Source code for qiskit.circuit.library.standard_gates.x

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# (C) Copyright IBM 2017.
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"""X, CX, CCX and multi-controlled X gates."""

from math import ceil
import numpy
from qiskit.circuit.controlledgate import ControlledGate
from qiskit.circuit.gate import Gate
from qiskit.circuit.quantumregister import QuantumRegister
from qiskit.circuit._utils import _compute_control_matrix, _ctrl_state_to_int
from qiskit.qasm import pi
from .h import HGate
from .t import TGate, TdgGate
from .u1 import U1Gate
from .u2 import U2Gate


[docs]class XGate(Gate): r"""The single-qubit Pauli-X gate (:math:`\sigma_x`). **Matrix Representation:** .. math:: X = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} **Circuit symbol:** .. parsed-literal:: ┌───┐ q_0: ┤ X ├ └───┘ Equivalent to a :math:`\pi` radian rotation about the X axis. .. note:: A global phase difference exists between the definitions of :math:`RX(\pi)` and :math:`X`. .. math:: RX(\pi) = \begin{pmatrix} 0 & -i \\ -i & 0 \end{pmatrix} = -i X The gate is equivalent to a classical bit flip. .. math:: |0\rangle \rightarrow |1\rangle \\ |1\rangle \rightarrow |0\rangle """ def __init__(self, label=None): """Create new X gate.""" super().__init__('x', 1, [], label=label) def _define(self): """ gate x a { u3(pi,0,pi) a; } """ # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit from .u3 import U3Gate q = QuantumRegister(1, 'q') qc = QuantumCircuit(q, name=self.name) rules = [ (U3Gate(pi, 0, pi), [q[0]], []) ] for instr, qargs, cargs in rules: qc._append(instr, qargs, cargs) self.definition = qc
[docs] def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None): """Return a (mutli-)controlled-X gate. One control returns a CX gate. Two controls returns a CCX gate. Args: num_ctrl_qubits (int): number of control qubits. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. Returns: ControlledGate: controlled version of this gate. """ gate = MCXGate(num_ctrl_qubits=num_ctrl_qubits, label=label, ctrl_state=ctrl_state) gate.base_gate.label = self.label return gate
[docs] def inverse(self): r"""Return inverted X gate (itself).""" return XGate() # self-inverse
[docs] def to_matrix(self): """Return a numpy.array for the X gate.""" return numpy.array([[0, 1], [1, 0]], dtype=complex)
[docs]class CXGate(ControlledGate): r"""Controlled-X gate. **Circuit symbol:** .. parsed-literal:: q_0: ──■── ┌─┴─┐ q_1: ┤ X ├ └───┘ **Matrix representation:** .. math:: CX\ q_0, q_1 = I \otimes |0\rangle\langle0| + X \otimes |1\rangle\langle1| = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \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: .. parsed-literal:: ┌───┐ q_0: ┤ X ├ └─┬─┘ q_1: ──■── .. math:: CX\ q_1, q_0 = |0 \rangle\langle 0| \otimes I + |1 \rangle\langle 1| \otimes X = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \end{pmatrix} In the computational basis, this gate flips the target qubit if the control qubit is in the :math:`|1\rangle` state. In this sense it is similar to a classical XOR gate. .. math:: `|a, b\rangle \rightarrow |a, a \oplus b\rangle` """ def __init__(self, label=None, ctrl_state=None): """Create new CX gate.""" super().__init__('cx', 2, [], num_ctrl_qubits=1, label=label, ctrl_state=ctrl_state, base_gate=XGate())
[docs] def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None): """Return a controlled-X gate with more control lines. Args: num_ctrl_qubits (int): number of control qubits. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. Returns: ControlledGate: controlled version of this gate. """ ctrl_state = _ctrl_state_to_int(ctrl_state, num_ctrl_qubits) new_ctrl_state = (self.ctrl_state << num_ctrl_qubits) | ctrl_state gate = MCXGate(num_ctrl_qubits=num_ctrl_qubits + 1, label=label, ctrl_state=new_ctrl_state) gate.base_gate.label = self.label return gate
