Measurement of relaxation time in a large-inductance superconducting flux qubit*

Superconducting flux qubits with large geometric inductance are promising candidates for scalable quantum computing because it is easier to couple many of them together to form a quantum circuit sufficiently large for useful computational task. Recently, it has been shown that the dominant decoherence mechanism in superconducting flux qubit carefully isolated from environment is energy relaxation. It is therefore important to understand various relaxation mechanisms. We report here a systematic study of relaxation time as a function of flux bias, temperature, and operating point of the readout circuit in an rf SQUID flux qubit. Determination of the qubit's parameters via microwave and resonant tunneling spectroscopies allow quantitative comparisons to theoretical models. Implications of the result will be discussed.