From bf649a66a83caf832de6f97ce71783488617c19e Mon Sep 17 00:00:00 2001
From: Feroz Ahmad <feroz.ahmad.email@gmail.com>
Date: Sat, 14 Sep 2024 10:14:52 +0500
Subject: [PATCH] fixes expect (#348)

---
 src/nonclifford.jl                     |  6 +--
 test/test_nonclifford_quantumoptics.jl | 64 +++++++++++---------------
 2 files changed, 31 insertions(+), 39 deletions(-)

diff --git a/src/nonclifford.jl b/src/nonclifford.jl
index eba12bd39..a9a5ecf62 100644
--- a/src/nonclifford.jl
+++ b/src/nonclifford.jl
@@ -98,13 +98,13 @@ end
 
 Expectation value for the [PauliOperator](@ref) observable given the [`GeneralizedStabilizer`](@ref) state `s`."""
 function expect(p::PauliOperator, s::GeneralizedStabilizer) # TODO optimize
-    e = zero(_dictvaltype(s.destabweights))
+    χ′ = zero(_dictvaltype(s.destabweights))
     phase, b, c = rowdecompose(p, s.stab)
     for ((dᵢ,dⱼ), χ) in s.destabweights
         _allthreesumtozero(dᵢ,dⱼ,b) || continue
-        e += χ * (-1)^(dᵢ'*c)
+        χ′ += χ * (-1)^(dᵢ'*c)
     end
-    return (-1)^(phase÷2) * e
+    return (im)^(phase) * χ′
 end
 
 """Same as `all(==(0), (a.+b.+c) .% 2)`"""
diff --git a/test/test_nonclifford_quantumoptics.jl b/test/test_nonclifford_quantumoptics.jl
index 48f51881c..48cd1b321 100644
--- a/test/test_nonclifford_quantumoptics.jl
+++ b/test/test_nonclifford_quantumoptics.jl
@@ -13,48 +13,40 @@ qo_tgate.data[2,2] = exp(im*pi/4)
 
 ##
 
-for s in [S"X", S"Y", S"Z", S"-X", S"-Y", S"-Z"]
-    for p in [P"X", P"Y", P"Z", P"-X", P"-Y", P"-Z"]
-        gs = GeneralizedStabilizer(s)
-        apply!(gs, pcT)
-        ρ = dm(qo_tgate*Ket(s))
-        @test Operator(gs) ≈ ρ
-        if isapprox(expect(p, gs), expect(Operator(p),ρ); atol=1e-5)
-        else
-            println("failure of expectation calculation for state = T*(", s, ") and observable = ", p)
+@testset "expect" begin
+    for s in [S"X", S"Y", S"Z", S"-X", S"-Y", S"-Z"]
+        for p in [P"X", P"Y", P"Z", P"-X", P"-Y", P"-Z"]
+            gs = GeneralizedStabilizer(s)
+            apply!(gs, pcT)
+            ρ = dm(qo_tgate*Ket(s))
+            @test Operator(gs) ≈ ρ
+            @test isapprox(expect(p, gs), expect(Operator(p),ρ); atol=1e-5)
         end
     end
-end
 
-##
-
-for _ in 1:10
-    for n in 1:1
-        i = rand(1:n)
-        stab = random_stabilizer(n)
-        genstab = GeneralizedStabilizer(stab)
-        ket = Ket(stab)
-        @test dm(ket) ≈ Operator(stab)
-        @test dm(ket) ≈ Operator(genstab)
+    for _ in 1:10
+        for n in 1:1
+            i = rand(1:n)
+            stab = random_stabilizer(n)
+            genstab = GeneralizedStabilizer(stab)
+            ket = Ket(stab)
+            @test dm(ket) ≈ Operator(stab)
+            @test dm(ket) ≈ Operator(genstab)
 
-        pauli = random_pauli(n; nophase=false, realphase=true)
-        qo_pauli = Operator(pauli)
+            pauli = random_pauli(n; nophase=false, realphase=true)
+            qo_pauli = Operator(pauli)
 
-        qo_bigtgate = n==1 ? qo_tgate : embed(qo_basis^n, i, qo_tgate)
-        bigtgate = embed(n,i, pcT)
-        @test qo_bigtgate ≈ Operator(bigtgate)
+            qo_bigtgate = n==1 ? qo_tgate : embed(qo_basis^n, i, qo_tgate)
+            bigtgate = embed(n,i, pcT)
+            @test qo_bigtgate ≈ Operator(bigtgate)
 
-        for step in 1:10
+            for step in 1:10
             # apply!(ket, qo_bigtgate) TODO implement this API
-            ket = qo_bigtgate*ket
-            apply!(genstab, bigtgate)
-            @test dm(ket) ≈ Operator(genstab)
-            if isapprox(expect(qo_pauli, ket), expect(pauli, genstab); atol=1e-5)
-            else
-                @show step
-                ref[] = (stab,pauli)
-                break
-            end
+                ket = qo_bigtgate*ket
+                apply!(genstab, bigtgate)
+                @test dm(ket) ≈ Operator(genstab)
+                @test isapprox(expect(qo_pauli, ket), expect(pauli, genstab); atol=1e-5)
+           end
         end
     end
-end
+end
\ No newline at end of file