[docs] def inverse(self): """Return inverted CX gate (itself).""" return CXGate(ctrl_state=self.ctrl_state) # self-inverse
[docs] def to_matrix(self): """Return a numpy.array for the CX gate.""" if self.ctrl_state: return numpy.array([[1, 0, 0, 0], [0, 0, 0, 1], [0, 0, 1, 0], [0, 1, 0, 0]], dtype=complex) else: return numpy.array([[0, 0, 1, 0], [0, 1, 0, 0], [1, 0, 0, 0], [0, 0, 0, 1]], dtype=complex)
[docs]class CCXGate(ControlledGate): r"""CCX gate, also known as Toffoli gate. **Circuit symbol:** .. parsed-literal:: q_0: ──■── q_1: ──■── ┌─┴─┐ q_2: ┤ X ├ └───┘ **Matrix representation:** .. math:: CCX q_0, q_1, q_2 = |0 \rangle \langle 0| \otimes I \otimes I + |1 \rangle \langle 1| \otimes CX = \begin{pmatrix} 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1\\ 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0\\ 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0\\ 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \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_2 and q_1. Thus a textbook matrix for this gate will be: .. parsed-literal:: ┌───┐ q_0: ┤ X ├ └─┬─┘ q_1: ──■── q_2: ──■── .. math:: CCX\ q_2, q_1, q_0 = I \otimes I \otimes |0 \rangle \langle 0| + CX \otimes |1 \rangle \langle 1| = \begin{pmatrix} 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0\\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1\\ 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 \end{pmatrix} """ def __init__(self, label=None, ctrl_state=None): """Create new CCX gate.""" super().__init__('ccx', 3, [], num_ctrl_qubits=2, label=label, ctrl_state=ctrl_state, base_gate=XGate()) def _define(self): """ gate ccx a,b,c { h c; cx b,c; tdg c; cx a,c; t c; cx b,c; tdg c; cx a,c; t b; t c; h c; cx a,b; t a; tdg b; cx a,b;} """ # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit q = QuantumRegister(3, 'q') qc = QuantumCircuit(q, name=self.name) rules = [ (HGate(), [q[2]], []), (CXGate(), [q[1], q[2]], []), (TdgGate(), [q[2]], []), (CXGate(), [q[0], q[2]], []), (TGate(), [q[2]], []), (CXGate(), [q[1], q[2]], []), (TdgGate(), [q[2]], []), (CXGate(), [q[0], q[2]], []), (TGate(), [q[1]], []), (TGate(), [q[2]], []), (HGate(), [q[2]], []), (CXGate(), [q[0], q[1]], []), (TGate(), [q[0]], []), (TdgGate(), [q[1]], []), (CXGate(), [q[0], q[1]], []) ] for instr, qargs, cargs in rules: qc._append(instr, qargs, cargs) self.definition = qc
[docs] def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None): """Controlled version of this gate. Args: num_ctrl_qubits (int): number of control qubits. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. Returns: ControlledGate: controlled version of this gate. """ ctrl_state = _ctrl_state_to_int(ctrl_state, num_ctrl_qubits) new_ctrl_state = (self.ctrl_state << num_ctrl_qubits) | ctrl_state gate = MCXGate(num_ctrl_qubits=num_ctrl_qubits + 2, label=label, ctrl_state=new_ctrl_state) gate.base_gate.label = self.label return gate
[docs] def inverse(self): """Return an inverted CCX gate (also a CCX).""" return CCXGate(ctrl_state=self.ctrl_state) # self-inverse
[docs] def to_matrix(self): """Return a numpy.array for the CCX gate.""" return _compute_control_matrix(self.base_gate.to_matrix(), self.num_ctrl_qubits, ctrl_state=self.ctrl_state)
