controlled_init.py

# This code is part of Qiskit.
#
# (C) Copyright IBM 2017.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

"""
Initialize qubit registers to desired arbitrary state.
"""

import math
import numpy as np

from qiskit.exceptions import QiskitError
from qiskit.circuit import QuantumCircuit
from qiskit.circuit import QuantumRegister
from qiskit.circuit import Instruction
from qiskit.circuit.exceptions import CircuitError
from qiskit.circuit.library.standard_gates.x import CXGate, XGate
from qiskit.circuit.library.standard_gates.h import HGate
from qiskit.circuit.library.standard_gates.s import SGate, SdgGate
from qiskit.circuit.library.standard_gates.ry import RYGate
from qiskit.circuit.library.standard_gates.rz import RZGate
from qiskit.circuit.reset import Reset
from qiskit.quantum_info import Statevector

_EPS = 1e-10  # global variable used to chop very small numbers to zero


class ctrl_Initialize(Instruction):
	"""Complex amplitude initialization.

	Class that implements the (complex amplitude) initialization of some
	flexible collection of qubit registers.
	Note that Initialize is an Instruction and not a Gate since it contains a reset instruction,
	which is not unitary.
	"""

	def __init__(self, params, ctrl_state, num_qubits=None):
		"""Create new initialize composite.

		params (str, list, int or Statevector):
		  * Statevector: Statevector to initialize to.
		  * list: vector of complex amplitudes to initialize to.
		  * string: labels of basis states of the Pauli eigenstates Z, X, Y. See
			   :meth:`~qiskit.quantum_info.states.statevector.Statevector.from_label`.
			   Notice the order of the labels is reversed with respect to the qubit index to
			   be applied to. Example label '01' initializes the qubit zero to `|1>` and the
			   qubit one to `|0>`.
		  * int: an integer that is used as a bitmap indicating which qubits to initialize
			   to `|1>`. Example: setting params to 5 would initialize qubit 0 and qubit 2
			   to `|1>` and qubit 1 to `|0>`.
		num_qubits (int): This parameter is only used if params is an int. Indicates the total
			number of qubits in the `initialize` call. Example: `initialize` covers 5 qubits
			and params is 3. This allows qubits 0 and 1 to be initialized to `|1>` and the
			remaining 3 qubits to be initialized to `|0>`.
		"""
		if isinstance(params, Statevector):
			params = params.data

		if not isinstance(params, int) and num_qubits is not None:
			raise QiskitError(
				"The num_qubits parameter to Initialize should only be"
				" used when params is an integer"
			)
		self._from_label = False
		self._from_int = False

		if isinstance(params, str):
			self._from_label = True
			self.num_qubits = len(params)
		elif isinstance(params, int):
			self._from_int = True
			if self.num_qubits is None:
				self.num_qubits = int(math.log2(params)) + 1
			params = [params]
		else:
			self.num_qubits = math.log2(len(params))

			# Check if param is a power of 2
			if self.num_qubits == 0 or not self.num_qubits.is_integer():
				raise QiskitError("Desired statevector length not a positive power of 2.")

			# Check if probabilities (amplitudes squared) sum to 1
			if not math.isclose(sum(np.absolute(params) ** 2), 1.0, abs_tol=_EPS):
				raise QiskitError("Sum of amplitudes-squared does not equal one.")

			self.num_qubits = int(self.num_qubits)
		
		self.ctrl_state = ctrl_state

		self.num_ctrl_qubits = len(ctrl_state)

		super().__init__("ctrl_initialize", self.num_qubits, 0, params)


	def _define(self):
		if self._from_label:
			self.definition = self._define_from_label()
		elif self._from_int:
			self.definition = self._define_from_int()
		else:
			self.definition = self._define_synthesis()

	def _define_from_label(self):
		q = QuantumRegister(self.num_qubits, "q")
		initialize_circuit = QuantumCircuit(q, name="init_def")

		for qubit, param in enumerate(reversed(self.params)):
			initialize_circuit.append(Reset(), [q[qubit]])

			if param == "1":
				initialize_circuit.append(XGate(), [q[qubit]])
			elif param == "+":
				initialize_circuit.append(HGate(), [q[qubit]])
			elif param == "-":
				initialize_circuit.append(XGate(), [q[qubit]])
				initialize_circuit.append(HGate(), [q[qubit]])
			elif param == "r":  # |+i>
				initialize_circuit.append(HGate(), [q[qubit]])
				initialize_circuit.append(SGate(), [q[qubit]])
			elif param == "l":  # |-i>
				initialize_circuit.append(HGate(), [q[qubit]])
				initialize_circuit.append(SdgGate(), [q[qubit]])

		return initialize_circuit

	def _define_from_int(self):
		q = QuantumRegister(self.num_qubits, "q")
		initialize_circuit = QuantumCircuit(q, name="init_def")

