2q gates - SNZ pulse optimisation

[aorgazf]

Implement a routine to determine the parameters of SNZ pulses to be used in CZ 2q gate flux pulses. These optimisation aims to minimise leakage to the second excited state. https://arxiv.org/abs/2008.07411

[andrea-pasquale]

About this I believe that we have two possible solutions. One is relatively quick while the second one is more complicated and require at least 3 new protocols in qibocal.

Option A : compute leakage from MSR

Currently the tune landscape works with MSR, which is not ideal, however it can already give us a rough estimate of the leakage and we can therefore start optimizing the SNZ pulse using that.

Option B: compute leakage from probabilities The other option is to use probabilities. Given that we are calibrating a CZ gate we expect an avoided crossing between the $\ket{11}$ state and the state $\ket{02}$, which require the ability to classify also the state $\ket{2}$ #477. I believe that these are the protocols needed to achieve it:

• [x] Extract $\omega_{12}$ or $\alpha$ (anharmonicity). There is also already a qubit attribute anharmonicity but it is currently set manually and it is used in the qubit flux spectroscopy flux. According to this source there are two ways to do it:

  1. Perform a frequency sweep starting from $\ket{0}$ at very high power
  2. Perform a frequency sweep starting from $\ket{1}$

• [x] Compute the amplitude of the pulse necessary to go from $\ket{1} \rightarrow \ket{2}$ which can be easily done through a rabi e-f experiment

• [x] Finally we need a new protocol to perform the classification of states $\ket{0}$, $\ket{1}$ and $\ket{2}$.

Once we have either A or B ready we should be ready to start with the exceptional flows #497