Do macroscopic properties dictate microscopic probabilities?

Aharonov and Reznik have recently (in quant-ph/0110093) argued that the form of the probabilistic predictions of quantum theory can be seen to follow from properties of macroscopic systems. An error in their argument is identified.Comment: LaTeX, 6 pages, no figure

Measuring Energy, Estimating Hamiltonians, and the Time-Energy Uncertainty Relation

Suppose that the Hamiltonian acting on a quantum system is unknown and one wants to determine what is the Hamiltonian. We show that in general this requires a time $\Delta t$ which obeys the uncertainty relation $\Delta t \Delta H \gtrsim 1$ where $\Delta H$ is a measure of how accurately the unknown Hamiltonian must be estimated. We then apply this result to the problem of measuring the energy of an unknown quantum state. It has been previously shown that if the Hamiltonian is known, then the energy can in principle be measured in an arbitrarily short time. On the other hand we show that if the Hamiltonian is not known then an energy measurement necessarily takes a minimum time $\Delta t$ which obeys the uncertainty relation $\Delta t \Delta E \gtrsim 1$ where $\Delta E$ is the precision of the energy measurement. Several examples are studied to address the question of whether it is possible to saturate these uncertainty relations. Their interpretation is discussed in detail.Comment: 12pages, revised version with small correction

Quantum Energies of Interfaces

We present a method for computing the one-loop, renormalized quantum energies of symmetrical interfaces of arbitrary dimension and codimension using elementary scattering data. Internal consistency requires finite-energy sum rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin

Hamiltonian and measuring time for analog quantum search

We derive in this study a Hamiltonian to solve with certainty the analog quantum search problem analogue to the Grover algorithm. The general form of the initial state is considered. Since the evaluation of the measuring time for finding the marked state by probability of unity is crucially important in the problem, especially when the Bohr frequency is high, we then give the exact formula as a function of all given parameters for the measuring time.Comment: 5 page

A Quantum Random Walk Search Algorithm

Quantum random walks on graphs have been shown to display many interesting properties, including exponentially fast hitting times when compared with their classical counterparts. However, it is still unclear how to use these novel properties to gain an algorithmic speed-up over classical algorithms. In this paper, we present a quantum search algorithm based on the quantum random walk architecture that provides such a speed-up. It will be shown that this algorithm performs an oracle search on a database of $N$ items with $O(\sqrt{N})$ calls to the oracle, yielding a speed-up similar to other quantum search algorithms. It appears that the quantum random walk formulation has considerable flexibility, presenting interesting opportunities for development of other, possibly novel quantum algorithms.Comment: 13 pages, 3 figure

Quantum search by measurement

We propose a quantum algorithm for solving combinatorial search problems that uses only a sequence of measurements. The algorithm is similar in spirit to quantum computation by adiabatic evolution, in that the goal is to remain in the ground state of a time-varying Hamiltonian. Indeed, we show that the running times of the two algorithms are closely related. We also show how to achieve the quadratic speedup for Grover's unstructured search problem with only two measurements. Finally, we discuss some similarities and differences between the adiabatic and measurement algorithms.Comment: 8 pages, 2 figure

Quantum random walks with decoherent coins

The quantum random walk has been much studied recently, largely due to its highly nonclassical behavior. In this paper, we study one possible route to classical behavior for the discrete quantum walk on the line: the presence of decoherence in the quantum ``coin'' which drives the walk. We find exact analytical expressions for the time dependence of the first two moments of position, and show that in the long-time limit the variance grows linearly with time, unlike the unitary walk. We compare this to the results of direct numerical simulation, and see how the form of the position distribution changes from the unitary to the usual classical result as we increase the strength of the decoherence.Comment: Minor revisions, especially in introduction. Published versio

Unforgeable Noise-Tolerant Quantum Tokens

The realization of devices which harness the laws of quantum mechanics represents an exciting challenge at the interface of modern technology and fundamental science. An exemplary paragon of the power of such quantum primitives is the concept of "quantum money". A dishonest holder of a quantum bank-note will invariably fail in any forging attempts; indeed, under assumptions of ideal measurements and decoherence-free memories such security is guaranteed by the no-cloning theorem. In any practical situation, however, noise, decoherence and operational imperfections abound. Thus, the development of secure "quantum money"-type primitives capable of tolerating realistic infidelities is of both practical and fundamental importance. Here, we propose a novel class of such protocols and demonstrate their tolerance to noise; moreover, we prove their rigorous security by determining tight fidelity thresholds. Our proposed protocols require only the ability to prepare, store and measure single qubit quantum memories, making their experimental realization accessible with current technologies.Comment: 18 pages, 5 figure

TYPOLOGIE ET STRUCTUREDE L’AVIFAUNE DES ZIBAN(BISKRA, ALGERIE) TYPOLOGY AND STRUCTURE OF THE ZIBAN’S AVIFAUNA (BISKRA, ALGERIA)

Le suivide l’Avifaune des Ziban durant 05annéessuccessives de 2006 à 2010 et pendant les mois, apermis d’inventorier 136 espèces réparties en 18 ordres et 44familles. L’ordre des passeriformes est le plusdiversifié, il est composé 63 espècesrangées dans 14 familles Les Turdidés et les Sylviidésviennent en tête avec 18 et 13 espèces. Du point de vue statut phénologique, l’avifaune des Ziban compte 47espèces nicheuses sédentaires, 56visiteuses de passage, 19 espèces hivernantes, 13espèces migratrices nicheuses et une espècenicheuse accidentelle. Le statutbiogéographique est dominé par les éléments paléarctiques (42espèces), il est suivi par les espèces éthiopiennes (17 espèces). Par contre,l’avifaune strictement méditerranéenne est représentée par seulement 07 espèces. La transition entre le domaine méditerranéen et le saharien de la région de Biskra est confirmé par la présence de 11 espèces sahariennes sur les 24 espèces notées en Algérie.  Monitoring of Ziban’s Avifauna during 05 years (January 2006 to September 2010) has allowed inventorying of 136 species divided into 18 orders and 44 families. Passerines are the most diverse with 14 families representedby 63 species. The families most represented are Turdidae and warblers, formed respectively by 18 and 13 species. Phenological point of view the Ziban avifauna with 47 resident breeding species, 56 visitors passing, 19 watering visitor, 13 migratory breeding species and 01 accidentally breeding species. Biogeographic status isdominated by Palaearctic’s species (42 species), followed by Ethiopian species including 17 species. For cons, the strictly Mediterranean avifauna is represented by only 07 species. The transition area between the Mediterranean and the Saharan region is confirmed by the presence of 11 desert species on 24 species recorded in Algeria