Quantum Communication in Rindler Spacetime

A state that an inertial observer in Minkowski space perceives to be the vacuum will appear to an accelerating observer to be a thermal bath of radiation. We study the impact of this Davies-Fulling-Unruh noise on communication, particularly quantum communication from an inertial sender to an accelerating observer and private communication between two inertial observers in the presence of an accelerating eavesdropper. In both cases, we establish compact, tractable formulas for the associated communication capacities assuming encodings that allow a single excitation in one of a fixed number of modes per use of the communications channel. Our contributions include a rigorous presentation of the general theory of the private quantum capacity as well as a detailed analysis of the structure of these channels, including their group-theoretic properties and a proof that they are conjugate degradable. Connections between the Unruh channel and optical amplifiers are also discussed.Comment: v3: 44 pages, accepted in Communications in Mathematical Physic

An international network to monitor the structure, composition and dynamics of Amazonian forests (RAINFOR)

The Amazon basin is likely to be increasingly affected by environmental changes: higher temperatures, changes in precipitation, CO2 fertilization and habitat fragmentation. To examine the important ecological and biogeochemical consequences of these changes, we are developing an international network, RAINFOR, which aims to monitor forest biomass and dynamics across Amazonia in a co-ordinated fashion in order to understand their relationship to soil and climate. The network will focus on sample plots established by independent researchers, some providing data extending back several decades. We will also conduct rapid transect studies of poorly monitored regions. Field expeditions analysed local soil and plant properties in the first phase (2001–2002). Initial results suggest that the network has the potential to reveal much information on the continental-scale relations between forest and environment. The network will also serve as a forum for discussion between researchers, with the aim of standardising sampling techniques and methodologies that will enable Amazonian forests to be monitored in a coherent manner in the coming decades

Control of Dynamical Localization

Control over the quantum dynamics of chaotic kicked rotor systems is demonstrated. Specifically, control over a number of quantum coherent phenomena is achieved by a simple modification of the kicking field. These include the enhancement of the dynamical localization length, the introduction of classical anomalous diffusion assisted control for systems far from the semiclassical regime, and the observation of a variety of strongly nonexponential lineshapes for dynamical localization. The results provide excellent examples of controlled quantum dynamics in a system that is classically chaotic and offer new opportunities to explore quantum fluctuations and correlations in quantum chaos.Comment: 9 pages, 7 figures, to appear in Physical Review

G\"odel Incompleteness and the Black Hole Information Paradox

Semiclassical reasoning suggests that the process by which an object collapses into a black hole and then evaporates by emitting Hawking radiation may destroy information, a problem often referred to as the black hole information paradox. Further, there seems to be no unique prediction of where the information about the collapsing body is localized. We propose that the latter aspect of the paradox may be a manifestation of an inconsistent self-reference in the semiclassical theory of black hole evolution. This suggests the inadequacy of the semiclassical approach or, at worst, that standard quantum mechanics and general relavity are fundamentally incompatible. One option for the resolution for the paradox in the localization is to identify the G\"odel-like incompleteness that corresponds to an imposition of consistency, and introduce possibly new physics that supplies this incompleteness. Another option is to modify the theory in such a way as to prohibit self-reference. We discuss various possible scenarios to implement these options, including eternally collapsing objects, black hole remnants, black hole final states, and simple variants of semiclassical quantum gravity.Comment: 14 pages, 2 figures; revised according to journal requirement

A Self Assembled Nanoelectronic Quantum Computer Based on the Rashba Effect in Quantum Dots

