The quantum computing stack

Six layers, ordered by distance from the qubit: physical infrastructure (L0), the signal chain (L1), control hardware (L2a), control software (L2b), error correction (L3) and hybrid orchestration. Sublayers are named by the job they do, so one row reads across all five types of qubit: drive generation is a microwave source for one and a laser for another. In superconducting and silicon spin machines the same order runs from near absolute zero to room temperature.

The framework comes from the research behind the series The Quantum Stack: Inside the Five Modalities, by Michal Sabol.

A company is placed on a sublayer for a type of qubit when a public source shows it supplies that part: a product page, a named customer or a paper that names the product. Where only the company or a partner says so, the placement stands, with a note on the company's card. Blogs, resellers and anonymous articles are not used, and partnerships and memoranda do not make a customer.

A placement shows where a company sits, not its size or quality, and the list is not complete.

Builders appear as in-house for the parts they make themselves and are never counted as independent suppliers, even when they sell the part, as AQT does with its traps. The one exception is a builder supplying another: QuiX Quantum, for the photonic processor in Aegiq's machine at the National Quantum Computing Centre. Public laboratories are listed but not counted.

Each constraint is a limit on growing from today's machines to ones with hundreds of thousands of qubits, sourced to papers, roadmaps or talks by named engineers. The classification is the editor's judgement: the decisive constraint for each type decides which part of the stack captures the value as machines scale, and hardest marks the most difficult problem where it is not the decisive one.

The view by builder shows each part of one builder's stack: the suppliers a source names for that builder, what it makes itself, and where nothing has been named. Plans, prototypes, memoranda and software offered to a builder's users are left out. None named does not mean made in-house: most builders do not publish their supply chains.

Shades count independent suppliers: 1 to 3, 4 to 7, 8 to 15, and 16 or more. A dashed square has none, because builders make the part themselves or nobody sells it yet; a hatched square is a part that type of qubit does not need. Within a sublayer, suppliers are grouped by what they sell, the main product first and then its parts and inputs.