Spectroscopy of transverse and longitudinal low-frequency noise and their temperature dependencies in a superconducting qubit

Details Spectroscopy of transverse and longitudinal low-frequency noise and their temperature dependencies in a superconducting qubit Spectroscopy of transverse and longitudinal low-frequency noise and their temperature dependencies in a superconducting qubit

2012-01-26

arxiv.org/abs/1201.5665v1

Physics

Condensed Matter

Superconductivity

12 p. incl. 6 p. supplement

Scientific paper

We report a direct measurement of the transverse and longitudinal low-frequency noise that causes dephasing of superconducting flux qubits. The former is due to flux fluctuations, and it affects the qubit's energy detuning; the latter is parameterized as effective critical-current or charge fluctuations, and affects the tunnel coupling between the qubit states. Our method uses repeated single-shot measurements of the qubit state to resolve the noise-power spectral density at frequencies limited only by the achievable repetition rate. This approach enables an explicit measurement of the noise over a range of frequencies that directly contributes to the dephasing observed in ensemble-averaged time-domain measurements. For both noises, we determine that the very same 1/f-type power laws measured at considerably higher frequencies (0.2-20 MHz) are consistent with the 0.01-100-Hz range. We find no evidence of temperature dependence of the noises over 65-200 mK, and also no evidence of time-domain correlations between the two noises. These results help us understand the properties of noise and dephasing pertinent to all superconducting qubits.

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