453 research outputs found
Twisted electron in a strong laser wave
Electrons carrying orbital angular momentum (OAM) have recently been
discovered theoretically and obtained experimentally that opens up
possibilities for using them in high-energy physics. We consider such a twisted
electron moving in external field of a plane electromagnetic wave and study how
this field influences the electron's OAM. Being motivated by the development of
high-power lasers, we focus our attention on a classically strong field regime
for which . It is shown that along with
the well-known "plane-wave" Volkov solution, Dirac equation also has the
"non-plane-wave" solutions, which possess OAM and a spin-orbit coupling, and
generalize the free-electron's Bessel states. Motion of the electron with OAM
in a circularly polarized laser wave reveals a twofold character: the
wave-packet center moves along a classical helical trajectory with some quantum
transverse broadening (due to OAM) existing even for a free electron. Using the
twisted states, we calculate the electron's total angular momentum and predict
its shift in the strong-field regime that is analogous to the well-known shifts
of the electron's momentum and mass (and to a less known shift of its spin) in
intense fields. Since the electron's effective angular momentum is conserved in
a plane wave, as well as in some more general field configurations, we discuss
several possibilities for accelerating non-relativistic twisted electrons by
using the focused and combined electromagnetic fields.Comment: to appear in PR
Quantum motion in superposition of Aharonov-Bohm with some additional electromagnetic fields
The structure of additional electromagnetic fields to the Aharonov-Bohm
field, for which the Schr\"odinger, Klein-Gordon, and Dirac equations can be
solved exactly are described and the corresponding exact solutions are found.
It is demonstrated that aside from the known cases (a constant and uniform
magnetic field that is parallel to the Aharonov-Bohm solenoid, a static
spherically symmetrical electric field, and the field of a magnetic monopole),
there are broad classes of additional fields. Among these new additional fields
we have physically interesting electric fields acting during a finite time, or
localized in a restricted region of space. There are additional time-dependent
uniform and isotropic electric fields that allow exact solutions of the
Schrodinger equation. In the relativistic case there are additional electric
fields propagating along the Aharonov-Bohm solenoid with arbitrary electric
pulse shape
On the exact Foldy-Wouthuysen transformation for a Dirac spinor in torsion and other CPT and Lorentz violating backgrounds
We discuss the possibility to perform and use the exact Foldy-Wouthuysen
transformation (EFWT) for the Dirac spinor coupled to different CPT and Lorentz
violating terms. The classification of such terms is performed, selecting those
of them which admit EFWT. For the particular example of an axial vector field,
which can be associated with the completely antisymmetric torsion, we construct
an explicit EFWT in the case when only a timelike component of this axial
vector is present. In the cases when EFWT is not possible, one can still use
the corresponding technique for deriving the perturbative Foldy-Wouthuysen
transformation, as is illustrated in a particular example in the Appendix
Charged particles in crossed and longitudinal electromagnetic fields and beam guides
We consider a class of electromagnetic fields that contains crossed fields
combined with longitudinal electric and magnetic fields. We study the motion of
a classical particle (solutions of the Lorentz equations) in such fields. Then,
we present an analysis that allows one to decide which fields from the class
act as a beam guide for charged particles, and we find some time-independent
and time-dependent configurations with beam guiding properties. We demonstrate
that the Klein-Gordon and Dirac equations with all the fields from the class
can be solved exactly. We study these solutions, which were not known before,
and prove that they form complete and orthogonal sets of functions.Comment: 14 page
Aspects of Two-Level Systems under External Time Dependent Fields
The dynamics of two-level systems in time-dependent backgrounds is under
consideration. We present some new exact solutions in special backgrounds
decaying in time. On the other hand, following ideas of Feynman, Vernon and
Hellwarth, we discuss in detail the possibility to reduce the quantum dynamics
to a classical Hamiltonian system. This, in particular, opens the possibility
to directly apply powerful methods of classical mechanics (e.g. KAM methods) to
study the quantum system. Following such an approach, we draw conclusions of
relevance for ``quantum chaos'' when the external background is periodic or
quasi-periodic in time.Comment: To appear in J. Phys. A. Mathematical and Genera
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