Superconductors: Google and IBM
Lesson 15 of 23 in the course “Quantum”. Free, with animations and a quiz.
An atom drawn on a chip
A superconducting qubit is a tiny loop of aluminium or niobium on a silicon chip. The key part is the Josephson junction, an ultra-thin layer of insulator between two superconductors. When deeply cooled, the current in the loop behaves like one huge quantum object with two energy levels: that’s 0 and 1. The 2025 Nobel Prize in Physics went to John Clarke, Michel Devoret and John Martinis for 1980s experiments where they first saw such quantum effects in a circuit you can hold in your hand.
Colder than space
Such a qubit only works at around 10 millikelvin, hundreds of times colder than outer space. That takes a dilution refrigerator: a multistage “chandelier” where each stage is colder than the one above, with the chip hanging at the very bottom. Wires run to every qubit from the warm world, and so many are needed that it becomes an engineering problem of its own. When you see a photo of a “golden chandelier” in articles about quantum computers, that’s this fridge.
Google Willow: below threshold
In December 2024 Google unveiled the 105-qubit Willow chip. The main achievement isn’t the count. The team built a logical qubit from ever more physical ones: grids of 3×3, 5×5 and 7×7. With each step the logical qubit’s error fell roughly by half. That’s called “below threshold”: more qubits mean fewer errors, not more. Physicists had dreamed of this for almost 30 years. The same chip ran Quantum Echoes in 2025, from the molecules lesson.
IBM: from a count record to a quality record
IBM has the most detailed public roadmap. In 2023 came Condor with 1,121 qubits, a record count but not quality, and the company itself pivoted to quality. In 2025 it released Nighthawk with 120 qubits and 218 tunable couplers, and the experimental Loon to test a new error-correction code. Next on the plan: Kookaburra in 2026, the first error-corrected module; Cockatoo in 2027, linking modules together; and Starling in 2029 with 200 logical qubits and 100 million operations.
Strengths and weaknesses
The main plus of superconductors is speed: a gate takes tens of nanoseconds, and the chips are made on familiar semiconductor lines. The minuses: extreme cold is needed, a qubit lives about a tenth of a millisecond, and it’s connected only to its nearest neighbours, so distant qubits must pass information along a chain. Hence the strategy: lots of fast but “short-lived” qubits plus powerful error correction.
Check yourself
- What’s the key point of Google Willow’s 2024 result?
Correct answer: As the code grows, the logical qubit’s error falls. “Below threshold” means adding qubits to the code makes errors fewer. Without it, scaling up makes no sense. - Why did IBM release a 120-qubit chip after the 1,121-qubit Condor?
Correct answer: Quality and connectivity matter more than raw qubit count. Noisy qubits without good links don’t give much. Nighthawk got 218 tunable couplers and better specs, with error-corrected modules coming next. - What’s the main engineering downside of superconducting qubits?
Correct answer: Extreme cold and a sea of wires. About 10 millikelvin and wires to every qubit are the main barrier to millions of qubits.