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Comment by adastra22 | Hacker News Reader

We only need the ability to make make 1 qubit with indefinite reliable / fully error corrected state. Quantum interconnects would allow for these to be connected into arbitrarily large quantum computers.

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So we only need to invent actual quantum computers. Got it, easy.

Yes, but since R&D and funding are in a feedback loop now (promising results -> more money -> better results etc), it might only take a couple more years to get there. https://arstechnica.com/science/2026/06/amazon-quera-promise...

It's more akin to "we only need to make reliable transistors to make classical computers." With the invention of the planar transistor, going from 1 transistor to 100 or 100k was not that big of a step, comparatively.

transistors are local unit, qubits are not

Transistors connect to other transistors, directly or in switched arrangements. Qubits can be connected to other qubits likewise. E.g. a single photon emitter next to a nuclear spin qubit that can send an entangled photon through a beam splitter in a photonic switch, routing that entangled pair through fiber optic cables to other qubits where a combination of electric fields, filters, and occupied energy levels cause gate operations to be applied during absorption & re-emission. Except for the long-lived, error-corrected qubit, everything I described there is off-the-shelf commercial technology.

Photonic quantum interfaces typically operate at glacial speeds and with terrible fidelities. There is a lot more missing than good qubits.

It's really really easy to eliminate noise in a digital system of transistors. For analog systems with subtle values, I would say we still can't arbitrarily scale that up with transistors. And quantum is like analog but far worse.

But those cannot exist, can they? Nature seems really opposed to the realisation of ideals.

My company is making them. You just need to have a sufficiently resilient surface code, which means a single device with millions of physical qubits (the standard brute-force approach) or use a qubit architecture that is intrinsically noise-free by comparison, and only needs 15-50 physical qubits (what my company is doing, and our competitors). The industry as a whole is probably only a few years away from achieving this, in some form.

A "perfect" or "indefinitely stable" qubit sounds impossible. But so would a DRAM cell to an electrical engineer in the 40's. A DRAM cell continuously refreshes to maintain state, and as a result a single bit in RAM can have a mean time to failure measured in geologic time. Likewise a quantum error correction algorithm with a sufficiently large factor, driven continuously, will maintain qubit state indefinitely.

Electrical engineers in the 1940s already had "infinitely stable" memory in the form of delay lines and Williams tubes. Quantum error correction is incomparably more difficult than using digital bits.

Why is it that every time I read about quantum computers, fusion, and high energy density batteries, the word "just" seems extremely load-bearing, but results are like just, nowhere to be seen

What does indefinitely stable mean?

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