Arbitrarily accurate twin composite $\pi$ pulse sequences. (arXiv:1802.00958v1 [quant-ph])

We present three classes of symmetric broadband composite pulse sequences.
The composite phases are given by analytic formulas (rational fractions of
$\pi$) valid for any number of constituent pulses. The transition probability
is expressed by simple analytic formulas and the order of pulse area error
compensation grows linearly with the number of pulses. Therefore, any desired
compensation order can be produced by an appropriate composite sequence; in
this sense, they are arbitrarily accurate. These composite pulses perform
equally well or better than previously published ones. Moreover, the current
sequences are more flexible as they allow total pulse areas of arbitrary
integer multiples of $\pi$.

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