Coherence-Induced Reversibility and Collective Operation of Quantum Heat Machines via Coherence Recycling

In $c{{0}{0ex}}o{{0}{0ex}}l{{0}{0ex}}l{{0}{0ex}}e{{0}{0ex}}c{{0}{0ex}}t{{0}{0ex}}i{{0}{0ex}}v{{0}{0ex}}e$ $o{{0}{0ex}}p{{0}{0ex}}e{{0}{0ex}}r{{0}{0ex}}a{{0}{0ex}}t{{0}{0ex}}i{{0}{0ex}}o{{0}{0ex}}n{{0}{0ex}}s$, units interact to generate synergistic effects beyond what the individual, noninteracting units could yield. A quantum collective with no classical analogue is even more intriguing. In the context of quantum thermodynamics, the authors use the concept of extracting and injecting c00exo00exh00exe00exr00exe00exn00exc00exe to envision a collective heat machine of the same efficiency as its individual engines, yet drawing more heat from thermal baths and producing more work, its power scaling quadratically with the number of engines. Surprisingly, the collective machine can be more reversible than its most reversible element.