Create superdense_coding.py (#7349)

* Create superdense_coding.py

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quantum/superdense_coding.py

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+"""
+Build the superdense coding protocol. This quantum
+circuit can send two classical bits using one quantum
+bit. This circuit is designed using the Qiskit
+framework. This experiment run in IBM Q simulator
+with 1000 shots.
+.
+References:
+https://qiskit.org/textbook/ch-algorithms/superdense-coding.html
+https://en.wikipedia.org/wiki/Superdense_coding
+"""
+
+import math
+
+import qiskit
+from qiskit import Aer, ClassicalRegister, QuantumCircuit, QuantumRegister, execute
+
+
+def superdense_coding(bit_1: int = 1, bit_2: int = 1) -> qiskit.result.counts.Counts:
+    """
+    The input refer to the classical message
+    that you wants to send. {'00','01','10','11'}
+    result for default values: {11: 1000}
+               ┌───┐          ┌───┐
+    qr_0: ─────┤ X ├──────────┤ X ├─────
+          ┌───┐└─┬─┘┌───┐┌───┐└─┬─┘┌───┐
+    qr_1: ┤ H ├──■──┤ X ├┤ Z ├──■──┤ H ├
+          └───┘     └───┘└───┘     └───┘
+    cr: 2/══════════════════════════════
+    Args:
+        bit_1: bit 1 of classical information to send.
+        bit_2: bit 2 of classical information to send.
+    Returns:
+        qiskit.result.counts.Counts: counts of send state.
+    >>> superdense_coding(0,0)
+    {'00': 1000}
+    >>> superdense_coding(0,1)
+    {'01': 1000}
+    >>> superdense_coding(-1,0)
+    Traceback (most recent call last):
+        ...
+    ValueError: inputs must be positive.
+    >>> superdense_coding(1,'j')
+    Traceback (most recent call last):
+        ...
+    TypeError: inputs must be integers.
+    >>> superdense_coding(1,0.5)
+    Traceback (most recent call last):
+        ...
+    ValueError: inputs must be exact integers.
+    >>> superdense_coding(2,1)
+    Traceback (most recent call last):
+        ...
+    ValueError: inputs must be less or equal to 1.
+    """
+    if (type(bit_1) == str) or (type(bit_2) == str):
+        raise TypeError("inputs must be integers.")
+    if (bit_1 < 0) or (bit_2 < 0):
+        raise ValueError("inputs must be positive.")
+    if (math.floor(bit_1) != bit_1) or (math.floor(bit_2) != bit_2):
+        raise ValueError("inputs must be exact integers.")
+    if (bit_1 > 1) or (bit_2 > 1):
+        raise ValueError("inputs must be less or equal to 1.")
+
+    # build registers
+    qr = QuantumRegister(2, "qr")
+    cr = ClassicalRegister(2, "cr")
+
+    quantum_circuit = QuantumCircuit(qr, cr)
+
+    # entanglement the qubits
+    quantum_circuit.h(1)
+    quantum_circuit.cx(1, 0)
+
+    # send the information
+    c_information = str(bit_1) + str(bit_2)
+
+    if c_information == "11":
+        quantum_circuit.x(1)
+        quantum_circuit.z(1)
+    elif c_information == "10":
+        quantum_circuit.z(1)
+    elif c_information == "01":
+        quantum_circuit.x(1)
+    else:
+        quantum_circuit.i(1)
+
+    # unentangled the circuit
+    quantum_circuit.cx(1, 0)
+    quantum_circuit.h(1)
+
+    # measure the circuit
+    quantum_circuit.measure(qr, cr)
+
+    backend = Aer.get_backend("qasm_simulator")
+    job = execute(quantum_circuit, backend, shots=1000)
+
+    return job.result().get_counts(quantum_circuit)
+
+
+if __name__ == "__main__":
+    print(f"Counts for classical state send: {superdense_coding(1,1)}")