Generating the noise effects of dephasing
T2 and T2* are similar in that they are both representing the dephasing of a qubit. The difference is in the experimental process they conduct to measure each circuit. Determining the decay time of T2* is conducted by placing the qubit in a superposition state using a Hadamard gate, then after some delay time, you apply another Hadamard gate and measure. This should result in the qubit returning to the originating state – in this case, the grounded state. This experiment is referred to as the Ramsey experiment.
To determine the decay time of T2, we will perform a similar experiment as we did for T2*, by first placing the qubit in a superposition state. The difference is that rather than waiting for some delay time before applying another Hadamard gate before measuring, you instead wait until half the delay time and then apply either an X or Y rotation, then wait until the second half delay time is complete before taking the measurement...
