Extend Base.zero to easily initialize empty `Qobj`

[labay11]

Problem Description

The zero_ket function already exists, but this is more general and allows the initialization of an empty object of the same type and dims of other objects. Useful, for instance, for reduce or other Julia functions.

Proposed Solution

Base.zero(x::AbstractQuantumObject) = QuantumObject(zero(x.data), dims=x.dims, type=x.type)

Alternate Solutions

No response

Additional Context

No response

[ytdHuang]

I think it's a good idea since this is a standard julia implementation.

For Base.zero(A::QuantumObject), I agree.

I'm not sure what should we do for QobjEvo, because SciMLOperators.jl also supports this functionality:

julia> zero(MatrixOperator([1 2; 3 4]))
NullOperator(2)

I don't know what can we do with this NullOperator ...

But I think it would be better to still define it as

Base.zero(A::QuantumObjectEvolution) = QuantumObjectEvolution(zero(A.data), dims=A.dims, type=A.type)

to avoid ambiguity ?

If this is the case, then we can simply define the function as:

Base.zero(A::AbstractQuantumObject) = get_typename_wrapper(A)(zero(A.data), dims=A.dims, type=A.type)

[ytdHuang]

@albertomercurio

Any comments ?

[albertomercurio]

I think it's a good idea. We can use the simplest definition for both constant and time dependent case. I don't see an easy definition for SciMLOperators, and maybe one should make a PR there for that specific case.

[ytdHuang]

I think it's a good idea. We can use the simplest definition for both constant and time dependent case. I don't see an easy definition for SciMLOperators, and maybe one should make a PR there for that specific case.

So you prefer the last implementation I mentioned ?

[albertomercurio]

Yes I would say.