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FP5

SQUBIT-2 Report Summary

Project ID: IST-2001-39083
Funded under: FP5-IST
Country: Germany

Low- and high-frequency noise from coherent two-level systems

Experiments of the NEC (Japan) group indicated a connection between the low- and high-frequency noises affecting super-conducting quantum systems. In addition experiments of the group of J. Martinis (NIST and UCSB) showed that coherent two-level fluctuators are present in the Josephson junction of the phase qubits.

We proposed that both noises can be produced by one ensemble of microscopic modes, made up by sufficiently coherent two-level systems (TLS's). This implies a relation between the noise powers in different frequency domains, which depends on the distribution of the parameters of the TLS's. We showed that a distribution, natural for tunneling TLS's, with a log-uniform distribution in the tunnel splitting and linear distribution in the bias, accounts for experimental observations. The work is important for understanding decoherence in Josephson qubits and for improving coherence by, e.g., better choice of materials.

Contact

Gerd SCHON, (Head of Institute)
Tel.: +49-721-6083361
Fax: +49-721-6087040
E-mail
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