def test_expected_tape(self):
"""Tests if QuantumPhaseEstimation populates the tape as expected for a fixed example"""
m = qml.RX(0.3, wires=0).matrix
op = qml.QuantumPhaseEstimation(m,
target_wires=[0],
estimation_wires=[1, 2])
tape = op.expand()
with qml.tape.QuantumTape() as tape2:
qml.Hadamard(1),
qml.ControlledQubitUnitary(m @ m, control_wires=[1], wires=[0]),
qml.Hadamard(2),
qml.ControlledQubitUnitary(m, control_wires=[2], wires=[0]),
qml.QFT(wires=[1, 2]).inv()
assert len(tape2.queue) == len(tape.queue)
assert all([
op1.name == op2.name for op1, op2 in zip(tape.queue, tape2.queue)
])
assert all([
op1.wires == op2.wires for op1, op2 in zip(tape.queue, tape2.queue)
])
assert np.allclose(tape.queue[1].matrix, tape2.queue[1].matrix)
assert np.allclose(tape.queue[3].matrix, tape2.queue[3].matrix)
def test_id(self):
"""Tests that the id attribute can be set."""
template = qml.QuantumPhaseEstimation(np.eye(2),
target_wires=[0, 1],
estimation_wires=[2, 3],
id="a")
assert template.id == "a"
def test_same_wires(self):
"""Tests if a QuantumFunctionError is raised if target_wires and estimation_wires contain a
common element"""
with pytest.raises(qml.QuantumFunctionError,
match="The target wires and estimation wires"):
qml.QuantumPhaseEstimation(np.eye(2),
target_wires=[0, 1],
estimation_wires=[1, 2])
def test_phase_estimated_two_qubit(self):
"""Tests that the QPE circuit can correctly estimate the phase of a random two-qubit
unitary."""
unitary = unitary_group.rvs(4, random_state=1967)
eigvals, eigvecs = np.linalg.eig(unitary)
state = eigvecs[:, 0]
eigval = eigvals[0]
phase = np.real_if_close(np.log(eigval) / (2 * np.pi * 1j))
estimates = []
wire_range = range(3, 11)
for wires in wire_range:
dev = qml.device("default.qubit", wires=wires)
target_wires = [0, 1]
estimation_wires = range(2, wires)
with qml.tape.QuantumTape() as tape:
# We want to prepare an eigenstate of RX, in this case |+>
qml.QubitStateVector(state, wires=target_wires)
qml.QuantumPhaseEstimation(unitary,
target_wires=target_wires,
estimation_wires=estimation_wires)
qml.probs(estimation_wires)
tape = tape.expand(depth=2,
stop_at=lambda obj: obj.name in dev.operations)
res = tape.execute(dev).flatten()
if phase < 0:
estimate = np.argmax(res) / 2**(wires - 2) - 1
else:
estimate = np.argmax(res) / 2**(wires - 2)
estimates.append(estimate)
# Check that the error is monotonically decreasing
for i in range(len(estimates) - 1):
err1 = np.abs(estimates[i] - phase)
err2 = np.abs(estimates[i + 1] - phase)
assert err1 >= err2
# This is quite a large error, but we'd need to push the qubit number up more to get it
# lower
assert np.allclose(estimates[-1], phase, rtol=1e-2)
def qpe_circuit():
qml.Hadamard(wires=0)
qml.PauliX(wires=1)
qml.QuantumPhaseEstimation(
qml.PauliX.matrix,
target_wires=[0],
estimation_wires=[1, 2],
)
qml.adjoint(qml.QuantumPhaseEstimation)(
qml.PauliX.matrix,
target_wires=[0],
estimation_wires=[1, 2],
)
qml.Hadamard(wires=0)
qml.PauliX(wires=1)
return qml.state()
def test_expected_circuit(self):
"""Test if the circuit applied when using the QMC template is the same as the expected
circuit for a fixed example"""
p = np.ones(4) / 4
target_wires, estimation_wires = Wires(range(3)), Wires(range(3, 5))
op = QuantumMonteCarlo(p, self.func, target_wires, estimation_wires)
tape = op.expand()
# Do expansion in two steps to avoid also decomposing the first QubitUnitary
queue_before_qpe = tape.operations[:2]
# 2-qubit decomposition has 10 operations, and after is a 3-qubit gate so start at 11
queue_after_qpe = tape.expand().operations[11:]
A = probs_to_unitary(p)
R = func_to_unitary(self.func, 4)
assert len(queue_before_qpe) == 2
assert queue_before_qpe[0].name == "QubitUnitary"
assert queue_before_qpe[1].name == "QubitUnitary"
assert np.allclose(queue_before_qpe[0].matrix, A)
assert np.allclose(queue_before_qpe[1].matrix, R)
assert queue_before_qpe[0].wires == target_wires[:-1]
assert queue_before_qpe[1].wires == target_wires
Q = make_Q(A, R)
with qml.tape.QuantumTape() as qpe_tape:
qml.QuantumPhaseEstimation(Q, target_wires, estimation_wires)
qpe_tape = qpe_tape.expand()
assert len(queue_after_qpe) == len(qpe_tape.operations)
assert all(o1.name == o2.name
for o1, o2 in zip(queue_after_qpe, qpe_tape.operations))
assert all(
np.allclose(o1.matrix, o2.matrix)
for o1, o2 in zip(queue_after_qpe, qpe_tape.operations))
assert all(o1.wires == o2.wires
for o1, o2 in zip(queue_after_qpe, qpe_tape.operations))
def test_phase_estimated(self, phase):
"""Tests that the QPE circuit can correctly estimate the phase of a simple RX rotation."""
