Multifrequency resonances in multiple-pulse NMR on a spin-1/2 system (9 pages)

S. A. Gerasev, A. V. Fedorova, Edward B. Fel’dman +1 more

Anatoly K. Khitrin, Hong Yue Sun, B. M. Fung

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 ${(}^{133}\mathrm{Cs})$ 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.

G. A. Bochkin, Edward B. Fel’dman, Sergey G. Vasil’ev

Gadi Goelman, David B. Zax, Shimon Vega

Experimentally achievable conditions where only weak off-resonant fields are used to excite coherence in a two-level system are explored. A brief review of previous theoretical results useful in treating multifrequency irradiation sequences is provided. Using an approximation method based on the Floquet formalism we derive an expression for the effective field strength as a function of the phases and amplitudes of the applied irradiation fields. Some of these results are rederived and/or explained in a simplified manner. Under conditions of four-frequency irradiation, three-photon excitation of a two-level system in NMR is experimentally demonstrated on the spin-1/2 system of the 31P nucleus in phosphoric acid. The behavior of the three-photon resonance is explored as a function of all important experimental parameters. The results of these tests conform closely to the theoretical predictions. Possible uses of multifrequency irradiation schemes in NMR are suggested.

Edward B. Fel’dman

Serge I. Doronin, Edward B. Fel’dman, E. I. Kuznetsova +2 more

We investigate analytically and numerically the multiple-quantum (MQ) NMR dynamics in systems of nuclear spins $1∕2$ coupled by the dipole-dipole interactions in the case of the dipolar ordered initial state. We suggest two different methods of MQ NMR. One of them is based on the measurement of the dipolar temperature in the quasiequilibrium state which is established after the time of order ${\ensuremath{\omega}}_{\mathit{loc}}^{\ensuremath{-}1}$ (${\ensuremath{\omega}}_{\mathit{loc}}$ is the dipolar local field) after the MQ NMR experiment. The other method uses an additional resonance ${(\ensuremath{\pi}∕4)}_{y}$ pulse after the preparation period of the standard MQ NMR experiment in solids. Many-spin clusters and correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.