[docs]class RCCXGate(Gate): """The simplified Toffoli gate, also referred to as Margolus gate. The simplified Toffoli gate implements the Toffoli gate up to relative phases. This implementation requires three CX gates which is the minimal amount possible, as shown in https://arxiv.org/abs/quant-ph/0312225. Note, that the simplified Toffoli is not equivalent to the Toffoli. But can be used in places where the Toffoli gate is uncomputed again. This concrete implementation is from https://arxiv.org/abs/1508.03273, the dashed box of Fig. 3. """ def __init__(self, label=None): """Create a new simplified CCX gate.""" super().__init__('rccx', 3, [], label=label) def _define(self): """ gate rccx a,b,c { u2(0,pi) c; u1(pi/4) c; cx b, c; u1(-pi/4) c; cx a, c; u1(pi/4) c; cx b, c; u1(-pi/4) c; u2(0,pi) c; } """ # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit q = QuantumRegister(3, 'q') qc = QuantumCircuit(q, name=self.name) rules = [ (U2Gate(0, pi), [q[2]], []), # H gate (U1Gate(pi / 4), [q[2]], []), # T gate (CXGate(), [q[1], q[2]], []), (U1Gate(-pi / 4), [q[2]], []), # inverse T gate (CXGate(), [q[0], q[2]], []), (U1Gate(pi / 4), [q[2]], []), (CXGate(), [q[1], q[2]], []), (U1Gate(-pi / 4), [q[2]], []), # inverse T gate (U2Gate(0, pi), [q[2]], []), # H gate ] for instr, qargs, cargs in rules: qc._append(instr, qargs, cargs) self.definition = qc
[docs] def to_matrix(self): """Return a numpy.array for the simplified CCX gate.""" return numpy.array([[1, 0, 0, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0, 0, 0], [0, 0, 1, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, -1j], [0, 0, 0, 0, 1, 0, 0, 0], [0, 0, 0, 0, 0, -1, 0, 0], [0, 0, 0, 0, 0, 0, 1, 0], [0, 0, 0, 1j, 0, 0, 0, 0]], dtype=complex)
[docs]class C3XGate(ControlledGate): """The 3-qubit controlled X gate. This implementation is based on Page 17 of [1]. References: [1] Barenco et al., 1995. https://arxiv.org/pdf/quant-ph/9503016.pdf """ def __init__(self, angle=numpy.pi/4, label=None, ctrl_state=None): """Create a new 3-qubit controlled X gate. Args: angle (float): The angle used in the controlled-U1 gates. An angle of π/4 yields the 3-qubit controlled X gate, an angle of π/8 the 3-qubit controlled sqrt(X) gate. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. """ super().__init__('mcx', 4, [], num_ctrl_qubits=3, label=label, ctrl_state=ctrl_state, base_gate=XGate()) self._angle = angle def _define(self): """ gate c3x a,b,c,d { h d; cu1(-pi/4) a,d; h d; cx a,b; h d; cu1(pi/4) b,d; h d; cx a,b; h d; cu1(-pi/4) b,d; h d; cx b,c; h d; cu1(pi/4) c,d; h d; cx a,c; h d; cu1(-pi/4) c,d; h d; cx b,c; h d; cu1(pi/4) c,d; h d; cx a,c; h d; cu1(-pi/4) c,d; h d; } """ # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit from .u1 import CU1Gate q = QuantumRegister(4, name='q') rules = [ (HGate(), [q[3]], []), (CU1Gate(-self._angle), [q[0], q[3]], []), (HGate(), [q[3]], []), (CXGate(), [q[0], q[1]], []), (HGate(), [q[3]], []), (CU1Gate(self._angle), [q[1], q[3]], []), (HGate(), [q[3]], []), (CXGate(), [q[0], q[1]], []), (HGate(), [q[3]], []), (CU1Gate(-self._angle), [q[1], q[3]], []), (HGate(), [q[3]], []), (CXGate(), [q[1], q[2]], []), (HGate(), [q[3]], []), (CU1Gate(self._angle), [q[2], q[3]], []), (HGate(), [q[3]], []), (CXGate(), [q[0], q[2]], []), (HGate(), [q[3]], []), (CU1Gate(-self._angle), [q[2], q[3]], []), (HGate(), [q[3]], []), (CXGate(), [q[1], q[2]], []), (HGate(), [q[3]], []), (CU1Gate(self._angle), [q[2], q[3]], []), (HGate(), [q[3]], []), (CXGate(), [q[0], q[2]], []), (HGate(), [q[3]], []), (CU1Gate(-self._angle), [q[2], q[3]], []), (HGate(), [q[3]], []) ] qc = QuantumCircuit(q) for instr, qargs, cargs in rules: qc._append(instr, qargs, cargs) self.definition = qc
