Dephasing of a superconducting flux qubit

Abstract

In order to gain a better understanding of the origin of decoherence in superconducting flux qubits, we have measured the magnetic field dependence of the characteristic energy relaxation time ($T_1$) and echo phase relaxation time ($T_2^{\mathrm{echo}}$) near the optimal operating point of a flux qubit. We have measured $T_2^{\mathrm{echo}}$ by means of the phase cycling method. At the optimal point, we found the relation $T_2^{\mathrm{echo}}\approx 2T_1$. This means that the echo decay time is {\it limited by the energy relaxation} ($T_1$ process). Moving away from the optimal point, we observe a {\it linear} increase of the phase relaxation rate ($1/T_2^{\mathrm{echo}}$) with the applied external magnetic flux. This behavior can be well explained by the influence of magnetic flux noise with a $1/f$ spectrum on the qubit.

References in corpus (6)

• Decoherence of flux qubits due to 1/f flux noise
• Dephasing of solid-state qubits at optimal points
• Multiphoton transitions in a macroscopic quantum two-state system
• Temperature square dependence of the low frequency 1/f charge noise in the Josephson junction qubits
• Parametric control of a superconducting flux qubit
• Coherent control of a flux qubit by phase-shifted resonant microwave pulses

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