Blog post: algassert.com/post/2603 "Unfathomable bugs #10: The Broken Windows Build" It's been awhile since I added to this particular series. But when a bug beyond your control steals a day of your life, you gotta vent somehow.

Blog post: "The French have the Quantum Circuits" algassert.com/post/2602 André Schrottenloher just published a preprint showing how to construct quantum ECDLP circuits with costs similar to the ones in our zero knowledge proofs.

Stim v1.16 released github.com/quantumlib/S... My favorite addition is "stim.Circuit.missing_detectors" for finding that last damn detector. Also, I packaged circuit gen tools from my papers into a library "stimflow." It's got jank, but also solid ideas for building circuits in chunks.

Release v1.16.0 - Flowing Circuits · quantumlib/Stim

Flagship Changes Started a new glue library "stimflow" for qec circuit creation Added class stim.CliffordString Added prebuilt wheels for python 3.13 and python 3.14 Breaking Changes: Dropped su...

github.com

I plotted the asteroid data from Kirkwood's 1887 paper (www.gutenberg.org/ebooks/41570) next to the 2007 plot from Wikipedia's page on Kirkwood gaps. I think it's a good example of available data going from convincing only if you know the theory to just blatantly speaking for itself.

Blog post: "The predictable failure of the QDay Prize" algassert.com/post/2601

Congrats to Keegan Ryan for being the first to exploit the simulator we used to validate the secret quantum circuits: blog.trailofbits.com/2026/04/17/w... It kills me that the (now fixed) bugs were simple (we didn't port the op validation code from C++ to Rust!), but that's to be expected.

We beat Google’s zero-knowledge proof of quantum cryptanalysis

Trail of Bits discovered and exploited memory safety and logic vulnerabilities in Google’s Rust zero-knowledge proof code to forge a proof claiming better quantum circuit performance metrics than Goog...

blog.trailofbits.com

My dream paper is a zero-knowledge proof that I know the answer to the Collatz conjecture.

A special blog post for today: On Eastin-Knill Being Wrong algassert.com/post/2600

As timelines tighten, details might benefit attackers more than defenders. So we're trying something weird: proving a circuit exists without revealing it. For example, here's a zero-knowledge proof that we found 10x smaller quantum circuits for ECDLP: github.com/tanujkhattar...

While I was attending APS March Meeting, I appeared in the 632nm podcast. The recording is available on youtube: www.youtube.com/watch?v=lnHg... Never been on a podcast before, and no doubt that shows, but it was fun.

How To Make Quantum Algorithms Cheaper | Craig Gidney on Magic-State Factories, Resource Estimates

YouTube video by 632nm

youtube.com

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

The slides from my talk "how to eat magic states" at APS 2026: docs.google.com/presentation... ...The content of the talk definitely drifted from when I picked the title. Mostly I talked about realizing I didn't understand reaction depth a few months ago.

[APS2026] How to eat magic states

How to eat magic states APS March Meeting 2026 Craig Gidney Google Quantum AI Hello everyone, My name is Craig and my talk is called "how to eat magic states". Now... I have a bit of a confession. The...

docs.google.com

Chevignard et al show residues also reduce the qubit cost of quantum attacks on elliptic curves: eprint.iacr.org/2026/280 The space savings is less dramatic than for factoring (1.6x instead of 6x), and they again pay a big gate count penalty (256x), but very interesting.

Reducing the Number of Qubits in Quantum Discrete Logarithms on Elliptic Curves

Solving the Discrete Logarithm problem on the group of points of an elliptic curve is one of the major cryptographic applications of Shor's algorithm. However, current estimates for the number of qubi...

eprint.iacr.org

Made a video tutorial of using crumble to create a quantum error correction circuit: youtu.be/SnpLSvyyEx8

How to make Quantum Error Correction circuits with Crumble

YouTube video by Craig Gidney

youtu.be

I've been asked several times to comment on arxiv.org/abs/2602.11457, which claims to reduce the qubit cost of factoring by 10x. My take is that they demand a *lot* more qubit connectivity for that number. Your mileage depends entirely on how plausible you find those demands.

The Pinnacle Architecture: Reducing the cost of breaking RSA-2048 to 100 000 physical qubits using quantum LDPC codes

The realisation of utility-scale quantum computing inextricably depends on the design of practical, low-overhead fault-tolerant architectures. We introduce the \textit{Pinnacle Architecture}, which us...

arxiv.org

A surface code that goes from a normal tiling to one where each row keeps using half as many qubits as the last. I can't think of a reason to do this, but it's visually interesting.

