Postquench

Postquench is a term used in physics to denote the regime and phenomena that occur after a quench—a rapid, non-adiabatic change of one or more parameters of a quantum or classical system. The word combines post- (after) with quench, reflecting the focus on the system's evolution in the time following the abrupt transition.

In practice, a quench may involve switching on or off an interaction, changing a field, or altering lattice depth in a quantum simulator. Immediately after the quench, the system is generally out of equilibrium and evolves under the post-quench Hamiltonian (or dynamical rules). Postquench dynamics are governed by unitary evolution in closed quantum systems and, in open systems, by coupling to an environment.

Common focus areas include how correlations spread, whether the system thermalizes or approaches a generalized Gibbs ensemble, and how entanglement grows. Observables include correlation functions, order parameters, Loschmidt echo, and energy/work distributions. Theoretical approaches include exact diagonalization, time-dependent density matrix renormalization group, and Keldysh formalism; experiments in ultracold atoms, trapped ions, and superconducting qubits implement quenches and track postquench signatures.

Related concepts include quantum quench, prethermalization, and non-equilibrium dynamics. The study of postquench phenomena provides insights into nonequilibrium statistical mechanics, thermalization processes, and emergent universal behavior in complex quantum systems.