		# Convert to int since QuantumCircuit converted to complex
		# and make a bit string and reverse it
		intstr = f"{int(np.real(self.params[0])):0{self.num_qubits}b}"[::-1]

		# Raise if number of bits is greater than num_qubits
		if len(intstr) > self.num_qubits:
			raise QiskitError(
				"Initialize integer has %s bits, but this exceeds the"
				" number of qubits in the circuit, %s." % (len(intstr), self.num_qubits)
			)

		for qubit, bit in enumerate(intstr):
			initialize_circuit.append(Reset(), [q[qubit]])
			if bit == "1":
				initialize_circuit.append(XGate(), [q[qubit]])

		return initialize_circuit

	def _define_synthesis(self):
		"""Calculate a subcircuit that implements this initialization

		Implements a recursive initialization algorithm, including optimizations,
		from "Synthesis of Quantum Logic Circuits" Shende, Bullock, Markov
		https://arxiv.org/abs/quant-ph/0406176v5

		Additionally implements some extra optimizations: remove zero rotations and
		double cnots.
		"""
		# call to generate the circuit that takes the desired vector to zero
		disentangling_circuit = self.gates_to_uncompute()

		# invert the circuit to create the desired vector from zero (assuming
		# the qubits are in the zero state)
		initialize_instr = disentangling_circuit.to_instruction().inverse()

		q = QuantumRegister(self.num_qubits, 'q')
		cq = QuantumRegister(self.num_ctrl_qubits, 'cq')
		initialize_circuit = QuantumCircuit(cq,q, name='init_def')
		'''
		for qubit in q:
			initialize_circuit.append(Reset(), [qubit])
		'''


		qregs = [i for i in cq]+[i for i in q]
		initialize_circuit.append(initialize_instr, qregs)

		return initialize_circuit

	def gates_to_uncompute(self):
		"""Call to create a circuit with gates that take the desired vector to zero.

		Returns:
			QuantumCircuit: circuit to take self.params vector to :math:`|{00\\ldots0}\\rangle`
		"""
		q = QuantumRegister(self.num_qubits)
		cq = QuantumRegister(self.num_ctrl_qubits)
		circuit = QuantumCircuit(cq,q, name='disentangler')

		# kick start the peeling loop, and disentangle one-by-one from LSB to MSB
		remaining_param = self.params

		for i in range(self.num_qubits):
			# work out which rotations must be done to disentangle the LSB
			# qubit (we peel away one qubit at a time)
			(remaining_param, thetas, phis) = ctrl_Initialize._rotations_to_disentangle(remaining_param)

			# perform the required rotations to decouple the LSB qubit (so that
			# it can be "factored" out, leaving a shorter amplitude vector to peel away)
			qregs = [q for q in cq] + [qubit for qubit in q[i:self.num_qubits]]
			add_last_cnot = True
			if np.linalg.norm(phis) != 0 and np.linalg.norm(thetas) != 0:
				add_last_cnot = False

			if np.linalg.norm(phis) != 0:
				rz_mult = self._multiplex(RZGate, phis, last_cnot=add_last_cnot)
				#circuit.append(rz_mult.to_instruction(), q[i : self.num_qubits])
				circuit.append(rz_mult.to_instruction(), qregs)

			if np.linalg.norm(thetas) != 0:
				ry_mult = self._multiplex(RYGate, thetas, last_cnot=add_last_cnot)
				#circuit.append(ry_mult.to_instruction().reverse_ops(), q[i : self.num_qubits])
				circuit.append(ry_mult.to_instruction().reverse_ops(), qregs)
		circuit.global_phase -= np.angle(sum(remaining_param))
		return circuit


	@staticmethod
	def _rotations_to_disentangle(local_param):
		"""
		Static internal method to work out Ry and Rz rotation angles used
		to disentangle the LSB qubit.
		These rotations make up the block diagonal matrix U (i.e. multiplexor)
		that disentangles the LSB.

		[[Ry(theta_1).Rz(phi_1)  0   .   .   0],
		 [0         Ry(theta_2).Rz(phi_2) .  0],
									.
										.
		  0         0           Ry(theta_2^n).Rz(phi_2^n)]]
		"""
		remaining_vector = []
		thetas = []
		phis = []

		param_len = len(local_param)

		for i in range(param_len // 2):
			# Ry and Rz rotations to move bloch vector from 0 to "imaginary"
			# qubit
			# (imagine a qubit state signified by the amplitudes at index 2*i
			# and 2*(i+1), corresponding to the select qubits of the
			# multiplexor being in state |i>)
			(remains, add_theta, add_phi) = ctrl_Initialize._bloch_angles(
				local_param[2 * i : 2 * (i + 1)]
			)

			remaining_vector.append(remains)

