# This code is part of Qiskit. # # (C) Copyright IBM 2017, 2020. # # 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. """Integer Comparator.""" from __future__ import annotations from qiskit.circuit import QuantumRegister, AncillaRegister, Gate from qiskit.circuit.exceptions import CircuitError from qiskit.synthesis.arithmetic.comparators import ( synth_integer_comparator_2s, synth_integer_comparator_greedy, ) from ..blueprintcircuit import BlueprintCircuit class IntegerComparator(BlueprintCircuit): r"""Integer Comparator. Operator compares basis states :math:`|i\rangle_n` against a classically given integer :math:`L` of fixed value and flips a target qubit if :math:`i \geq L` (or :math:`<` depending on the parameter ``geq``): .. math:: |i\rangle_n |0\rangle \mapsto |i\rangle_n |i \geq L\rangle This operation is based on two's complement implementation of binary subtraction but only uses carry bits and no actual result bits. If the most significant carry bit (the results bit) is 1, the :math:`\geq` condition is ``True`` otherwise it is ``False``. """ def __init__( self, num_state_qubits: int | None = None, value: int | None = None, geq: bool = True, name: str = "cmp", ) -> None: """ Args: num_state_qubits: Number of state qubits. If this is set it will determine the number of qubits required for the circuit. value: The fixed value to compare with. geq: If True, evaluate a ``>=`` condition, else ``<``. name: Name of the circuit. """ super().__init__(name=name) self._value = None self._geq = None self._num_state_qubits = None self.value = value self.geq = geq self.num_state_qubits = num_state_qubits @property def value(self) -> int: """The value to compare the qubit register to. Returns: The value against which the value of the qubit register is compared. """ return self._value @value.setter def value(self, value: int) -> None: if value != self._value: self._invalidate() self._value = value @property def geq(self) -> bool: """Return whether the comparator compares greater or less equal. Returns: True, if the comparator compares ``>=``, False if ``<``. """ return self._geq @geq.setter def geq(self, geq: bool) -> None: """Set whether the comparator compares greater or less equal. Args: geq: If True, the comparator compares ``>=``, if False ``<``. """ if geq != self._geq: self._invalidate() self._geq = geq @property def num_state_qubits(self) -> int: """The number of qubits encoding the state for the comparison. Returns: The number of state qubits. """ return self._num_state_qubits @num_state_qubits.setter def num_state_qubits(self, num_state_qubits: int | None) -> None: """Set the number of state qubits. Note that this will change the quantum registers. Args: num_state_qubits: The new number of state qubits. """ if self._num_state_qubits is None or num_state_qubits != self._num_state_qubits: self._invalidate() # reset data self._num_state_qubits = num_state_qubits if num_state_qubits is not None: # set the new qubit registers qr_state = QuantumRegister(num_state_qubits, name="state") q_compare = QuantumRegister(1, name="compare") self.qregs = [qr_state, q_compare] # add ancillas is required num_ancillas = num_state_qubits - 1 if num_ancillas > 0: qr_ancilla = AncillaRegister(num_ancillas) self.add_register(qr_ancilla) def _check_configuration(self, raise_on_failure: bool = True) -> bool: """Check if the current configuration is valid.""" valid = True if self._num_state_qubits is None: valid = False if raise_on_failure: raise AttributeError("Number of state qubits is not set.") if self._value is None: valid = False if raise_on_failure: raise AttributeError("No comparison value set.") required_num_qubits = 2 * self.num_state_qubits if self.num_qubits != required_num_qubits: valid = False if raise_on_failure: raise CircuitError("Number of qubits does not match required number of qubits.") return valid def _build(self) -> None: """If not already built, build the circuit.""" if self._is_built: return super()._build() circuit = synth_integer_comparator_2s(self.num_state_qubits, self.value, self.geq) self.append(circuit.to_gate(), self.qubits) class IntegerComparatorGate(Gate): r"""Perform a :math:`\geq` (or :math:`<`) on a qubit register against a classical integer. This operator compares basis states :math:`|i\rangle_n` against a classically given integer :math:`L` of fixed value and flips a target qubit if :math:`i \geq L` (or :math:`<` depending on the parameter ``geq``): .. math:: |i\rangle_n |0\rangle \mapsto |i\rangle_n |i \geq L\rangle """ def __init__( self, num_state_qubits: int, value: int, geq: bool = True, label: str | None = None ): r""" Args: num_state_qubits: The number of qubits in the registers. value: The value :math:`L` to compre to. geq: If ``True`` compute :math:`i \geq L`, otherwise compute :math:`i < L`. label: An optional label for the gate. """ super().__init__("IntComp", num_state_qubits + 1, [], label=label) self.value = value self.geq = geq def _define(self): self.definition = synth_integer_comparator_greedy(self.num_qubits - 1, self.value, self.geq)