17,620 research outputs found

    Quantum chaos of a mixed, open system of kicked cold atoms

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    The quantum and classical dynamics of particles kicked by a gaussian attractive potential are studied. Classically, it is an open mixed system (the motion in some parts of the phase space is chaotic, and in some parts it is regular). The fidelity (Lochshmidt echo) is found to exhibit oscillations that can be determined from classical considerations but are sensitive to phase space structures that are smaller than Planck's constant. Families of quasi-energies are determined from classical phase space structures. Substantial differences between the classical and quantum dynamics are found for time dependent scattering. It is argued that the system can be experimentally realized by cold atoms kicked by a gaussian light beam.Comment: 19 pages, 21 figures, (accepted for publication in Phys. Rev. E

    Virtual RTCP: A Case Study of Monitoring and Repair for UDP-based IPTV Systems

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    IPTV systems have seen widespread deployment, but often lack robust mechanisms for monitoring the quality of experience. This makes it difficult for network operators to ensure that their services match the quality of traditional broadcast TV systems, leading to consumer dissatisfaction. We present a case study of virtual RTCP, a new framework for reception quality monitoring and reporting for UDP-encapsulated MPEG video delivered over IP multicast. We show that this allows incremental deployment of reporting infrastructure, coupled with effective retransmission-based packet loss repair

    Magnetic properties of PrCu2_2 at high pressure

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    We report a study of the low-temperature high-pressure phase diagram of the intermetallic compound PrCu2_2, by means of molecular-field calculations and 63,65^{63,65}Cu nuclear-quadrupole-resonance (NQR) measurements under pressure. The pressure-induced magnetically-ordered phase can be accounted for by considering the influence of the crystal electric field on the 4f4f electron orbitals of the Pr3+^{3+} ions and by introducing a pressure-dependent exchange interaction between the corresponding local magnetic moments. Our experimental data suggest that the order in the induced antiferromagnetic phase is incommensurate. The role of magnetic fluctuations both at high and low pressures is also discussed.Comment: 7 pages, 6 figures, submitted to Eur. Phys. J.

    Classical diffusion in double-delta-kicked particles

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    We investigate the classical chaotic diffusion of atoms subjected to {\em pairs} of closely spaced pulses (`kicks) from standing waves of light (the 2δ2\delta-KP). Recent experimental studies with cold atoms implied an underlying classical diffusion of type very different from the well-known paradigm of Hamiltonian chaos, the Standard Map. The kicks in each pair are separated by a small time interval ϵ1\epsilon \ll 1, which together with the kick strength KK, characterizes the transport. Phase space for the 2δ2\delta-KP is partitioned into momentum `cells' partially separated by momentum-trapping regions where diffusion is slow. We present here an analytical derivation of the classical diffusion for a 2δ2\delta-KP including all important correlations which were used to analyze the experimental data. We find a new asymptotic (tt \to \infty) regime of `hindered' diffusion: while for the Standard Map the diffusion rate, for K1K \gg 1, DK2/2[1J2(K)..]D \sim K^2/2[1- J_2(K)..] oscillates about the uncorrelated, rate D0=K2/2D_0 =K^2/2, we find analytically, that the 2δ2\delta-KP can equal, but never diffuses faster than, a random walk rate. We argue this is due to the destruction of the important classical `accelerator modes' of the Standard Map. We analyze the experimental regime 0.1Kϵ10.1\lesssim K\epsilon \lesssim 1, where quantum localisation lengths L0.75L \sim \hbar^{-0.75} are affected by fractal cell boundaries. We find an approximate asymptotic diffusion rate DK3ϵD\propto K^3\epsilon, in correspondence to a DK3D\propto K^3 regime in the Standard Map associated with 'golden-ratio' cantori.Comment: 14 pages, 10 figures, error in equation in appendix correcte
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