In this paper, we present the experimental realization of multi-qubit gates in macroscopic ensemble of three-qubit and four-qubit molecules. Instead of depending heavily on the two-bit universal gate, which served as the basic quantum operation in quantum computing, we use pulses of well-defined frequency and length that simultaneously apply to all qubits in a quantum register. It appears that this method is experimentally convenient when this procedure is extended to more qubits on some quantum computation, and it can also be used in other physical systems.
@article{arxiv.quant-ph/0008110,
title = {Implementing universal multi-qubit quantum logic gates in three and four-spin systems at room temperature},
author = {J. F. Du and M. J. Shi and J. H. Wu and X. Y. Zhou and R. D. Han},
journal= {arXiv preprint arXiv:quant-ph/0008110},
year = {2009}
}