Method of multifrequency excitation for creating pseudopure states for NMR quantum computing

An alternative method of preparing pseudopure states for NMR quantum computing is presented. The method involves population transfer by the use of a multifrequency excitation pulse. The system studied was a spin-7/2 nucleus (¹³³Cs) in a liquid-crystalline environment. It is shown that all eight pseudopure quantum states for this three-qubit system can be prepared by using only 1--3 pulses, while the intensities of the relevant peaks increase by a factor of up to 4 compared to the equilibrium NMR spectrum. A comparison of the intensity enhancement by population transfer for quadrupolar nuclei and that for coupled spin-1/2 systems is given.