I would like to ask you a question because I cannot clearly understand the difference between T2 and T2* in the decoherence graph provided by IBM. Let me summarize the questions I have as follows.
[Circuit] The gate-based circuit for measuring the Decoherence characteristics of the device is as follows. It's a common method, so it doesn't seem necessary to explain it.
[Decoherence Graph] Below is a graph of the measurements released by IBM. Of course, there are slight differences between devices, but I think the patterns will be similar.
The results of T1 are very intuitive. As the amplitude decreases gradually, it changes from |1> to |0> and this pattern seems to be fitable in the form of a function.
The results of T2* are understandable to some extent. It seems that the states of |1> and |0> can be measured in the form of sine curves as shown in the graph when measuring after the second H according to the phase change by frequency fluctuation in the state of |+>. In other words, T2* can be said to detect a phase change in qubit.
Q1) In the case of T2, I'm not sure what kind of change we're observing. Unlike T1 and T2*, which are interpreted intuitively, I would like to know how to interpret the graph of T2. In other words, what causes affect T2 and how does it change the state?
Q2) In addition, if you look at the Legend of each graph, the numerical values are specified, and I am curious about the criteria. For example, T1, T2, and T2* for qubit0 are 24.1, 21.7, and 22.8, respectively, and I wonder how the constants of T1, T2, and T2* are determined from the measurement results of the graph.