Lower bounds for ballistic current and noise in non-equilibrium quantum steady states

Understand

Let an infinite, homogeneous, many-body quantum system be unitarily evolved for a long time from a state where two halves are independently thermalized.

• One says that a non-equilibrium steady state emerges if there are nonzero steady currents in the central region.
• In particular, their presence is a signature of ballistic transport.
• We analyze the consequences of the current observable being a conserved density; near equilibrium this is known to give rise to linear wave propagation and a nonzero Drude peak.