We stop for a...(quick/quickly) commercial break,and then we come back to the traditional systems

 We stop for a quick commercial break, and then we come back to the traditional systems.

Quick is an adjective. Quickly is an adverb. We use adjectives to describe nouns and we use adverbs to describe actions. Adjectives stand before noun and adverbs stand at the end of the sentences. We form adverbs with the help of the suffix – ly (adjectives + ly — adverb).

Quick + ly — quickly.