Esha Swaroop

LDPC Logic gates started looking a lot more concrete -- explicit constructions with realistic overheads for near but interesting codes we know (BB, lifted product codes,..) coming soon.

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

some visuals to complement 3 recent papers on logical gate schemes for arbitrary quantum LDPC codes. :)

Here are slides from our @qip2025.bsky.social talk on Logical gates on quantum LDPC codes by surgery / Universal Adapters. doi.org/10.5281/zenodo.14997472

Thiago put together a nice plot summarizing how this result fits into other results about bounds of time/space overhead vs locality. In terms of this plot, the paper's goal was to put a circle in the O(1) column, but not in the "all" row.

Next week is QIP, which is the main conference in theoretical question information science. I am delighted that three of my group members have accepted talks: Paula Belzig, Esha Swaroop, and Peixue Wu.
With an acceptance rate of 20%, this is a big accomplishment for each of them!

there must be some trickle down effect onto efficacy of two stages?

ah, P_{1,17} is ~e^14 so it's still cubic suppression, but the qutrit code offers much better constants.

Trading hundreds of qubits for just 20 qutrits isn't a big ask in terms of temporarily switching dimension of the system either.

where is this from?
if one throws out everything but the leading order, error^16 suppression sounds pretty good...

Curious how did you get the initial depth as 4 specifically? guessing here that a minimum of 3 time steps arise from pairwise gates between 3 pairs of qubits, and an extra gate somewhere?
Will check out the relevant section for technical details

I see, it's depth 1 exactly, not just depth O(1). That would be a pretty specialized code indeed.
Pieceably transversal CCZs (which are applicable to arbitrary CSS codes) are targeted, but they would need a depth of O(d).
Interesting to see how much better tailored targeted codes can do!

quick edit in my previous comment: the adapters were designed for LDPC regime, but simplifications for higher-weight codes would only make it easier to teleport info. But this is all side-tracking from the main story, for which I'll check out your paper.

ah so the motivation is towards code construction tailored towards these gates rather than a generic gate scheme. Pretty neat! One can still hook these codes up to arbitrary LDPC codes using our adapters (arxiv.org/abs/2410.03628) for using these more generically in other codes.

Congrats on these results on a very interesting problem -- Looking forward to reading this work! Are the check weights bounded during the CCZ circuit? (If not by constants, then what is the extent to which they increase?)

Experimental Demonstration of Logical Magic State Distillation Realizing universal fault-tolerant quantum computation is a key goal in quantum information science. By encoding quantum information into logical qubits utilizing quantum error correcting codes, physi...

Interesting paper implementing magic state distillation with neutral atoms: arxiv.org/abs/2412.15165

They're in a weird regime: below the distillation threshold but over the color code threshold. They see improvements!... But hit a ceiling imposed by their d=3 memory error (because d=5 does worse).

Scaling and logic in the color code on a superconducting quantum processor Quantum error correction is essential for bridging the gap between the error rates of physical devices and the extremely low logical error rates required for quantum algorithms. Recent error-correctio...

We've been getting a lot of questions about alternate QEC codes, and are we looking into any? Yes! Here's experiments for two on Willow.

The color code: arxiv.org/abs/2412.14256

Dynamic surface codes: arxiv.org/abs/2412.14360

Congrats! Curious, how did you verify the quantum computer's output is correct? (due to inability to reproduce this classically in feasible time)

👋 Anyone need some codes? We've got 566 classical & quantum codes.

ahhh it's LDPC specific. thanks for clarifying!

thanks! ok i see why good soundness isn't contained in the good confinement condition (as small syndromes can be caused by large errors).
Reg the other way around (good confinement ⊆ good soundness), it's also somehow implicit that small errors trigger a small syndrome?

my current guess it's the same inequality (f(|σ(e)|) ≥ |e|_red) , but enforced on a smaller set of errors to get a weaker condition.

@quantumearl.bsky.social A question: maybe i'm missing something obvious, but confinement and soundness like the same thing here? 🙈 As I understand it, they both involve a proportionality between the weight of the syndrome (perhaps addnl wrapped as input to a function) and the weight of the error.

Universal adapters between quantum LDPC codes We propose the repetition code adapter as a way to perform joint logical Pauli measurements within a quantum low-density parity check (LDPC) codeblock or between separate such codeblocks. This adapter...

Sharing our work "Universal adapters for quantum LDPC codes" posted today to arxiv arxiv.org/abs/2410.03628

We provide a flexible tool to enable joint measurements between logical operators in arbitrary LDPC codes, and also a variant to implement targeted CNOT gates using Dehn twists.

‘Magical’ Error Correction Scheme Proved Inherently Inefficient | Quanta Magazine Locally correctable codes need barely any information to fix errors, but they’re extremely long. Now we know that the simplest versions can’t get any shorter.

Wonderful article by @benbenbrubaker.bsky.social on the recent breakthrough result of Pravesh Kothari and Peter Manohar on locally correctable codes (LCCs). Even beyond this result, one of the best expositions of error-correcting codes I've read!
www.quantamagazine.org/magical-erro...

Assistant Professor – Quantum Information / Computer Science | Institute for Quantum Computing The David R. Cheriton School of Computer Science and the Institute for Quantum Computing (IQC) at the University of Waterloo

Apply for a faculty position in quantum computing at the University of Waterloo’s School of Computer Science & Institute for Quantum Computing. Deadline December 22.

uwaterloo.ca/institute-fo...

The Quest to Quantify Quantumness | Quanta Magazine What makes a quantum computer more powerful than a classical computer? It’s a surprisingly subtle question that physicists are still grappling with, decades into the quantum age.

There are at least three mathematical ways of quantifying how “quantum” a computation may be, but there doesn't appear to be one quantum metric to rule them all. www.quantamagazine.org/the-quest-to...

Tensor Network Decoding Beyond 2D Decoding algorithms based on approximate tensor network contraction have proven tremendously successful in decoding 2D local quantum codes such as surface/toric codes and color codes, effectively achi

Do you want to correct a quantum code? Do you like tensor networks? Do you live in 3D? Well I have the paper for you! scirate.com/arxiv/2310.1...