We argue that the analog nature of quantum computing makes the usual design approach of constructing complicated logical operations from many simple gates inappropriate. Instead, we propose to design multi-spin quantum gates in which the input and output two-state systems (spins) are not necessarily identical. We outline the design criteria for such devices and then review recent results for single-unit Hamiltonians that accomplish the NOT and XOR functions.
@article{arxiv.quant-ph/9705026,
title = {Hamiltonians for Quantum Computing},
author = {Vladimir Privman and Dima Mozyrsky and Steven P. Hotaling},
journal= {arXiv preprint arXiv:quant-ph/9705026},
year = {2014}
}