Developing the Deutsch-Hayden approach to quantum mechanics

The formalism of Deutsch and Hayden is a useful tool for describing quantum mechanics explicitly as local and unitary, and therefore quantum information theory as concerning a "flow" of information between systems. In this paper we show that these physical descriptions of flow are unique, and develop the approach further to include the measurement interaction and mixed states. We then give an analysis of entanglement swapping in this approach, showing that it does not in fact contain non-local effects or some form of superluminal signalling.Comment: 14 pages. Added section on entanglement swappin

Layer by layer generation of cluster states

Cluster states can be used to perform measurement-based quantum computation. The cluster state is a useful resource, because once it has been generated only local operations and measurements are needed to perform universal quantum computation. In this paper, we explore techniques for quickly and deterministically building a cluster state. In particular we consider generating cluster states on a qubus quantum computer, a computational architecture which uses a continuous variable ancilla to generate interactions between qubits. We explore several techniques for building the cluster, with the number of operations required depending on whether we allow the ability to destroy previously created controlled-phase links between qubits. In the case where we can not destroy these links, we show how to create an n x m cluster using just 3nm -2n -3m/2 + 3 operations. This gives more than a factor of 2 saving over a naive method. Further savings can be obtained if we include the ability to destroy links, in which case we only need (8nm-4n-4m-8)/3 operations. Unfortunately the latter scheme is more complicated so choosing the correct order to interact the qubits is considerably more difficult. A half way scheme, that keeps a modular generation but saves additional operations over never destroying links requires only 3nm-2n-2m+4 operations. The first scheme and the last scheme are the most practical for building a cluster state because they split up the generation into the repetition of simple sections.Comment: 16 pages, 11 figure

Enhancement of melphalan-induced tumour cell killing by misonidazole: an interaction of competing mechanisms.

In the present studies we have used the RIF-1 tumour in C3H mice to try to identify the mechanism(s) responsible for the enhancement of melphalan (L-PAM) induced tumour cell killing by the 2-nitroimidazole misonidazole (MISO). Most of this work was done with a single large dose of MISO (750 mg kg-1) given 30 min before injection of L-PAM. We found no effect of MISO on the repair of L-PAM-induced potentially lethal damage (PLD) as measured using an in vitro clonogenic survival assay. However, we identified three interrelated and competing processes which affect tumour cell killing by L-PAM subsequent to MISO injection. First, MISO reduces the clearance rate of L-PAM from the blood, an effect which enhances the cell killing by L-PAM. Second, MISO reduces the body temperature which produces a significant reduction in L-PAM cytotoxicity. Third, there is an enhancement of L-PAM cell killing by MISO over and above these two competing processes which is probably a result of the same mechanism by which cells in vitro are sensitized to L-PAM by pre-exposure to MISO under hypoxic conditions

Influence of Conserved and Hypervariable Genetic Markers on Genotyping Circulating Strains of Neisseria gonorrhoeae

Presently there is no vaccine against Neisseria gonorrhoeae and therefore accurate information on gonococcal transmission plays a crucial role for interventions designed to limit the spread of infections caused by this microorganism. We evaluated the impact of two different categories of genetic markers, (i) concatenated sequences of 10 housekeeping genes and (ii) hypervariable porB DNA sequences, on the genetic relatedness and subsequently on genotyping analysis of this human pathogen. Eighty gonococcal isolates from Canada, China, the US, Argentina, Venezuela and Chile, collected over different times, were analyzed. Our results show that the choice of genetic marker had a profound effect on the interpretation of genotyping results associated with N. gonorrhoeae. The concatenated sequences of the housekeeping genes preserved the genetic relatedness of closely related isolates, enabling detection of the predominant strains circulating within a community (Saskatchewan, Canada) over an extended period of time. In contrast, a genetic marker based on antigen gene, porB, may lead to a failure to detect these predominant circulating strains. Based on the analysis of the DNA sequences of the 10 housekeeping genes, we identified two major clonal complexes, CC33 and CC22, which comprised STs from China, and Argentina as well as two STs from Canada. Several minor clonal complexes were observed among isolates from Saskatchewan. eBURST analysis suggested that the majority of the tested gonococcal isolates from Saskatchewan, Canada were endemic, with only a couple of genotypes introduced