33 research outputs found
Dissipative two-level systems under ultrastrong off-resonant driving
We study the dissipative dynamics of a two-level system under ultrastrong
driving when the frequency and strength of the exciting field exceed
significantly the transition frequency. We find three qualitatively different
regimes of such dynamics: 1) the collapse and revival of oscillations in the
population difference, 2) the simple exponential decay of the oscillations
resulting in their steady state with the finite amplitude, and 3) the
steady-state stabilization of the equally populated levels. The nonmonotonic
Bessel-function-like dependence on the driving strength is also predicted for
the decay rate of these oscillations. The features of this dependence are
determined by the relative rates of energetic relaxation and pure dephasing.Comment: 7 pages, 4 figure
Emission spectrum of a qubit under its deep strong driving in the high-frequency dispersive regime
We study the emission spectrum of a qubit under deep strong driving in the
high-frequency dispersive regime when the driving frequency and strength exceed
significantly the qubit transition frequency. Closed-form expressions for the
steady-state first-order field correlation function and the multiphoton
emission spectrum are obtained. The spectrum comprises a series of narrow
delta-like lines that stem from coherent processes and Lorenzian peaks that
result from the incoherent scattering of photons. The oscillating dependence of
the widths of the emission lines on the driving strength is predicted. We show
how the features of this dependence are governed by the qubit dephasing and
relaxation rates.Comment: 11 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1705.0174
Suppression of electron spin decoherence in Rabi oscillations induced by an inhomogeneous microwave field
The decay of Rabi oscillations provides direct information about coherence of
electron spins. When observed in EPR experiments, it is often shortened by
spatial inhomogeneity of the microwave field amplitude in a bulk sample. In
order to suppress this undesired loss of coherence, we propose an additional
dressing of spin states by a weak longitudinal continuous radiofrequency field.
Our calculations of the Rabi oscillations between the doubly dressed spin
states show that the maximum suppression of decoherence is achieved at the
so-called Rabi resonance when the radio-field frequency is in resonance with
the Rabi frequency of spins in the microwave field. This effect is feasible
even in the absence of phase matching in the radiofrequency field and for
different types of inhomogeneity of the microwave field. The manifestations of
such suppression in the published EPR experiments with the bichromatic driving
are discussed. The realization of the Rabi resonance using the radiofrequency
field could open new possibilities for separating the contributions of
relaxation mechanisms from those due to the inhomogeneous driving in spin
decoherence.Comment: 20 pages, 8 figure
Microwave Photon Antibunching at the Modulation of the Resonance Frequency of a Qubit Emitter
The statistics photons in the resonance fluorescence of a qubit excited by
microwave and radio-frequency (RF) fields have been studied. It has been
established that the coherent dissipative dynamics of the qubit with allowance
for multiphoton emission and absorption of RF photons in each act of emission
and absorption of a microwave photon results in periodic alternation of photon
bunching and antibunching. It has been shown that periodically varying
statistics photons can be smoothly transformed to the purely sub-Poisson
statistics by varying the parameters of the RF field. The conditions for the
formation of the "collapse-revival" of oscillations in the second-order
correlation function photons have been determined. The described effects can be
implemented on spin and superconducting qubits, quantum dots, and
qubit-mechanical hybrid systems.Comment: 7 pages, 4 figure
Higher-order geometric phase for qubits in a bichromatic field
The geometric phase in the dynamics of a spin qubit driven by transverse
microwave (MW) and longitudinal radiofrequency (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 \omega_{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
\omega_{rf} / \omega_{1}, where \omega_{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.Comment: 11 pages, 4 figure
Multi-photon transitions and Rabi resonance in continuous wave EPR
The study of microwave and 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 time-resolved 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 linesComment: 20 pages, 9 figure
Multiphoton Raman transitions and Rabi oscillations in driven spin systems
In the framework of the non-secular perturbation theory based on the
Bogoliubov averaging method, the coherent dynamics of multiphoton Raman
transitions in a two-level spin system driven by an amplitude-modulated
microwave field is studied. Closed-form expressions for the Rabi frequencies of
these transitions have been obtained beyond the rotating wave approximation for
the low-frequency driving component. It is shown that spin states dressed by
the high-frequency component of the driving field are shifted due to the
Bloch-Siegert-like effect caused by antiresonant interactions with the strong
low-frequency driving. We predict that with increasing the order of the Raman
transition the Rabi frequency decreases and the contribution of the
Bloch-Siegert shift to this frequency becomes dominant. It is found that the
amplitude and phase of the Rabi oscillations strongly depend on the initial
phase of the low-frequency field as well as on detuning from multiphoton
resonance. The recent experimental data for the second- and third-order Raman
transitions observed for nitrogen-vacancy center in diamond [Z. Shu, et al.,
arXiv:1804. 10492] are well described in the frame of our approach. Our results
provide new possibilities for coherent control of quantum systems.Comment: 9 pages, 7 figures, Accepted to Phys. Rev. A (18 Sep 2018
Relaxation, decoherence and steady-state population inversion in qubits doubly dressed by microwave and radiofrequency fields
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 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.Comment: 18 pages, 8 figure
Kerr-like nonlinearities in an optomechanical system with an asymmetric anharmonic mechanical resonator
In the framework of the nonsecular perturbation theory based on the
Bogoliubov averaging method, an optomechanical system with an asymmetric
anharmonic mechanical resonator is studied. The cross-Kerr interaction and the
Kerr-like self-interaction of photons and vibration quanta arise in the
Hamiltonian. These interactions are induced by both cubic and quartic
nonlinearities of oscillations of the mechanical resonator and the
cavity-resonator interaction that is linear in mechanical displacements. We
demonstrate a bistable behavior of the number of vibration quanta and find that
this behavior is controlled by the cross-Kerr interaction. It is shown that,
without driving and dissipation, the constructed superposition
Yurke-Stoler-like states of the cavity (or the mechanical resonator)
disentangle at certain times the entangled modes of the system. The obtained
results offer new possibilities for control of optomechanical systems with
asymmetric mechanical oscillations.Comment: 5 pages, 1 figure
Detuning-dependent narrowing of Mollow triplet lines of driven quantum dots
We study the two-time correlation function and the resonance fluorescence
spectrum of a semiconductor quantum dot excited by a strong off-resonant laser
pulse. The obtained analytical expressions exhibit a specific
detuning-dependent damping of Rabi oscillations of the dressed quantum dot as
well as a detuning-dependent width of Mollow-triplet lines. In the absence of
pure dephasing, the central peak of the triplet is broadened, upon increasing
detuning, but the blue and red side peaks are narrowed. We demonstrate that
pure dephasing processes can invert these dependences. A crossover between the
regimes of detuning-dependent narrowing and broadening of the side and central
peaks is identified. The predicted effects are consistent with resent
experimental results and numerical calculations.Comment: 13 pages, 5 figure