scqubits.TunableTransmon.cos_phi_operator

TunableTransmon.cos_phi_operator(energy_esys=False)

Returns operator \(\cos \varphi\) in the charge or eigenenergy basis.

Parameters:

energy_esys (Union[bool, Tuple[ndarray, ndarray]]) – If False (default), returns operator \(\cos \varphi\) in the charge basis. If True, the energy eigenspectrum is computed, returns operator \(\cos \varphi\) in the energy eigenbasis. If energy_esys = esys, where esys is a tuple containing two ndarrays (eigenvalues and energy eigenvectors), returns operator \(\cos \varphi\) in the energy eigenbasis, and does not have to recalculate eigenspectrum.

Return type:

ndarray

Returns:

Operator \(\cos \varphi\) in chosen basis as ndarray. If the eigenenergy basis is chosen, unless energy_esys is specified, \(\cos \varphi\) has dimensions of truncated_dim x truncated_dim. Otherwise, if eigenenergy basis is chosen, \(\cos \varphi\) has dimensions of m x m, for m given eigenvectors.