			# rotations for all imaginary qubits of the full vector
			# to move from where it is to zero, hence the negative sign
			thetas.append(-add_theta)
			phis.append(-add_phi)

		return remaining_vector, thetas, phis

	@staticmethod
	def _bloch_angles(pair_of_complex):
		"""
		Static internal method to work out rotation to create the passed-in
		qubit from the zero vector.
		"""
		[a_complex, b_complex] = pair_of_complex
		# Force a and b to be complex, as otherwise numpy.angle might fail.
		a_complex = complex(a_complex)
		b_complex = complex(b_complex)
		mag_a = np.absolute(a_complex)
		final_r = float(np.sqrt(mag_a ** 2 + np.absolute(b_complex) ** 2))
		if final_r < _EPS:
			theta = 0
			phi = 0
			final_r = 0
			final_t = 0
		else:
			theta = float(2 * np.arccos(mag_a / final_r))
			a_arg = np.angle(a_complex)
			b_arg = np.angle(b_complex)
			final_t = a_arg + b_arg
			phi = b_arg - a_arg

		return final_r * np.exp(1.0j * final_t / 2), theta, phi

	def _multiplex(self, target_gate, list_of_angles, last_cnot=True):
		"""
		Return a recursive implementation of a multiplexor circuit,
		where each instruction itself has a decomposition based on
		smaller multiplexors.

		The LSB is the multiplexor "data" and the other bits are multiplexor "select".

		Args:
			target_gate (Gate): Ry or Rz gate to apply to target qubit, multiplexed
				over all other "select" qubits
			list_of_angles (list[float]): list of rotation angles to apply Ry and Rz
			last_cnot (bool): add the last cnot if last_cnot = True

		Returns:
			DAGCircuit: the circuit implementing the multiplexor's action
		"""
		list_len = len(list_of_angles)
		local_num_qubits = int(math.log2(list_len)) + 1

		cq = QuantumRegister(self.num_ctrl_qubits)
		q = QuantumRegister(local_num_qubits)
		circuit = QuantumCircuit(cq,q, name="multiplex" + local_num_qubits.__str__())

		lsb = q[0]
		msb = q[-1]#q[local_num_qubits - 1]

		# case of no multiplexing: base case for recursion
		if local_num_qubits == 1:
			qregs = [i for i in cq] + [q[0]]
			
			for i,j in zip(range(self.num_ctrl_qubits),reversed(range(self.num_ctrl_qubits))):
				if self.ctrl_state[i] == '0':
					circuit.x(cq[j])
				
			#circuit.append(target_gate(list_of_angles[0]), [q[0]])
			#ctrl_gate = target_gate(list_of_angles[0]).control(num_ctrl_qubits = self.num_ctrl_qubits,ctrl_state=self.ctrl_state)
			ctrl_gate = target_gate(list_of_angles[0]).control(num_ctrl_qubits = self.num_ctrl_qubits)
			circuit.append(ctrl_gate,qregs)

			for i,j in zip(range(self.num_ctrl_qubits),reversed(range(self.num_ctrl_qubits))):
				if self.ctrl_state[i] == '0':
					circuit.x(cq[j])
			return circuit

		# calc angle weights, assuming recursion (that is the lower-level
		# requested angles have been correctly implemented by recursion
		angle_weight = np.kron([[0.5, 0.5], [0.5, -0.5]], np.identity(2 ** (local_num_qubits - 2)))

		# calc the combo angles
		list_of_angles = angle_weight.dot(np.array(list_of_angles)).tolist()

		# recursive step on half the angles fulfilling the above assumption
		multiplex_1 = self._multiplex(target_gate, list_of_angles[0 : (list_len // 2)], False)
		qregs = [i for i in cq] + [i for i in q[0:-1]]
		circuit.append(multiplex_1.to_instruction(), qregs)

		# attach CNOT as follows, thereby flipping the LSB qubit
		circuit.append(CXGate(), [msb, lsb])

		# implement extra efficiency from the paper of cancelling adjacent
		# CNOTs (by leaving out last CNOT and reversing (NOT inverting) the
		# second lower-level multiplex)
		multiplex_2 = self._multiplex(target_gate, list_of_angles[(list_len // 2) :], False)
		qregs = [i for i in cq] + [i for i in q[0:-1]]
		if list_len > 1:
			circuit.append(multiplex_2.to_instruction().reverse_ops(), qregs)
		else:

			circuit.append(multiplex_2.to_instruction(), qregs)

		# attach a final CNOT
		if last_cnot:
			circuit.append(CXGate(), [msb, lsb])

		return circuit

	def broadcast_arguments(self, qargs, cargs):
		flat_qargs = [qarg for sublist in qargs for qarg in sublist]
		if (self.num_qubits + self.num_ctrl_qubits) != len(flat_qargs):
			raise QiskitError("Initialize parameter vector has %d elements, therefore expects %s "
							  "qubits. However, %s were provided." %
							  (2**(self.num_qubits), self.num_qubits, len(flat_qargs)))

		yield flat_qargs, []


	'''
	def validate_parameter(self, parameter):
		"""Initialize instruction parameter can be str, int, float, and complex."""