[docs] def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None): """Controlled version of this gate. Args: num_ctrl_qubits (int): number of control qubits. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. Returns: ControlledGate: controlled version of this gate. """ ctrl_state = _ctrl_state_to_int(ctrl_state, num_ctrl_qubits) new_ctrl_state = (self.ctrl_state << num_ctrl_qubits) | ctrl_state gate = MCXGate(num_ctrl_qubits=num_ctrl_qubits + 3, label=label, ctrl_state=new_ctrl_state) gate.base_gate.label = self.label return gate
[docs] def inverse(self): """Invert this gate. The C3X is its own inverse.""" return C3XGate(angle=-self._angle, ctrl_state=self.ctrl_state)
# This matrix is only correct if the angle is pi/4 # def to_matrix(self): # """Return a numpy.array for the C3X gate.""" # return numpy.array([[1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1], # [0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0], # [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0], # [0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0]], dtype=complex)
[docs]class RC3XGate(Gate): """The simplified 3-controlled Toffoli gate. The simplified Toffoli gate implements the Toffoli gate up to relative phases. Note, that the simplified Toffoli is not equivalent to the Toffoli. But can be used in places where the Toffoli gate is uncomputed again. This concrete implementation is from https://arxiv.org/abs/1508.03273, the complete circuit of Fig. 4. """ def __init__(self, label=None): """Create a new RC3X gate.""" super().__init__('rcccx', 4, [], label=label) def _define(self): """ gate rc3x a,b,c,d { u2(0,pi) d; u1(pi/4) d; cx c,d; u1(-pi/4) d; u2(0,pi) d; cx a,d; u1(pi/4) d; cx b,d; u1(-pi/4) d; cx a,d; u1(pi/4) d; cx b,d; u1(-pi/4) d; u2(0,pi) d; u1(pi/4) d; cx c,d; u1(-pi/4) d; u2(0,pi) d; } """ # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit q = QuantumRegister(4, 'q') qc = QuantumCircuit(q, name=self.name) rules = [ (U2Gate(0, pi), [q[3]], []), # H gate (U1Gate(pi / 4), [q[3]], []), # T gate (CXGate(), [q[2], q[3]], []), (U1Gate(-pi / 4), [q[3]], []), # inverse T gate (U2Gate(0, pi), [q[3]], []), (CXGate(), [q[0], q[3]], []), (U1Gate(pi / 4), [q[3]], []), (CXGate(), [q[1], q[3]], []), (U1Gate(-pi / 4), [q[3]], []), (CXGate(), [q[0], q[3]], []), (U1Gate(pi / 4), [q[3]], []), (CXGate(), [q[1], q[3]], []), (U1Gate(-pi / 4), [q[3]], []), (U2Gate(0, pi), [q[3]], []), (U1Gate(pi / 4), [q[3]], []), (CXGate(), [q[2], q[3]], []), (U1Gate(-pi / 4), [q[3]], []), (U2Gate(0, pi), [q[3]], []), ] for instr, qargs, cargs in rules: qc._append(instr, qargs, cargs) self.definition = qc
[docs] def to_matrix(self): """Return a numpy.array for the RC3X gate.""" return numpy.array([[1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 1j, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1j, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0], [0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0]], dtype=complex)
[docs]class C4XGate(ControlledGate): """The 4-qubit controlled X gate. This implementation is based on Page 21, Lemma 7.5, of [1]. References: [1] Barenco et al., 1995. https://arxiv.org/pdf/quant-ph/9503016.pdf """ def __init__(self, label=None, ctrl_state=None): """Create a new 4-qubit controlled X gate.""" super().