Three-slit experiments and quantum nonlocality

An interesting link between two very different physical aspects of quantum mechanics is revealed; these are the absence of third-order interference and Tsirelson's bound for the nonlocal correlations. Considering multiple-slit experiments - not only the traditional configuration with two slits, but also configurations with three and more slits - Sorkin detected that third-order (and higher-order) interference is not possible in quantum mechanics. The EPR experiments show that quantum mechanics involves nonlocal correlations which are demonstrated in a violation of the Bell or CHSH inequality, but are still limited by a bound discovered by Tsirelson. It now turns out that Tsirelson's bound holds in a broad class of probabilistic theories provided that they rule out third-order interference. A major characteristic of this class is the existence of a reasonable calculus of conditional probability or, phrased more physically, of a reasonable model for the quantum measurement process.Comment: 9 pages, no figur

On defining the Hamiltonian beyond quantum theory

Energy is a crucial concept within classical and quantum physics. An essential tool to quantify energy is the Hamiltonian. Here, we consider how to define a Hamiltonian in general probabilistic theories, a framework in which quantum theory is a special case. We list desiderata which the definition should meet. For 3-dimensional systems, we provide a fully-defined recipe which satisfies these desiderata. We discuss the higher dimensional case where some freedom of choice is left remaining. We apply the definition to example toy theories, and discuss how the quantum notion of time evolution as a phase between energy eigenstates generalises to other theories.Comment: Authors' accepted manuscript for inclusion in the Foundations of Physics topical collection on Foundational Aspects of Quantum Informatio

Three-dimensionality of space and the quantum bit: an information-theoretic approach

It is sometimes pointed out as a curiosity that the state space of quantum two-level systems, i.e. the qubit, and actual physical space are both three-dimensional and Euclidean. In this paper, we suggest an information-theoretic analysis of this relationship, by proving a particular mathematical result: suppose that physics takes place in d spatial dimensions, and that some events happen probabilistically (not assuming quantum theory in any way). Furthermore, suppose there are systems that carry "minimal amounts of direction information", interacting via some continuous reversible time evolution. We prove that this uniquely determines spatial dimension d=3 and quantum theory on two qubits (including entanglement and unitary time evolution), and that it allows observers to infer local spatial geometry from probability measurements.Comment: 13 + 22 pages, 9 figures. v4: some clarifications, in particular in Section V / Appendix C (added Example 39

Rainforest transformation reallocates energy from green to brown food webs.

Terrestrial animal biodiversity is increasingly being lost because of land-use change1,2. However, functional and energetic consequences aboveground and belowground and across trophic levels in megadiverse tropical ecosystems remain largely unknown. To fill this gap, we assessed changes in energy fluxes across 'green' aboveground (canopy arthropods and birds) and 'brown' belowground (soil arthropods and earthworms) animal food webs in tropical rainforests and plantations in Sumatra, Indonesia. Our results showed that most of the energy in rainforests is channelled to the belowground animal food web. Oil palm and rubber plantations had similar or, in the case of rubber agroforest, higher total animal energy fluxes compared to rainforest but the key energetic nodes were distinctly different: in rainforest more than 90% of the total animal energy flux was channelled by arthropods in soil and canopy, whereas in plantations more than 50% of the energy was allocated to annelids (earthworms). Land-use change led to a consistent decline in multitrophic energy flux aboveground, whereas belowground food webs responded with reduced energy flux to higher trophic levels, down to -90%, and with shifts from slow (fungal) to fast (bacterial) energy channels and from faeces production towards consumption of soil organic matter. This coincides with previously reported soil carbon stock depletion3. Here we show that well-documented animal biodiversity declines with tropical land-use change4-6 are associated with vast energetic and functional restructuring in food webs across aboveground and belowground ecosystem compartments

