ZX-Diagram Quantum Circuit Rewriting for Qubit Reduction

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Solution Overview

Problem

Existing quantum computing technologies face inefficiencies in minimizing the number of qubits required for quantum circuits without increasing the number of non-Clifford gates, which is crucial for optimizing computational resources and reducing computational depth.

Innovation Solution

A data processing method utilizing ZX-calculus and graph theoretical techniques to transform quantum circuits into ZX-diagrams, applying operations such as rearrangement, fusion, and lattice surgery to reduce the number of qubits while preserving the number of non-Clifford gates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If additional qubits are used to reduce computational depth and number of operations, then the efficiency of quantum computation is improved, but the number of qubits increases which counteracts the gains

Engineering Contradiction:

Improvecomputational efficiencyVSAvoidnumber of qubits

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The patent changes the representation parameters of the quantum circuit by transforming it into a ZX-diagram format, which enables different optimization approaches. This parameter change allows the application of graph theoretical techniques and rewriting rules that can reduce qubit count while maintaining computational efficiency

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces traditional quantum circuit optimization methods with a diagrammatic calculus approach (ZX-calculus). This substitution enables the use of graph rewriting rules and lattice surgery techniques that systematically reduce the number of qubits required while preserving the computational functionality

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Quantity of substance

If quantum circuit is optimized to reduce qubit number, then resource utilization is improved, but the complexity of optimization process increases

Engineering Contradiction:

Improvenumber of qubitsVSAvoidoptimization process complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent introduces ZX-diagrams as an intermediary representation between the original quantum circuit and the optimized circuit. This intermediary format with its graph structure and rewriting rules provides a systematic framework that manages the optimization complexity while achieving qubit reduction

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the quantum circuit into discrete ZX-diagram elements (spiders, wires, nodes) that can be independently analyzed and transformed. This segmentation allows the application of local rewriting rules that systematically reduce qubit count without requiring global redesign of the entire circuit

Inventive Principle:

Principle #1Segmentation

Data Source

PatentEP4657331A1Data processing method and apparatuses for implementing the same

Publication Date: 2025.12.03 BULL SA

Figure 1a~1d
Figure 2a~3b
Figure 4a~4c

AI summary

A data processing method for processing a first quantum circuit that can be implemented using n qubits is proposed, which comprises: Determining a first ZX-diagram that represents the first quantum circuit; Performing one or more operations on the first ZX-diagram to generate a second ZX-diagram; Determining a second quantum circuit that is represented by the second ZX-diagram, wherein the one or more operations on the first ZX-diagram are configured to reduce the number of qubits with which the second quantum circuit can be implemented to be less than the n qubits.