Quantum computers promise vastly enhanced computational power and an uncanny ability to solve classically intractable problems. However, few proposals exist for robust, solid state implementation of such computers where the quantum gates are sufficiently miniaturized to have nanometer-scale dimensions. Here I present a new approach whereby a complete computer with nanoscale gates might be self-assembled using chemical synthesis. Specifically, I demonstrate how to self-assemble the fundamental unit of this quantum computer - a 2-qubit universal quantum controlled-NOT gate - based on two exchange coupled multilayered quantum dots. Then I show how these gates can be wired using thiolated conjugated molecules as electrical connectors. A qubit is encoded in the ground state of a quantum dot spin-split by the Rashba interaction. Arbitrary qubit rotations are effected by bringing the spin splitting energy in a target quantum dot in resonance with a global ac magnetic field by applying a potential pulse of appropriate amplitude and duration to the dot. The controlled dynamics of the 2-qubit controlled-NOT operation (XOR) can be realized by exploiting the exchange coupling with the nearest neighboring dot. A complete prescription for initialization of the computer and data input/output operations is presented.Comment: 22 pages, 4 figure

Cosmic Background Bose Condensation (CBBC)

Degeneracy effects for bosons are more important for smaller particle mass, smaller temperature and higher number density. Bose condensation requires that particles be in the same lowest energy quantum state. We propose a cosmic background Bose condensation, present everywhere, with its particles having the lowest quantum energy state, A c/lambda, with lambda about the size of the visible universe, and therefore unlocalized. This we identify with the quantum of the self gravitational potential energy of any particle, and with the bit of information of minimum energy. The entropy of the universe (similar to 10(122) bits) has the highest number density (similar to 10(36) bits/cm(3)) of particles inside the visible universe, the smallest mass, similar to 10(-66) g, and the smallest temperature, similar to 10(-29) K. Therefore it is the best candidate for a Cosmic Background Bose Condensation (CBBC), a completely calmed fluid, with no viscosity, in a superfluidity state, and possibly responsible for the expansion of the universe.Alfonso-Faus, A.; Fullana Alfonso, MJ. (2013). Cosmic Background Bose Condensation (CBBC). Astrophysics and Space Science. 347(1):193-196. doi:10.1007/s10509-013-1500-8S1931963471Alfonso-Faus, A.: Universality of the self gravitational potential energy of any fundamental particle. Astrophys. Space Sci. 337, 363 (2010a)Alfonso-Faus, A.: The case for the Universe to be a quantum black hole. Astrophys. Space Sci. 325, 113 (2010b)Alfonso-Faus, A.: Galaxies: kinematics as a proof of the existence of a universal field of minimum acceleration. arXiv:0708.0308 (2010c, preprint)Alfonso-Faus, A.: Quantum gravity and information theories linked by the physical properties of the bit. arXiv:1105.3143 (2011, preprint)Anderson, J.D., et al.: Indication, from Pioneer 10/11, Galileo, and Ulysses data, of an apparent anomalous, weak, long-range acceleration. Phys. Rev. Lett. 81, 2858 (1998)Bekenstein, J.D.: Phys. Rev. D 23(2), 287 (1981)Bérut, A., et al.: Experimental verification of Landauer’s principle linking information and thermodynamics. Nature 483, 187 (2012)Drees, M., Chung-Lin, S.: Theoretical interpretation of experimental data from direct dark matter detection. J. Cosmol. Astropart. Phys. 0706, 011 (2007)Eisberg, R., Resnick, R.: Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, 2nd edn. Wiley, New York (1985)Funo, K., Watanabe, Y., Ueda, M.: Thermodynamic work gain from entanglement. arXiv:1207.6872 [quant-ph] (2012, preprint)Hawking, S.W.: Black hole explosions? Nature 248, 30 (1974)Landauer, R.: Irreversibility and heat generation in the computing process. IBM J. Res. Dev. 5, 183 (1961)Landauer, R.: Dissipation and noise immunity in computation and communication. Nature 335, 779 (1988)Lloyd, S.: Computational capacity of the universe. Phys. Rev. Lett. 88, 237901 (2002)Misner, C.W., Thorne, K.S., Wheeler, J.A.: Gravitation. Freeman, Reading (1973), p. 466 (“Why the energy of the gravitational field cannot be localized”)Scarpa, R., Falomo, R.: Testing Newtonian gravity in the low acceleration regime with globular clusters: the case of omega Centauri revisited. Astron. Astrophys. 523, A43 (2010)Sivaram, C.: Cosmological and quantum constraint on particle masses. Am. J. Phys. 50, 279 (1982)Susskind, L.: The World as a hologram. J. Math. Phys. 36, 6377 (1995)’t Hooft, G.: Dimensional reduction in quantum gravity. arXiv:gr-qc/9310026 (1993, preprint)Toyabe, S., et al.: Experimental demonstration of information-to-energy conversion and validation of the generalized Jarzynski equality. Nat. Phys. 6, 988 (2010)Unruh, W.G.: Notes on black-hole evaporation. Phys. Rev. D, Part. Fields 14(4), 870 (1976)Weinberg, S.: Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity p. 619. Wiley, New York (1972

