A state of matter in which quarks and gluons are not confined into baryons and mesons but exist as a hot plasma. It is thought that this state existed in the early universe until there was a phase transition about 10⁻⁵ s after the big bang, when the universe had cooled to a sufficiently low temperature that quark confinement into hadrons occurred. This state was created in the laboratory in the early years of the 21st century.