Universal constraint for efficiency and power of a low-dissipation heat engine

The constraint relation for efficiency and power is crucial for the design of optimal heat engines operating within finite time. We find a universal constraint between efficiency and output power for heat engines operating in the low-dissipation regime. Such a constraint is validated with an example of a Carnot-like engine. Its microscopic dynamics is governed by the master equation. Based on the master equation, we connect the microscopic coupling strengths to the generic parameters in the phenomenological model. We find the usual assumption of low-dissipation is achieved when the coupling to thermal environments is stronger than the driving speed. Additionally, such a connection allows the design of a practical cycle to optimize the engine performance.