Source code for qrisp.alg_primitives.arithmetic.adders.fourier_adder

"""
\********************************************************************************
* Copyright (c) 2025 the Qrisp authors
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the Eclipse
* Public License, v. 2.0 are satisfied: GNU General Public License, version 2
* with the GNU Classpath Exception which is
* available at https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
********************************************************************************/
"""

import numpy as np

from qrisp.alg_primitives import QFT
from qrisp.core.gate_application_functions import p, cz
from qrisp.environments import QuantumEnvironment, conjugate
from qrisp.circuit import Operation, PGate, QuantumCircuit



[docs]
def fourier_adder(a, b, perform_QFT = True):
    """
    In-place adder function based on `this paper <https://arxiv.org/abs/quant-ph/0410184>`__
    Performs the addition
    
    ::
        
        b += a
    

    Parameters
    ----------
    a : int or QuantumVariable or list[Qubit]
        The value that should be added.
    b : QuantumVariable or list[Qubit]
        The value that should be modified in the in-place addition.
    perform_QFT : bool, optional
        If set to ``False``, no QFT is executed. The default is ``True``.

    Examples
    --------
    
    We add two integers:
        
    >>> from qrisp import QuantumFloat, fourier_adder
    >>> a = QuantumFloat(4)
    >>> b = QuantumFloat(4)
    >>> a[:] = 4
    >>> b[:] = 5
    >>> fourier_adder(a,b)
    >>> print(b)
    {9: 1.0}

    """
    
    if perform_QFT:
        env = conjugate(QFT)(b, exec_swap = False)
    else:
        env = QuantumEnvironment()
    
    with env:
        
                    
        b = list(b)
        b = b[::-1]

        
        if isinstance(a, int):
            for i in range(len(b)):
                p(a*np.pi*2**(1+i-len(b)), b[i])
                
        else:
            
            if len(a) > len(b):
                raise Exception("Tried to add QuantumFloat of higher precision onto QuantumFloat of lower precision")
            
            phase_correction_a = np.zeros(len(a))
            phase_correction_b = np.zeros(len(b))
            for j in range(len(a)):
                for i in range(len(b)):    
                    
                    if 1+j+i-len(b) >= 1:
                        continue
                    if 1+j+i-len(b) == 0:
                        cz(a[j], b[i])
                    else:
                        b[i].qs().append(QuasiRZZ(-np.pi*2**(1+j+i-len(b))/2), [a[j], b[i]])
                        
                        phase_correction_a[j] += np.pi*2**(1+j+i-len(b))/2
                        phase_correction_b[i] += np.pi*2**(1+j+i-len(b))/2
            
            for i in range(len(b)):
                if phase_correction_b[i]%(2*np.pi) != 0:
                    p(phase_correction_b[i], b[i])
            for i in range(len(a)):
                if phase_correction_a[i]%(2*np.pi) != 0:
                    p(phase_correction_a[i], a[i])



class QuasiRZZ(Operation):
    
    def __init__(self, angle):
        qc = QuantumCircuit(2)
        qc.cx(qc.qubits[1], qc.qubits[0])
        qc.p(angle, qc.qubits[0])
        qc.cx(qc.qubits[1], qc.qubits[0])
        
        Operation.__init__(self, "quasi_rzz", num_qubits = 2, definition = qc, params = [angle])
        
        self.permeability = {0 : True, 1 : True}
        self.is_qfree = True        
    
    def inverse(self):
        return QuasiRZZ(-self.params[0])
    
    def control(self, num_ctrl_qubits=1, ctrl_state=-1, method=None):
        
        qc = QuantumCircuit(2 + num_ctrl_qubits)
        qc.cx(qc.qubits[-1], qc.qubits[-2])
        qc.append(PGate(self.params[0]).control(num_ctrl_qubits, ctrl_state=ctrl_state, method=method), qc.qubits[:-1])
        qc.cx(qc.qubits[-1], qc.qubits[-2])
        
        res = Operation.control(self, num_ctrl_qubits, ctrl_state=ctrl_state, method=method)
        
        res.definition = qc
        return res