The boson-sampling problem has triggered a lot of interest in the scientific community because of its potential of demonstrating the computational power of quantum interference without the need of ...non-linear processes. However, the intractability of such a problem with any classical device relies on the realization of single photons approximately identical in their spectra. In this paper, we discuss the physics of boson sampling with non-identical single-photon sources, which is strongly relevant in view of scalable experimental realizations and triggers fascinating questions in the complexity theory.
Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Because of their unique coherence properties, Bose-Einstein condensates ...are ideal sources for an atom interferometer in extended free fall. In this Letter we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far field of a double slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.
A new invisibility cloak was recently proposed for hiding objects in front of a highly reflecting mirror. This cloak requires only modest values of optical constants with minimal anisotropy and thus ...can be implemented by using non-resonant dielectric materials, making it an ideal system for optical frequency operation. We implemented the cloak using an array of silicon nanorods fabricated by electron-beam lithography. We then directly visualized the cloaking effect by monitoring the light propagation inside the device using the near-field optical microscopy.
We report the microelectromechanical systems (MEMS)-enabled mechanically tunable negative-index photonic crystal lens, which was comprised of 2-D photonic crystal and symmetrical electro-thermal ...actuators. The 2-D photonic crystal was made of a honeycomb lattice of silicon rods embedded in an SU-8 membrane. A silicon input waveguide and deflection block were also fabricated for light in-coupling and monitoring of focused spot size, respectively. When actuated, the electro-thermal actuators stretched the photonic crystal and consequently modified the photonic band structure. This, in turn, modified the focal length of the photonic crystal lens. The fabricated device was fully characterized using a tunable laser and an infrared camera while being actuated with a constant current source. The intensity and lateral spot size observed at the deflection block gradually increased as the applied current increased from 0 to 0.3 A. The observed behavior was in excellent agreement with finite-difference time-domain (FDTD) simulations, confirming the mechanical tuning of negative-index imaging.
We present the theory of a new amplification regime in traveling wave tubes (TWTs) composed of a slow wave periodic structure that supports multiple electromagnetic modes that can all be synchronized ...with the electron beam. The interaction between the multimodal slow wave structure and the electron beam is quantified using a multi-transmission line (MTL) approach based on a generalized Pierce model and transfer matrix analysis, leading to the identification of modes with complex Bloch wavenumber. In particular, we address a new possible operation condition for TWTs based on the supersynchronism between an electron beam and four modes exhibiting a degeneracy condition near a band edge of the periodic slow wave MTL. We show a phenomenological change in the band structure of a periodic MTL, where we observe at least two growing modal cooperating solutions as opposed to a uniform MTL, interacting with an electron beam where there is rigorously only one growing modal solution. We discuss the advantage of using such a degeneracy condition in TWTs that leads to larger gain conditions in amplifier regimes and also to very low starting beam current in high-power oscillators.
The issue of knowledge sharing has permeated the field of distributed AI and, in particular, its successor, multiagent systems. Through the years, many research and engineering efforts have tackled ...the problem of encoding and sharing knowledge without the need for a single, centralized knowledge base. The proposed solutions to this problem are based, more or less, on stringent assumptions, such as static, shared ontological models, or the existence of a common blackboard (or "Linda Space") environment where entities can share knowledge. However, the uptake of the World Wide Web and the emergence of modern computing paradigms, such as distributed, open systems, have highlighted the importance of sharing distributed and heterogeneous knowledge on a larger scale-possibly on the scale of the Internet.
In this article we present our experience developing QuestSemantics (QS), an agent-based platform that uses fine-grained business knowledge to support semiautomatic discovery, annotation, filtering ...and retrieval of information resources on the Internet and in intranets. We designed QS to maximize the separation between the different types of knowledge represented-domain versus task-specific knowledge, and application versus generic knowledge. The goal of this separation is to achieve reusability and easy customization of the platform's various agents, thus allowing semantics based search in various task and domain scenarios.
Toward open negotiation Phelps, S.; Tamma, V.; Wooldridge, M. ...
IEEE internet computing,
03/2004, Letnik:
8, Številka:
2
Journal Article
Recenzirano
This article describes an approach to automated negotiation that agents can use in any marketplace, regardless of the negotiation mechanism in use. Because it expresses negotiation mechanisms via ...shared ontologies rather than hard-coding in participating agents, this approach is particularly suitable for open and dynamic environments, such as the Internet, in which the choice of negotiation protocol is subject to change. The authors address the problem of determining which negotiation strategies to use for a given mechanism by introducing an expert system to reason about bidding strategies according to the negotiation mechanism's declarative description.
A possible route toward achieving high-power microwave (HPM) devices is through the use of novel slow-wave structures, represented by multiple coupled transmission lines (MTLs), and whose behavior ...when coupled to electron beams has not been sufficiently explored. We present the extension of the 1-D linearized Pierce theory to MTLs coupled to a single electron beam. We develop multiple formalisms to calculate the k-ω dispersion relation of the system and find that the existence of a growing wave solution is always guaranteed if the electron propagation constant is larger than or equal to the largest propagation constant of the MTL system. We verify our findings with illustrative examples that bring to light unique properties of the system in which growing waves were found to exist within finite bands of the electron propagation constant and also present possible means to improve the gain. By treating the beam-MTL interaction as distributed dependent current generators in the MTL, we derive relations characterizing the power flux and energy exchange between the beam and the MTLs. For the growing wave, we show that the beam always behaves as an energy source causing power flux along the transmission lines. The theory developed in this paper is the basis for the possible use of degenerate band edges in periodic MTL systems for HPM amplifiers.
Artificial nanocomposite structures offer a pathway to the development of engineered materials with novel macroscopic properties. Manufacturing the composite materials in a highly efficient yet ...precise manner remains a challenge and self-assembly of functional nanomaterials offers an attractive solution. In this paper, shape-persistent three-dimensional cage molecules have been used, for the first time, for the self-assembly of gold nanoparticles. The modular construction of cage molecules allows for precise control of inter-particle spacing down to the molecular level. Furthermore, the ability to change the number and flexibility of binding sites provides a means to tune the self-assembly process. We have designed and synthesized two types of cage molecules equipped with different numbers of binding groups with different flexibility. A systematic analysis of the optical and structural characterizations show that the inter-particle spacing within the self-assembled structures are precisely controlled by the choice of the cage molecules. These results highlight that the new self-assembly approach based on molecular cage linkers provides nanometric control over the self-assembled structure.
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