def iterated_entanglement_swap(n_iter):
# Iterate the entanglement swapping protocol n_iter times
it_es = Circuit()
ava = it_es.add_q_register("a", 1)
bella = it_es.add_q_register("b", 2)
charlie = it_es.add_q_register("c", 1)
data = it_es.add_c_register("d", 2)
# Start with an initial Bell state
it_es.H(ava[0])
it_es.CX(ava[0], bella[0])
for i in range(n_iter):
if i % 2 == 0:
# Teleport bella[0] to charlie[0] to give a Bell pair between ava[0] and charlier[0]
tel_to_c = qtel.copy()
tel_to_c.rename_units(
{alice[0]: bella[0], alice[1]: bella[1], bob[0]: charlie[0]}
)
it_es.append(tel_to_c)
it_es.add_gate(OpType.Reset, [bella[0]])
it_es.add_gate(OpType.Reset, [bella[1]])
else:
# Teleport charlie[0] to bella[0] to give a Bell pair between ava[0] and bella[0]
tel_to_b = qtel.copy()
tel_to_b.rename_units(
{alice[0]: charlie[0], alice[1]: bella[1], bob[0]: bella[0]}
)
it_es.append(tel_to_b)
it_es.add_gate(OpType.Reset, [bella[1]])
it_es.add_gate(OpType.Reset, [charlie[0]])
# Return the circuit and the qubits expected to share a Bell pair
if n_iter % 2 == 0:
return it_es, [ava[0], bella[0]]
else:
return it_es, [ava[0], charlie[0]]
es = Circuit()
ava = es.add_q_register("a", 1)
bella = es.add_q_register("b", 2)
charlie = es.add_q_register("c", 1)
data = es.add_c_register("d", 2)
# Bell state between Ava and Bella:
es.H(ava[0])
es.CX(ava[0], bella[0])
# Teleport `bella[0]` to `charlie[0]`:
tel_to_c = qtel.copy()
tel_to_c.rename_units({alice[0]: bella[0], alice[1]: bella[1], bob[0]: charlie[0]})
es.append(tel_to_c)
print(es.get_commands())
# Let's start by running a noiseless simulation of this to verify that what we get looks like a Bell pair.
from pytket.extensions.qiskit import AerBackend
# Connect to a simulator:
backend = AerBackend()
# Make a ZZ measurement of the Bell pair:
bell_test = es.copy()
bell_test.Measure(ava[0], data[0])
