feat: Fix compute_chsh

src/qibocal/protocols/two_qubit_interaction/chsh/circuits.py

@@ -7,7 +7,7 @@
 from .utils import READOUT_BASIS
 
 
-def create_bell_circuit(theta=np.pi / 4, bell_state=0):
+def create_bell_circuit(bell_state=0):
     """Creates the circuit to generate the bell states and with a theta-measurement
     bell_state chooses the initial bell state for the test:
     0 -> |00>+|11>
@@ -32,7 +32,7 @@ def create_bell_circuit(theta=np.pi / 4, bell_state=0):
     return c
 
 
-def create_bell_circuit_native(theta=np.pi / 4, bell_state=0):
+def create_bell_circuit_native(bell_state=0):
     """Creates the circuit to generate the bell states and with a theta-measurement
     bell_state chooses the initial bell state for the test:
     0 -> |00>+|11>
@@ -43,30 +43,22 @@ def create_bell_circuit_native(theta=np.pi / 4, bell_state=0):
     """
 
     c = Circuit(2)
-    p = [0, 0]
     c.add(gates.GPI2(0, np.pi / 2))
     c.add(gates.GPI2(1, np.pi / 2))
     c.add(gates.CZ(0, 1))
-    c.add(gates.GPI2(1, np.pi / 2))
+    c.add(gates.GPI2(1, -np.pi / 2))
 
-    c.add(gates.GPI2(0, p[0]))
     if bell_state == 0:
-        p[0] += np.pi
-    elif bell_state == 1:
-        p[0] += 0
+        c.add(gates.Z(0))
     elif bell_state == 2:
-        p[0] += 0
-        c.add(gates.GPI2(0, p[0]))
-        c.add(gates.GPI2(0, p[0]))
+        c.add(gates.GPI(0, 0))
     elif bell_state == 3:
-        p[0] += np.pi
-        c.add(gates.GPI2(0, p[0]))
-        c.add(gates.GPI2(0, p[0]))
+        c.add(gates.Z(0))
+        c.add(gates.GPI(0, 0))
 
-    p[0] += theta
-    c.add(gates.GPI2(0, np.pi))
+    c.add(gates.GPI2(0, 0))
 
-    return c, p
+    return c
 
 
 def create_chsh_circuits(
@@ -82,7 +74,7 @@ def create_chsh_circuits(
     create_bell = create_bell_circuit_native if native else create_bell_circuit
     chsh_circuits = {}
     for basis in readout_basis:
-        c = create_bell(theta, bell_state)
+        c = create_bell(bell_state)
         c.add(gates.RY(0, theta))
         for i, base in enumerate(basis):
             if base == "X":

src/qibocal/protocols/two_qubit_interaction/chsh/protocol.py

@@ -361,7 +361,8 @@ def _fit(data: CHSHData) -> CHSHResults:
             #                         mitigated_freq[format(j, f"0{2}b")].append(float(val))
             #                 mitigated_freq_list.append(mitigated_freq)
             results[pair[0], pair[1], bell_state] = [
-                compute_chsh(bell_pair_data, l) for l in range(len(data.thetas))
+                compute_chsh(bell_pair_data, l, bell_state)
+                for l in range(len(data.thetas))
             ]
 
     #         if data.mitigation_matrix:

src/qibocal/protocols/two_qubit_interaction/chsh/utils.py

@@ -3,7 +3,7 @@
 READOUT_BASIS = ["ZZ", "ZX", "XZ", "XX"]
 
 
-def compute_chsh(frequencies, i):
+def compute_chsh(frequencies, i, bell_state):
     """Computes the chsh inequality out of the frequencies of the 4 circuits executed."""
 
     zz = frequencies["ZZ"]
@@ -17,5 +17,6 @@ def compute_chsh(frequencies, i):
     result_zx = zx["11"][i] + zx["00"][i] - zx["10"][i] - zx["01"][i]
     result_xz = xz["11"][i] + xz["00"][i] - xz["10"][i] - xz["01"][i]
     result_xx = xx["11"][i] + xx["00"][i] - xx["10"][i] - xx["01"][i]
-
-    return (result_zz + result_xz - result_zx + result_xx) / nshots
+    if bell_state % 2 == 0:
+        return (result_zz + result_xz - result_zx + result_xx) / nshots
+    return (result_zz + result_xz + result_zx - result_xx) / nshots