Add commutator and anticommutator functions

src/QuantumInterface.jl

@@ -53,6 +53,20 @@ function traceout! end
 
 function variance end
 
+"""
+    commutator(A, B)
+
+Compute the commutator [A, B] = AB - BA of two operators.
+"""
+function commutator end
+
+"""
+    anticommutator(A, B)
+
+Compute the anticommutator {A, B} = AB + BA of two operators.
+"""
+function anticommutator end
+
 ##
 # Qubit specific
 ##

src/linalg.jl

@@ -8,3 +8,46 @@ directsum(a::AbstractOperator...) = reduce(directsum, a)
 ptrace(a::AbstractOperator, index) = arithmetic_unary_error("Partial trace", a)
 _index_complement(b::CompositeBasis, indices) = complement(length(b.bases), indices)
 reduced(a, indices) = ptrace(a, _index_complement(basis(a), indices))
+
+# Commutator and anticommutator operations
+"""
+    commutator(A, B)
+
+Compute the commutator [A, B] = AB - BA of two operators.
+
+# Arguments
+- `A::AbstractOperator`: First operator
+- `B::AbstractOperator`: Second operator
+
+# Returns
+The commutator [A, B] = AB - BA
+
+# Examples
+```julia
+σx = sigmax()
+σy = sigmay()
+comm = commutator(σx, σy)  # Returns 2i*σz
+```
+"""
+commutator(A::AbstractOperator, B::AbstractOperator) = A*B - B*A
+
+"""
+    anticommutator(A, B)
+
+Compute the anticommutator {A, B} = AB + BA of two operators.
+
+# Arguments
+- `A::AbstractOperator`: First operator
+- `B::AbstractOperator`: Second operator
+
+# Returns
+The anticommutator {A, B} = AB + BA
+
+# Examples
+```julia
+σx = sigmax()
+σz = sigmaz()
+anticomm = anticommutator(σx, σz)  # Returns zero for Pauli matrices
+```
+"""
+anticommutator(A::AbstractOperator, B::AbstractOperator) = A*B + B*A