We experimentally investigate a superconducting qubit coupled to the end of an open transmission line, in a regime where the qubit decay rates to the transmission line and to its own environment are comparable. We perform measurements of coherent and incoherent scattering, on- and off-resonant fluorescence, and time-resolved dynamics to determine the decay and decoherence rates of the qubit. In particular, these measurements let us discriminate between non-radiative decay and pure dephasing. We combine and contrast results across all methods and find consistent values for the extracted rates. The results show that the pure dephasing rate is one order of magnitude smaller than the non-radiative decay rate for our qubit. Our results indicate a pathway to benchmark decoherence rates of superconducting qubits in a resonator-free setting.

我们通过实验研究耦合到开放式传输线末端的超导量子位，在这种情况下，对传输线及其自身环境的量子位衰减率是可比的。我们执行相干和非相干散射，on和off共振荧光以及时间分辨动力学的测量，以确定量子位的衰减和去相干速率。尤其是，这些测量值使我们可以区分非辐射衰减和纯相移。我们将所有方法的结果进行合并和对比，并为提取率找到一致的值。结果表明，纯移相速率比我们的量子比特的非辐射衰减速率小一个数量级。我们的结果表明在无谐振器设置中基准超导量子位的退相干速率的途径。