Added good_state validation for VerifyOp and included test for it (#557)

Co-authored-by: Sai Rohan Reddy Kondlapudi <[email protected]>

Author: brohan-byte

src/misc_ops.jl

@@ -134,9 +134,15 @@ end
 # TODO this one needs more testing
 function applywstatus!(s::AbstractQCState, v::VerifyOp) # XXX It assumes the other qubits are measured or traced out
     # TODO QuantumClifford should implement some submatrix comparison
+    r,n = size(v.good_state)
+    if(r!=n)
+        throw(ArgumentError("""The argument you have provided for good_state is not a logical state within the codespace. Expected a pure $n - qubit stabilizer state (i.e. $n independent stabilizer generators on $n qubits), but good_state has only $r independent stabilizer generators."""))
+    end
     canonicalize_rref!(quantumstate(s),v.indices) # Document why rref is used
     sv = tab(s)
     good_state = tab(v.good_state)
+    
+    
     for i in eachindex(good_state)
         (sv.phases[end-i+1]==good_state.phases[end-i+1]) || return s, false_success_stat
         for (j,q) in zip(eachindex(good_state),v.indices)

test/test_noisycircuits.jl

@@ -295,4 +295,35 @@
             @test stabilizerview(r) == expectedFinalState
         end
     end
+
+    @testset "VerifyOp" begin
+        using QuantumClifford.ECC: Steane7, parity_checks, naive_encoding_circuit
+        @testset "Stabilizer passed as good_state is not a logical state" begin
+            good_state = parity_checks(Steane7()) #passing in a code instead of a state within codespace
+            verify = VerifyOp(good_state, 1:7)
+            reg = Register(one(MixedDestabilizer,7),6) #dummy register to pass into applywstatus!
+        
+            
+            @test_throws ArgumentError applywstatus!(reg, verify) #should throw an error since good_state isn't a logical state
+            
+    
+        end
+    
+        @testset "Accepts pure good_state argument" begin
+            good_state = S"ZZI
+                            IZZ 
+                            XXX" # passing in GHZ state as good_state argument since it exists within the repetition code's codespace
+            verify = VerifyOp(good_state, 1:3)
+            reg = Register(one(MixedDestabilizer,3),2) 
+            encoding = [sHadamard(1)  ,  sCNOT(1,2)   ,sCNOT(1,3) ] # encoding the register's state into a logical state within the repetition code's codespace
+            for i in encoding
+                apply!(reg, i)
+            end
+    
+            _, status = applywstatus!(reg, verify)
+            @test status == true_success_stat
+        end
+    
+      
+    end
 end