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arxiv: 2604.21656 · v1 · submitted 2026-04-23 · 🪐 quant-ph

Speed-oriented quantum circuit backend

S\"oren Wilkening This is my paper

Pith reviewed 2026-05-09 21:52 UTC · model grok-4.3

classification 🪐 quant-ph
keywords quantum circuit generationquantum Fourier transformQiskitQ#classical preprocessingcombinatorial optimizationsoftware backend
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The pith

A new quantum circuit backend generates circuits for up to 2000 qubits faster than Qiskit and Q#

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents a new software package for quantum circuit generation that prioritizes runtime speed. It uses the quantum Fourier transform as a benchmark to show faster circuit creation for systems up to 2000 qubits compared to Qiskit and Q#. This matters for quantum algorithms in combinatorial optimization, where time spent on classical circuit generation can reduce or eliminate any quantum speedup. The package also supplies high-level primitives for bit and integer operations to simplify use with other quantum tools.

Core claim

We present a new software package for efficient quantum circuit generation, designed to achieve optimal runtime performance. Despite being in an early stage of development, our implementation demonstrates significant advantages over existing tools. Using the quantum Fourier transform (QFT) as a benchmark, we show that our backend can generate circuits for systems with up to 2000 qubits faster than widely used frameworks such as Qiskit and Q#. This improvement is particularly relevant for applications where classical preprocessing time, including circuit generation, must be minimized to not diminish any potential quantum advantage - for example, in combinatorial optimization tasks. Our new Q#

What carries the argument

The speed-oriented quantum circuit backend, which is built for minimal runtime in circuit generation and supplies high-level primitives for bit- and integer-level manipulations

Load-bearing premise

The benchmark comparisons are fair, representative of real workloads, and that the early-stage implementation will maintain its reported speed advantages once fully developed and tested across diverse circuit types

What would settle it

An independent timing test that generates a 2000-qubit QFT circuit with this backend and finds it slower than or equal to Qiskit or Q# would falsify the performance claim

Figures

Figures reproduced from arXiv: 2604.21656 by S\"oren Wilkening.

Figure 1
Figure 1. Figure 1: Circuit of a 5-qubit QFT without swaps. value. Some gates may require multiple parameters, but in our description we consider only single-parameter gates. The implementation can easily be extended to support gates with multiple parameters. Data Structure 1: Structure to store data of a quantum gate. 1 typedef struct gate_t { 2 int *controls; // index of control qubits 3 int num_controls; 4 int *targets; //… view at source ↗
Figure 3
Figure 3. Figure 3: Visualization of gate_index (left) and last_layer_of_qubit (top and bottom right) within the circuit_t data structure for a 5-qubit QFT without swaps. The table on the bottom right shows how the data structure is adjusted after applying an additional Hadamard gate to qubit 4, eliminating the previously applied gate. The thick boxes indicate the current head of the list for the respective qubit. Whenever a … view at source ↗
Figure 4
Figure 4. Figure 4: Comparison of running times for building the QFT circuit across state-of-the-art software packages. For all instance [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Comparison of memory requirements for building the QFT circuit across state-of-the-art software packages. Compared [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
read the original abstract

We present a new software package for efficient quantum circuit generation, designed to achieve optimal runtime performance. Despite being in an early stage of development, our implementation demonstrates significant advantages over existing tools. Using the quantum Fourier transform (QFT) as a benchmark, we show that our backend can generate circuits for systems with up to 2000 qubits faster than widely used frameworks such as Qiskit and Q#. This improvement is particularly relevant for applications where classical preprocessing time, including circuit generation, must be minimized to not diminish any potential quantum advantage - for example, in combinatorial optimization tasks. Additionally, our software provides high-level primitives for bit- and integer-level manipulations, offering a simplified interface for integration with high-level quantum programming languages.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript introduces an early-stage software package for quantum circuit generation optimized for runtime performance. It claims significant speed advantages over Qiskit and Q# when generating quantum Fourier transform (QFT) circuits for systems with up to 2000 qubits and provides high-level primitives for bit- and integer-level manipulations to simplify integration with high-level quantum languages. The work emphasizes relevance to applications where classical preprocessing time must be minimized.

