Arrays of operators

I working on simulating quantum systems described by [the SLH framework](https://arxiv.org/abs/1611.00375). I am interested in using QuantumSymbolics because I have the [same interest described here](https://github.com/qojulia/QuantumOpticsBase.jl/issues/70#issue-1419860820) in using both QuantumCumulants and QuantumOptics as backends to simulate system dynamics. I want to manipulate vectors and matrices of operators, for example the following code could create a vector containing quadrature operators from a vector of creation and annihilation operators. ``` using QuantumSymbolics X = [Destroy; Create] A = 1/sqrt(2)*[1 1; -1im 1im] Y = A*X ``` however this throws the error ``` ERROR: MethodError: no method matching zero(::Type{QuantumInterface.AbstractOperator}) ``` I can work around this by defining a new method for zero() like so: ``` import QuantumInterface import Base.zero function zero(::Type{QuantumInterface.AbstractOperator}) return 0.0*I end ``` I am curious to hear if supporting arrays of operators is within the scope of this package. If so, what other methods might need to be defined?