fix: QEC decoding

src/func.jl

@@ -89,16 +89,16 @@ Calculate the expectation value for quantum states or density matrices given an
 - The expectation value as a `Float64` or a vector of `Float64` for multiple qubits.
 """
 expect(state::AbstractVectorS,op::QuantumOps)=real(state'*op.expand(get_N(state))*state)
-expect(rho::sa.SparseMatrixCSC,op::QuantumOps)=real(la.tr(rho*op.expand(get_N(rho))))
+expect(rho::AbstractMatrixS,op::QuantumOps)=real(la.tr(rho*op.expand(get_N(rho))))
 
 # expect(state::AbstractVectorS,op_str::String,qubit::Int)=real(state'*expand_multi_op(op_str,[qubit],get_N(state))*state)
 # expect(rho::sa.SparseMatrixCSC,op_str::String,qubit::Int)=real(la.tr(rho*expand_multi_op(op_str,[qubit],get_N(rho))))
 
 expect(state::AbstractVectorS,op_str::String)=[real(state'*expand_multi_op(op_str,[qubit],get_N(state))*state) for qubit=1:get_N(state)]
-expect(rho::sa.SparseMatrixCSC,op_str::String)=[real(la.tr(rho*expand_multi_op(op_str,[qubit],get_N(rho)))) for qubit=1:get_N(rho)]
+expect(rho::AbstractMatrixS,op_str::String)=[real(la.tr(rho*expand_multi_op(op_str,[qubit],get_N(rho)))) for qubit=1:get_N(rho)]
 
-expect(state::AbstractVectorS,matrix::sa.SparseMatrixCSC)=real(state'*matrix*state)
-expect(rho::sa.SparseMatrixCSC,matrix::sa.SparseMatrixCSC)=real(la.tr(rho*matrix))
+expect(state::AbstractVectorS,matrix::AbstractMatrixS)=real(state'*matrix*state)
+expect(rho::AbstractMatrixS,matrix::AbstractMatrixS)=real(la.tr(rho*matrix))
 
 """
 Alias:
@@ -141,7 +141,7 @@ function correlation(state::AbstractVectorS,list_of_operators::String,qubits_app
     return real(state'*matrix*state)
 end
 
-function correlation(rho::sa.SparseMatrixCSC,list_of_operators::String,qubits_applied::Vector)
+function correlation(rho::AbstractMatrixS,list_of_operators::String,qubits_applied::Vector)
     matrix=expand_multi_op(list_of_operators,qubits_applied,get_N(rho))
     return real(la.tr(rho*matrix))
 end

src/gates.jl

@@ -31,6 +31,7 @@ const gate = (
     T  = [1. 0; 0 exp(im * π / 4)],
     HSp = (1/sqrt(2)) * [1.0+0im  0-1im;1+0im  0+1im],
     HY = (1/sqrt(2)) * [1  -1im;1im -1.0],
+    H2 = [0.5 0.5 0.5 0.5;0.5 -0.5 0.5 -0.5;0.5 0.5 -0.5 -0.5;0.5 -0.5 -0.5 0.5],
     # HS = (1/sqrt(2)) * [1.0  1;1im  -1im],
     P0=[1.0 0; 0 0], #|0><0> #projector
     P1=[0 0; 0 1.0], #|1><1> #projector #n

src/ops.jl

@@ -1,9 +1,9 @@
 """
     get_N(state::AbstractVectorS) -> Int
-    get_N(rho::sa.SparseMatrixCSC) -> Int
+    get_N(rho::AbstractMatrixS) -> Int
 """
 get_N(state::AbstractVectorS)=Int(log(2,length(state)))
-get_N(rho::sa.SparseMatrixCSC)=Int(log(2,size(rho,1)))
+get_N(rho::AbstractMatrixS)=Int(log(2,size(rho,1)))
 
 get_M(state::it.MPS)=it.siteinds(state)
 get_N(psi::it.MPS)=length(get_M(psi))

src/qec.jl

@@ -410,7 +410,12 @@ struct StabilizerCode #alpha version
             state_partial=partial_trace(state,collect(n-k+1:n))
             e,v=la.eigen(state_partial)
 
-            return sa.sparse(v[:,findfirst(isapprox(1), e)])
+            e_pos=findfirst(isapprox(1), e)
+            if isa(e_pos,Number)
+                return sa.sparse(v[:,e_pos])
+            else
+                return state_partial
+            end
 
         end