What it is not

It does not try every answer at once. It holds every answer's amplitude at once, which is different, because you can only read one out. The whole art is in getting the wrong ones to cancel before you read. For most problems nobody knows how to do that, and for some it has been proved impossible.

It is not a faster computer. For adding up a spreadsheet, rendering a game or serving a web page, a quantum computer is slower, by a lot, and always will be. The gates are slow, the readout is slow, and there is no wave trick for those jobs. The speed-ups are for particular problems: factoring, searching, and above all simulating molecules and materials, which are quantum themselves.

Bigger qubit counts are not the score. A thousand noisy qubits are worth less than a hundred clean ones. The numbers that matter are the error rate per gate, how long a qubit lasts, and how many error-corrected logical qubits a machine can hold. Companies lead with the count because it is the number that goes up.

It has not broken any code. Every announced 'factoring record' either used a toy number, or used a shortcut that does not scale, or was an annealer doing something Shor's method is not. The internet's locks are being changed anyway, ahead of time, because a recording made today can be opened later.

Annealers and gate machines are different things. D-Wave's machines settle into a low-energy state to answer optimisation questions. They are quantum, they are big, and they cannot run Shor's or Grover's method or any general program. When a headline says 'a 5,000-qubit quantum computer', check which kind.

The cat is a joke. Schrödinger meant the alive-and-dead cat as an argument that something was wrong with the theory as read. The current reading is that a cat is far too big and warm to stay in superposition for any length of time; it decoheres in less time than light takes to cross it. A qubit is the smallest, coldest, most isolated thing people can make, so that it stays in superposition for a fraction of a second. That is the whole engineering problem.