You are correct in the details, but not the distinction. This is exactly how classical error correction works as well.

This happens to be the same way that classical error correction works, but quantum.

Just an example to expand on what others are saying: in the N^2-qubit Shor code, the X information is recorded redundantly in N disjoint sets of N qubits each, and the Z information is recorded redundantly in a different partitioning of N disjoint sets of N qubits each. You could literally have N observers each make separate measurements on disjoint regions of space and all access the X information about the qubit. And likewise for Z. In that sense it's a repetition code.

I don't believe it is the result of a LLM, more like an oversimplification, or maybe a minor fuckup on the part of the author as simple majority voting is often used in redundant systems, just not for memories as there are better ways.

And for a LLM result, this is what ChatGPT says when asked "How does memory error correction differ from quantum error correction?", among other things.

> Relies on redundancy by encoding extra bits into the data using techniques like parity bits, Hamming codes, or Reed-Solomon codes.

And when asked for a simplified answer

> Classical memory error correction fixes mistakes in regular computer data (0s and 1s) by adding extra bits to check for and fix any errors, like a safety net catching flipped bits. Quantum error correction, on the other hand, protects delicate quantum bits (qubits), which can hold more complex information (like being 0 and 1 at the same time), from errors caused by noise or interference. Because qubits are fragile and can’t be directly measured without breaking their state, quantum error correction uses clever techniques involving multiple qubits and special rules of quantum physics to detect and fix errors without ruining the quantum information.

Absolutely no mention of majority voting here.

EDIT: GPT-4o mini does mention majority voting as an example of a memory error correction scheme but not as the way to do it. The explanation is overall more clumsy, but generally correct, I don't know enough about quantum error correction to fact-check.

People always have made bad assumptions or had misunderstandings. Maybe the author just doesn't understand ECC and always assumed it was consensus-based. I do things like that (I try not to write about them without verifying); I'm confident that so do you and everyone reading this.

I've gone to lots of talks on quantum error correction, and most of them start out with explaining the repetition code. Not because it's widely used, but because it is very easy to explain to someone who knows nothing about classical coding theory. And because the surface code is essentially the product of two repetition codes, so if you want to understand surface code quantum error correction you don't need to understand any classical codes besides the repetition code.

All that is to say that someone who had been to a few talks on quantum error correction but didn't directly work on that problem might reasonably believe that the repetition code is an important classical code.

RAID-1 does not do on the fly error detection or correction. When you do a read you read from one of the disks with a copy but don't validate. You can probably initiate an explicit recovery if you suspect there's an error but that's not automatic. RAID is meant to protect against the entire disk failing but you just blindly assume the non-failing disk is completely error free. FWIW no formal RAID level I'm aware of does majority voting. Any error detection/correction is implemented through parity bits with all the problems that parity bits entail unless you use erasure code versions of RAID 6.

The reason things work this way is you'd have 2x read amplification on the bus for error detection and 3x read amplification on the bus for majority-voting error correction & something in the read I/O hot path validating the data reducing latency further. Additionally, RAID-1 is 1:1 mirroring so it can't do error correction automatically at all because it doesn't know which copy is the error-free. At best it can transparently handle errors when the disk refuses to service the request but it cannot handle corrupt data errors that the disk doesn't notice. If you do FDE then you probably would notice corruption at least and be able to reliably correct even with just RAID-1 but I'm not sure if anyone leverages this.

RAID-1 and other backup / duplication strategies are for durability and availability but importantly not for error correction. Error correction for durable storage is typically handled by modern techniques based on erasure codes while memory typically uses Hamming codes because they were the first ones, are cheaper to implement, and match better to RAM needs than Reed Solomon codes. Raptor codes are more recent but patents are owned by Qualcomm; some have expired but there are continuation patents that might cover it.

Yes, and it's worth pointing out these examples because they don't work as quantum memories. Two more: magnetic memory based on magnets which are magnetic because they are build from many tiny (atomic) magnets, all (mostly) in agreement. Optical storage is similar, much like parent's example of a signal being slowly sent over a wire.

So the next question is why doesn't this work for quantum information? And this is a really great question which gets at the heart of quantum versus classical. Classical information is just so fantastically easy to duplicate that normally we don't even notice this, it's just too obvious a fact... until we get to quantum.

Regardless of whether the parent's sentence is a tautology, the explanation in the article is categorically wrong.

This is not about AlphaQubit. It's about a different paper, https://arxiv.org/abs/2408.13687 and they do demonstrate real-time decoding.

> we show that we can maintain below-threshold operation on the 72-qubit processor even when decoding in real time, meeting the strict timing requirements imposed by the processor’s fast 1.1 μs cycle duration

Yeah, I didn't want to just accuse the article of being AI generated since quantum isn't my specialty, but this kind of error instantly tripped my "it doesn't sound like this person knows what they're talking about alarm" which likely indicates a bad LLM helped summarize the quantum paper for the author.