__init__('mcx', 5, [], num_ctrl_qubits=4, label=label, ctrl_state=ctrl_state, base_gate=XGate()) # seems like open controls not hapening? def _define(self): """ gate c3sqrtx a,b,c,d { h d; cu1(-pi/8) a,d; h d; cx a,b; h d; cu1(pi/8) b,d; h d; cx a,b; h d; cu1(-pi/8) b,d; h d; cx b,c; h d; cu1(pi/8) c,d; h d; cx a,c; h d; cu1(-pi/8) c,d; h d; cx b,c; h d; cu1(pi/8) c,d; h d; cx a,c; h d; cu1(-pi/8) c,d; h d; } gate c4x a,b,c,d,e { h e; cu1(-pi/2) d,e; h e; c3x a,b,c,d; h d; cu1(pi/4) d,e; h d; c3x a,b,c,d; c3sqrtx a,b,c,e; } """ # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit from .u1 import CU1Gate q = QuantumRegister(5, name='q') qc = QuantumCircuit(q, name=self.name) rules = [ (HGate(), [q[4]], []), (CU1Gate(-numpy.pi / 2), [q[3], q[4]], []), (HGate(), [q[4]], []), (C3XGate(), [q[0], q[1], q[2], q[3]], []), (HGate(), [q[4]], []), (CU1Gate(numpy.pi / 2), [q[3], q[4]], []), (HGate(), [q[4]], []), (C3XGate(), [q[0], q[1], q[2], q[3]], []), (C3XGate(numpy.pi / 8), [q[0], q[1], q[2], q[4]], []), ] for instr, qargs, cargs in rules: qc._append(instr, qargs, cargs) self.definition = qc
[docs] def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None): """Controlled version of this gate. Args: num_ctrl_qubits (int): number of control qubits. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. Returns: ControlledGate: controlled version of this gate. """ ctrl_state = _ctrl_state_to_int(ctrl_state, num_ctrl_qubits) new_ctrl_state = (self.ctrl_state << num_ctrl_qubits) | ctrl_state gate = MCXGate(num_ctrl_qubits=num_ctrl_qubits + 4, label=label, ctrl_state=new_ctrl_state) gate.base_gate.label = self.label return gate
[docs] def inverse(self): """Invert this gate. The C4X is its own inverse.""" return C4XGate(ctrl_state=self.ctrl_state)
[docs] def to_matrix(self): """Return a numpy.array for the C4X gate.""" return _compute_control_matrix(self.base_gate.to_matrix(), self.num_ctrl_qubits, ctrl_state=self.ctrl_state)
[docs]class MCXGate(ControlledGate): """The general, multi-controlled X gate.""" def __new__(cls, num_ctrl_qubits=None, label=None, ctrl_state=None): """Create a new MCX instance. Depending on the number of controls, this creates an explicit CX, CCX, C3X or C4X instance or a generic MCX gate. """ # these gates will always be implemented for all modes of the MCX if the number of control # qubits matches this explicit = { 1: CXGate, 2: CCXGate } if num_ctrl_qubits in explicit.keys(): gate_class = explicit[num_ctrl_qubits] gate = gate_class.__new__(gate_class, label=label, ctrl_state=ctrl_state) # if __new__ does not return the same type as cls, init is not called gate.__init__(label=label, ctrl_state=ctrl_state) return gate return super().__new__(cls) def __init__(self, num_ctrl_qubits, label=None, ctrl_state=None, _name='mcx'): """Create new MCX gate.""" num_ancilla_qubits = self.__class__.get_num_ancilla_qubits(num_ctrl_qubits) super().__init__(_name, num_ctrl_qubits + 1 + num_ancilla_qubits, [], num_ctrl_qubits=num_ctrl_qubits, label=label, ctrl_state=ctrl_state, base_gate=XGate())
[docs] def inverse(self): """Invert this gate. The MCX is its own inverse.""" return MCXGate(num_ctrl_qubits=self.num_ctrl_qubits, ctrl_state=self.ctrl_state)
[docs] @staticmethod def get_num_ancilla_qubits(num_ctrl_qubits, mode='noancilla'): """Get the number of required ancilla qubits without instantiating the class. This staticmethod might be necessary to check the number of ancillas before creating the gate, or to use the number of ancillas in the initialization. """ if mode == 'noancilla': return 0 if mode in ['recursion', 'advanced']: return int(num_ctrl_qubits > 4) if mode[:7] == 'v-chain' or mode[:5] == 'basic': return max(0, num_ctrl_qubits - 2) raise AttributeError('Unsupported mode ({}) specified!'.format(mode))
def _define(self): """The standard definition used the Gray code implementation.""" # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit q = QuantumRegister(self.num_qubits, name='q') qc = QuantumCircuit(q) qc._append(MCXGrayCode(self.num_ctrl_qubits), q[:], []) self.definition = qc @property def num_ancilla_qubits(self): """The number of ancilla qubits.""" return self.__class__.get_num_ancilla_qubits(self.num_ctrl_qubits)
