Three-Qubit Gate with ZZX Interaction for Superconducting Circuits

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Solution Overview

Problem

Existing three-qubit gates, such as the Toffoli gate, face challenges in high-fidelity implementation due to the need for multiple two-qubit gates, resulting in long gate lengths and limited interaction capabilities, especially in two-dimensional circuits.

Innovation Solution

A new three-qubit gate is realized by configuring a circuit structure with couplers between qubits to achieve a mainly ZZX interaction, reducing the number of CNOT gates required and enhancing interaction strength, thereby improving fidelity and reducing resource usage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the Toffoli gate is decomposed into single- and two-qubit gates, then the gate can be implemented using existing quantum circuit elements, but the number of gates increases and fidelity decreases

Engineering Contradiction:

Improvegate fidelityVSAvoidnumber of two-qubit gates

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

providing a first coupler arranged between the first and second qubits; providing a second coupler arranged between the second and third qubits; providing a third coupler arranged between the first and third qubits

Inventive Principle:

Principle #1Segmentation

2Productivity

If three microwave pulses are applied to three qubits coupled on a chain to realize the Toffoli gate, then the gate operation is achieved, but the gate length becomes long and operation speed decreases

Engineering Contradiction:

Improvegate operation speedVSAvoidgate length

Core Design Contradiction:

ProductivityVSDuration of action of moving object

Solution Approach 1:

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Adaptability or versatility

If the Toffoli gate is implemented in one-dimensional linear chain-like interaction, then the gate can be realized with simple coupling, but additional interaction terms appear in two-dimensional circuits making realization difficult

Engineering Contradiction:

Improvecompatibility with 2d circuitsVSAvoidinteraction term imbalance

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

controlling circuit parameters of the circuit structure so as to result in the total interaction to become mainly ZZX

Inventive Principle:

Principle #3Local quality

Data Source

PatentEP4571596A1Three-qubit gate and method for its realization

Publication Date: 2025.06.18 FORSCHUNGSZENTRUM JULICH GMBH

Figure 1~2

AI summary

The invention proposes a three-qubit gate with mainly ZZX interaction. The gate is fast and is of high fidelity.