# 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. """Rotation around the X axis.""" from __future__ import annotations import math from typing import Optional, Union import numpy from qiskit.circuit.controlledgate import ControlledGate from qiskit.circuit.gate import Gate from qiskit.circuit.parameterexpression import ParameterValueType from qiskit._accelerate.circuit import StandardGate class RXGate(Gate): r"""Single-qubit rotation about the X axis. Can be applied to a :class:`~qiskit.circuit.QuantumCircuit` with the :meth:`~qiskit.circuit.QuantumCircuit.rx` method. Circuit symbol: .. code-block:: text ┌───────┐ q_0: ┤ Rx(ϴ) ├ └───────┘ Matrix representation: .. math:: \newcommand{\rotationangle}{\frac{\theta}{2}} RX(\theta) = \exp\left(-i \rotationangle X\right) = \begin{pmatrix} \cos\left(\rotationangle\right) & -i\sin\left(\rotationangle\right) \\ -i\sin\left(\rotationangle\right) & \cos\left(\rotationangle\right) \end{pmatrix} """ _standard_gate = StandardGate.RX def __init__(self, theta: ParameterValueType, label: Optional[str] = None): """ Args: theta: The rotation angle. label: An optional label for the gate. """ super().__init__("rx", 1, [theta], label=label) def _define(self): """Default definition""" # pylint: disable=cyclic-import from qiskit.circuit import QuantumCircuit # ┌────────┐ # q: ┤ R(θ,0) ├ # └────────┘ self.definition = QuantumCircuit._from_circuit_data( StandardGate.RX._get_definition(self.params), legacy_qubits=True, name=self.name ) def control( self, num_ctrl_qubits: int = 1, label: str | None = None, ctrl_state: str | int | None = None, annotated: bool | None = None, ): """Return a (multi-)controlled-RX gate. Args: num_ctrl_qubits: number of control qubits. label: An optional label for the gate [Default: ``None``] ctrl_state: control state expressed as integer, string (e.g.``'110'``), or ``None``. If ``None``, use all 1s. annotated: indicates whether the controlled gate should be implemented as an annotated gate. If ``None``, this is set to ``True`` if the gate contains free parameters and more than one control qubit, in which case it cannot yet be synthesized. Otherwise it is set to ``False``. Returns: ControlledGate: controlled version of this gate. """ # deliberately capture annotated in [None, False] here if not annotated and num_ctrl_qubits == 1: gate = CRXGate(self.params[0], label=label, ctrl_state=ctrl_state) gate.base_gate.label = self.label else: gate = super().control( num_ctrl_qubits=num_ctrl_qubits, label=label, ctrl_state=ctrl_state, annotated=annotated, ) return gate def inverse(self, annotated: bool = False): r"""Return inverted RX gate. :math:`RX(\lambda)^{\dagger} = RX(-\lambda)` Args: annotated: when set to ``True``, this is typically used to return an :class:`.AnnotatedOperation` with an inverse modifier set instead of a concrete :class:`.Gate`. However, for this class this argument is ignored as the inverse of this gate is always a :class:`.RXGate` with an inverted parameter value. Returns: RXGate: inverse gate. """ return RXGate(-self.params[0]) def __array__(self, dtype=None, copy=None): """Return a numpy.array for the RX gate.""" if copy is False: raise ValueError("unable to avoid copy while creating an array as requested") cos = math.cos(self.params[0] / 2) sin = math.sin(self.params[0] / 2) return numpy.array([[cos, -1j * sin], [-1j * sin, cos]], dtype=dtype) def power(self, exponent: float, annotated: bool = False): (theta,) = self.params return RXGate(exponent * theta) def __eq__(self, other): if isinstance(other, RXGate): return self._compare_parameters(other) return False class CRXGate(ControlledGate): r"""Controlled-RX gate. Can be applied to a :class:`~qiskit.circuit.QuantumCircuit` with the :meth:`~qiskit.circuit.QuantumCircuit.crx` method. Circuit symbol: .. code-block:: text q_0: ────■──── ┌───┴───┐ q_1: ┤ Rx(ϴ) ├ └───────┘ Matrix representation: .. math:: \newcommand{\rotationangle}{\frac{\theta}{2}} CRX(\theta)\ q_0, q_1 = I \otimes |0\rangle\langle 0| + RX(\theta) \otimes |1\rangle\langle 1| = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & \cos\left(\rotationangle\right) & 0 & -i\sin\left(\rotationangle\right) \\ 0 & 0 & 1 & 0 \\ 0 & -i\sin\left(\rotationangle\right) & 0 & \cos\left(\rotationangle\right) \end{pmatrix} .. note:: In Qiskit's convention, higher qubit indices are more significant (little endian convention). In many textbooks, controlled gates are presented with the assumption of more significant qubits as control, which in our case would be q_1. Thus a textbook matrix for this gate will be: .. code-block:: text ┌───────┐ q_0: ┤ Rx(ϴ) ├ └───┬───┘ q_1: ────■──── .. math:: \newcommand{\rotationangle}{\frac{\theta}{2}} CRX(\theta)\ q_1, q_0 = |0\rangle\langle0| \otimes I + |1\rangle\langle1| \otimes RX(\theta) = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & \cos\left(\rotationangle\right) & -i\sin\left(\rotationangle\right) \\ 0 & 0 & -i\sin\left(\rotationangle\right) & \cos\left(\rotationangle\right) \end{pmatrix} """ _standard_gate = StandardGate.CRX def __init__( self, theta: ParameterValueType, label: Optional[str] = None, ctrl_state: Optional[Union[str, int]] = None, *, _base_label=None, ): """Create new CRX gate.""" super().__init__( "crx", 2, [theta], num_ctrl_qubits=1, label=label, ctrl_state=ctrl_state, base_gate=RXGate(theta, label=_base_label), ) def _define(self): """Default definition""" # pylint: disable=cyclic-import from qiskit.circuit import QuantumCircuit # q_0: ───────■────────────────────■────────────────────── # ┌───┐┌─┴─┐┌──────────────┐┌─┴─┐┌───────────┐┌─────┐ # q_1: ┤ S ├┤ X ├┤ Ry((-0.5)*θ) ├┤ X ├┤ Ry(0.5*θ) ├┤ Sdg ├ # └───┘└───┘└──────────────┘└───┘└───────────┘└─────┘ self.definition = QuantumCircuit._from_circuit_data( StandardGate.CRX._get_definition(self.params), legacy_qubits=True, name=self.name ) def inverse(self, annotated: bool = False): """Return inverse CRX gate (i.e. with the negative rotation angle). Args: annotated: when set to ``True``, this is typically used to return an :class:`.AnnotatedOperation` with an inverse modifier set instead of a concrete :class:`.Gate`. However, for this class this argument is ignored as the inverse of this gate is always a :class:`.CRXGate` with an inverted parameter value. Returns: CRXGate: inverse gate. """ return CRXGate(-self.params[0], ctrl_state=self.ctrl_state) def __array__(self, dtype=None, copy=None): """Return a numpy.array for the CRX gate.""" if copy is False: raise ValueError("unable to avoid copy while creating an array as requested") half_theta = float(self.params[0]) / 2 cos = math.cos(half_theta) isin = 1j * math.sin(half_theta) if self.ctrl_state: return numpy.array( [[1, 0, 0, 0], [0, cos, 0, -isin], [0, 0, 1, 0], [0, -isin, 0, cos]], dtype=dtype ) else: return numpy.array( [[cos, 0, -isin, 0], [0, 1, 0, 0], [-isin, 0, cos, 0], [0, 0, 0, 1]], dtype=dtype ) def __eq__(self, other): if isinstance(other, CRXGate): return self._compare_parameters(other) and self.ctrl_state == other.ctrl_state return False