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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
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