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Abstract: We study the effects of noise and decoherence for a double-potential wellsystem, suitable for the fabrication of qubits and quantum logic elements. Arandom noise term is added to the hamiltonian, the resulting wavefunction foundnumerically and the density matrix obtained by averaging over noise signals.Analytic solutions using the two-state model are obtained and found to begenerally in agreement.In particular, a simple formula for the decoherence rate in terms of thenoise parameters in the two-state model is reviewed and verified for the fullsimulation with the multi-level system. The formalism is extended to describemultiple sources of noise or different -dephasing- axes at the same time.Furthermore, the old formula for the -Turing-Watched Pot- effect is generalizedto the case where the environmental interactions do not conserve the -quality-in question.Various forms for the noise signal are investigated. An interesting result isthe importance of the noise power at low frequency. If it vanishes there is, inleading order, no decoherence. This is verified in a numerical simulation wheretwo apparently similar noise signals, but differing in the power at zerofrequency, give strikingly different decoherence effects. A short discussion ofsituations dominated by low frequency noise is given.



Autor: P. Korcyl, J. Wosiek, L. Stodolsky

Fuente: https://arxiv.org/



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