636 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
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
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
Towards optimal quantum tomography with unbalanced homodyning
Balanced homodyning, heterodyning and unbalanced homodyning are the three
well-known sampling techniques used in quantum optics to characterize all
possible photonic sources in continuous-variable quantum information theory. We
show that for all quantum states and all observable-parameter tomography
schemes, which includes the reconstructions of arbitrary operator moments and
phase-space quasi-distributions, localized sampling with unbalanced homodyning
is always tomographically more powerful (gives more accurate estimators) than
delocalized sampling with heterodyning. The latter is recently known to often
give more accurate parameter reconstructions than conventional marginalized
sampling with balanced homodyning. This result also holds for realistic
photodetectors with subunit efficiency. With examples from first- through
fourth-moment tomography, we demonstrate that unbalanced homodyning can
outperform balanced homodyning when heterodyning fails to do so. This new
benchmark takes us one step towards optimal continuous-variable tomography with
conventional photodetectors and minimal experimental components.Comment: 9 pages, 4 figure
The many facets of the Fabry-Perot
We address the response, both in amplitude and intensity, of a Fabry-Perot
from a variety of viewpoints. These complementary pictures conspire to achieve
a comprehensive and consistent theory of the operation of this system.Comment: 15 pages, 9 figure
Simple factorization of unitary transformations
We demonstrate a method for general linear optical networks that allows one
to factorize any SU() matrix in terms of two SU( blocks coupled by an
SU(2) entangling beam splitter. The process can be recursively continued in an
efficient way, ending in a tidy arrangement of SU(2) transformations. The
method hinges only on a linear relationship between input and output states,
and can thus be applied to a variety of scenarios, such as microwaves,
acoustics, and quantum fields.Comment: 5 pages, 4 figures. Comments welcome
Inequivalent classes of closed three-level systems
We show here that the and V configurations of three-level atomic
systems, while they have recently been shown to be equivalent for many
important physical quantities when driven with classical fields [M. B. Plenio,
Phys. Rev. A \textbf{62}, 015802 (2000)], are no longer equivalent when coupled
via a quantum field. We analyze the physical origin of such behavior and show
how the equivalence between these two configurations emerges in the
semiclassical limit.Comment: 4 pages, 1 figure. To appear as Brief Report in Physical Review
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