xQIT MIT|RLE The Keck Foundation Center for Extreme Quantum Information Theory has been established at RLE under directive to investigate the fundamental limitations to quantum computing, communications, sensing and control. Seth Lloyd and Jeff Shapiro will lead the initiative.

Entangled Quantum Networks ICFO|ICREA|Max-Planck Institute In Nature Physics advance publication 10.1038/nphys549, Acin et al. draw upon the classical percolation methods of statistical mechanics to optimize entanglement distribution through quantum networks. " We argue that there exists an entanglement phase transition in quantum networks which may be exploited to obtain very efficient protocols. This work opens a new set of problems in quantum information theory, which are related to statistical physics, but pose completely new challenges in these fields [...] The work leads to a novel type of critical phenomenon, an entanglement phase transition that we call entanglement percolation. "





Maximizing entanglement in quantum networks. Each node is connected by a state consisting of two copies of the same two-qubit state. The nodes marked in (a) make the optimal measurement for the one-repeater configuration on pairs of qubits belonging to different connections. (b) A triangular lattice is obtained where the maximally entangled state for each connection is the same as for the two-qubit state. Acin et al., Nature Physics, 25 February 2007.

Entanglement engineering for quantum metrology Innsbruck Entanglement-assisted metrology has previously been demonstrated to enhance measurement sensitivity and improve fidelity in noisy conditions. In a quant-ph update to Nature 443 (316), Roos et al. obtain precision atomic clock measurements in the presence of magnetic field noise by engineering a decoherence-free subspace to enhance coherence times. " We find that entangled states are not only useful for enhancing the signal-to-noise ratio in frequency measurements – a suitably designed pair of atoms also allows clock measurements in the presence of strong technical noise. The applied technique makes explicit use of nonlocality as an entanglement property, and constitutes a new paradigm for designed quantum metrology."

        

Signatures for generalized macroscopic superpositions Queensland In quant-ph 0701204 and Phys. Rev. Lett. 97, Cavalcanti and Reid develop signature detection criteria for macroscopic quantum coherence in situations which are not limited to only two macrosopically distinct measurement outcomes. " The criteria provide a means to distinguish a single macroscopic quantum state from one based on a mixture of several microscopic superpositions of pointer-measurement eigenstates." Calculations are provided for the case of Gaussian-squeezed and spin-entangled states.

∂-wave throws down the gauntlet Vancouver Pending third-party referee, peer review or independent verification, D-Wave's press release has been received with expected enthusiasm in the mainstream press and restrained skepticism in the scientific community. "I'll be a bit of a skeptic until I see what they have done. I'm happy these guys are doing it. But the proof of the pudding is in the eating." – Seth Lloyd