Quantum Annealing vs Gate-Based Computing
A gate-model QPU executes an ordered circuit of gates followed by measurement; a quantum annealer physically relaxes toward low-energy configurations of an energy function and returns samples. The two models give qubits entirely different jobs — and annealers spend many physical qubits per logical variable — so raw qubit counts across the two models cannot be ranked.
Two ways to program a quantum machine
A gate-based quantum processor (also called a gate-model QPU) runs a circuit: an ordered list of operations, called gates, applied to qubits, followed by a measurement that reads each qubit out as a 0 or a 1. Everything in the QPU137 Lab uses this model.
A quantum annealer is programmed completely differently. You never write a circuit. Instead you describe your problem as an energy model: a scoring function that assigns a number (the energy) to every possible assignment of its variables, arranged so that better answers score lower. The machine then physically settles toward low-energy configurations and returns samples — candidate answers, drawn many times over.
These are two different kinds of machine, and the word qubit does a different job in each. An annealer with 5,000 qubits and a gate-model QPU with 100 are not two points on one scale. The counts describe different resources, so they cannot be ranked against each other — this lesson shows exactly why.
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