Fix entropy tests, clean up braiding code

Author: Randl

README.md

@@ -2,4 +2,11 @@
 
 This repo contains reimplementaton of the paper
 "[Realizing topologically ordered states on a quantum processor](https://arxiv.org/abs/2104.01180)" by Satzinger et al.
-in Qiskit.
+in Qiskit.
+
+## GS preparation
+### Matching boundary conditions
+### Mixed boundary conditions
+## Entropy and topological entropy
+
+## Braiding

requirements.txt

@@ -0,0 +1,3 @@
+tqdm
+qiskit
+numpy

tests/test_entropy.py

@@ -6,7 +6,7 @@
 from qiskit import transpile
 from tqdm import tqdm
 
-from topo_entropy import ABC_DIVISION_2x2, ABC_DIVISION_2x3_LEFT, ABC_DIVISION_2x3_RIGHT
+from topo_entropy import ABC_DIVISION_2x2, ABC_DIVISION_2x3_LEFT, ABC_DIVISION_2x3_RIGHT,ABC_DIVISION_3x3
 from topo_entropy import calculate_s_subsystems
 from topo_entropy import get_all_2x2_non_corner, get_all_2x3_non_corner, get_all_3x3_non_corner
 from topo_entropy import get_all_2x3_left_non_corner, get_all_2x3_right_non_corner
@@ -30,15 +30,14 @@ def test_topo_entropy(backend, size, qubits, subsystems, expected_values, type='
         elif type == 'pauli':
             tc.measure_pauli(qubits, gates)
 
-        job = backend.run(transpile(tc.circ, backend), shots=1024)
+        job = backend.run(transpile(tc.circ, backend), shots=15000) # note: number of shots is important
         result = job.result()
         counts = result.get_counts(tc.circ)
         all_counts.append(counts)
     calculated_values = calculate_s_subsystems(all_counts, subsystems)
     print(expected_values, [c / np.log(2) for calc in calculated_values for c in calc])
     for expect, calc in zip(expected_values, calculated_values):
         for ve, vc in zip(expect, calc):
-            continue
             np.testing.assert_allclose(vc / np.log(2), ve, rtol=rtol, atol=0.)
     return
 
@@ -55,7 +54,7 @@ def test_2x2_entropy_pauli(self):
         backend_sim = Aer.get_backend('aer_simulator')
         x, y = 5, 7
         for qubits in get_all_2x2_non_corner((x, y)):
-            test_topo_entropy(backend_sim, (x, y), qubits, ABC_DIVISION_2x2, expected_values, type='pauli', rtol=0.06)
+            test_topo_entropy(backend_sim, (x, y), qubits, ABC_DIVISION_2x2, expected_values, type='pauli', rtol=0.01)
 
     def test_2x2_entropy_haar(self):
         expected_values = [(2., 1., 1.), (3., 3., 2.), (3.,)]
@@ -67,7 +66,7 @@ def test_2x2_entropy_haar(self):
                               rtol=0.05)
 
     def test_2x3_entropy_pauli(self):
-        expected_values = [(2., 2., 2.), (4., 4., 3.), (4.,)]
+        expected_values = [(2., 2., 2.), (4., 3., 4.), (4.,)]
 
         backend_sim = Aer.get_backend('aer_simulator')
         x, y = 5, 7
@@ -84,8 +83,15 @@ def test_2x3_entropy_haar(self):
         for qubits in get_all_2x3_left_non_corner((x, y)):
             test_topo_entropy(backend_sim, (x, y), qubits, ABC_DIVISION_2x3_LEFT, expected_values, type='haar', cnt=100)
         for qubits in get_all_2x3_right_non_corner((x, y)):
-            test_topo_entropy(backend_sim, (x, y), qubits, ABC_DIVISION_2x3_RIGHT, expected_values, type='haar',
-                              cnt=100)
+            test_topo_entropy(backend_sim, (x, y), qubits, ABC_DIVISION_2x3_RIGHT, expected_values, type='haar', cnt=100)
+
+    def test_3x3_entropy_haar(self):
+        expected_values = [(3., 3., 3.), (6., 5., 4.), (5.,)]
+
+        backend_sim = Aer.get_backend('aer_simulator')
+        x, y = 5, 7
+        for qubits in get_all_3x3_non_corner((x, y)):
+            test_topo_entropy(backend_sim, (x, y), qubits, ABC_DIVISION_3x3, expected_values,  type='haar', cnt=1000)
 
