  We study theoretically the efficiency of an asymmetric superconducting
quantum interference device (SQUID) which is constructed as a loop with three
capacitively and resistively shunted Josephson junctions. Two junctions are
placed in series in one arm and the remaining one is located in the other arm.
The SQUID is threaded by an external magnetic flux and driven by an external
current of both constant (dc) and time periodic (ac) components. This system
acts as a nonequilibrium ratchet for the dc voltage across the SQUID with the
external current as a source of energy. We analyze the power delivered by the
external current and find that it strongly depends on thermal noise and the
external magnetic flux. We explore a space of the system parameters to reveal a
set for which the SQUID efficiency is globally maximal. We detect the
intriguing feature of the thermal noise enhanced efficiency and show how the
efficiency of the device can be tuned by tailoring the external magnetic flux.