Photoluminescence of Er3+-implanted amorphous hydrogenated silicon suboxides

Erbium ions incorporated into amorphous hydrogenated silicon suboxides (a-SiOx:H) allow to overcome the disadvantages of Er3+ in c-Si such as the limited solubility, the strong quenching of the luminescence at room temperature, and the need for co-doping with electronegative atoms. a-SiOx:H alloys have an enhanced Er solubility and easily variable oxygen content, thereby providing favorable atomic environments for an efficient Er luminescence and reduced excitation backtransfer due to deeper localized band-tail states. In the present study, Er3+ doses up to 7x10(14) cm(-2) were implanted into a-SiOx:H with oxygen content between 0 and 44 at. %. Optical properties such as the absorption coefficients and the photoluminescence (PL) spectra of the Er3+ ions and of the SiOx host were investigated as a function of erbium implantation dose, oxygen content, defect density, temperature, and annealing treatment. It was found that annealing is a requirement for activating the characteristic Er PL at 1.54 mum mainly due to a reduction of implantation induced defects. The intensity of both the intrinsic SiOx and the Er PL was found to be inversely proportional to the defect density as measured by electron spin resonance or subgap absorption. The Er PL is additionally enhanced upon annealing, probably as a result of better structural arrangements of the Er ions. The Er PL intensity increases approximately linearly with the implantation dose. An increase of the oxygen content (and correspondingly of the optical band gap) of a-SiOx:H causes no drastic changes in the erbium luminescence energy and intensity, whereas the intrinsic PL shifts to higher photon energies according to the larger band gap. Already low O concentrations of a few percent provide favorable Er environments. The main advantage of a-SiOx:H as a host matrix is revealed by temperature-dependent PL measurements. For high oxygen contents, the thermal quenching of both the Er3+ and the intrinsic PL is strongly reduced. In an a-SiOx sample with 44 at. % oxygen, the Er PL is only quenched by 20% between 77 and 300 K. In contrast, the quenching of the intrinsic PL for all [O] is roughly one order of magnitude stronger than that of the Er PL. These PL measurements were complemented by PL excitation experiments over a wide spectral range. We have observed that the Er3+ PL is excited about one order of magnitude more efficiently when pumped with sub-band-gap light compared to band-to-band excitation. The experimental results are discussed with regard to the two currently proposed Er3+ excitation models, the defect-related Auger effect and the Forster transfer mechanism

Light-induced modification of a-SiOx (II): Laser crystallisation

Amorphous hydrogenated silicon suboxides (a-SiOx:H) were deposited by plasma enhanced chemical vapor deposition from the source gases SiH4, H-2, and CO2. The band gap of the samples can be tuned from 1.9 to 3.0 eV by varying the oxygen content from 0 to 50 at. %. H-effused samples were irradiated by ultraviolet laser pulses with intensities up to 480 mJ/cm2. The structural changes and the crystallization behavior were investigated as a function of oxygen content and laser intensity. A decrease of the melting threshold by a factor of two with increasing oxygen content (0-44 at. %) was observed for the SiOx samples. Above the respective melting thresholds, not only a deterioration of the structural properties but also indications of a segregation of Si crystallites were found. Raman spectroscopy and transmission electron microscopy gave evidence for the existence of Si crystallites up to oxygen contents of 40 at. %. The crystal size reached an optimum for oxygen concentrations between 10 and 30 at. %. (C) 2004 American Institute of Physics

IMPROVING GOOGLE'S CARTOGRAPHER 3D MAPPING BY CONTINUOUS-TIME SLAM

This paper shows how to use the result of Google's SLAM solution, called Cartographer, to bootstrap our continuous-time SLAM algorithm. The presented approach optimizes the consistency of the global point cloud, and thus improves on Google’s results. We use the algorithms and data from Google as input for our continuous-time SLAM software. We also successfully applied our software to a similar backpack system which delivers consistent 3D point clouds even in absence of an IMU

Er3+ luminescence in a-SiOx:H

Among the luminescent rare earth ions erbium. is a favourable candidate for the incorporation into silicon based host materials due to its intra-4f transition at 1.54 mum, the transmission maximum of optical fibres. Disadvantages of Er in c-Si such as the limited solubility, the strongly quenched room temperature luminescence (PL) and the need for co-doping with oxygen could be overcome by using amorphous hydrogenated silicon suboxides (a-SiOx:H) as a host matrix. Suboxides have enhanced Er solubility and variable oxygen contents provide favourable erbium environments and reduced excitation backtransfer. Er3+ doses up to 7 x 10(14) cm(-2) were implanted into SiOx with oxygen contents from 0 to 50 at.%. The behaviour of the intrinsic SiOx and the erbiurn photoluminescence (PL) was measured and analysed as a function of Er implantation dose, oxygen content. defect density and temperature. (C) 2002 Elsevier Science B.V. All rights reserved