fix typo

Author: ytdHuang

src/negativity.jl

@@ -71,7 +71,7 @@ Return the partial transpose of a density matrix ``\rho``, where `mask` is an ar
 - `ρ_pt::QuantumObject`: The density matrix with the selected subsystems transposed.
 """
 function partial_transpose(ρ::QuantumObject{Operator}, mask::Vector{Bool})
-    any(s -> s isa EnrSpace, QO.dimensions.to) && throw(ArgumentError("partial_transpose does not support EnrSpace"))
+    any(s -> s isa EnrSpace, ρ.dimensions.to) && throw(ArgumentError("partial_transpose does not support EnrSpace"))
 
     (length(mask) != length(ρ.dimensions)) &&
         throw(ArgumentError("The length of \`mask\` should be equal to the length of \`ρ.dims\`."))