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Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Kolasa A.,University Of Szczecin
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2012

The geometric phase in the dynamics of a spin qubit driven by transverse microwave (MW) and longitudinal radio frequency (RF) fields is studied. The phase acquired by the qubit during the full period of the 'slow' RF field manifests in the shift of Rabi frequency 1 of a spin qubit in the MW field. We find out that, for a linearly polarized RF field, this shift does not vanish at the second and higher even orders in the adiabaticity parameter rf/1, where rf is the RF frequency. As a result, the adiabatic (Berry) phases for the rotating and counter-rotating RF components compensate each other, and only the higher order geometric phase is observed. We experimentally identify that phase in the frequency shift of the Rabi oscillations detected by a time-resolved electron paramagnetic resonance. © 2012 IOP Publishing Ltd.


Troyanchuk I.O.,Scientific Practical Materials Research Center of Belarus | Bushinsky M.V.,Scientific Practical Materials Research Center of Belarus | Sikolenko V.,Karlsruhe Institute of Technology | Efimov V.,Joint Institute for Nuclear Research | And 3 more authors.
European Physical Journal B | Year: 2013

The anion deficient cobaltite La0.5Ba0.5CoO 2.8 with the formal cobalt valence state close to 3+ has been studied as function of pressure up to 6.5 GPa at different temperatures by neutron powder diffraction. At ambient pressure the crystal structure of this compound has cubic symmetry (space group Pm-3m) and is found to become antiferromagnetic with TN close to 250 K. Applied pressure induces a gradual transition from the antiferromagnetic into a ferromagnetic state through a mixed magnetic state. The transition is not accompanied by obvious changes in the macroscopic crystal symmetry. It is suggested that the magnetic ground state strongly depends on the unit cell volume and that the transition is associated with a spin state crossover of the cobalt ions whereas the formal Co3+/Co4+ ratio is less important than expected following the double exchange scenario for the appearance of ferromagnetism.© EDP Sciences Società Italiana di Fisica Springer-Verlag 2013.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Markevich S.A.,Scientific Practical Materials Research Center of Belarus
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2014

The coherent dynamics of relaxing spin qubits driven by a classical bichromatic field comprising a strong resonant component and a weaker component with a frequency close to the strong-field Rabi frequency is studied. The double dressing by the bichromatic field modifies the dephasing and dissipation processes. We demonstrate that detuning of the weaker-field frequency from the strong-field Rabi frequency prolongs the decay of Rabi oscillations between some doubly dressed states. The sensitivity of Rabi oscillations to the modified detuning-dependent relaxation is illustrated for nitrogen-vacancy qubits in diamond. We discuss a steady-state population inversion of the doubly dressed-state levels. © 2014 IOP Publishing Ltd.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Kolasa A.,University Of Szczecin | Markevich S.A.,Scientific Practical Materials Research Center of Belarus
Physica Scripta | Year: 2012

We study the coherent dynamics of relaxing qubits driven by a bichromatic radiation in the dispersive regime in the case when the detuning of the frequency ω rf of a longitudinal radio-frequency field from the Rabi frequency ω 1 in a transverse microwave field is comparable in magnitude to ω rf and ω 1. We analytically describe this regime beyond the rotating wave approximation and find that the dominant feature of the dynamics of qubits is the shift in the Rabi frequency caused by the dynamical Zeeman and Bloch-Siegert-like effects. These fundamental effects can be experimentally separated because, unlike the Bloch-Siegert effect, the dynamical Zeeman effect depends on the detuning sign. Our theoretical results are in good agreement with the experimental data obtained in pulse electron paramagnetic resonance for the E′ 1 centers in crystalline quartz. © 2012 The Royal Swedish Academy of Sciences.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Markevich S.A.,Scientific Practical Materials Research Center of Belarus
Journal of Magnetic Resonance | Year: 2015

The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines. © 2015 Elsevier Inc. All rights reserved.

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