Quantum Zeno Effect in the Decoherent Histories

The quantum Zeno effect arises due to frequent observation. That implies the existence of some experimenter and its interaction with the system. In this contribution, we examine what happens for a closed system if one considers a quantum Zeno type of question, namely: "what is the probability of a system, remaining always in a particular subspace". This has implications to the arrival time problem that is also discussed. We employ the decoherent histories approach to quantum theory, as this is the better developed formulation of closed system quantum mechanics, and in particular, dealing with questions that involve time in a non-trivial way. We get a very restrictive decoherence condition, that implies that even if we do introduce an environment, there will be very few cases that we can assign probabilities to these histories, but in those cases, the quantum Zeno effect is still present.Comment: 7 pages, To appear in DICE 2006 (Decoherence Information Complexity and Entropy) conference proceeding

Quantum Zeno Effect in the Decoherent Histories

The quantum Zeno effect arises due to frequent observation. That implies the existence of some experimenter and its interaction with the system. In this contribution, we examine what happens for a closed system if one considers a quantum Zeno type of question, namely: "what is the probability of a system, remaining always in a particular subspace". This has implications to the arrival time problem that is also discussed. We employ the decoherent histories approach to quantum theory, as this is the better developed formulation of closed system quantum mechanics, and in particular, dealing with questions that involve time in a non-trivial way. We get a very restrictive decoherence condition, that implies that even if we do introduce an environment, there will be very few cases that we can assign probabilities to these histories, but in those cases, the quantum Zeno effect is still present.Comment: 7 pages, To appear in DICE 2006 (Decoherence Information Complexity and Entropy) conference proceeding

Secure quantum signatures using insecure quantum channels

Digital signatures are widely used in modern communication to guarantee authenticity and transferability of messages. The security of currently used classical schemes relies on computational assumptions. We present a quantum signature scheme that does not require trusted quantum channels. We prove that it is unconditionally secure against the most general coherent attacks, and show that it requires the transmission of significantly fewer quantum states than previous schemes. We also show that the quantum channel noise threshold for our scheme is less strict than for distilling a secure key using quantum key distribution. This shows that “direct” quantum signature schemes can be preferable to signature schemes relying on secret shared keys generated using quantum key distribution.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) under EP/G009821/1 and EP/K022717/1. P.W. gratefully acknowledges support from the COST Action MP1006. A.K. was partially supported by a grant from FQXi and by Perimeter Institute for Theoretical Physics. Research at Perimeter Institute is supported by the Government of Canada through Industry Canada and by the Province of Ontario through the Ministry of Research and Innovation.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevA.93.03232

Valence-Electron Resonances in Alkali-Metal Overlayers Observed via Photoemission Line-Shape Changes

Valence-electron resonances for Na overlayers on Ag(111) and Cu(111) are observed by photoemission via line-shape changes for the substrate s,p-band emission in a narrow range of photon energies. The effect is ascribed to interfering contributions to the photoelectron wave from the substrate and the vacuum barrier

Coverage-dependent frequency for Li-atom vibrations on Cu(111)

Electron-energy-loss spectra recorded for monolayer amounts of Li adsorbed on Cu(111) show a loss peak associated with Li vibrations perpendicular to the substrate. The loss energy shifts from 38 meV at low coverage to 43 meV at 0.3 ML and remains constant for coverages between 0.3 and 0.5 ML. The loss intensity passes a maximum at a Li coverage of 0.15 ML and gradually decreases such that it is difficult to resolve a loss peak at coverages above 0.5 ML. The high loss energy indicates that the adatom resides on the surfaces rather than in substitutional sites. The frequency shift is much too large to be explained by dipole-dipole interactions. The above results are obtained with the evaporation source loaded with the natural Li isotope mixture (92.6% 7Li, 7.4% 6Li). Measurements with 6Li show that the increase of the vibration frequency with increasing coverage is not an isotope effect

Observation of structure changes for Li/Cu(111) by photoemission from Li core and quantum-well states

Via photoemission from discrete quantum-well valence states and the Li 1s core level, three different types of atom rearrangements are observed for Cu(111)/Li. In the monolayer coverage range gradual energy shifts for the core-level as well as a quantum-well state reflect a gradual lateral compression of the Li overlayer as more atoms are adsorbed. The onset of Li substitution and formation of a (2×2) structure when, at RT, monolayer Li coverage is exceeded, is monitored via the disappearance and appearance of quantum-well states characteristic of the adsorbed full monolayer of Li and the part substitutional (2×2) structure, respectively. A splitting of the Li 1s emission peak into a doublet reflects the two different Li sites characteristic of the (2×2) phase. A small energy shift of the quantum-well state (25 meV) indicates that, if it is cooled (170 K), the substitutional structure is unstable with respect to Li adsorption

Views on the TRIPS Agreement to find an approach to increase the access to pharmaceutical products in developing countries : a need for transforming the global medicine regime?

Lack of access to pharmaceutical products in developing countries is major problem due to strict patent protection. The aim of the thesis is to find out whether one of the suggested approaches could increase the access to pharmaceutical products by analyzing the TRIPS Agreement and discussing few ways to view it. The views are from the perspectives of public health, right to health as well as generic medicines. The analyzed approaches are the Medicine Patent Pool, Open-Source model and Orphan medicines. An analysis of whether the global medicine regime needs transforming will be discussed before concluding the thesis that in order to increase access to pharmaceuticals in developing countries, it is essential to choose the right view on the TRIPS Agreement and then chose the right approach for practical application that supports the chosen vision. The theoretical analysis and discussion are conducted by examining the TRIPS Agreement and Doha Declaration as well as by critically analyzing and commenting on the books and articles written by legal scholars on the similar topics.Kehitysmaiden pääsy farmaseuttisiin tuotteisiin johtuu tiukoista patenttisuojauksista. Analysoimalla TRIPS sopimusta ja keskustelemalla sen eri tulkintatavoista, tämän tutkielman tavoite on selvittää, josko yksi ehdotetuista lähestymistavoista voisi lisätä farmaseuttisten tuotteiden saatavuutta. Tulkintatapoja ovat kansanterveyden, oikeus terveyteen sekä geneeristen lääkkeiden perspektiivit. Lähestymistavat, joita analysoidaan ovat lääkkeiden patenttipooli, avoimen lähdekoodin malli ja orpolääkkeet. Analysoinnista, josko maailmanlaajuinen lääkejärjestelmä tulisi muuttaa, keskustellaan, ennen kuin tutkielma lopettaa toteumaan, että jotta farmaseuttisten tuotteiden saatavuutta kehitysmaissa voidaan parantaa, on tärkeää valita oikea tulkintatapa TRIPS sopimuksesta ja sitten valita oikea lähestymistapa käytännön toteutukseen, joka tukee valittua näkemystä. Teoreettinen analysointi ja keskustelu on toteutettu tutkimalla TRIPS sopimusta, Dohan julistusta sekä kriittisesti analysoimalla ja kommentoimalla kirjoja ja artikkeleja samanlaisista aiheista, jotka ovat kirjoittaneet oikeustieteilijät