Environment-Induced Decoherence and the Transition From Quantum to Classical

We study dynamics of quantum open systems, paying special attention to those aspects of their evolution which are relevant to the transition from quantum to classical. We begin with a discussion of the conditional dynamics of simple systems. The resulting models are straightforward but suffice to illustrate basic physical ideas behind quantum measurements and decoherence. To discuss decoherence and environment-induced superselection einselection in a more general setting, we sketch perturbative as well as exact derivations of several master equations valid for various systems. Using these equations we study einselection employing the general strategy of the predictability sieve. Assumptions that are usually made in the discussion of decoherence are critically reexamined along with the ``standard lore'' to which they lead. Restoration of quantum-classical correspondence in systems that are classically chaotic is discussed. The dynamical second law -it is shown- can be traced to the same phenomena that allow for the restoration of the correspondence principle in decohering chaotic systems (where it is otherwise lost on a very short time-scale). Quantum error correction is discussed as an example of an anti-decoherence strategy. Implications of decoherence and einselection for the interpretation of quantum theory are briefly pointed out.Comment: 80 pages, 7 figures included, Lectures given by both authors at the 72nd Les Houches Summer School on "Coherent Matter Waves", July-August 199

Measurement of event shape distributions and moments in e+e- -> hadrons at 91-209 GeV and a determination of alpha_s

We have studied hadronic events from e+e- annihilation data at centre-of-mass energies from 91 to 209 GeV. We present distributions of event shape observables and their moments at each energy and compare with QCD Monte Carlo models. From the event shape distributions we extract the strong coupling alpha_s and test its evolution with energy scale. The results are consistent with the running of alpha_s expected from QCD. Combining all data, the value of alpha_s(M_Z) is determined to be alpha_s(M_Z) = 0.1191 +- 0.0005 (stat.) +- 0.0010 (expt.) +- 0.0011 (hadr.) +- 0.0044 (theo.). The energy evolution of the moments is also used to determine a value of alpha_s with slightly larger errors: alpha_s(M_Z) = 0.1223 +- 0.0005 (stat.) +- 0.0014 (expt.) +- 0.0016 (hadr.) +0.0054 -0.0036 (theo.).Comment: 63 pages 26 fi

Flavour Independent hA Search and Two Higgs Doublet Model Interpretation of Neutral Higgs Boson Searches at LEP

Upper limits on the cross-section of the pair-production process e+e- -> h0A0 assuming 100% decays into hadrons, are derived from a new search for the h0A0 -> hadrons topology, independent of the hadronic flavour of the decay products. Searches for the neutral Higgs bosons h0 and A0, are used to obtain constraints on the Type II Two Higgs Doublet Model (2HDM(11)) with no CP violation in the Higgs sector and no additional non Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detctor up to the highest available centre-of-mass energies. The searches are sensitive to the h0, A0 -> qq, gg,tau+tau- and h0 -> A0A0 decay modes of the Higgs bosons. The 2HDM(II) parameter space is explored in a detailed scan. Large regions of the 2HDM(II) parameter space are excluded at the 95% CL in the (mh, mA), (mh, tanb) and (mA, tanb) planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region 1 lesssim mh lesssim 55 GeV and 3 lesssim mA lesssim 63 GeV is excluded at 95% CL independently of the choice of the 2HDM(II) parameters.Comment: 37 pages, 11 figures, Submitted to Eur. Phys. J.