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---
title: RGQFTMultiplier (v0.31)
description: API reference for qiskit.circuit.library.RGQFTMultiplier in qiskit v0.31
in_page_toc_min_heading_level: 1
python_api_type: class
python_api_name: qiskit.circuit.library.RGQFTMultiplier
---
# RGQFTMultiplier
<Class id="qiskit.circuit.library.RGQFTMultiplier" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.18/qiskit/circuit/library/arithmetic/multipliers/rg_qft_multiplier.py" signature="RGQFTMultiplier(num_state_qubits, num_result_qubits=None, name='RGQFTMultiplier')" modifiers="class">
Bases: `qiskit.circuit.library.arithmetic.multipliers.multiplier.Multiplier`
A QFT multiplication circuit to store product of two input registers out-of-place.
Multiplication in this circuit is implemented using the procedure of Fig. 3 in \[1], where weighted sum rotations are implemented as given in Fig. 5 in \[1]. QFT is used on the output register and is followed by rotations controlled by input registers. The rotations transform the state into the product of two input registers in QFT base, which is reverted from QFT base using inverse QFT. As an example, a circuit that performs a modular QFT multiplication on two 2-qubit sized input registers with an output register of 2 qubits, is as follows:
```python
a_0: ────────────────────────────────────────■───────■──────■──────■────────────────
│ │ │ │
a_1: ─────────■───────■───────■───────■──────┼───────┼──────┼──────┼────────────────
│ │ │ │ │ │ │ │
b_0: ─────────┼───────┼───────■───────■──────┼───────┼──────■──────■────────────────
│ │ │ │ │ │ │ │
b_1: ─────────■───────■───────┼───────┼──────■───────■──────┼──────┼────────────────
┌──────┐ │P(4π) │ │P(2π) │ │P(2π) │ │P(π) │ ┌───────┐
out_0: ┤0 ├─■───────┼───────■───────┼──────■───────┼──────■──────┼───────┤0 ├
│ qft │ │P(2π) │P(π) │P(π) │P(π/2) │ iqft │
out_1: ┤1 ├─────────■───────────────■──────────────■─────────────■───────┤1 ├
└──────┘ └───────┘
```
**References:**
\[1] Ruiz-Perez et al., Quantum arithmetic with the Quantum Fourier Transform, 2017. [arXiv:1411.5949](https://arxiv.org/pdf/1411.5949.pdf)
**Parameters**
* **num\_state\_qubits** (`int`) The number of qubits in either input register for state $|a\rangle$ or $|b\rangle$. The two input registers must have the same number of qubits.
* **num\_result\_qubits** (`Optional`\[`int`]) The number of result qubits to limit the output to. If number of result qubits is $n$, multiplication modulo $2^n$ is performed to limit the output to the specified number of qubits. Default value is `2 * num_state_qubits` to represent any possible result from the multiplication of the two inputs.
* **name** (`str`) The name of the circuit object.
## Attributes
### ancillas
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.ancillas">
Returns a list of ancilla bits in the order that the registers were added.
</Attribute>
### calibrations
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.calibrations">
Return calibration dictionary.
**The custom pulse definition of a given gate is of the form**
\{gate\_name: \{(qubits, params): schedule}}
</Attribute>
### clbits
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.clbits">
Returns a list of classical bits in the order that the registers were added.
</Attribute>
### data
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.data">
Return the circuit data (instructions and context).
**Returns**
a list-like object containing the tuples for the circuits data.
Each tuple is in the format `(instruction, qargs, cargs)`, where instruction is an Instruction (or subclass) object, qargs is a list of Qubit objects, and cargs is a list of Clbit objects.
**Return type**
QuantumCircuitData
</Attribute>
### extension\_lib
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.extension_lib" attributeValue="'include &#x22;qelib1.inc&#x22;;'" />
### global\_phase
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.global_phase">
Return the global phase of the circuit in radians.
</Attribute>
### header
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.header" attributeValue="'OPENQASM 2.0;'" />
### instances
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.instances" attributeValue="16" />
### metadata
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.metadata">
The user provided metadata associated with the circuit
The metadata for the circuit is a user provided `dict` of metadata for the circuit. It will not be used to influence the execution or operation of the circuit, but it is expected to be passed between all transforms of the circuit (ie transpilation) and that providers will associate any circuit metadata with the results it returns from execution of that circuit.
</Attribute>
### num\_ancillas
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.num_ancillas">
Return the number of ancilla qubits.
</Attribute>
### num\_clbits
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.num_clbits">
Return number of classical bits.
</Attribute>
### num\_parameters
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.num_parameters">
Convenience function to get the number of parameter objects in the circuit.
</Attribute>
### num\_qubits
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.num_qubits">
Return number of qubits.
</Attribute>
### num\_result\_qubits
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.num_result_qubits">
The number of result qubits to limit the output to.
**Return type**
`int`
**Returns**
The number of result qubits.
</Attribute>
### num\_state\_qubits
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.num_state_qubits">
The number of state qubits, i.e. the number of bits in each input register.
**Return type**
`int`
**Returns**
The number of state qubits.
</Attribute>
### parameters
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.parameters">
Convenience function to get the parameters defined in the parameter table.
</Attribute>
### prefix
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.prefix" attributeValue="'circuit'" />
### qubits
<Attribute id="qiskit.circuit.library.RGQFTMultiplier.qubits">
Returns a list of quantum bits in the order that the registers were added.
</Attribute>
</Class>