3,365 research outputs found
Why you should not use the electric field to quantize in nonlinear optics
We show that using the electric field as a quantization variable in nonlinear
optics leads to incorrect expressions for the squeezing parameters in
spontaneous parametric down-conversion and conversion rates in frequency
conversion. This observation is related to the fact that if the electric field
is written as a linear combination of bosonic creation and annihilation
operators one cannot satisfy Maxwell's equations in a nonlinear dielectric.Comment: This version corrects a minor typo from the published version in
Optics Letters. Eq. 22 should have an \epsilon_0 that is lacking in the OL
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High efficiency in mode selective frequency conversion
Frequency conversion (FC) is an enabling process in many quantum information
protocols. Recently, it has been observed that upconversion efficiencies in
single-photon, mode-selective FC are limited to around 80%.In this letter we
argue that these limits can be understood as time-ordering corrections (TOCs)
that modify the joint conversion amplitude of the process. Furthermore we show,
using a simple scaling argument, that recently proposed cascaded FC protocols
that overcome the aforementioned limitations act as "attenuators" of the TOCs.
This observation allows us to argue that very similar cascaded architectures
can be used to attenuate TOCs in photon generation via spontaneous parametric
down-conversion. Finally, by using the Magnus expansion, we argue that the
TOCs, which are usually considered detrimental for FC efficiency, can also be
used to increase the efficiency of conversion in partially mode selective FC
Regimes of classical simulability for noisy Gaussian boson sampling
As a promising candidate for exhibiting quantum computational supremacy,
Gaussian Boson Sampling (GBS) is designed to exploit the ease of experimental
preparation of Gaussian states. However, sufficiently large and inevitable
experimental noise might render GBS classically simulable. In this work, we
formalize this intuition by establishing a sufficient condition for approximate
polynomial-time classical simulation of noisy GBS --- in the form of an
inequality between the input squeezing parameter, the overall transmission rate
and the quality of photon detectors. Our result serves as a non-classicality
test that must be passed by any quantum computationalsupremacy demonstration
based on GBS. We show that, for most linear-optical architectures, where photon
loss increases exponentially with the circuit depth, noisy GBS loses its
quantum advantage in the asymptotic limit. Our results thus delineate
intermediate-sized regimes where GBS devices might considerably outperform
classical computers for modest noise levels. Finally, we find that increasing
the amount of input squeezing is helpful to evade our classical simulation
algorithm, which suggests a potential route to mitigate photon loss.Comment: 13 pages, 4 figures, final version accepted for publication in
Physical Review Letter
How wide is the gap? An investigation of gender wage differences using quantile regression
In this paper we examine the determinants of wages and decompose the observed differences across genders into the "explained by different characteristics" and "explained by different returns components" using a sample of Spanish workers. Apart from the conditional expectation of wages, we estimate the conditional quantile functions for men and women and find that both the absolute wage gap and the part attributed to different returns at each of the quantiles, far from being well represented by their counterparts at the mean, are greater as we move up in the wage range.Gender wage gap, quantile regression, education
Branching rate expansion around annihilating random walks
We present some exact results for branching and annihilating random walks. We
compute the nonuniversal threshold value of the annihilation rate for having a
phase transition in the simplest reaction-diffusion system belonging to the
directed percolation universality class. Also, we show that the accepted
scenario for the appearance of a phase transition in the parity conserving
universality class must be improved. In order to obtain these results we
perform an expansion in the branching rate around pure annihilation, a theory
without branching. This expansion is possible because we manage to solve pure
annihilation exactly in any dimension.Comment: 5 pages, 5 figure
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