Fix classical shadows

rcs/fc_elided_time.py

@@ -16,27 +16,21 @@
 from scipy.stats import binom
 
 
-# sin(math.pi / 4) / 2
-epsilon = 0.353553390593273762
-
-
 def ct_pair_prob(sim, q1, q2):
-    r = [0] * 4
-
-    r[0] = sim.prob(q1)
-    r[1] = sim.prob(q2)
-    r[2] = r[0]
-    r[3] = q2
-    if r[0] < r[1]:
-        r[3] = q1
-        r[2] = r[1]
+    p1 = sim.prob(q1)
+    p2 = sim.prob(q2)
+    p1Hi = p1 > p2
+    pHi = p1 if p1Hi else p2
+    pLo = p2 if p1Hi else p1
+    cState = abs(pHi - 0.5) > abs(pLo - 0.5)
+    t = q1 if p1Hi == cState else q2
 
-    return r
+    return cState, t
 
 
 def cz_shadow(sim, q1, q2):
-    prob1, prob2, prob_max, t = ct_pair_prob(sim, q1, q2)
-    if prob_max > (0.5 + epsilon):
+    cState, t = ct_pair_prob(sim, q1, q2)
+    if cState:
         sim.z(t)
 
 

rcs/rcs_nn_elided.py

@@ -31,23 +31,25 @@ def factor_width(width):
 
 
 def ct_pair_prob(sim, q1, q2):
-    r = [0] * 4
+    p1 = sim.prob(q1)
+    p2 = sim.prob(q2)
+    p1Hi = p1 > p2
+    pHi = p1 if p1Hi else p2
+    pLo = p2 if p1Hi else p1
+    cState = abs(pHi - 0.5) > abs(pLo - 0.5)
+    t = q1 if p1Hi == cState else q2
 
-    r[0] = sim.prob(q1)
-    r[1] = sim.prob(q2)
-    r[2] = r[0]
-    r[3] = q2
-    if r[0] < r[1]:
-        r[3] = q1
-        r[2] = r[1]
-
-    return r
+    return cState, t
 
 
 def cz_shadow(sim, q1, q2, anti = False):
-    prob1, prob2, prob_max, t = ct_pair_prob(sim, q1, q2)
-    if ((not anti) and (prob_max > (0.5 + epsilon))) or (anti and (prob_max < (0.5 - epsilon))):
+    if (anti):
+        sim.x(q1)
+    cState, t = ct_pair_prob(sim, q1, q2)
+    if cState:
         sim.z(t)
+    if (anti):
+        sim.x(q1)
 
 
 def cx_shadow(sim, c, t, anti = False):

rcs/rcs_nn_elided_time.py

@@ -15,10 +15,6 @@
 from pyqrack import QrackSimulator, Pauli
 
 
-# sin(math.pi / 4) / 2
-epsilon = 0.353553390593273762
-
-
 def factor_width(width):
     row_len = math.floor(math.sqrt(width))
     while (((width // row_len) * row_len) != width):
@@ -31,23 +27,25 @@ def factor_width(width):
 
 
 def ct_pair_prob(sim, q1, q2):
-    r = [0] * 4
-
-    r[0] = sim.prob(q1)
-    r[1] = sim.prob(q2)
-    r[2] = r[0]
-    r[3] = q2
-    if r[0] < r[1]:
-        r[3] = q1
-        r[2] = r[1]
+    p1 = sim.prob(q1)
+    p2 = sim.prob(q2)
+    p1Hi = p1 > p2
+    pHi = p1 if p1Hi else p2
+    pLo = p2 if p1Hi else p1
+    cState = abs(pHi - 0.5) > abs(pLo - 0.5)
+    t = q1 if p1Hi == cState else q2
 
-    return r
+    return cState, t
 
 
 def cz_shadow(sim, q1, q2, anti = False):
-    prob1, prob2, prob_max, t = ct_pair_prob(sim, q1, q2)
-    if ((not anti) and (prob_max > (0.5 + epsilon))) or (anti and (prob_max < (0.5 - epsilon))):
+    if (anti):
+        sim.x(q1)
+    cState, t = ct_pair_prob(sim, q1, q2)
+    if cState:
         sim.z(t)
+    if (anti):
+        sim.x(q1)
 
 
 def cx_shadow(sim, c, t, anti = False):

