Quantum Computing Explained

Context: 2024-25 brought the biggest real news the field has had in years

Quantum computing spent much of the past two decades as a field whose most exciting claims were years away from verification. That changed, genuinely, with two announcements in quick succession: Google's Willow chip in December 2024, and Microsoft's Majorana 1 claim in February 2025. Both are worth understanding on their actual merits — including the real scepticism each has faced — rather than through the hype that inevitably surrounds them.

The data: the basic physics, and what actually happened in 2024-25

Classical computers process information as bits, holding a value of either 0 or 1. Quantum computers use qubits, which can exist in superposition — effectively a combination of 0 and 1 simultaneously — and can be entangled with other qubits in ways that allow certain calculations to be performed fundamentally differently, and potentially far faster, than any classical approach for specific problem types.

Google's Willow chip, announced in December 2024, demonstrated "below threshold" quantum error correction — a milestone researchers had targeted for years. Historically, adding more physical qubits to build a single error-corrected "logical" qubit tended to introduce more opportunities for error, offsetting the benefit. Willow showed the opposite: as Google added more physical qubits per logical qubit, the error rate went down. Google also reported Willow completing a specifically chosen benchmark computation in minutes that it estimated a leading classical supercomputer would take an astronomically long time to complete — an impressive but narrow demonstration, since these benchmarks are deliberately chosen to favour quantum approaches rather than reflecting general-purpose computing usefulness.

Microsoft followed in February 2025 with Majorana 1, which it described as demonstrating a topological qubit — a fundamentally different, theoretically more error-resistant qubit architecture Microsoft has pursued for well over a decade. The claim drew real scrutiny: Microsoft had previously published and then retracted a related claim in 2021 after independent researchers could not replicate the results, and parts of the physics community treated the 2025 announcement with corresponding caution pending independent verification.

"Extraordinary claims in quantum computing need extraordinary evidence, and a company's own press release, however credible the company, is not that evidence on its own. The field has been burned by premature claims before." — a caution widely echoed across independent physics commentary following the Majorana 1 announcement, given Microsoft's own 2021 retraction in related research.

What's changing: where the major players actually stand

IBM's public roadmap targets a fault-tolerant quantum system, which it has named Starling, for around 2029 — a useful marker of how far even a leading industry player believes full fault tolerance remains, despite Willow and Majorana 1's genuine progress on component pieces of the puzzle. Current-generation machines across Google, IBM and other developers remain what researchers call NISQ — Noisy Intermediate-Scale Quantum — systems: capable of interesting, genuinely useful computations in controlled research settings, but not yet at the scale or error-correction maturity for the large, general-purpose applications long promised for the technology.

What it means for you (businesses and technologists)

For most businesses, the practical planning implication of 2024-25's progress is about long-term risk management rather than immediate deployment. The clearest concrete action already underway is post-quantum cryptography migration: the US National Institute of Standards and Technology has finalised standards specifically designed to replace encryption methods — including RSA — that would eventually be vulnerable to a sufficiently powerful fault-tolerant quantum computer running Shor's algorithm. Organisations handling long-lived sensitive data, where information encrypted today needs to remain secure for a decade or more, are the ones with the strongest near-term reason to begin planning migration now, well ahead of when a cryptographically relevant quantum computer might actually exist. For a broader look at how this connects to national quantum strategy and investment, see our coverage of quantum computing progress specifically within the UK.

Investment and talent flows are a useful leading indicator worth tracking alongside the technical milestones themselves. Venture funding into quantum computing startups rose sharply following the Willow announcement, and national governments — including the UK, US, EU and China — have each maintained or expanded dedicated quantum research funding programmes, treating the field as a strategic technology priority comparable to how many governments now treat AI infrastructure investment, reflecting a widely shared view that whichever country or company achieves practical fault tolerance first will hold a durable strategic advantage in cryptography, materials science and drug discovery simulation. For readers wanting the underlying computer science grounding before tackling quantum-specific concepts, our plainer explainer on what an algorithm actually is covers the classical-computing basics that make the qubit comparison in this piece easier to follow, particularly the distinction between how a classical algorithm and a quantum one actually approach the same underlying problem differently.

What to watch next

Watch whether Microsoft's Majorana 1 claims receive independent experimental replication over the coming year — the single clearest test of whether the February 2025 announcement represents a genuine breakthrough or a repeat of the company's 2021 retracted claim. Also watch whether Google, IBM and other developers continue scaling error-corrected logical qubit counts at the pace Willow's below-threshold result implied is now possible, since sustained scaling — not a single benchmark result — is what would actually move the field meaningfully closer to IBM's 2029 fault-tolerance target and, eventually, genuinely disruptive real-world applications.