183 research outputs found
Multiphoton Transitions in a Spin System Driven by Strong Bichromatic Field
EPR transient nutation spectroscopy is used to measure the effective field
(Rabi frequency) for multiphoton transitions in a two-level spin system
bichromatically driven by a transverse microwave (MW) field and a longitudinal
radio-frequency (RF) field. The behavior of the effective field amplitude is
examined in the case of a relatively strong MW field, when the derivation of
the effective Hamiltonian cannot be reduced to first-order perturbation theory
in w_{1} / w_{rf} (w_{1} is the microwave Rabi frequency, w_{rf} is the RF
frequency). Experimental results are consistently interpreted by taking into
account the contributions of second and third order in w_{1} / w_{rf} evaluated
by Krylov-Bogolyubov-Mitropolsky averaging. In the case of inhomogeneously
broadened EPR line, the third-order correction modifies the nutation frequency,
while the second-order correction gives rise to a change in the nutation
amplitude due to a Bloch-Siegert shift.Comment: 7 pages, 6 figure
Effective Field and the Bloch-Siegert Shift at Bihromatic Excitation of Multiphoton EPR
The dynamics of multiphoton transitions in a two-level spin system excited by
transverse microwave and longitudinal RF fields with the frequencies w_{mw} and
w_{rf}, respectively, is analyzed. The effective time-independent Hamiltonian
describing the "dressed" spin states of the "spin + bichromatic field" system
is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The
direct detection of the time behavior of the spin system by the method of
nonstationary nutations makes it possible to identify the multiphoton
transitions for resonances w_{0} = w_{mw} + rw_{rf} (w_{0} is the central
frequency of the EPR line, r = 1, 2), to measure the amplitudes of the
effective fields of these transitions, and to determine the features generated
by the inhomogeneous broadening of the EPR line. It is shown that the
Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening
of spectral lines reduce only the nutation amplitude but do not change their
frequencies.Comment: 6 pages, 5 figure
New Super Calogero Models and OSp(4|2) Superconformal Mechanics
We report on the new approach to constructing superconformal extensions of
the Calogero-type systems with an arbitrary number of involved particles. It is
based upon the superfield gauging of non-abelian isometries of some
supersymmetric matrix models. Among its applications, we focus on the new N=4
superconformal system yielding the U(2) spin Calogero model in the bosonic
sector, and the one-particle case of this system, which is a new OSp(4|2)
superconformal mechanics with non-dynamical U(2) spin variables. The
characteristic feature of these models is that the strength of the conformal
inverse-square potential is quantized.Comment: 12 pages, talk presented by E.Ivanov at the XIII International
Conference "Symmetry Methods in Physics", Dubna, July 6-9, 200
Dynamical supersymmetry of spin particle-magnetic field interaction
We study the super and dynamical symmetries of a fermion in a monopole
background. The Hamiltonian also involves an additional spin-orbit coupling
term, which is parameterized by the gyromagnetic ratio. We construct the
superinvariants associated with the system using a SUSY extension of a
previously proposed algorithm, based on Grassmann-valued Killing tensors.
Conserved quantities arise for certain definite values of the gyromagnetic
factor: SUSY requires ; a Kepler-type dynamical symmetry only
arises, however, for the anomalous values and . The two anomalous
systems can be unified into an SUSY system built by doubling the number
of Grassmann variables. The planar system also exhibits an supersymmetry
without Grassmann variable doubling.Comment: 23 page
Dissipative dynamics of qubits driven by a bichromatic field in the dispersive regime
We study the coherent dynamics of relaxing qubits driven by a bichromatic
radiation in the dispersive regime, when detuning of the frequency
of a longitudinal radiofrequency field from the Rabi frequency
in a transverse microwave field is comparable in magnitude to
and . We analytically describe this regime beyond the
rotating wave approximation and find that the dominant feature of dynamics of
qubits is the shift of 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 a good agreement
with the experimental data obtained in pulse EPR for the centers in
crystalline quartz.Comment: 11 pages, 4 figure
Taming the zoo of supersymmetric quantum mechanical models
We show that in many cases nontrivial and complicated supersymmetric quantum
mechanical (SQM) models can be obtained from the simple model describing free
dynamics in flat complex space by two operations: (i) Hamiltonian reduction and
(ii) similarity transformation of the complex supercharges. We conjecture that
it is true for any SQM model.Comment: final version published in JHE
Massive Superparticle with Tensorial Central Charges
We construct the manifestly Lorenz-invariant formulation of the N=1 D=4
massive superparticle with tensorial central charges. The model contains a real
parameter k and at possesses one -symmetry while at k=0 the
number of -symmetry is two. The equivalence of the formulations at all
is obtained. The local transformations of -symmetry are
written out. It is considered the using of index spinor for construction of the
tensorial central charges. It is obtained the equivalence at classical level
between the massive D=4 superparticle with one -symmetry and the
massive D=4 spinning particleComment: 20 pages, Late
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