 
 if __name__ == '__main__':

topo_braiding.py

@@ -21,17 +21,12 @@ def create_m_particles(tc, string):
 
 
 def apply_cxxxx_on_square(tc, upper_corner):
-    cXXXX = np.kron(np.array([[1, 0], [0, 0]]), np.kron(sx, np.kron(sx, np.kron(sx, sx)))) + \
-            np.kron(np.array([[0, 0], [0, 1]]), np.kron(s0, np.kron(s0, np.kron(s0, s0))))
-
     x, y = upper_corner
     if x % 2 == 0:
         locs = [(x, y), (x + 1, y), (x + 2, y), (x + 1, y + 1)]
     else:
         locs = [(x, y), (x + 1, y - 1), (x + 2, y), (x + 1, y)]
-    #print(locs)
     tc.circ.mct(control_qubits=[tc.ancillas[0]], target_qubit=[tc.regs[l[0]][l[1]] for l in locs])
-    # tc.circ.unitary(cXXXX, [tc.regs[l[0]][l[1]] for l in locs] + [tc.ancillas[0]])
 
 
 def apply_cxxyyzz_on_square(tc, upper_corner):
@@ -54,7 +49,7 @@ def em_braiding_phase(backend, x, y):
     x_string = [(2, 1), (2, 2)]
     create_e_particles(tc, x_string)
 
-    z_string = [(1, 4), (0, 3), (1, 3)]  # , (0,2), (1,2)]
+    z_string = [(1, 4), (0, 3), (1, 3)]
     create_m_particles(tc, z_string)
 
     tc.circ.h(tc.ancillas[0])

topo_entropy.py

@@ -28,12 +28,8 @@ def purity_single_realization(counts):
         for s2 in counts:
             factor = (-2) ** (-hamming_distance(s1, s2))
             p2 = counts[s2] / N
-            pur += factor * p1 * (N * p2 - 1) / (N - 1)  # TODO unbias?
-    #         if q_cnt==4:
-    #             print(s1,s2,factor, p1,p2, factor * p1 * p2, pur, np.log(pur)/np.log(2))
-    # print(len(counts), N, q_cnt, np.log(pur)/np.log(2), -q_cnt-np.log(pur)/np.log(2))
-    # -log(pur) = -qcnt* log(2) - log(pur)
-    return 2 ** q_cnt * pur
+            pur += 2 ** q_cnt * factor * p1 * (N * p2 - 1) / (N - 1)
+    return pur
 
 
 def second_renyi_entropy(all_counts):
@@ -42,7 +38,6 @@ def second_renyi_entropy(all_counts):
 
 
 def get_subsystem_counts(full_counts, sub_idx):
-    print(sub_idx)
     all_subsystem_counts = []
     for counts in full_counts:
         subsystem_counts = defaultdict(lambda: 0)
@@ -60,8 +55,6 @@ def subsystem_sre(full_counts, sub_idx):
 def calculate_s_subsystems(full_counts, subsystems):
     one = [subsystem_sre(full_counts, sub_idx) for sub_idx in subsystems]
     two_subsystems = [subsystems[0] + subsystems[1], subsystems[0] + subsystems[2], subsystems[1] + subsystems[2]]
-    print(subsystems)
-    print(two_subsystems)
     two = [subsystem_sre(full_counts, sub_idx) for sub_idx in two_subsystems]
     three = [second_renyi_entropy(full_counts)]
     return one, two, three