def mcu1(self, theta, control_qubits, target_qubit):
"""
Apply Multiple-Controlled U1 gate
Args:
self (QuantumCircuit): The QuantumCircuit object to apply the mcu1 gate on.
theta (float): angle theta
control_qubits (list of Qubit): The list of control qubits
target_qubit (Qubit): The target qubit
"""
if isinstance(target_qubit, QuantumRegister) and len(target_qubit) == 1:
target_qubit = target_qubit[0]
temp = []
self._check_qargs(control_qubits)
temp += control_qubits
self._check_qargs([target_qubit])
temp.append(target_qubit)
self._check_dups(temp)
n_c = len(control_qubits)
if n_c == 1: # cu1
apply_cu1(self, theta, control_qubits[0], target_qubit)
else:
_apply_mcu1(self, theta, control_qubits, target_qubit)
def _apply_mcu1(circuit, theta, ctls, tgt, global_phase=0):
"""Apply multi-controlled u1 gate from ctls to tgt with angle theta."""
n = len(ctls)
gray_code = list(GrayCode(n).generate_gray())
last_pattern = None
theta_angle = theta * (1 / (2**(n - 1)))
gp_angle = angle(global_phase) * (1 / (2**(n - 1)))
for pattern in gray_code:
if '1' not in pattern:
continue
if last_pattern is None:
last_pattern = pattern
# find left most set bit
lm_pos = list(pattern).index('1')
# find changed bit
comp = [i != j for i, j in zip(pattern, last_pattern)]
if True in comp:
pos = comp.index(True)
else:
pos = None
if pos is not None:
if pos != lm_pos:
circuit.cx(ctls[pos], ctls[lm_pos])
else:
indices = [i for i, x in enumerate(pattern) if x == '1']
for idx in indices[1:]:
circuit.cx(ctls[idx], ctls[lm_pos])
# check parity
if pattern.count('1') % 2 == 0:
# inverse
apply_cu1(circuit, -theta_angle, ctls[lm_pos], tgt)
if global_phase:
circuit.u1(-gp_angle, ctls[lm_pos])
else:
apply_cu1(circuit, theta_angle, ctls[lm_pos], tgt)
if global_phase:
circuit.u1(gp_angle, ctls[lm_pos])
last_pattern = pattern
