What is the actual difference between quantum annealing and gate-based quantum computing?

[ReacherOtter]

There are two broad, fundamentally different families of quantum computer being built today. Gate based quantum computers, the approach used by IBM, Google and most other major players, manipulate qubits through a sequence of precise quantum gate operations, similar in spirit to how classical computers apply logical operations to bits, and are considered universal, meaning they can in principle be programmed to solve a very wide range of problems. Quantum annealers, the approach commercialized by D-Wave, work completely differently, using a process called adiabatic evolution where the system is slowly guided from an easy starting configuration toward the lowest energy state of a much more complex problem, with that final low energy state representing the answer

Quantum annealing is specialized almost entirely for optimization and sampling problems, finding the minimum or maximum of some function, rather than being a general purpose computing platform. It works by translating a real world optimization problem into an energy landscape, then exploiting quantum tunneling to help the system explore that landscape more effectively than it could classically, functioning as a physically motivated heuristic rather than a machine that mathematically guarantees the best possible answer every time. Gate based computers, by contrast, can implement any algorithm expressible as a quantum circuit, giving them a much broader potential range of applications once the hardware matures

In theory, an idealized version of adiabatic quantum computing is mathematically equivalent in computational power to the gate based model, but in practice today the two approaches serve very different purposes. Quantum annealers have already scaled to thousands of qubits and serve as genuinely useful experimental platforms for certain optimization and physics simulation tasks, while gate based systems remain smaller in qubit count but are the platform essentially all major fault tolerant quantum computing roadmaps, including error correction and algorithms like Shor's, are actually being built around

Quantum Annealing Vs. Gate-based Quantum Computingquantumzeitgeist.com