Quellcode fΓΌr qiskit.circuit.library.arithmetic.adders.vbe_ripple_carry_adder

# This code is part of Qiskit.
# (C) Copyright IBM 2017, 2021.
# This code is licensed under the Apache License, Version 2.0. You may
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"""Compute the sum of two qubit registers using Classical Addition."""
from __future__ import annotations
from qiskit.circuit.bit import Bit

from qiskit.circuit import QuantumCircuit, QuantumRegister, AncillaRegister

from .adder import Adder

[Doku]class VBERippleCarryAdder(Adder): r"""The VBE ripple carry adder [1]. This circuit performs inplace addition of two equally-sized quantum registers. As an example, a classical adder circuit that performs full addition (i.e. including a carry-in bit) on two 2-qubit sized registers is as follows: .. parsed-literal:: β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β” β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”β”Œβ”€β”€β”€β”€β”€β”€β” cin_0: ─0 β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€0 β”œβ”€0 β”œ β”‚ β”‚ β”‚ β”‚β”‚ β”‚ a_0: ─1 β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€1 β”œβ”€1 β”œ β”‚ β”‚β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β” β”Œβ”€β”€β”€β”€β”€β”€β”β”‚ β”‚β”‚ Sum β”‚ a_1: ─ β”œβ”€1 β”œβ”€β”€β– β”€β”€β”€1 β”œβ”€ β”œβ”€ β”œ β”‚ β”‚β”‚ β”‚ β”‚ β”‚ β”‚β”‚ β”‚β”‚ β”‚ b_0: ─2 Carry β”œβ”€ β”œβ”€β”€β”Όβ”€β”€β”€ β”œβ”€2 Carry_dg β”œβ”€2 β”œ β”‚ β”‚β”‚ β”‚β”Œβ”€β”΄β”€β”β”‚ β”‚β”‚ β”‚β””β”€β”€β”€β”€β”€β”€β”˜ b_1: ─ β”œβ”€2 Carry β”œβ”€ X β”œβ”€2 Sum β”œβ”€ β”œβ”€β”€β”€β”€β”€β”€β”€β”€ β”‚ β”‚β”‚ β”‚β””β”€β”€β”€β”˜β”‚ β”‚β”‚ β”‚ cout_0: ─ β”œβ”€3 β”œβ”€β”€β”€β”€β”€β”€ β”œβ”€ β”œβ”€β”€β”€β”€β”€β”€β”€β”€ β”‚ β”‚β”‚ β”‚ β”‚ β”‚β”‚ β”‚ helper_0: ─3 β”œβ”€0 β”œβ”€β”€β”€β”€β”€β”€0 β”œβ”€3 β”œβ”€β”€β”€β”€β”€β”€β”€β”€ β””β”€β”€β”€β”€β”€β”€β”€β”€β”˜β””β”€β”€β”€β”€β”€β”€β”€β”€β”˜ β””β”€β”€β”€β”€β”€β”€β”˜β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜ Here *Carry* and *Sum* gates correspond to the gates introduced in [1]. *Carry_dg* correspond to the inverse of the *Carry* gate. Note that in this implementation the input register qubits are ordered as all qubits from the first input register, followed by all qubits from the second input register. This is different ordering as compared to Figure 2 in [1], which leads to a different drawing of the circuit. **References:** [1] Vedral et al., Quantum Networks for Elementary Arithmetic Operations, 1995. `arXiv:quant-ph/9511018 <https://arxiv.org/pdf/quant-ph/9511018.pdf>`_ """ def __init__( self, num_state_qubits: int, kind: str = "full", name: str = "VBERippleCarryAdder" ) -> None: """ Args: num_state_qubits: The size of the register. kind: The kind of adder, can be ``'full'`` for a full adder, ``'half'`` for a half adder, or ``'fixed'`` for a fixed-sized adder. A full adder includes both carry-in and carry-out, a half only carry-out, and a fixed-sized adder neither carry-in nor carry-out. name: The name of the circuit. Raises: ValueError: If ``num_state_qubits`` is lower than 1. """ if num_state_qubits < 1: raise ValueError("The number of qubits must be at least 1.") super().__init__(num_state_qubits, name=name) # define the input registers registers: list[QuantumRegister | list[Bit]] = [] if kind == "full": qr_cin = QuantumRegister(1, name="cin") registers.append(qr_cin) else: qr_cin = QuantumRegister(0) qr_a = QuantumRegister(num_state_qubits, name="a") qr_b = QuantumRegister(num_state_qubits, name="b") registers += [qr_a, qr_b] if kind in ["half", "full"]: qr_cout = QuantumRegister(1, name="cout") registers.append(qr_cout) else: qr_cout = QuantumRegister(0) self.add_register(*registers) if num_state_qubits > 1: qr_help = AncillaRegister(num_state_qubits - 1, name="helper") self.add_register(qr_help) else: qr_help = AncillaRegister(0) # the code is simplified a lot if we create a list of all carries and helpers carries = qr_cin[:] + qr_help[:] + qr_cout[:] # corresponds to Carry gate in [1] qc_carry = QuantumCircuit(4, name="Carry") qc_carry.ccx(1, 2, 3) qc_carry.cx(1, 2) qc_carry.ccx(0, 2, 3) carry_gate = qc_carry.to_gate() carry_gate_dg = carry_gate.inverse() # corresponds to Sum gate in [1] qc_sum = QuantumCircuit(3, name="Sum") qc_sum.cx(1, 2) qc_sum.cx(0, 2) sum_gate = qc_sum.to_gate() circuit = QuantumCircuit(*self.qregs, name=name) # handle all cases for the first qubits, depending on whether cin is available i = 0 if kind == "half": i += 1 circuit.ccx(qr_a[0], qr_b[0], carries[0]) elif kind == "fixed": i += 1 if num_state_qubits == 1: circuit.cx(qr_a[0], qr_b[0]) else: circuit.ccx(qr_a[0], qr_b[0], carries[0]) for inp, out in zip(carries[:-1], carries[1:]): circuit.append(carry_gate, [inp, qr_a[i], qr_b[i], out]) i += 1 if kind in ["full", "half"]: # final CX (cancels for the 'fixed' case) circuit.cx(qr_a[-1], qr_b[-1]) if len(carries) > 1: circuit.append(sum_gate, [carries[-2], qr_a[-1], qr_b[-1]]) i -= 2 for j, (inp, out) in enumerate(zip(reversed(carries[:-1]), reversed(carries[1:]))): if j == 0: if kind == "fixed": i += 1 else: continue circuit.append(carry_gate_dg, [inp, qr_a[i], qr_b[i], out]) circuit.append(sum_gate, [inp, qr_a[i], qr_b[i]]) i -= 1 if kind in ["half", "fixed"] and num_state_qubits > 1: circuit.ccx(qr_a[0], qr_b[0], carries[0]) circuit.cx(qr_a[0], qr_b[0]) self.append(circuit.to_gate(), self.qubits)