Quantum Computers and Decoherence: Exorcising the Demon from the Machine

Decoherence is the main obstacle to the realization of quantum computers. Until recently it was thought that quantum error correcting codes are the only complete solution to the decoherence problem. Here we present an alternative that is based on a combination of a decoherence-free subspace encoding and the application of strong and fast pulses: ``encoded recoupling and decoupling'' (ERD). This alternative has the advantage of lower encoding overhead (as few as two physical qubits per logical qubit suffice), and direct application to a number of promising proposals for the experimental realization of quantum computers.Comment: 15 pages, no figures. Invited contribution to the proceedings of the SPIE Conference on Fluctuations and Noise. Section 8 contains a new result: how to eliminate off-resonant transitions induced by generic "bang-bang" pulses, by using a special type of "bang-bang" pulse

CARE: An integrated framework to support continuous, adaptable, reflective evaluation of egovernment systems: A research note

CARE: an Integrated Framework to Support Continuous, Adaptable, Reflective Evaluation of Egovernment SystemsThis is an eGISE network paper. It is motivated by a concern to develop a better approach to learning from the experience of an eGovernment project and applying that knowledge in future projects. The proposed project is based on previous work in the construction industry that developed COLA, a Cross Organisational Learning Approach. Developing a similar strategy for Knowledge Management is likely to be effective because the ‘silo’ culture of local government organisations has parallels with the segmented organisational structures within the construction industry.Engineering and Physical Sciences Research Council, UK (grant GR/T27020/01

Probing the fermionic Higgs portal at lepton colliders

We study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator $H^\dagger H \bar \chi \chi$. Measurements of precision electroweak $S$ and $T$ parameters and the $e^+e^- \to Zh$ cross section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also provide full one-loop results for $S$ and $T$ in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.Comment: 33 pages, 5 figures. Published versio