Significance. If the reported speed advantages are substantiated through detailed, reproducible benchmarks on diverse circuit types, the package could help address a practical bottleneck in quantum workflows by reducing classical overhead in circuit generation. This would be particularly relevant for large-scale or time-sensitive tasks such as combinatorial optimization. The high-level primitives represent a usability strength.

major comments (2)
  1. [Abstract] Abstract: The central performance claim (faster QFT circuit generation for up to 2000 qubits than Qiskit/Q#) is stated without any timing data, methods description, hardware specifications, error bars, baseline details, or verification steps. This absence makes it impossible to evaluate whether the data supports the claim.
  2. [Abstract] Abstract: The benchmark is restricted to QFT circuits, which possess a highly regular structure (uniform controlled-phase ladder). No results are shown for unstructured, random, or irregular circuits of comparable size and gate density, leaving open whether any speedup is general-purpose or an artifact of QFT-specific optimizations. This directly affects the broader claim of a speed-oriented backend for minimizing classical preprocessing.
minor comments (2)
  1. [Abstract] The early-stage status is noted but should be reflected more explicitly in the title and abstract to manage reader expectations.
  2. Consider adding a dedicated methods or implementation section that describes the circuit generation algorithm, data structures used, and exact benchmarking protocol (including how timings were measured and what versions of Qiskit/Q# were compared).

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive feedback on our manuscript. We address each major comment point by point below, providing clarifications and indicating revisions made to strengthen the presentation of our results.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central performance claim (faster QFT circuit generation for up to 2000 qubits than Qiskit/Q#) is stated without any timing data, methods description, hardware specifications, error bars, baseline details, or verification steps. This absence makes it impossible to evaluate whether the data supports the claim.

    Authors: The abstract is intended as a concise overview rather than a complete technical report. All requested details—timing measurements with error bars from repeated runs, hardware specifications (CPU model, memory, and OS), baseline tool versions, and circuit verification procedures—are provided in the dedicated Benchmarks section of the full manuscript. To address the concern directly, we have revised the abstract to incorporate a brief summary of the benchmark setup and representative performance metrics, making the central claim more self-contained while preserving its brevity. revision: yes

  2. Referee: [Abstract] Abstract: The benchmark is restricted to QFT circuits, which possess a highly regular structure (uniform controlled-phase ladder). No results are shown for unstructured, random, or irregular circuits of comparable size and gate density, leaving open whether any speedup is general-purpose or an artifact of QFT-specific optimizations. This directly affects the broader claim of a speed-oriented backend for minimizing classical preprocessing.

    Authors: QFT was selected as the benchmark because it is a standard, scalable circuit (directly relevant to phase estimation and other algorithms) that exercises the backend at the extreme qubit counts (2000) where generation time becomes a practical bottleneck. Although the gate pattern is regular, the implementation relies on general-purpose optimizations for gate storage, parameter management, and construction loops that are not tailored to QFT. We agree that results on unstructured circuits would further support generality. In the revised manuscript we have added a short discussion of the backend’s design principles and included supplementary benchmark data for random circuits of moderate size in an appendix, while retaining the QFT results as the primary large-scale demonstration. revision: partial

Circularity Check

0 steps flagged

No circularity: performance claims rest on external benchmarks

full rationale

The manuscript presents a software implementation for quantum circuit generation and reports runtime measurements on QFT circuits up to 2000 qubits compared directly against Qiskit and Q#. No mathematical derivations, equations, fitted parameters, or self-citations appear in the abstract or described content. The central claim is an empirical timing result against named external frameworks; it does not reduce to any internal definition, ansatz, or prior self-work by construction. This is a standard non-circular engineering benchmark paper.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical derivations, fitted parameters, or new physical entities are introduced. The work is a software implementation whose claims rest on empirical timing benchmarks rather than axioms or invented constructs.

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