12,433 research outputs found

    Relation between fundamental estimation limit and stability in linear quantum systems with imperfect measurement

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    From the noncommutative nature of quantum mechanics, estimation of canonical observables q^\hat{q} and p^\hat{p} is essentially restricted in its performance by the Heisenberg uncertainty relation, \mean{\Delta \hat{q}^2}\mean{\Delta \hat{p}^2}\geq \hbar^2/4. This fundamental lower-bound may become bigger when taking the structure and quality of a specific measurement apparatus into account. In this paper, we consider a particle subjected to a linear dynamics that is continuously monitored with efficiency η∈(0,1]\eta\in(0,1]. It is then clarified that the above Heisenberg uncertainty relation is replaced by \mean{\Delta \hat{q}^2}\mean{\Delta \hat{p}^2}\geq \hbar^2/4\eta if the monitored system is unstable, while there exists a stable quantum system for which the Heisenberg limit is reached.Comment: 4 page

    Kinetic simulations of ladder climbing by electron plasma waves

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    The energy of plasma waves can be moved up and down the spectrum using chirped modulations of plasma parameters, which can be driven by external fields. Depending on whether the wave spectrum is discrete (bounded plasma) or continuous (boundless plasma), this phenomenon is called ladder climbing (LC) or autoresonant acceleration of plasmons. It was first proposed by Barth \textit{et al.} [PRL \textbf{115}, 075001 (2015)] based on a linear fluid model. In this paper, LC of electron plasma waves is investigated using fully nonlinear Vlasov-Poisson simulations of collisionless bounded plasma. It is shown that, in agreement with the basic theory, plasmons survive substantial transformations of the spectrum and are destroyed only when their wave numbers become large enough to trigger Landau damping. Since nonlinear effects decrease the damping rate, LC is even more efficient when practiced on structures like quasiperiodic Bernstein-Greene-Kruskal (BGK) waves rather than on Langmuir waves \textit{per~se}

    Core structure of EAS in 10(15) to 10(17) eV

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    With the use of Akeno calorimeter, the attenuation of particles in concrete is analyzed as the function of the shower size of 10 to the 5th power to 10 to the 7th power. The attenuation length does not depend much on the shower size but depends a little on the shower age. The average value is approx. 150 g/sq cm for s = 0.5 to 0.85 and approx. 40 g/sq cm for s = 0.85 to 1.15. These values and their fluctuations are consistent with the equi-intensity curves of extensive air showers (EAS)

    Measurement of energy muons in EAS at energy region larger thean 10(17) eV

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    A measurement of low energy muons in extensive air showers (EAS) (threshold energies are 0.25, 0.5, 0.75 and 1.38 GeV) was carried out. The density under the concrete shielding equivalent to 0.25 GeV at core distance less than 500 m and 0.5 GeV less than 150 m suffers contamination of electromagnetic components. Therefore the thickness of concrete shielding for muon detectors for the giant air shower array is determined to be 0.5 GeV equivalence. Effects of photoproduced muons are found to be negligible in the examined ranges of shower sizes and core distances. The fluctuation of the muon density in 90 sq m is at most 25% between 200 m and 600 m from the core around 10 to the 17th power eV
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