Methods, systems, and apparatus for designing an artificial quantum thermal bath. In one aspect, an apparatus includes a primary quantum system; an auxiliary quantum system comprising a plurality of modes and that interacts with the primary quantum system, wherein: the auxiliary system interacts with the primary quantum system through one or more couplings, wherein the one or more couplings are controllable; a steady state of the auxiliary system, a response function of the auxiliary quantum system, an auxiliary system operator, and a spectrum of the auxiliary quantum system are determined to meet a respective condition; and the auxiliary system is controllable to relax the primary quantum system to an equilibrium state using a controllable function of the auxiliary system operator.