[docs] def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None): """Return a multi-controlled-X gate with more control lines. Args: num_ctrl_qubits (int): number of control qubits. label (str or None): An optional label for the gate [Default: None] ctrl_state (int or str or None): control state expressed as integer, string (e.g. '110'), or None. If None, use all 1s. Returns: ControlledGate: controlled version of this gate. """ if ctrl_state is None: # use __class__ so this works for derived classes gate = self.__class__(self.num_ctrl_qubits + num_ctrl_qubits, label=label, ctrl_state=ctrl_state) gate.base_gate.label = self.label return gate return super().control(num_ctrl_qubits, label=label, ctrl_state=ctrl_state)
[docs]class MCXGrayCode(MCXGate): r"""Implement the multi-controlled X gate using the Gray code. This delegates the implementation to the MCU1 gate, since :math:`X = H \cdot U1(\pi) \cdot H`. """ def __init__(self, num_ctrl_qubits, label=None, ctrl_state=None): super().__init__(num_ctrl_qubits, label=label, ctrl_state=ctrl_state, _name='mcx_gray')
[docs] def inverse(self): """Invert this gate. The MCX is its own inverse.""" return MCXGrayCode(num_ctrl_qubits=self.num_ctrl_qubits, ctrl_state=self.ctrl_state)
def _define(self): """Define the MCX gate using the Gray code.""" # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit from .u1 import MCU1Gate q = QuantumRegister(self.num_qubits, name='q') qc = QuantumCircuit(q, name=self.name) qc._append(HGate(), [q[-1]], []) qc._append(MCU1Gate(numpy.pi, num_ctrl_qubits=self.num_ctrl_qubits), q[:], []) qc._append(HGate(), [q[-1]], []) self.definition = qc
[docs]class MCXRecursive(MCXGate): """Implement the multi-controlled X gate using recursion. Using a single ancilla qubit, the multi-controlled X gate is recursively split onto four sub-registers. This is done until we reach the 3- or 4-controlled X gate since for these we have a concrete implementation that do not require ancillas. """ def __init__(self, num_ctrl_qubits, label=None, ctrl_state=None): super().__init__(num_ctrl_qubits, label=label, ctrl_state=ctrl_state, _name='mcx_recursive')
[docs] @staticmethod def get_num_ancilla_qubits(num_ctrl_qubits, mode='recursion'): """Get the number of required ancilla qubits.""" return MCXGate.get_num_ancilla_qubits(num_ctrl_qubits, mode)
[docs] def inverse(self): """Invert this gate. The MCX is its own inverse.""" return MCXRecursive(num_ctrl_qubits=self.num_ctrl_qubits, ctrl_state=self.ctrl_state)
def _define(self): """Define the MCX gate using recursion.""" # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit q = QuantumRegister(self.num_qubits, name='q') qc = QuantumCircuit(q, name=self.name) if self.num_qubits == 4: qc._append(C3XGate(), q[:], []) self.definition = qc elif self.num_qubits == 5: qc._append(C4XGate(), q[:], []) self.definition = qc else: for instr, qargs, cargs in self._recurse(q[:-1], q_ancilla=q[-1]): qc._append(instr, qargs, cargs) self.definition = qc def _recurse(self, q, q_ancilla=None): # recursion stop if len(q) == 4: return [(C3XGate(), q[:], [])] if len(q) == 5: return [(C4XGate(), q[:], [])] if len(q) < 4: raise AttributeError('Something went wrong in the recursion, have less than 4 qubits.') # recurse num_ctrl_qubits = len(q) - 1 middle = ceil(num_ctrl_qubits / 2) first_half = [*q[:middle], q_ancilla] second_half = [*q[middle:num_ctrl_qubits], q_ancilla, q[num_ctrl_qubits]] rule = [] rule += self._recurse(first_half, q_ancilla=q[middle]) rule += self._recurse(second_half, q_ancilla=q[middle - 1]) rule += self._recurse(first_half, q_ancilla=q[middle]) rule += self._recurse(second_half, q_ancilla=q[middle - 1]) return rule
