Quantum refrigerator driven by current noise

We proposed a scheme for the implementation of a "self-contained" quantum refrigerator system by three rf-SQUID qubits, or rather, flux-biased phase qubits. The three qubits play the role of the target, the refrigerator and the heat engine, respectively. We provide the three qubits with different effective temperatures, by imposing external current noises of different strengths. When the effective temperatures satisfy proper conditions, the target qubit could be cooled down. We also show that the efficiency of this system approaches the Carnot upper bound.