Add Quantum Teleportation to examples. (#1449)

examples/examples_perf_test.py

@@ -8,6 +8,7 @@
 import examples.bcs_mean_field
 import examples.phase_estimator
 import examples.basic_arithmetic
+import examples.quantum_teleportation
 import examples.superdense_coding
 
 
@@ -49,6 +50,8 @@ def test_example_runs_grover_perf(benchmark):
 def test_example_runs_phase_estimator_perf(benchmark):
     benchmark(examples.phase_estimator.main, qnums=(2,), repetitions=2)
 
+def test_example_runs_quantum_teleportation(benchmark):
+    benchmark(examples.quantum_teleportation.main)
 
 def test_example_runs_superdense_coding(benchmark):
     benchmark(examples.superdense_coding.main)

examples/examples_test.py

@@ -9,6 +9,7 @@
 import examples.bcs_mean_field
 import examples.phase_estimator
 import examples.basic_arithmetic
+import examples.quantum_teleportation
 import examples.superdense_coding
 
 
@@ -58,6 +59,8 @@ def test_example_runs_basic_arithmetic():
 def test_example_runs_phase_estimator():
     examples.phase_estimator.main(qnums=(2,), repetitions=2)
 
+def test_example_runs_quantum_teleportation():
+    examples.quantum_teleportation.main()
 
 def test_example_runs_superdense_coding():
     examples.superdense_coding.main()

examples/quantum_teleportation.py

@@ -0,0 +1,94 @@
+"""Quantum Teleportation.
+Quantum Teleportation is a process by which a quantum state can be transmitted
+by sending only two classical bits of information. This is accomplished by
+pre-sharing an entangled state between the sender (Alice) and the receiver
+(Bob). This entangled state allows the receiver (Bob) of the two classical
+bits of information to possess a qubit with the same state as the one held by
+the sender (Alice).
+
+In the following example output, qubit 0 (the Message) is set to a random state
+by applying X and Y gates. By sending two classical bits of information after
+qubit 0 (the Message) and qubit 1 (Alice's entangled qubit) are measured, the
+final state of qubit 2 (Bob's entangled qubit) will be identical to the
+original random state of qubit 0 (the Message). This is only possible given
+that an entangled state is pre-shared between Alice and Bob.
+
+=== REFERENCE ===
+https://en.wikipedia.org/wiki/Quantum_teleportation
+https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.70.1895
+
+=== EXAMPLE OUTPUT ===
+Circuit:
+0: -----------X^0.25---Y^0.125---@---H---M-------@---
+                                 |       |       |
+1: ---H---@----------------------X-------M---@---|---
+          |                                  |   |
+2: -------X----------------------------------X---@---
+
+Bloch Sphere of Message After Random X and Y Gates:
+x:  0.2706 y:  -0.7071 z:  0.6533
+
+Bloch Sphere of Qubit 2 at Final State:
+x:  0.2706 y:  -0.7071 z:  0.6533
+
+"""
+
+import random
+import numpy as np
+import cirq
+
+
+def make_quantum_teleportation_circuit(ranX, ranY):
+    circuit = cirq.Circuit()
+    msg, alice, bob = cirq.LineQubit.range(3)
+
+    # Creates Bell state to be shared between Alice and Bob
+    circuit.append([cirq.H(alice), cirq.CNOT(alice, bob)])
+    # Creates a random state for the Message
+    circuit.append([cirq.X(msg)**ranX, cirq.Y(msg)**ranY])
+    # Bell measurement of the Message and Alice's entangled qubit
+    circuit.append([cirq.CNOT(msg, alice), cirq.H(msg)])
+    circuit.append(cirq.measure(msg, alice))
+    # Uses the two classical bits from the Bell measurement to recover the
+    # original quantum Message on Bob's entangled qubit
+    circuit.append([cirq.CNOT(alice, bob), cirq.CZ(msg, bob)])
+
+    return circuit
+
+
+def main():
+    ranX = random.random()
+    ranY = random.random()
+    circuit = make_quantum_teleportation_circuit(ranX, ranY)
+
+    print("Circuit:")
+    print(circuit)
+
+    sim = cirq.Simulator()
+
+    # Produces the message using random X and Y gates
+    message = sim.simulate(cirq.Circuit.from_ops(
+        [cirq.X(0)**ranX, cirq.Y(0)**ranY]))
+
+    print("\nBloch Sphere of Message After Random X and Y Gates:")
+    # Prints the Bloch Sphere of the Message after the X and Y gates
+    b0X, b0Y, b0Z = cirq.bloch_vector_from_state_vector(
+        message.final_state, 0)
+    print("x: ", np.around(b0X, 4),
+          "y: ", np.around(b0Y, 4),
+          "z: ", np.around(b0Z, 4))
+
+    # Records the final state of the simulation
+    final_results = sim.simulate(circuit)
+
+    print("\nBloch Sphere of Qubit 2 at Final State:")
+    # Prints the Bloch Sphere of Bob's entangled qubit at the final state
+    b2X, b2Y, b2Z = cirq.bloch_vector_from_state_vector(
+        final_results.final_state, 2)
+    print("x: ", np.around(b2X, 4),
+          "y: ", np.around(b2Y, 4),
+          "z: ", np.around(b2Z, 4))
+
+
+if __name__ == '__main__':
+    main()