Decoherence in flux qubits due to 1/f noise

Dale J. Van Harlingen, B. L. T. Plourde, Timothy L. Robertson +2 more

Chun-Yao Liu, Chun-Yan Wu, Yongjun Xiao +1 more

Tsamouo Tsokeng Arthur, Tchoffo Martin, Lukong Cornelius Fai

John L. Clarke

Fumiki Yoshihara, K. Harrabi, A. O. Niskanen +2 more

We have investigated decoherence in Josephson-junction flux qubits. Based on the measurements of decoherence at various bias conditions, we discriminate contributions of different noise sources. We present a Gaussian decay function extracted from the echo signal as evidence of dephasing due to 1/f flux noise whose spectral density is evaluated to be about (10(-6)Phi0)2/Hz at 1 Hz. We also demonstrate that, at an optimal bias condition where the noise sources are well decoupled, the coherence observed in the echo measurement is limited mainly by energy relaxation of the qubit.

Fumiki Yoshihara, Yasunobu Nakamura, J. S. Tsai

We have studied decoherence in a system where two Josephson-junction flux qubits share a part of their superconducting loops and are inductively coupled. By tuning the flux-bias condition, we control the sensitivities of the energy levels to flux noises in each qubit. The dephasing rate of the first excited state is enhanced or suppressed depending on the amplitudes and the signs of the sensitivities. We have quantified the $1/f$ flux noises and their correlations and found that the dominant contribution is by local fluctuations.