Quantum Computing with Globally Controlled Exchange-type Interactions

If the interaction between qubits in a quantum computer has a non-diagonal form (e.g. the Heisenberg interaction), then one must be able to "switch it off" in order to prevent uncontrolled propagation of states. Therefore, such QC schemes typically demand local control of the interaction strength between each pair of neighboring qubits. Here we demonstrate that this degree of control is not necessary: it suffices to switch the interaction collectively - something that can in principle be achieved by global fields rather than with local manipulations. This observation may offer a significant simplification for various solid state, optical lattice and NMR implementations.Comment: 3 pages inc. 3 figure

Quantum Computing in Arrays Coupled by 'Always On' Interactions

It has recently been shown that one can perform quantum computation in a Heisenberg chain in which the interactions are 'always on', provided that one can abruptly tune the Zeeman energies of the individual (pseudo-)spins. Here we provide a more complete analysis of this scheme, including several generalizations. We generalize the interaction to an anisotropic form (incorporating the XY, or Forster, interaction as a limit), providing a proof that a chain coupled in this fashion tends to an effective Ising chain in the limit of far off-resonant spins. We derive the primitive two-qubit gate that results from exploiting abrupt Zeeman tuning with such an interaction. We also demonstrate, via numerical simulation, that the same basic scheme functions in the case of smoothly shifted Zeeman energies. We conclude with some remarks regarding generalisations to two- and three-dimensional arrays.Comment: 16 pages (preprint format) inc. 3 figure

The Effects of a Rapidly-Fluctuating Random Environment on Systems of Interacting Species

Some models of interacting species in a random environment are analyzed. Approximate solutions of the stochastic differential or delay-differential equations describing the systems are obtained, on the assumption that the random environment is fluctuating rapidly

Do Living Wages alter the Effect of the Minimum Wage on Income Inequality?

Anker (2006) proposed a new methodology for calculating the living wage in countries around the world. By looking at OECD nations between 2000-2010, we look to see if countries with a national minimum wage higher than this living wage value see a notable difference in the effect of the minimum wage on income inequality. Our results show that countries with the minimum wage higher than the living wage value do see lower inequality, although there is a key value of the minimum wage, at which countries start to see disemployment effects that increase inequality

High threshold distributed quantum computing with three-qubit nodes

In the distributed quantum computing paradigm, well-controlled few-qubit `nodes' are networked together by connections which are relatively noisy and failure prone. A practical scheme must offer high tolerance to errors while requiring only simple (i.e. few-qubit) nodes. Here we show that relatively modest, three-qubit nodes can support advanced purification techniques and so offer robust scalability: the infidelity in the entanglement channel may be permitted to approach 10% if the infidelity in local operations is of order 0.1%. Our tolerance of network noise is therefore a order of magnitude beyond prior schemes, and our architecture remains robust even in the presence of considerable decoherence rates (memory errors). We compare the performance with that of schemes involving nodes of lower and higher complexity. Ion traps, and NV- centres in diamond, are two highly relevant emerging technologies.Comment: 5 figures, 12 pages in single column format. Revision has more detailed comparison with prior scheme

Determining the Effect of the Minimum Wage on Income Inequality

Many recent studies have shown a significant increase to income inequality since the 1980s. One of the proposed methods for fixing this trend is to increase the minimum wage, since this policy would help those at the low end of the income spectrum to see economic growth. To analyze the effectiveness of this policy, we studied data from countries that are part of the Organization for Economic Development and Cooperation. By forming an econometric model to account for many factors that affect income inequality in nations around the world, including the real value of the minimum wage, we can determine the relationship and provide recommendations for future policy. We conclude that increases to the minimum wage can cause a decrease to income inequality until the minimum wage exceeds a maximum effectiveness value, at which point the effect starts to reverse itself. [excerpt