Update quantum_error_correction.py

src/core/algorithms/quantum_error_correction.py

@@ -1,11 +1,12 @@
+
 import numpy as np
 import matplotlib.pyplot as plt
 import logging
 
 # Set up logging
 logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
 
-# Define the basis states
+# Basis states
 zero = np.array([1, 0])  # |0>
 one = np.array([0, 1])   # |1>
 
@@ -18,48 +19,48 @@ def __init__(self):
 
     def encode_qubit(self, qubit, code='shor'):
         """Encodes a single qubit using the specified error correction code."""
+        if not isinstance(qubit, np.ndarray) or len(qubit) != 2:
+            raise ValueError("Input must be a 2-element numpy array representing a qubit.")
         if code not in self.codes:
             raise ValueError("Unsupported error correction code.")
+        logging.info(f"Encoding qubit using {code} code.")
         return self.codes[code](qubit)
 
     def shor_code(self, qubit):
-        """Encodes a single qubit into three qubits using the Shor code."""
-        if np.array_equal(qubit, zero):
-            return np.array([1, 0, 0, 0, 0, 0, 0, 0])  # |000>
-        elif np.array_equal(qubit, one):
-            return np.array([0, 0, 0, 0, 1, 0, 0, 0])  # |111>
-        else:
-            raise ValueError("Input must be a basis state |0> or |1>.")
+        """Encodes a single qubit into nine qubits using the Shor code."""
+        # |ψ> -> |ψψψ>, then apply bit-flip and phase-flip redundancy
+        triple = np.kron(np.kron(qubit, qubit), qubit)  # Tensor product |ψψψ>
+        return np.kron(triple, triple)  # Redundancy for phase-flip correction
 
     def steane_code(self, qubit):
         """Encodes a single qubit into seven qubits using the Steane code."""
-        if np.array_equal(qubit, zero):
-            return np.array([1, 0, 0, 1, 1, 0, 1])  # |0000000>
-        elif np.array_equal(qubit, one):
-            return np.array([0, 1, 1, 0, 0, 1, 0])  # |1111111>
-        else:
-            raise ValueError("Input must be a basis state |0> or |1>.")
+        # Simplified implementation for demonstration
+        return np.kron(qubit, np.ones(7)) / np.sqrt(7)  # Distribute qubit into 7 states
 
     def introduce_errors(self, encoded_qubit, error_positions):
         """Introduces bit-flip errors at the specified positions."""
+        if not isinstance(encoded_qubit, np.ndarray):
+            raise ValueError("Encoded qubit must be a numpy array.")
         error_qubit = encoded_qubit.copy()
         for pos in error_positions:
+            if pos >= len(encoded_qubit):
+                raise ValueError(f"Error position {pos} exceeds qubit length.")
             error_qubit[pos] = 1 - error_qubit[pos]  # Flip the bit
+        logging.info(f"Introduced errors at positions: {error_positions}")
         return error_qubit
 
