off a NISQ algorithm.

What does early FTQC mean? It seems to be an increasingly popular term, but usage seems to split into two camps.

One is FTQC but early. So you have logical qubits with a decent distance, magic state production to support logical non-Cliffords. It's just early because you don't have a lot of it.

You are commuting to your dinner with me ;)

An image of a volleyball against a blue background. The text says: In my home state of Massachusetts, ICE is hunting a man who has an expired visa. They find the man’s car, but the driver is just the man’s son, a teen heading to volleyball practice. ICE arrests the teen.

A conversation between two people in speech bubbles: “Do you know why you’re under arrest?” “No.” “Because you’re illegal. You’re an immigrant.” “Ma’am, I was seven years old.” Then, text at the bottom says: The teen is put into a concrete cell with 35 men.

The community rallies behind him. There's an image of yard signs with the smiling face of the teen that say Free Marcelo. Some quotes from locals: “He’s one of our brothers. Without him, it just kind of feels like a dark, empty room.” -volleyball team captain. “This administration isn’t keeping us safe by putting 18-year-old honors students in prison.” -MA Rep. Moulton

In the cell, the teen helps translate for those who don’t speak English. Many are ill. After 6 days, he’s released. There's an image of a hand and arm, with a crinkly foil bracelet tied around the wrist. Wearing a bracelet that another detainee made him from one of the thin mylar blankets they were given, he says: “ I don’t want to cry. But I want to say...nobody should be in here.”

Something a little different. Some cartoonists put out a call for comics about local ICE experiences. This one happened a few months ago so it's a little older than current events, but it's a story that I never stopped thinking about. #ICEoutcomics