Efficiency at maximum power output of quantum heat engines under finite-time operation

We study the efficiency at maximum power, eta(m), of irreversible quantum Carnot engines (QCEs) that perform finite-time cycles between a hot and a cold reservoir at temperatures T-h and T-c, respectively. For QCEs in the reversible limit (long cycle period, zero dissipation), eta(m) becomes identical to the Carnot efficiency. eta(C) = 1 - T-c/T-h. For QCE cycles in which nonadiabatic dissipation and the time spent on two adiabats are included, the efficiency eta(m) at maximum power output is bounded from above by eta(C)/(2 - eta(C)) and from below by eta(C)/2. In the case of symmetric dissipation, the Curzon-Ahlborn efficiency eta(CA) = 1 root T-c/T-h is recovered under the condition that the time allocation between the adiabats and the contact time with the reservoir satisfy a certain relation.