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]]
class QASMParser(object):
"""Class for parsing OpenQASM files into CQC t|ket> Circuits."""
def __init__(self):
self.circuit = Circuit()
self.register_dict = dict()
def parse_qasm(self, qasm):
lines = qasm.splitlines()
rows = []
#first, get rid of comments and whitespace lines
for l in lines:
i = l.find("//")
if i != -1:
s = l[0:i].strip()
else:
s = l.strip()
if s: rows.append(s)
#now, throw away OPENQASM descriptor etc.
if not (rows[0].startswith("OPENQASM 2.0")
and rows[1].startswith('include "qelib1.inc";')):
raise TypeError(
"File must declare OPENQASM version and its includes.")
data = "\n".join(rows[2:])
#now, separate out the custom gates to deal with elsewhere
while True:
i = data.find("gate ")
if i == -1: break
j = data.find("}", i)
if j == -1: raise TypeError("Custom gate definition is invalid.")
self.parse_custom_gate(data[i:j + 1]) #TODO: deal with custom gate
data = data[:i] + data[j + 1:]
#now, parse the regular instructions
instructions = [s.strip() for s in data.split(";") if s.strip()]
for i in instructions:
self.parse_instruction(i)
return self.circuit
def parse_custom_gate(self, data):
raise TypeError("Cannot currently parse custom gates")
def parse_instruction(self, instruction):
if instruction.find("->") != -1:
###handle measure gates
###currently assumes that there is just 1 qb being read to 1 bit
name_and_qbs, bits = instruction.split("->", 1)
if (name_and_qbs.find("measure") == -1):
raise Exception(
"Error in parsing: cannot accept a non-Measure gate writing to classical register"
)
name_and_qbs = name_and_qbs.replace("measure", "")
name_and_qbs = name_and_qbs.replace(" ", "")
name_and_qbs.strip()
qregname, qbindex = name_and_qbs.split("[")
qbindex = int(qbindex[0])
qubit = self.circuit.q_regs[qregname][qbindex]
bits = bits.replace(" ", "")
bitreg, bitindex = bits.split("[")
bitindex = int(bitindex[0])
bit = self.circuit.c_regs[bitreg][bitindex]
self.circuit.add_measure(qubit, bit)
return
if instruction.find("(") != -1:
name, rest = instruction.split(") ", 1)
name = name.replace(" ", "")
else:
name, rest = instruction.split(" ", 1)
args = [s.strip() for s in rest.split(",") if s.strip()]
#deal with qubit register declarations
if name == "qreg" or name == "creg":
regname, size = args[0].split("[", 1)
regname.strip()
size = int(size[:-1])
if name == "qreg":
self.circuit.add_q_register(regname, size)
else:
self.circuit.add_c_register(regname, size)
return
#get qubits to append operation to
qubits = []
for a in args:
if "[" in a:
regname, val = a.split("[", 1)
val = int(val[:-1])
qubits.append(self.circuit.q_regs[regname][val])
else:
raise Exception(
"Unknown error in parsing: Cannot parse argument {}".
format(a))
#if the gate is parameterised, get these parameters
if name.find("(") != -1:
name, params = name.split("(", 1)
if name in PARAM_COMMANDS:
angles = [s.strip() for s in params.split(",") if s.strip()]
halfturn_angles = []
for ang in angles:
ang = ang.replace("pi", str(math.pi))
try:
halfturns = sympify(ang) / math.pi
halfturn_angles.append(halfturns)
except:
raise TypeError("Cannot parse angle: {}".format(ang))
self.circuit.add_gate(PARAM_COMMANDS[name], halfturn_angles,
qubits, [])
else:
raise TypeError("Cannot parse gate of type: {}".format(name))
else:
if name in NOPARAM_COMMANDS:
self.circuit.add_gate(NOPARAM_COMMANDS[name], [], qubits, [])
else:
raise TypeError("Cannot parse gate of type: {}".format(name))
# `measure a[0] -> c[0];`
# `measure a[1] -> c[1];`
# `// Correction of Bob's qubit`
# `if(c==1) z b[0];`
# `if(c==3) z b[0];`
# `if(c==2) x b[0];`
# `if(c==3) x b[0];`
#
# This corresponds to the following `pytket` code:
from pytket import Circuit
qtel = Circuit()
alice = qtel.add_q_register("a", 2)
bob = qtel.add_q_register("b", 1)
data = qtel.add_c_register("d", 2)
# Bell state between Alice and Bob:
qtel.H(alice[1])
qtel.CX(alice[1], bob[0])
# Bell measurement of Alice's qubits:
qtel.CX(alice[0], alice[1])
qtel.H(alice[0])
qtel.Measure(alice[0], data[0])
qtel.Measure(alice[1], data[1])
# Correction of Bob's qubit:
# - can be provided with a `qiskit.providers.Aer.noise.NoiseModel` on instantiation to perform a noisy simulation.
# Useful features:
# - support for fast expectation value calculations according to `QubitPauliString`s or `QubitPauliOperator`s.
from pytket import Circuit
from pytket.extensions.qiskit import AerBackend
from itertools import combinations
from qiskit.providers.aer.noise import NoiseModel, depolarizing_error
# Quantum teleportation circuit:
c = Circuit()
alice = c.add_q_register("a", 2)
bob = c.add_q_register("b", 1)
data = c.add_c_register("d", 2)
final = c.add_c_register("f", 1)
# Start in an interesting state:
c.Rx(0.3, alice[0])
# Set up a Bell state between Alice and Bob:
c.H(alice[1]).CX(alice[1], bob[0])
# Measure Alice's qubits in the Bell basis:
c.CX(alice[0], alice[1]).H(alice[0])
c.Measure(alice[0], data[0])
c.Measure(alice[1], data[1])
