Quantum supremacy
The point where a quantum computer does something no classical computer can keep up with — reached in 2019, on a task with no practical use.
In October 2019 Google ran its 53-qubit Sycamore processor on a random circuit sampling task and reported that the computation took 200 seconds against an estimated 10,000 years classically. IBM objected that a better classical method managed it in a couple of days, and later work has cut that figure further.
The task was chosen precisely for being hard to simulate, not for being useful. The milestone is nonetheless real as a demonstration that the hardware behaves as theory predicts. Many now prefer the term quantum advantage, partly to avoid the word supremacy, partly because it better describes what actually remains: being better at something someone wants done.