Minimal Self-Contained Quantum Refrigeration Machine Based on Four   Quantum Dots
  We present a theoretical study of an electronic quantum refrigerator based on four quantum dots arranged in a square configuration, in contact with as many thermal reservoirs. We show that the system implements the basic minimal mechanism for acting as a self-contained quantum refrigerator, by demonstrating heat extraction from the coldest reservoir and the cooling of the nearby quantum-dot. 
Davide Venturelli, Rosario Fazio, and Vittorio Giovannetti
cond-mat.mes-hall quant-ph