Monday, February 24, 2020
When an approximate conservation law protects some quantity, even weak driving can cause its strong response. A simple classical example is a greenhouse, which can be heated up significantly even by weak sunlight, due to the approximate conservation of the energy.
Quantum platforms with macroscopically many conserved quantities are integrable and many-body localized (MBL) systems. When perfectly closed, these systems exhibit exceptional properties, such as ballistic transport in integrable systems and a complete absence of transport in MBL systems. Both properties are a direct consequence of the nature of corresponding conservation laws. However, in realistic setups conservation laws are weakly broken, for example, due to coupling to phonons. Latter causes decay of local conservation laws towards a thermal value and all special properties are gone.
I will show that this decay can be compensated by weak driving which pumps into the conservation laws and stabilizes exceptional non-thermal steady states. This allows us to study the MBL transition in open driven setups, previously believed impossible. For nearly integrable systems, driving re-establishes description in terms of generalized Gibbs ensembles. In spin chain materials approximately described by the Heisenberg model, weak driving stabilizes steady states with huge heat and spin currents and suggests a new type of heat and spin pumps. Our approach can thus be used to probe the quantum matter, but also to engineer non-equilibrium steady states inaccessible in equilibrium.