quantum processor (QPU)

A quantum processor is the chip at the heart of a quantum computer. Like a classical CPU it is a piece of fabricated silicon, but instead of billions of transistors it holds an array of physical qubits, plus the small circuits that connect them, control them, and read them out. Almost all of today's quantum processors only work when chilled to a fraction of a degree above absolute zero inside a special fridge, so when people say 'the quantum computer' they usually mean this tiny chip and the room-sized machine wrapped around it.

Zoom in and a QPU is really a system of parts working together. The qubits sit in a grid; couplers let neighbouring qubits interact so the machine can do two-qubit operations; readout resonators act like little tuning forks that tell the control electronics what state each qubit is in; and a forest of control lines carries microwave or voltage pulses from outside the fridge down to each device. The whole thing is built layer by layer on a substrate using chip-fabrication tools borrowed from the classical semiconductor industry.

It helps to be honest about scale and role. A QPU is not a faster CPU and will not replace your laptop; it is a special-purpose device that may one day accelerate a narrow set of problems. Today's chips hold from tens to roughly a thousand or more physical qubits, and those qubits are noisy and error-prone. The hardest engineering problems are not 'more qubits' but wiring all those control lines in, getting enough good chips off the line (yield), and fitting every qubit's frequency in without two of them colliding (frequency crowding).