303 research outputs found
A Dual Model of Open Source License Growth
Every open source project needs to decide on an open source license. This
decision is of high economic relevance: Just which license is the best one to
help the project grow and attract a community? The most common question is:
Should the project choose a restrictive (reciprocal) license or a more
permissive one? As an important step towards answering this question, this
paper analyses actual license choice and correlated project growth from ten
years of open source projects. It provides closed analytical models and finds
that around 2001 a reversal in license choice occurred from restrictive towards
permissive licenses.Comment: 14 pages, 6 figure
Multi-mode states in decoy-based quantum key distribution protocols
Every security analysis of quantum key distribution (QKD) relies on a
faithful modeling of the employed quantum states. Many photon sources, like for
instance a parametric down conversion (PDC) source, require a multi-mode
description, but are usually only considered in a single-mode representation.
In general, the important claim in decoy-based QKD protocols for
indistinguishability between signal and decoy states does not hold for all
sources. We derive new bounds on the single photon transmission probability and
error rate for multi-mode states, and apply these bounds to the output state of
a PDC source. We observe two opposing effects on the secure key rate. First,
the multi-mode structure of the state gives rise to a new attack that decreases
the key rate. Second, more contributing modes change the photon number
distribution from a thermal towards a Poissonian distribution, which increases
the key rate
Theory of quantum frequency conversion and type-II parametric down-conversion in the high-gain regime
Frequency conversion (FC) and type-II parametric down-conversion (PDC)
processes serve as basic building blocks for the implementation of quantum
optical experiments: type-II PDC enables the efficient creation of quantum
states such as photon-number states and Einstein-Podolsky-Rosen-states
(EPR-states). FC gives rise to technologies enabling efficient atom-photon
coupling, ultrafast pulse gates and enhanced detection schemes. However,
despite their widespread deployment, their theoretical treatment remains
challenging. Especially the multi-photon components in the high-gain regime as
well as the explicit time-dependence of the involved Hamiltonians hamper an
efficient theoretical description of these nonlinear optical processes.
In this paper, we investigate these effects and put forward two models that
enable a full description of FC and type-II PDC in the high-gain regime. We
present a rigorous numerical model relying on the solution of coupled
integro-differential equations that covers the complete dynamics of the
process. As an alternative, we develop a simplified model that, at the expense
of neglecting time-ordering effects, enables an analytical solution.
While the simplified model approximates the correct solution with high
fidelity in a broad parameter range, sufficient for many experimental
situations, such as FC with low efficiency, entangled photon-pair generation
and the heralding of single photons from type-II PDC, our investigations reveal
that the rigorous model predicts a decreased performance for FC processes in
quantum pulse gate applications and an enhanced EPR-state generation rate
during type-II PDC, when EPR squeezing values above 12 dB are considered.Comment: 26 pages, 4 figure
- …