[docs]class MCXVChain(MCXGate): """Implement the multi-controlled X gate using a V-chain of CX gates.""" def __new__(cls, num_ctrl_qubits=None, dirty_ancillas=False, # pylint: disable=unused-argument label=None, ctrl_state=None): """Create a new MCX instance. This must be defined anew to include the additional argument ``dirty_ancillas``. """ return super().__new__(cls, num_ctrl_qubits, label=label, ctrl_state=ctrl_state) def __init__(self, num_ctrl_qubits, dirty_ancillas=False, label=None, ctrl_state=None): super().__init__(num_ctrl_qubits, label=label, ctrl_state=ctrl_state, _name='mcx_vchain') self._dirty_ancillas = dirty_ancillas
[docs] def inverse(self): """Invert this gate. The MCX is its own inverse.""" return MCXVChain(num_ctrl_qubits=self.num_ctrl_qubits, dirty_ancillas=self._dirty_ancillas, ctrl_state=self.ctrl_state)
[docs] @staticmethod def get_num_ancilla_qubits(num_ctrl_qubits, mode='v-chain'): """Get the number of required ancilla qubits.""" return MCXGate.get_num_ancilla_qubits(num_ctrl_qubits, mode)
def _define(self): """Define the MCX gate using a V-chain of CX gates.""" # pylint: disable=cyclic-import from qiskit.circuit.quantumcircuit import QuantumCircuit q = QuantumRegister(self.num_qubits, name='q') qc = QuantumCircuit(q, name=self.name) q_controls = q[:self.num_ctrl_qubits] q_target = q[self.num_ctrl_qubits] q_ancillas = q[self.num_ctrl_qubits + 1:] definition = [] if self._dirty_ancillas: i = self.num_ctrl_qubits - 3 ancilla_pre_rule = [ (U2Gate(0, numpy.pi), [q_target], []), (CXGate(), [q_target, q_ancillas[i]], []), (U1Gate(-numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_controls[-1], q_ancillas[i]], []), (U1Gate(numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_target, q_ancillas[i]], []), (U1Gate(-numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_controls[-1], q_ancillas[i]], []), (U1Gate(numpy.pi / 4), [q_ancillas[i]], []), ] for inst in ancilla_pre_rule: definition.append(inst) for j in reversed(range(2, self.num_ctrl_qubits - 1)): definition.append( (RCCXGate(), [q_controls[j], q_ancillas[i - 1], q_ancillas[i]], [])) i -= 1 definition.append((RCCXGate(), [q_controls[0], q_controls[1], q_ancillas[0]], [])) i = 0 for j in range(2, self.num_ctrl_qubits - 1): definition.append((RCCXGate(), [q_controls[j], q_ancillas[i], q_ancillas[i + 1]], [])) i += 1 if self._dirty_ancillas: ancilla_post_rule = [ (U1Gate(-numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_controls[-1], q_ancillas[i]], []), (U1Gate(numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_target, q_ancillas[i]], []), (U1Gate(-numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_controls[-1], q_ancillas[i]], []), (U1Gate(numpy.pi / 4), [q_ancillas[i]], []), (CXGate(), [q_target, q_ancillas[i]], []), (U2Gate(0, numpy.pi), [q_target], []), ] for inst in ancilla_post_rule: definition.append(inst) else: definition.append((CCXGate(), [q_controls[-1], q_ancillas[i], q_target], [])) for j in reversed(range(2, self.num_ctrl_qubits - 1)): definition.append((RCCXGate(), [q_controls[j], q_ancillas[i - 1], q_ancillas[i]], [])) i -= 1 definition.append((RCCXGate(), [q_controls[0], q_controls[1], q_ancillas[i]], [])) if self._dirty_ancillas: for i, j in enumerate(list(range(2, self.num_ctrl_qubits - 1))): definition.append( (RCCXGate(), [q_controls[j], q_ancillas[i], q_ancillas[i + 1]], [])) for instr, qargs, cargs in definition: qc._append(instr, qargs, cargs) self.definition = qc