Implementing universal multi-qubit quantum logic gates in three and   four-spin systems at room temperature
  In this paper, we present the experimental realization of multi-qubit gates $% \Lambda_n(not) $ 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. 
J. F. Du, M. J. Shi, J. H. Wu, X. Y. Zhou, and R. D. Han