When a quantum computing company announces a new chip with thousands of qubits, that number is usually the one that lands in press releases and investor decks. It is also, in most cases, the least useful number for understanding what the machine can actually do. To make sense of it, you need to understand the difference between physical qubits and logical qubits, and why that gap matters differently depending on the type of quantum hardware you are working with.

What a Physical Qubit Is, and Why It Is Not Enough