2,324 research outputs found
A sum rule for charged elementary particles
There may be a link between the quantum properties of the vacuum and the
parameters describing the properties of light propagation, culminating in a sum
over all types of elementary particles existing in Nature weighted only by
their squared charges and independent of their masses. The estimate for that
sum is of the order of 100.Comment: Accepted for publication in European Physical Journal
Variations on the adiabatic invariance: the Lorentz pendulum
We analyze a very simple variant of the Lorentz pendulum, in which the length
is varied exponentially, instead of uniformly, as it is assumed in the standard
case. We establish quantitative criteria for the condition of adiabatic changes
in both pendula and put in evidence their substantially different physical
behavior with regard to adiabatic invariance.Comment: To appear in American Journal of Physic
Practical implementation of mutually unbiased bases using quantum circuits
The number of measurements necessary to perform the quantum state
reconstruction of a system of qubits grows exponentially with the number of
constituents, creating a major obstacle for the design of scalable tomographic
schemes. We work out a simple and efficient method based on cyclic generation
of mutually unbiased bases. The basic generator requires only Hadamard and
controlled-phase gates, which are available in most practical realizations of
these systems. We show how complete sets of mutually unbiased bases with
different entanglement structures can be realized for three and four qubits. We
also analyze the quantum circuits implementing the various entanglement
classes.Comment: 5 pages, 2 color figures. Comments welcome
Invisibility and PT Symmetry: A Simple Geometrical Viewpoint
We give a simplified account of the properties of the transfer matrix for a
complex one-dimensional potential, paying special attention to the particular
instance of unidirectional invisibility. In appropriate variables, invisible
potentials appear as performing null rotations, which lead to the
helicity-gauge symmetry of massless particles. In hyperbolic geometry, this can
be interpreted, via M\"{o}bius transformations, as parallel displacements, a
geometric action that has no Euclidean analogy.Comment: 13 pages. No figure. Accepted for publication in Symmetr
Simple quantum model for light depolarization
Depolarization of quantum fields is handled through a master equation of the
Lindblad type. The specific feature of the proposed model is that it couples
dispersively the field modes to a randomly distributed atomic reservoir, much
in the classical spirit of dealing with this problem. The depolarizing dynamics
resulting from this model is analyzed for relevant states.Comment: Improved version. Accepted for publication in the Journal of the
Optical Society of America
Quantum field theory and classical optics: determining the fine structure constant
The properties of the vacuum are described by quantum physics including the
response to external fields such as electromagnetic radiation. Of the two
parameters that govern the details of the electromagnetic field dynamics in
vacuum, one is fixed by the requirement of Lorentz invariance . The other one, and its relation to the
quantum vacuum, is discussed in this contribution. Deriving
from the properties of the quantum vacuum implies the derivation of the fine
structure constant.Comment: 3 pages. Invited contribution to MPLP 2017 Novosibirsk "Modern
Problems in Laser Physics". Comments welcome
Structure of the sets of mutually unbiased bases with cyclic symmetry
Mutually unbiased bases that can be cyclically generated by a single unitary
operator are of special interest, since they can be readily implemented in
practice. We show that, for a system of qubits, finding such a generator can be
cast as the problem of finding a symmetric matrix over the field
equipped with an irreducible characteristic polynomial of a given Fibonacci
index. The entanglement structure of the resulting complete sets is determined
by two additive matrices of the same size.Comment: 20 page
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