It appears that there is a bug with ExpressOperator handling ShiftAndPolarizationOperatorBasis in SD 2.55. The result after evaluating

`SetSpinSystem[1];`

ExpressOperator[

opI[1, "\[Alpha]"],

ShiftAndPolarizationOperatorBasis[]

]

gives an operator with norm Sqrt[2], whereas the correct norm is 1. For the following cases, however, everything works as expected, i.e. the operator norm is preserved:

`ExpressOperator[`

opI[1, "z"],

CartesianProductOperatorBasis[]

]

and

`ExpressOperator[`

opI[1, "\[Alpha]"],

CartesianProductOperatorBasis[]

]