1,562 research outputs found
Full counting statistics of weak measurement
A weak measurement consists in coupling a system to a probe in such a way
that constructive interference generates a large output. So far, only the
average output of the probe and its variance were studied. Here, the
characteristic function for the moments of the output is provided. The outputs
considered are not limited to the eigenstates of the pointer or of its
conjugate variable, so that the results apply to any observable \Hat{o} of
the probe. Furthermore, a family of well behaved complex quantities, the normal
weak values, is introduced, in terms of which the statistics of the weak
measurement can be described. It is shown that, within a good approximation,
the whole statistics of weak measurement is described by a complex parameter,
the weak value, and a real one.Comment: Expanded version: 9 pages, 3 Figs. Now the validity of the expansion
for the moments is analysed. Introduced a one-parameter family of weak
values, useful to express the correct characteristic function. More figures
added. Thanks to Referee C of PRL for asking stimulating question
Preliminary evidence for the influence of physiography and scale upon the autocorrelation function of remotely sensed data
Previously established results demonstrate that LANDSAT data are autocorrelated and can be described by a univariate linear stochastic process known as auto-regressive-integrated-moving-average model of degree 1, 0, 1 or ARIMA (1, 0, 1). This model has two coefficients of interest for interpretation phi(1) and theta(1). In a comparison of LANDSAT thematic mapper simulator (TMS) data and LANDSAT MSS data several results were established: (1) The form of the relatedness as described by this model is not dependent upon system look angle or pixel size. (2) The phi(1) coefficient increases with decreasing pixel size and increasing topographic complexity. (3) Changes in topography have a greater influence upon phi(1) than changes in land cover class. (4) The theta(1) seems to vary with the amount of atmospheric haze. These patterns of variation in phi(1) and theta(1) are potentially exploitable by the remote sensing community to yield stochastically independent sets of observations, characterize topography, and reduce the number of bytes needed to store remotely sensed data
Uncertainty Relations for Positive Operator Valued Measures
How much unavoidable randomness is generated by a Positive Operator Valued
Measure (POVM)? We address this question using two complementary approaches.
First we study the variance of a real variable associated to the POVM outcomes.
In this context we introduce an uncertainty operator which measures how much
additional noise is introduced by carrying out a POVM rather than a von Neumann
measurement. We illustrate this first approach by studying the variances of
joint estimates of \sigma_x and \sigma_z for spin 1/2 particles. We show that
for unbiased measurements the sum of these variances is lower bounded by 1. In
our second approach we study the entropy of the POVM outcomes. In particular we
try to establish lower bounds on the entropy of the POVM outcomes. We
illustrate this second approach by examples.Comment: 5 pages, minor modifications and clarification
Integrated Silicon Photonics for High-Speed Quantum Key Distribution
Integrated photonics offers great potential for quantum communication devices
in terms of complexity, robustness and scalability. Silicon photonics in
particular is a leading platform for quantum photonic technologies, with
further benefits of miniaturisation, cost-effective device manufacture and
compatibility with CMOS microelectronics. However, effective techniques for
high-speed modulation of quantum states in standard silicon photonic platforms
have been limited. Here we overcome this limitation and demonstrate high-speed
low-error quantum key distribution modulation with silicon photonic devices
combining slow thermo-optic DC biases and fast (10~GHz bandwidth)
carrier-depletion modulation. The ability to scale up these integrated circuits
and incorporate microelectronics opens the way to new and advanced integrated
quantum communication technologies and larger adoption of quantum-secured
communications
With Freedom Comes Responsibility: Ensuring That the Next Generation of Technologies is Accessible, Usable and Affordable
The cosine law at the atomic scale: Toward realistic simulations of Knudsen diffusion
We propose to revisit the diffusion of atoms in the Knudsen regime in terms
of a complex dynamical reflection process. By means of molecular dynamics
simulation we emphasize the asymptotic nature of the cosine law of reflection
at the atomic scale, and carefully analyze the resulting strong correlations in
the reflection events. A dynamical interpretation of the accomodation
coefficient associated to the slip at the wall interface is also proposed.
Finally, we show that the first two moments of the stochastic process of
reflection non uniformly depend on the incident angle
The study of ionospheric anomalies in Japan area during 1998–2010 by Kon et al.: An inaccurate claim of earthquake-related signatures?
The problem of identifying precursory signals of earthquakes in the hope of mitigate the seismic hazard is a very important topic, but inaccurate documentations of precursory signatures decrease the credibility of this field of research. The statistical analysis by Kon et al. (2011) shows that there is tendency of positive total electron content (TEC) anomalies to occur 1–5 days before 52 M > 6 earthquakes which struck Japan during 1998–2010. Kon et al. (2011) also report in detail three selected case studies claiming the occurrence of TEC anomalies possibly related to large and destructive earthquakes. This paper casts doubts on the possibility that in the three cases the TEC disturbances were caused by seismic events suggesting that these TEC changes could be induced by normal variations of the global geomagnetic activity.
As a consequence, also the results of the Superimposed Epoch Analysis performed by Kon et al. (2011) could be seriously influenced by global magnetospheric signals
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