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Diego Ruiz @diego-ruiz.bsky.social · 19/01/2026

I am pretty optimistic that this number of 7x10^4 (to reach a logical error rate of 10^(-12)) can go down quite a lot with further improvements, and that these codes will be used in practice for cat qubits.

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Diego Ruiz @diego-ruiz.bsky.social · 19/01/2026

Here, we apply this idea to biased-noise qubits and show that, for sufficiently high noise bias, correcting bit-flips only at the outer-code level is more advantageous than correcting it at the inner-code level, as done by the surface or XZZX codes.

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Diego Ruiz @diego-ruiz.bsky.social · 19/01/2026

Recently, Refs. arxiv.org/abs/2303.04798 and arxiv.org/abs/2312.04522 have shown that concatenating the surface code with a higher-rate outer code can reduce the overall overhead, while staying with a 2D architecture.

arxiv.org

Hierarchical memories: Simulating quantum LDPC codes with local gates

Constant-rate low-density parity-check (LDPC) codes are promising candidates for constructing efficient fault-tolerant quantum memories. However, if physical gates are subject to geometric-locality co...

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Diego Ruiz @diego-ruiz.bsky.social · 18/07/2025

And for instance, you can also prepare a Cx-Cx-X state (a Hadamard CCZ) by unfolding the [[8,3,2]] 3D color code The suppression scales in p², which is a bit weak, but maybe larger unfolded codes can push the fidelity further, something to explore! cc @christophe.vuillot.info

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Diego Ruiz @diego-ruiz.bsky.social · 18/07/2025

Why does it work? The 15 Reed-Muller is 3D, but if one error type dominates, you only need to measure the weight-4 stabilizers, not the weight-8 ones The nice part is you can unfold these weight-4 checks in 2D! And this unfolded code can be also merged with a thin surface code

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Diego Ruiz @diego-ruiz.bsky.social · 18/07/2025

And even with a noise bias as low as 80, a magic state of the same fidelity can be prepared with 175 qubits in the same amount of time The key insight is that the noise bias enables you to perform distillation at the physical level rather than at the logical level

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Diego Ruiz @diego-ruiz.bsky.social · 18/07/2025

Probably the last paper of my PhD! We show that biased-noise qubits can greatly reduce the cost of magic state preparation With high noise bias, just 53 qubits and ~10 error correction cycles are enough to prepare a magic state with logical error≈1e-7 arxiv.org/abs/2507.12511

arxiv.org

Unfolded distillation: very low-cost magic state preparation for biased-noise qubits

Magic state distillation enables universal fault-tolerant quantum computation by implementing non-Clifford gates via the preparation of high-fidelity magic states. However, it comes at the cost of sub...

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Reposted by Diego Ruiz

Christophe Vuillot @christophe.vuillot.info · 21/03/2025

Two talks of Alice&Bob QEC team in parallel this morning: @diego-ruiz.bsky.social presented his new results on distillation with biased-noise qubits: with bias=30 he already gets 150x reduction! I talked about implementing rotor codes So many fun subjects to work on, join our team we are hiring!🐱

Diego presenting his work under the expert eye of Craig Gidney

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Diego Ruiz @diego-ruiz.bsky.social · 14/02/2025

1️⃣ It's surprisingly close to the theory, the suppression of bitflips has never been this strong, the lifetime is multiplied by e^4≈50 for every added photon instead of e^2≈7 2️⃣ The bitflip saturates at the same value as the normal cat, a few minutes (cosmic rays?)

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Diego Ruiz @diego-ruiz.bsky.social · 14/02/2025

First realization of a dissipatively stabilized squeezed cat qubit (a slight variation that we called a moon cat 🌛 actually), it was super interesting to work on this with experimentalists! arxiv.org/abs/2502.07892 My two key takeaways ⬇️⬇️

arxiv.org

Enhancing dissipative cat qubit protection by squeezing

Dissipative cat-qubits are a promising architecture for quantum processors due to their built-in quantum error correction. By leveraging two-photon stabilization, they achieve an exponentially suppres...

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