Another paper related to simulating magic state cultivation. This time it's algorithmic insights, rather than hulk-smashing at the circuit with GPUs: scirate.com/arxiv/2512.2... (...¿porque no los dos?)

Efficient simulation of logical magic state preparation protocols

Developing space- and time-efficient logical magic state preparation protocols will likely be an essential step towards building a large-scale fault-tolerant quantum computer. Motivated by this need, ...

scirate.com

Papers citing stim doubled again in 2025. Stim is a python package for analyzing/simulating quantum error correction circuits. It was thousands of times faster than prior tools and popularized modelling fault tolerance in terms of "detectors" (see quantum-journal.org/papers/q-202...).

Better simulations of magic state cultivation: scirate.com/arxiv/2512.2... . In my initial paper, I approximated T with S by using a 2x safety factor measured at d=3. IMO this paper suggests another 2x at d=5. They *claim* another 7.65x; an attempts-vs-error curve would help tell.

SOFT: a high-performance simulator for universal fault-tolerant quantum circuits

Circuit simulation tools are critical for developing and assessing quantum-error-correcting and fault-tolerant strategies. In this work, we present SOFT, a high-performance SimulatOr for universal Fau...

scirate.com

An upbeat blog post for Christmas: Quantum Error Correction goes FOOM algassert.com/post/2503

History of quantum rep code error rates from the UCSB→Google team 2014: 0.1% arxiv.org/abs/1411.7403 2015: 2016: 2017: 2018: 2019: 2020: 2021: 0.01% arxiv.org/abs/2102.06132 2022: 2023: 0.0001% arxiv.org/abs/2207.06431 2024: 0.00000001% arxiv.org/abs/2408.13687 I call this pattern "QEC goes foom"

We did some experimental testing of magic state cultivation! arxiv.org/abs/2512.13908 A ~1e-4 end2end infidelity is tricky to measure with tomography, so we checked it vs more cultivation. The full escape stage is too wide for the chip, but we did try ending in the grafted code.

This new quanta article (www.quantamagazine.org/physicists-t... arxiv.org/pdf/0810.1923) claims my blog post on spoofing real-only tests is a new discovery. I'm flattered... but since writing the post I learned McKague et al knew it in 2008 (see section II.C of arxiv.org/pdf/0810.1923).

Physicists Take the Imaginary Numbers Out of Quantum Mechanics | Quanta Magazine

Quantum mechanics has at last been formulated exclusively with real numbers, bringing a mathematical puzzle at the heart of the theory into a new era of inquiry.

quantamagazine.org

OpenSSH added a "your session isn't secure against store-now-decrypt-later quantum attacks" warning: www.openssh.org/pq.html I love it. Waiting until the problem is manifest is a great way to have waited too long. Fix shit now.

Stim has received its first AI slop pull request: github.com/quantumlib/S... (It's actually not the first AI generated pull request that's been submitted, but the other one was actually a correct bug fix thus not slop.)

Here's the recording of my talk at the Simons institute quantum industry day: www.youtube.com/live/SULOaOQ... And the slides: docs.google.com/presentation... I was also on the panel discussion at the end of the day (also in the linked playlist).

Optimizing the Annoying Stuff: Reducing Costs Obscured by the Abstract Circuit Model

YouTube video by Simons Institute for the Theory of Computing

youtube.com

My contribution to arxiv.org/abs/2510.10967 is a space-efficient strategy for modular division under superposition. It's based on recording the branches taken during a GCD, to decompose a number+modulus into their "dialog representation", which unlike binary is entirely linear.

I'll be speaking at the Simons Institute this Thursday: simons.berkeley.edu/events/quant... (Hopefully my flight doesn't get cancelled this time.) Talk Title: Optimizing the Annoying Stuff: Reducing Costs Obscured by the Abstract Circuit Model Abstract: attached as image

For their student researcher-ship, Satoshi Yoshida extended our work on dynamic surface code circuits to color codes. They built and simulated iswap color code circuits and wiggling color code circuits. The iswap circuits use fewer entangling layers than CX circuits! arxiv.org/abs/2510.00370

Low Depth Color Code Circuits with CXSWAP gate

We present two new types of syndrome extraction circuits for the color code. Our first construction, which after [M. McEwen, D. Bacon, and C. Gidney, Quantum 7, 1172 (2023)] we call the semi-wiggling ...

arxiv.org

This HSBC paper reminds me of www.youtube.com/watch?v=EbfJ... In the clip at 38:10, a speaker relays Pons being told a light water control had excess heat. Instead of "oh no", Pons replies "That's the most exciting thing, we see it too!". The audience bursts into laughter at the clear self-fooling.