Benchmarking quantum master equations beyond ultraweak coupling

Open quantum systems are ubiquitous, however, their description beyond ultraweak system-bath coupling is challenging. The standard Redfield master equation can violate positivity. Recently, Nathan and Rudner proposed an alternative equation, not suffering from this problem. The authors compare here both equations to the exact solution of a simple model. The Redfield equation performs noticeably better for transient dynamics. For the steady state it is slightly better for high temperatures, but fails at low temperatures, where the Nathan-Rudner equation is still accurate.