1,384 research outputs found
Organic food prices and the consumer - review of the evidence
There is a lack of research on actual organic price knowledge and on how consumers deal with prices during information search and purchase decision at the point of sale. Further research into this can help market actors to strike the balance between price as a barrier and as a cue to quality perception. Research on consumers and organic food prices should increasingly differentiate between organic consumer segments, product categories, distribution channel and brands. Such research will guide market actors towards more targeted pricing strategies that can support further market growth
Universal pulse sequence to minimize spin dephasing in the central spin decoherence problem
We present a remarkable finding that a recently discovered [G. S. Uhrig,
Phys. Rev. Lett. 98, 100504 (2007)] series of pulse sequences, designed to
optimally restore coherence to a qubit in the spin-boson model of decoherence,
is in fact completely model-independent and generically valid for arbitrary
dephasing Hamiltonians given sufficiently short delay times between pulses. The
series maximizes qubit fidelity versus number of applied pulses for
sufficiently short delay times because the series, with each additional pulse,
cancels successive orders of a time expansion for the fidelity decay. The
"magical" universality of this property, which was not appreciated earlier,
requires that a linearly growing set of "unknowns" (the delay times) must
simultaneously satisfy an exponentially growing set of nonlinear equations that
involve arbitrary dephasing Hamiltonian operators.Comment: Published in PRL, revise
Concatenated dynamical decoupling in a solid-state spin bath
Concatenated dynamical decoupling (CDD) pulse sequences hold much promise as
a strategy to mitigate decoherence in quantum information processing. It is
important to investigate the actual performance of these dynamical decoupling
strategies in real systems that are promising qubit candidates. In this Rapid
Communication, we compute the echo decay of concatenations of the Hahn echo
sequence for a solid-state electronic spin qubit in a nuclear spin bath using a
cluster expansion technique. We find that each level of concatenation reverses
the effect of successive levels of intrabath fluctuations. On the one hand,
this advances CDD as a versatile and realistic decoupling strategy. On the
other hand, this invalidates, as overly optimistic, results of the simple pair
approximation used previously to study restoration, through CDD, of coherence
lost to a mesoscopic spin bath
Electron Spin Dephasing due to Hyperfine Interactions with a Nuclear Spin Bath
We investigate pure dephasing decoherence (free induction decay and spin
echo) of a spin qubit interacting with a nuclear spin bath. While for infinite
magnetic field B the only decoherence mechanism is spectral diffusion due to
dipolar flip-flops of nuclear spins, with decreasing B the hyperfine-mediated
interactions between the nuclear spins become important. We give a theory of
decoherence due to these interactions which takes advantage of their long-range
nature. For a thermal uncorrelated bath we show that our theory is applicable
down to B~10 mT, allowing for comparison with recent experiments in GaAs
quantum dots.Comment: Published version, new title suggested by the PRL edito
Symmetric and Synchronous Communication in Peer-to-Peer Networks
Motivated by distributed implementations of game-theoretical algorithms, we study symmetric process systems and the problem of attaining common knowledge between processes. We formalize our setting by defining a notion of peer-to-peer networks and appropriate symmetry concepts in the context of Communicating Sequential Processes (CSP) [1]. We then prove that CSP with input and output guards makes common knowledge in symmetric peer-to-peer networks possible, but not the restricted version which disallows output statements in guards and is commonly implemented. Our results extend [2]
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