estimates = []
wire_range = range(2, 10)
for wires in wire_range:
dev = qml.device("default.qubit", wires=wires)
m = qml.RX(phase, wires=0).matrix
target_wires = [0]
estimation_wires = range(1, wires)
with qml.tape.QuantumTape() as tape:
# We want to prepare an eigenstate of RX, in this case |+>
qml.Hadamard(wires=target_wires)
qml.QuantumPhaseEstimation(m,
target_wires=target_wires,
estimation_wires=estimation_wires)
qml.probs(estimation_wires)
tape = tape.expand(depth=2,
stop_at=lambda obj: obj.name in dev.operations)
res = tape.execute(dev).flatten()
initial_estimate = np.argmax(res) / 2**(wires - 1)
# We need to rescale because RX is exp(- i theta X / 2) and we expect a unitary of the
# form exp(2 pi i theta X)
rescaled_estimate = (1 - initial_estimate) * np.pi * 4
estimates.append(rescaled_estimate)
# Check that the error is monotonically decreasing
for i in range(len(estimates) - 1):
err1 = np.abs(estimates[i] - phase)
err2 = np.abs(estimates[i + 1] - phase)
assert err1 >= err2
# This is quite a large error, but we'd need to push the qubit number up more to get it
# lower
assert np.allclose(estimates[-1], phase, rtol=1e-2)
def test_nested_tapes(self):
with qml.tape.QuantumTape() as tape:
with qml.tape.QuantumTape():
qml.PauliX(0)
qml.CNOT(wires=[0, 2])
with qml.tape.QuantumTape():
qml.QuantumPhaseEstimation(
qml.PauliY.matrix, target_wires=[1], estimation_wires=[2]
)
qml.CNOT(wires=[1, 2])
qml.Hadamard(1)
with qml.tape.QuantumTape():
qml.SWAP(wires=[0, 1])
qml.state()
expected = (
" 0: ──╭QuantumTape:T0─────╭QuantumTape:T1──╭┤ State \n"
+ " 1: ──├QuantumTape:T0──H──╰QuantumTape:T1──├┤ State \n"
+ " 2: ──╰QuantumTape:T0──────────────────────╰┤ State \n"
+ "T0 =\n"
+ " 0: ──X──╭C───────────────────┤ \n"
+ " 2: ─────╰X──╭QuantumTape:T2──┤ \n"
+ " 1: ─────────╰QuantumTape:T2──┤ \n"
+ "T2 =\n"
+ " 1: ──╭QuantumPhaseEstimation(M0)──╭C──┤ \n"
+ " 2: ──╰QuantumPhaseEstimation(M0)──╰X──┤ \n"
+ "M0 =\n"
+ "[[ 0.+0.j -0.-1.j]\n"
+ " [ 0.+1.j 0.+0.j]]\n"
+ "\n"
+ "\n"
+ "T1 =\n"
+ " 0: ──╭SWAP──┤ \n"
+ " 1: ──╰SWAP──┤ \n"
+ "\n"
)
assert tape.draw(wire_order=qml.wires.Wires([0, 1, 2])) == expected