rcs/sycamore_2019_elided.py

@@ -13,10 +13,6 @@
 from pyqrack import QrackSimulator, Pauli
 
 
-# sin(math.pi / 4) / 2
-epsilon = 0.353553390593273762
-
-
 def factor_width(width):
     col_len = math.floor(math.sqrt(width))
     while (((width // col_len) * col_len) != width):
@@ -29,23 +25,25 @@ def factor_width(width):
 
 
 def ct_pair_prob(sim, q1, q2):
-    r = [0] * 4
-
-    r[0] = sim.prob(q1)
-    r[1] = sim.prob(q2)
-    r[2] = r[0]
-    r[3] = q2
-    if r[0] < r[1]:
-        r[3] = q1
-        r[2] = r[1]
+    p1 = sim.prob(q1)
+    p2 = sim.prob(q2)
+    p1Hi = p1 > p2
+    pHi = p1 if p1Hi else p2
+    pLo = p2 if p1Hi else p1
+    cState = abs(pHi - 0.5) > abs(pLo - 0.5)
+    t = q1 if p1Hi == cState else q2
 
-    return r
+    return cState, t
 
 
 def cz_shadow(sim, q1, q2, anti = False):
-    prob1, prob2, prob_max, t = ct_pair_prob(sim, q1, q2)
-    if ((not anti) and (prob_max > (0.5 + epsilon))) or (anti and (prob_max < (0.5 - epsilon))):
+    if (anti):
+        sim.x(q1)
+    cState, t = ct_pair_prob(sim, q1, q2)
+    if cState:
         sim.z(t)
+    if (anti):
+        sim.x(q1)
 
 
 def cx_shadow(sim, c, t, anti = False):
@@ -146,8 +144,8 @@ def bench_qrack(width, depth):
                 if ((b1 < patch_bound) and (b2 >= patch_bound)) or ((b2 < patch_bound) and (b1 >= patch_bound)):
                     # This is our version of ("semi-classical") gate "elision":
 
-                    prob1, prob2, prob_max, t = ct_pair_prob(patch_sim, b1, b2)
-                    if prob_max > (0.5 + epsilon):
+                    cState, t = ct_pair_prob(patch_sim, b1, b2)
+                    if cState:
                         # FSim controlled phase
                         patch_sim.u(t, 0, 0, -math.pi / 6)
 

rcs/sycamore_2019_elided_time.py

@@ -13,10 +13,6 @@
 from pyqrack import QrackSimulator, Pauli
 
 
-# sin(math.pi / 4) / 2
-epsilon = 0.353553390593273762
-
-
 def factor_width(width):
     col_len = math.floor(math.sqrt(width))
     while (((width // col_len) * col_len) != width):
@@ -29,23 +25,25 @@ def factor_width(width):
 
 
 def ct_pair_prob(sim, q1, q2):
-    r = [0] * 4
-
-    r[0] = sim.prob(q1)
-    r[1] = sim.prob(q2)
-    r[2] = r[0]
-    r[3] = q2
-    if r[0] < r[1]:
-        r[3] = q1
-        r[2] = r[1]
+    p1 = sim.prob(q1)
+    p2 = sim.prob(q2)
+    p1Hi = p1 > p2
+    pHi = p1 if p1Hi else p2
+    pLo = p2 if p1Hi else p1
+    cState = abs(pHi - 0.5) > abs(pLo - 0.5)
+    t = q1 if p1Hi == cState else q2
 
-    return r
+    return cState, t
 
 
 def cz_shadow(sim, q1, q2, anti = False):
-    prob1, prob2, prob_max, t = ct_pair_prob(sim, q1, q2)
-    if ((not anti) and (prob_max > (0.5 + epsilon))) or (anti and (prob_max < (0.5 - epsilon))):
+    if (anti):
+        sim.x(q1)
+    cState, t = ct_pair_prob(sim, q1, q2)
+    if cState:
         sim.z(t)
+    if (anti):
+        sim.x(q1)
 
 
 def cx_shadow(sim, c, t, anti = False):
@@ -141,8 +139,8 @@ def bench_qrack(width, depth):
                 if ((b1 < patch_bound) and (b2 >= patch_bound)) or ((b2 < patch_bound) and (b1 >= patch_bound)):
                     # This is our version of ("semi-classical") gate "elision":
 
-                    prob1, prob2, prob_max, t = ct_pair_prob(patch_sim, b1, b2)
-                    if prob_max > (0.5 + epsilon):
+                    cState, t = ct_pair_prob(patch_sim, b1, b2)
+                    if cState:
                         # FSim controlled phase
                         patch_sim.u(t, 0, 0, -math.pi / 6)