diff --git a/src/base.jl b/src/base.jl
index b8390b8..18d312e 100644
--- a/src/base.jl
+++ b/src/base.jl
@@ -40,10 +40,10 @@ Return Hermitian conjugate \$\\langle val| = |val\\rangle^\\dagger\$ of the ket
 """
 bra(val::Int, dim::Int) = bra(Vector{ComplexF64}, val, dim)
 
-function ketbra(::Type{T}, valk::Int, valb::Int, dimin::Int, dimout::Int) where T<:AbstractMatrix{<:Number}
-    dimin > 0 && dimout > 0 ? () : throw(ArgumentError("Matrix dimension has to be nonnegative"))
-    1 <= valk <= dimin && 1 <= valb <= dimout ? () : throw(ArgumentError("Ket and bra labels have to be smaller than operator dimension"))
-    ρ = T(undef, dimout, dimin)
+function ketbra(::Type{T}, valk::Int, valb::Int, idim::Int, odim::Int) where T<:AbstractMatrix{<:Number}
+    idim > 0 && odim > 0 ? () : throw(ArgumentError("Matrix dimension has to be nonnegative"))
+    1 <= valk <= idim && 1 <= valb <= odim ? () : throw(ArgumentError("Ket and bra labels have to be smaller than operator dimension"))
+    ρ = T(undef, odim, idim)
     fill!(ρ, zero(eltype(T)))
     ρ[valk,valb] = one(eltype(T))
     ρ
@@ -70,12 +70,12 @@ ketbra(valk::Int, valb::Int, dim::Int) = ketbra(Matrix{ComplexF64}, valk, valb,
 """
 - `valk`: non-zero entry - label.
 - `valb`: non-zero entry - label.
-- `dimin`: length of the ket vector
-- `dimout`: length of the bra vector
+- `idim`: length of the ket vector
+- `odim`: length of the bra vector
 
 # Return outer product \$|valk\\rangle\\langle vakb|\$ of states \$|valk\\rangle\$ and \$|valb\\rangle\$.
 """
-ketbra(valk::Int, valb::Int, dimin::Int, dimout::Int) = ketbra(Matrix{ComplexF64}, valk, valb, dimin, dimout)
+ketbra(valk::Int, valb::Int, idim::Int, odim::Int) = ketbra(Matrix{ComplexF64}, valk, valb, idim, odim)
 
 """
 $(SIGNATURES)
diff --git a/src/channels.jl b/src/channels.jl
index 54c9b56..00b3a70 100644
--- a/src/channels.jl
+++ b/src/channels.jl
@@ -73,16 +73,16 @@ end
 """
 $(SIGNATURES)
 - `channel`: quantum channel map.
-- `dim`: square root of the [super-operator](https://en.wikipedia.org/wiki/Superoperator) matrix dimension.
+- `idim`: square root of the [super-operator](https://en.wikipedia.org/wiki/Superoperator) matrix input dimension.
+- `odim`: square root of the [super-operator](https://en.wikipedia.org/wiki/Superoperator) matrix output dimension.
 
 Transforms quntum channel into super-operator matrix.
 """
 function SuperOperator{T}(channel::Function, idim::Int, odim::Int) where T<:AbstractMatrix{<:Number}
-    error("Broken")
-    odim > 0 ? () : error("Channel dimension has to be nonnegative") # TODO: fix
+    odim > 0 && idim > 0 ? () : throw(ArgumentError("Channel dimensions have to be nonnegative"))
 
-    m = zeros(T, idim^2, odim^2)
-    for (i, e) in enumerate(base_matrices(idim)) # TODO : base_matrices should be not only square
+    m = zeros(eltype(T), idim^2, odim^2)
+    for (i, e) in enumerate(ElementaryBasisIterator{Matrix{Int}}(idim, odim))
         m[:, i] = res(channel(e))
     end
     SuperOperator(m, idim, odim)
diff --git a/src/matrixbases.jl b/src/matrixbases.jl
index bb0768e..cd0306a 100644
--- a/src/matrixbases.jl
+++ b/src/matrixbases.jl
@@ -1,11 +1,18 @@
 import .Base: length, iterate
-export AbstractMatrixBasisIterator, HermitianBasisIterator, AbstractBasis,
-    AbstractMatrixBasis, HermitianBasis, hermitianbasis, represent, combine
+export AbstractMatrixBasisIterator, HermitianBasisIterator, ElementaryBasisIterator, AbstractBasis,
+    AbstractMatrixBasis, HermitianBasis, ElementaryBasis, hermitianbasis,
+    represent, combine
+
 abstract type AbstractMatrixBasisIterator{T<:AbstractMatrix} end
 struct HermitianBasisIterator{T} <: AbstractMatrixBasisIterator{T} 
     dim::Int
 end
 
+struct ElementaryBasisIterator{T} <: AbstractMatrixBasisIterator{T} 
+    idim::Int
+    odim::Int
+end
+
 abstract type AbstractBasis end
 abstract type AbstractMatrixBasis{T} <: AbstractBasis where T<:AbstractMatrix{<:Number} end 
 
@@ -17,6 +24,18 @@ struct HermitianBasis{T} <: AbstractMatrixBasis{T}
     end
 end
 
+struct ElementaryBasis{T} <: AbstractMatrixBasis{T} 
+    iterator::ElementaryBasisIterator{T}
+
+    function ElementaryBasis{T}(idim::Integer, odim::Integer) where T<:AbstractMatrix{<:Number}
+        new(ElementaryBasisIterator{T}(idim, odim)) 
+    end
+end
+
+function ElementaryBasis{T}(dim::Integer) where T<:AbstractMatrix{<:Number}
+    ElementaryBasisIterator{T}(dim, dim)
+end
+
 """
 $(SIGNATURES)
 - `dim`: dimensions of the matrix.
@@ -46,6 +65,18 @@ end
 
 length(itr::HermitianBasisIterator) = itr.dim^2
 
+function iterate(itr::ElementaryBasisIterator{T}, state=(1,1)) where T<:AbstractMatrix{<:Number}
+    idim, odim = itr.idim, itr.odim
+    (a, b) = state
+    a > idim  && return nothing
+
+    x = zeros(eltype(T), odim, idim)
+    x[b, a] = one(eltype(T))
+    return x, b == odim ? (a+1, 1) : (a, b+1)
+end
+
+length(itr::ElementaryBasisIterator) = itr.idim * itr.odim
+
 function represent(basis::T, m::Matrix{<:Number}) where T<:AbstractMatrixBasis
     real.(tr.([m] .* basis.iterator))
 end
diff --git a/test/channels.jl b/test/channels.jl
index de565c9..ec717b8 100644
--- a/test/channels.jl
+++ b/test/channels.jl
@@ -56,8 +56,8 @@ end
     @testset "construction from function" begin
         ρ = [0.25 0.25im; -0.25im 0.75]
         t = hcat([ComplexF64[0.25, 0.25im, -0.25im, 0.75] for i=1:4]...) #stack res ρ
-        @test_throws ErrorException m = SuperOperator{Matrix{ComplexF64}}(x -> ρ, 2, 2).matrix
-        @test_broken norm(t-m) ≈ 0. atol=1e-15
+        m = SuperOperator{Matrix{ComplexF64}}(x -> ρ, 2, 2).matrix
+        @test norm(t-m) ≈ 0. atol=1e-15
     end
 
     @testset "convert to KrausOperators" begin