		# Initialize instruction parameter can be str
		if self._from_label:
			if parameter in ["0", "1", "+", "-", "l", "r"]:
				return parameter
			raise CircuitError(
				"invalid param label {} for instruction {}. Label should be "
				"0, 1, +, -, l, or r ".format(type(parameter), self.name)
			)
		print(parameter)
		print("fck")
		# Initialize instruction parameter can be int, float, and complex.
		if isinstance(parameter, (int, float, complex)):
			return complex(parameter)
		elif isinstance(parameter, np.number):
			return complex(parameter.item())
		else:
			
			raise CircuitError(
				"invalid param type {} for instruction  " "{}".format(type(parameter), self.name)
			)
	'''


def ctrl_initialize(self, statevector=None ,ctrl_state=None, ctrl_qubits=None, qubits=None):
	r"""Initialize qubits in a specific state.

	Qubit initialization is done by first resetting the qubits to :math:`|0\rangle`
	followed by an state preparing unitary. Both these steps are included in the
	`Initialize` instruction.

	Args:
		params (str or list or int):
			* str: labels of basis states of the Pauli eigenstates Z, X, Y. See
				:meth:`~qiskit.quantum_info.states.statevector.Statevector.from_label`.
				Notice the order of the labels is reversed with respect to the qubit index to
				be applied to. Example label '01' initializes the qubit zero to `|1>` and the
				qubit one to `|0>`.
			* list: vector of complex amplitudes to initialize to.
			* int: an integer that is used as a bitmap indicating which qubits to initialize
			   to `|1>`. Example: setting params to 5 would initialize qubit 0 and qubit 2
			   to `|1>` and qubit 1 to `|0>`.
		qubits (QuantumRegister or int):
			* QuantumRegister: A list of qubits to be initialized [Default: None].
			* int: Index of qubit to initialized [Default: None].

	Returns:
		qiskit.circuit.Instruction: a handle to the instruction that was just initialized

	Examples:
		Prepare a qubit in the state :math:`(|0\rangle - |1\rangle) / \sqrt{2}`.

		.. jupyter-execute::

			import numpy as np
			from qiskit import QuantumCircuit

			circuit = QuantumCircuit(1)
			circuit.initialize([1/np.sqrt(2), -1/np.sqrt(2)], 0)
			circuit.draw()

		output:
			 ┌──────────────────────────────┐
		q_0: ┤ initialize(0.70711,-0.70711) ├
			 └──────────────────────────────┘


		Initialize from a string two qubits in the state `|10>`.
		The order of the labels is reversed with respect to qubit index.
		More information about labels for basis states are in
		:meth:`~qiskit.quantum_info.states.statevector.Statevector.from_label`.

		.. jupyter-execute::

			import numpy as np
			from qiskit import QuantumCircuit

			circuit = QuantumCircuit(2)
			circuit.initialize('01', circuit.qubits)
			circuit.draw()

		output:
			 ┌──────────────────┐
		q_0: ┤0                 ├
			 │  initialize(0,1) │
		q_1: ┤1                 ├
			 └──────────────────┘


		Initialize two qubits from an array of complex amplitudes
		.. jupyter-execute::

			import numpy as np
			from qiskit import QuantumCircuit

			circuit = QuantumCircuit(2)
			circuit.initialize([0, 1/np.sqrt(2), -1.j/np.sqrt(2), 0], circuit.qubits)
			circuit.draw()

		output:
			 ┌────────────────────────────────────┐
		q_0: ┤0                                   ├
			 │  initialize(0,0.70711,-0.70711j,0) │
		q_1: ┤1                                   ├
			 └────────────────────────────────────┘
	"""
	if statevector is None:
		raise QiskitError("Null State vector")
	if ctrl_qubits is None:
		raise QiskitError("Control qubits not specified")
	if ctrl_state is None:
		ctrl_state = "1"*len(ctrl_qubits)

	if qubits is None:
		qubits = self.qubits
	else:
		if isinstance(qubits, list):
			qubits = [qubits]
		#qubits = self._bit_argument_conversion(qubits, self.qubits)

	if not isinstance(ctrl_qubits,list):
		ctrl_qubits = [ctrl_qubits]

	num_qubits = None if not isinstance(statevector, int) else len(qubits)
	regs=[i for i in ctrl_qubits]+[i for i in qubits]
	return self.append(ctrl_Initialize(statevector, ctrl_state), regs)


QuantumCircuit.ctrl_initialize = ctrl_initialize