Possibility of direct observation of the Bloch-Siegert shift in coherent dynamics of multiphoton Raman transitions
A. P. Saiko+, S. A. Markevich+, R. Fedaruk*
+Scientific-Practical Material Research Centre, Belarus National Academy of Sciences, 20072 Minsk, Belarus
*Institute of Physics, University of Szczecin, 70-451 Szczecin, Poland
Abstract
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.