Efficient Quantum Circuits for Non-Qubit Quantum Error-Correcting Codes

We present two methods for the construction of quantum circuits for quantum error-correcting codes (QECC). The underlying quantum systems are tensor products of subsystems (qudits) of equal dimension which is a prime power. For a QECC encoding k qudits into n qudits, the resulting quantum circuit has O(n(n-k)) gates. The running time of the classical algorithm to compute the quantum circuit is O(n(n-k)^2).Comment: 18 pages, submitted to special issue of IJFC

Two flavor chiral phase transition from nonperturbative flow equations

We employ nonperturbative flow equations to compute the equation of state for two flavor QCD within an effective quark meson model. This yields the temperature and quark mass dependence of quantities like the chiral condensate or the pion mass. A precision estimate of the universal critical equation of state for the three-dimensional O(4) Heisenberg model is presented. We explicitly connect the O(4) universal behavior near the critical temperature and zero quark mass with the physics at zero temperature and a realistic pion mass. For realistic quark masses the pion correlation length near T_c turns out to be smaller than its zero temperature value.Comment: 49 pages including 15 figures, LaTeX, uses epsf.sty and rotate.st

Renormalization Flow of Bound States

A renormalization group flow equation with a scale-dependent transformation of field variables gives a unified description of fundamental and composite degrees of freedom. In the context of the effective average action, we study the renormalization flow of scalar bound states which are formed out of fundamental fermions. We use the gauged Nambu--Jona-Lasinio model at weak gauge coupling as an example. Thereby, the notions of bound state or fundamental particle become scale dependent, being classified by the fixed-point structure of the flow of effective couplings.Comment: 25 pages, 3 figures, v2: minor corrections, version to appear in PR

TG7r1 channel model document for high rate PD communications

Purpose Providing channel models which allow a fair comparison of different physical layer (PHY) High Rate PD Communications proposals submitted to TG7r1 in response to the Call for Proposals (CFP). Notice This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein

Structural Characterization And Condition For Measurement Statistics Preservation Of A Unital Quantum Operation

We investigate the necessary and sufficient condition for a convex cone of positive semidefinite operators to be fixed by a unital quantum operation $\phi$ acting on finite-dimensional quantum states. By reducing this problem to the problem of simultaneous diagonalization of the Kraus operators associated with $\phi$, we can completely characterize the kind of quantum states that are fixed by $\phi$. Our work has several applications. It gives a simple proof of the structural characterization of a unital quantum operation that acts on finite-dimensional quantum states --- a result not explicitly mentioned in earlier studies. It also provides a necessary and sufficient condition for what kind of measurement statistics is preserved by a unital quantum operation. Finally, our result clarifies and extends the work of St{\o}rmer by giving a proof of a reduction theorem on the unassisted and entanglement-assisted classical capacities, coherent information, and minimal output Renyi entropy of a unital channel acting on finite-dimensional quantum state.Comment: 9 pages in revtex 4.1, minor revision, to appear in J.Phys.

(Meta-)stable reconstructions of the diamond(111) surface: interplay between diamond- and graphite-like bonding

Off-lattice Grand Canonical Monte Carlo simulations of the clean diamond (111) surface, based on the effective many-body Brenner potential, yield the $(2\times1)$ Pandey reconstruction in agreement with \emph{ab-initio} calculations and predict the existence of new meta-stable states, very near in energy, with all surface atoms in three-fold graphite-like bonding. We believe that the long-standing debate on the structural and electronic properties of this surface could be solved by considering this type of carbon-specific configurations.Comment: 4 pages + 4 figures, Phys. Rev. B Rapid Comm., in press (15Apr00). For many additional details (animations, xyz files) see electronic supplement to this paper at http://www.sci.kun.nl/tvs/carbon/meta.htm

uptake, intracellular distribution and cellular responses

Silver nanoparticles (SNP) are among the most commercialized nanoparticles worldwide. They can be found in many diverse products, mostly because of their antibacterial properties. Despite its widespread use only little data on possible adverse health effects exist. It is difficult to compare biological data from different studies due to the great variety in sizes, coatings or shapes of the particles. Here, we applied a novel synthesis approach to obtain SNP, which are covalently stabilized by a small peptide. This enables a tight control of both size and shape. We applied these SNP in two different sizes of 20 or 40 nm (Ag20Pep and Ag40Pep) and analyzed responses of THP-1-derived human macrophages. Similar gold nanoparticles with the same coating (Au20Pep) were used for comparison and found to be non-toxic. We assessed the cytotoxicity of particles and confirmed their cellular uptake via transmission electron microscopy and confocal Raman microscopy. Importantly a majority of the SNP could be detected as individual particles spread throughout the cells. Furthermore we studied several types of oxidative stress related responses such as induction of heme oxygenase I or formation of protein carbonyls. In summary, our data demonstrate that even low doses of SNP exerted adverse effects in human macrophages

Exact Flow Equations and the U(1)-Problem

The effective action of a SU(N)-gauge theory coupled to fermions is evaluated at a large infrared cut-off scale k within the path integral approach. The gauge field measure includes topologically non-trivial configurations (instantons). Due to the explicit infrared regularisation there are no gauge field zero modes. The Dirac operator of instanton configurations shows a zero mode even after the infrared regularisation, which leads to U_A(1)-violating terms in the effective action. These terms are calculated in the limit of large scales k.Comment: 22 pages, latex, no figures, with stylistic changes and some arguments streamlined, typos corrected, References added, to appear in Phys. Rev.

Dirac Operators and the Calculation of the Connes Metric on arbitrary (Infinite) Graphs

As an outgrowth of our investigation of non-regular spaces within the context of quantum gravity and non-commutative geometry, we develop a graph Hilbert space framework on arbitrary (infinite) graphs and use it to study spectral properties of graph-Laplacians and graph-Dirac-operators. We define a spectral triplet sharing most of the properties of what Connes calls a spectral triple. With the help of this scheme we derive an explicit expression for the Connes-distance function on general directed or undirected graphs. We derive a series of apriori estimates and calculate it for a variety of examples of graphs. As a possibly interesting aside, we show that the natural setting of approaching such problems may be the framework of (non-)linear programming or optimization. We compare our results (arrived at within our particular framework) with the results of other authors and show that the seeming differences depend on the use of different graph-geometries and/or Dirac operators.Comment: 27 pages, Latex, comlementary to an earlier paper, general treatment of directed and undirected graphs, in section 4 a series of general results and estimates concerning the Connes Distance on graphs together with examples and numerical estimate