The bloch-siegert effect in dynamic nuclear polarization

G. B. Furman, I. M. Kadzhaya

Keith R. Wald

E. Arimondo, G. Moruzzi

The Bloch-Siegert shift displayed by a spin 1/2 particle system is measured in a double resonance experiment on the ground state of an optically oriented 199 Hg vapour. The displacement of the nuclear magnetic resonance peaks corresponding to the one and three quantum transitions are studied as a function of the radiofrequency field intensity. Similarly, the displacement of the component of the vapour polarization which is modulated at twice the RF field frequency is observed. The experimental results are compared with the existing theoretical approaches to the Bloch-Siegert effect, and a good agreement is found with the semiclassical theory leading to the continued fraction solution.

Edward B. Fel’dman, Anatoly K. Khitrin

A. P. Saǐko, S A Markevich, Ryhor Fedaruk

Abstract We study the coherent dynamics of a qubit excited by an amplitude-modulated electromagnetic field under the Rabi resonance when the frequency of the low-frequency modulation field matches the Rabi frequency in the high-frequency field. Due to the destructive interference of multiple photon processes within the ultrastrong coupling between the qubit and the low-frequency driving field, Rabi oscillations result exclusively from the Bloch–Siegert effect. It is directly observed in the time-resolved coherent dynamics as the Bloch–Siegert oscillation. In this case, triplets in the Fourier spectra of the coherent response are transformed into doublets with the splitting between the lines equal to twice the Bloch–Siegert shift. These unusual properties are demonstrated in the conditions of experiments with a nitrogen vacancy center in the diamond.

A. P. Saǐko, S. A. Markevich, Ryhor Fedaruk

We study Rabi oscillations of the second-order Raman transition realized on dressed states of a qubit excited by an amplitude-modulated microwave field. The co-rotating component of the ultrastrong low-frequency modulation field excites virtual multiple photon processes between the dressed states and forms the Rabi frequency in the so-called rotating wave approximation. The counter-rotating modulation component also gives a significant contribution to the Rabi frequency owing to the Bloch-Siegert effect. It is shown that for properly chosen parameters of the modulation field and qubit, the Rabi oscillations in the rotating wave approximation vanish due to destructive interference of multiple photon processes. In this case the Rabi oscillation results exclusively from the Bloch-Siegert effect and is directly observed in the time-resolved coherent dynamics as the Bloch-Siegert oscillation. Correspondingly, in Fourier spectra of the coherent response, triplets are transformed into doublets with the splitting between the lines equal to twice the Bloch-Siegert shift. We demonstrate these features by calculations of the qubit’s evolution in the conditions of experiments with a NV center in diamond, where Raman transitions were observed. The direct observation of the Bloch-Siegert oscillation offers new possibilities for studying driven quantum systems in the ultastrong regime.