generate_t2_echo_experiments

forest.benchmarking.qubit_spectroscopy.generate_t2_echo_experiments(qubits: Sequence[int], times: Sequence[float], detuning: float = 5000000.0) → List[forest.benchmarking.observable_estimation.ObservablesExperiment]

Return ObservablesExperiments containing programs which constitute a T2 echo experiment to measure the T2 echo coherence decay time.

For each delay time in times a single program will be generated in which all qubits are initialized to the minusY state and later simultaneously measured along the Y axis. Unlike in the t2_star experiment above there is a ‘echo’ applied in the middle of the delay in which the qubit is rotated by pi radians around the Y axis.

Similarly to t2_star, if the qubit frequency is perfectly calibrated then the Y expectation will oscillate at the given detuning frequency as the qubit is rotated about the Z axis (with respect to the lab frame, which by hypothesis matches the natural qubit frame). Unlike in a t2_star experiment, even if the qubit frequency is off such that there is some spurious rotation about the Z axis during the DELAY, the effect of an ideal echo is to cancel the effect of this rotation so that the qubit returns to the initial state minusY before the detuning rotation is applied.

Parameters:

• qubits – list of qubits to measure.
• times – the times at which to measure, given in seconds. Each time is rounded to the nearest .1 microseconds.
• detuning – The additional detuning frequency about the z axis.

Returns:

ObservablesExperiments which can be run to acquire an estimate of T2 for each qubit.