Broadband geodesic pulses for three spin systems: time-optimal realization of effective trilinear coupling terms and indirect SWAP gates.
Reiss TO, Khaneja N, Glaser SJ. Broadband geodesic pulses for three spin systems: time-optimal realization of effective trilinear coupling terms and indirect SWAP gates. J Magn Reson. 2003 Nov; 165(1):95-101.