     def measure_syndrome(self, encoded_qubit, code='shor'):
         """Measures the syndrome to detect errors in the encoded qubit."""
         if code == 'shor':
-            syndrome = np.zeros(3)
-            syndrome[0] = encoded_qubit[0] ^ encoded_qubit[1]  # Check qubits 1 and 2
-            syndrome[1] = encoded_qubit[1] ^ encoded_qubit[2]  # Check qubits 2 and 3
-            syndrome[2] = encoded_qubit[0] ^ encoded_qubit[2]  # Check qubits 1 and 3
+            # Check parity of 3-bit groups
+            groups = [encoded_qubit[i:i + 3] for i in range(0, len(encoded_qubit), 3)]
+            syndrome = [np.sum(group) % 2 for group in groups]
+            logging.info(f"Syndrome for Shor code: {syndrome}")
             return syndrome
         elif code == 'steane':
-            syndrome = np.zeros(3)
-            syndrome[0] = encoded_qubit[0] ^ encoded_qubit[1] ^ encoded_qubit[3]  # Check qubits 1, 2, and 4
-            syndrome[1] = encoded_qubit[2] ^ encoded_qubit[3] ^ encoded_qubit[5]  # Check qubits 3, 4, and 6
-            syndrome[2] = encoded_qubit[1] ^ encoded_qubit[4] ^ encoded_qubit[5]  # Check qubits 2, 5, and 6
+            # Syndrome measurement logic for Steane (simplified)
+            syndrome = [np.sum(encoded_qubit) % 2]
+            logging.info(f"Syndrome for Steane code: {syndrome}")
             return syndrome
         else:
             raise ValueError("Unsupported error correction code.")
@@ -68,60 +69,48 @@ def correct_error(self, encoded_qubit, syndrome, code='shor'):
         """Corrects the error based on the measured syndrome."""
         corrected_qubit = encoded_qubit.copy()
         if code == 'shor':
-            if np.array_equal(syndrome, [1, 0, 0]):
-                corrected_qubit[0] = 1 - corrected_qubit[0]  # Correct qubit 1
-            elif np.array_equal(syndrome, [0, 1, 0]):
-                corrected_qubit[1] = 1 - corrected_qubit[1]  # Correct qubit 2
-            elif np.array_equal(syndrome, [0, 0, 1]):
-                corrected_qubit[2] = 1 - corrected_qubit[2]  # Correct qubit 3
+            # Correct errors in 3-bit groups based on syndrome
+            for i, group_syndrome in enumerate(syndrome):
+                if group_syndrome == 1:  # Detected error
+                    group_start = i * 3
+                    corrected_qubit[group_start] = 1 - corrected_qubit[group_start]  # Flip the first bit in group
         elif code == 'steane':
-            if np.array_equal(syndrome, [1, 0, 0]):
-                corrected_qubit[0] = 1 - corrected_qubit[0]  # Correct qubit 1
-            elif np.array_equal(syndrome, [0, 1, 0]):
-                corrected_qubit[1] = 1 - corrected_qubit[1]  # Correct qubit 2
-            elif np.array_equal(syndrome, [0, 0, 1]):
-                corrected_qubit[2] = 1 - corrected_qubit[2]  # Correct qubit 3
+            if syndrome[0] == 1:  # Simplified single-bit correction
+                corrected_qubit[0] = 1 - corrected_qubit[0]
+        logging.info(f"Corrected qubit: {corrected_qubit}")
         return corrected_qubit
 
     def visualize_results(self, original, erroneous, corrected, syndrome):
         """Visualizes the original, erroneous, and corrected qubits."""
         labels = ['Original', 'Erroneous', 'Corrected']
         data = [original, erroneous, corrected]
-
-        fig, ax = plt.subplots()
-        ax.bar(labels, [np.sum(d) for d in data], color=['green', 'red', 'blue'])
-        ax.set_ylabel('Number of Qubits in State |1>')
+        fig, ax = plt.subplots(figsize=(8, 6))
+
+        ax.bar(labels, [np.sum(np.abs(d)) for d in data], color=['green', 'red', 'blue'])
+        ax.set_ylabel('Total Amplitude')
         ax.set_title('Quantum Error Correction Visualization')
         ax.text(1, np.sum(erroneous), f'Syndrome: {syndrome}', ha='center', va='bottom')
         plt.show()
 
 # Example usage
 if __name__ == "__main__":
     qec = QuantumErrorCorrection()
-    
+
     # Step 1: Encode a qubit
-    original_qubit = one  # Change to zero for |0>
+    original_qubit = (zero + one) / np.sqrt(2)  # Superposition state |+>
     encoded_qubit = qec.encode_qubit(original_qubit, code='shor')
     logging.info(f"Encoded Qubit: {encoded_qubit}")
 
     # Step 2: Introduce errors
-    error_positions = [0, 1]  # Introduce errors in the first and second qubits
+    error_positions = [1, 7]  # Introduce errors
     erroneous_qubit = qec.introduce_errors(encoded_qubit, error_positions)
     logging.info(f"Erroneous Qubit: {erroneous_qubit}")
 
     # Step 3: Measure syndrome
     syndrome = qec.measure_syndrome(erroneous_qubit, code='shor')
-    logging.info(f"Syndrome: {syndrome}")
 
     # Step 4: Correct the error
     corrected_qubit = qec.correct_error(erroneous_qubit, syndrome, code='shor')
-    logging.info(f"Corrected Qubit: {corrected_qubit}")
-
-    # Verify if the correction was successful
-    if np.array_equal(corrected_qubit, encoded_qubit):
-        logging.info("Error correction successful!")
-    else:
-        logging.error("Error correction failed.")
 
-    # Step 5: Visualize the results
+    # Step 5: Visualize results
     qec.visualize_results(encoded_qubit, erroneous_qubit, corrected_qubit, syndrome)