We investigate the fundamental dimensional limits to thermodynamic machines. In particular we show that it is possible to construct self-contained refrigerators (i.e. not requiring external sources of work) consisting of only a small number of qubits and/or qutrits. We present three different models, consisting of two qubits, a qubit and a qutrit with nearest-neighbour interactions, and a single qutrit respectively. We then investigate fundamental limits to their performance; in particular we show that it is possible to cool towards absolute zero.
@article{arxiv.0908.2076,
title = {How small can thermal machines be? The smallest possible refrigerator},
author = {Noah Linden and Sandu Popescu and Paul Skrzypczyk},
journal= {arXiv preprint arXiv:0908.2076},
year = {2012}
}