Quantum
The physics one level deeper than the headlines and the ways to build a qubit; error correction, now shown below threshold on three platforms, and the roadmaps to fault-tolerant machines around 2029; the algorithms that matter and the advantage claims, weighed; the threat to encryption and the argument over Q-Day; the sensors and clocks already in service; and the companies, from Quantinuum's listing to Washington's new stakes in quantum firms. Worked examples include a surface code's overhead, one bank's migration, and IonQ's revenue against its market value. Opens with a dated table of the state of the art and a Who's Who.