Towards Fullerene-Based Quantum Computing Oxford In quant-ph 0511198, Benjamin et al. report on recent investigation of C60 arrays as a potential architecture for coherent quantum information processing. "Molecular structures appear to be natural candidates for a quantum technology: individual atoms can support quantum superpositions for long periods, and such atoms can in principle be embedded in a permanent molecular scaffolding to form an array [...] Here we report our efforts, both experimental and theoretical, to create such a technology based on endohedral fullerenes or ‘buckyballs’. We describe our successes with respect to these criteria, along with the obstacles we are currently facing and the questions that remain to be addressed."




Fullerene Molecules Left: A model of N@C60, illustrating that the nitrogen atom sits at the centre of the fullerene cage. Its electron wavefunction lies almost entirely inside, extending on the cage with only a 2% overlap. Right: The ‘peapod’ nanotube contains fullerenes packed in a pseudo-helical phase.

Efficient evaluation of decoherence rates in complex Josephson circuits IBM Watson Theoretical analysis of the variables contributing to decoherence in Josephson flux qubits has led to order-of-magnitude extensions of coherence time in these circuits over recent years, assisting in both the design phase and control parameter optimization for increasingly-complex qubit circuitry. In cond-mat 0510843, DiVincenzo, Brito and Koch perform a complete quantitative analysis of the decoherence properties of a Josephson flux qubit, exploring relaxation and dephasing times from two different control circuits along an optimal line in the space of applied fluxes.

Quantum Time Machines: What, Why and How? Queensland/Tokyo Tim Ralph presents a Qulink seminar on closed timelike curves in context of quantum information processing. "Whether time travel into the past is possible is an undecided physical question. Recently it has been noted that certain models of time travel for quantum particles do not lead to the same difficult paradoxes that arise for classical particles. Furthermore the types of quantum evolutions predicted for these 'quantum time machines' could give rise to a 'super' quantum computer, able to solve problems thought to be intractable by any other means. In this talk I will discuss time machines in general, how quantum mechanics avoids the paradoxes and the unusual evolutions predicted. I will then argue that the requirements for realizing such machines are not as stringent as previously thought and I will propose "horizon technology" experiments which could test these ideas."

Theoretical and Experimental Exploration of Time Reversal Formalism Applied to Entanglement IQC, Waterloo In quant-ph/0510048, Laforest, Laflamme and Baugh investigate time reversal of the Schrodinger equation in the context of teleportation. Experimental results are consistent with the interpretation that information can be seen as flowing backward in time through entanglement. "In this paper, we analyze whether the acausal flow of information in a teleportation protocol can actually be physical, or should only consist of a mathematical model. Using an NMR spectrometer, we have demonstrated experimental results faithful with the interpretation that, conditionally and in principle, entanglement seems like it can break the causality of time."

RSFQ Circuits with Selective Dissipation for Coherent Quantum Information Processing VTT, Finland RSFQ, or rapid single flux quantum logic serves as a central component of HTMT, hybrid technology multi-threaded computing and other prototype high-performance architectures. In cond-mat/0510189, Hassel et al. investigate frequency-dependent damping as a means to reduce dissipation and subsequent decoherence in Josephson junction RSFQ/qubit circuits. "We derive criteria for the stability of such an arrangement, and discuss the effect on decoherence and the optimisation issues. We also design a simple flux generator aimed at manipulating flux qubits."

Life, the Universe and The Complexity Zoo IQC Waterloo In Shtetl-Optimized, Scott Aaronson waxes poetic on complexity theory: "Why is it so hard to explain that we don't worry about [complexity classes] because we're eccentric anal-retentives, but because we want to know whether a never-ending cavalcade of machines, each richer and more complicated than the last, might possibly succeed at a task on which any one machine must inevitably flounder – namely, the task of outracing time itself, of simulating cosmic history in an eyeblink, of seeing in the unformed clumps of an embryonic universe the swirl of every galaxy and flight of every hummingbird billions of years hence, like Almighty God Himself?"