A bit is a coin on the table. A qubit is a coin in the air. This site is about what you can do with a coin in the air, who worked it out, and how far the machines have got.

39 events since 1900, 10 chapters of theory with 9 things to press, 7 ways of building a qubit, 46 developments since 2025, 35 words defined, 107 sources. The Now page refreshes itself each week from arXiv and the news.

The whole idea in four sentences

Everything small is a wave, and waves can add up or cancel. A qubit is the smallest thing you can hold in a mix of two states, and the mix has a phase, which is where in its rise and fall the wave is. A quantum program is a set of turns that gets the phases of the wrong answers to cancel and the right answer to pile up. Then you look, and most of the time you see the right answer.

The reason it is hard: anything that touches a qubit counts as looking. The reason it is worth it: chemistry, materials and codes are problems where the waves matter, and for those, a room full of ordinary computers cannot keep up with a few thousand good qubits.

Latest

• 2026-09-17
  US Department of Energy — DOE opened the Quantum Genesis Q Competition: up to 215 million dollars, up to ten teams, a 10-logical-qubit prototype within about a year and a 100-logical-qubit fault-tolerant machine by autumn 2028, with a 100 million dollar pool for finishers.
• 2026-07-31
  IonQ — IonQ completed its 1.8 billion dollar purchase of SkyWater after US Federal Trade Commission clearance.
• 2026-07-20
  Google Quantum AI — Google published in Nature a reinforcement-learning system that retunes Willow's control settings during error correction instead of pausing to recalibrate, making logical error rates about 3.5 times more stable and roughly 20 percent lower.

All 46 developments →

Start here

1. A coin on the table, a coin in the air — the qubit.
2. Ripples that cancel — the engine.
3. Two coins that always match — the resource.
4. Fixing errors without looking — the problem that the whole field is.
5. What it is not — before the next headline.