Surface Code Qubit Encoding With Reduced CNOT Operations

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Solution Overview

Problem

Existing encoding methods for qubits are inefficient and require a large number of operations, ancilla qubits, and readouts, making them impractical for fault-tolerant quantum computing.

Innovation Solution

A novel encoding method involving a specific sequence of two-qubit gates is employed to encode a surface code with a code distance of 3, reducing the number of required operations and improving fault tolerance by performing controlled-NOT gates eight times instead of the traditional 36 times, and incorporating error detection and correction mechanisms.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If traditional encoding methods are used for qubits, then encoding can be performed, but the number of operations, ancilla qubits, and readouts becomes excessively large, making the process inefficient and impractical

Engineering Contradiction:

Improveencoding efficiencyVSAvoidnumber of operations and resources

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The encoding process is divided into distinct stages: preparing initial states of qubits, performing specific two-qubit gates (CNOT gates) in a predetermined sequence, and conducting measurements. This segmentation allows for systematic optimization of each stage, reducing the total number of operations required while maintaining encoding effectiveness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The method performs preliminary preparation of qubit initial states and establishes a predetermined gate sequence before execution. By pre-planning the encoding sequence and preparing ancilla qubits in advance, the system avoids unnecessary operations during the actual encoding process, thereby improving efficiency and reducing resource requirements.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If more operations and ancilla qubits are used, then encoding accuracy and fault tolerance can be improved, but the complexity and resource requirements increase significantly

Engineering Contradiction:

Improvefault toleranceVSAvoidnumber of ancilla qubits and operations

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies a specific number of CNOT gates (eight times) which is sufficient to achieve the desired encoding and fault tolerance without over-provisioning. This partial action approach ensures adequate error correction capability while avoiding the excessive resource consumption that would result from using more gates than necessary.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The method optimizes key parameters including the sequence of two-qubit gates, the number of ancilla qubits required, and the measurement timing. By carefully adjusting these parameters, the system achieves high fault tolerance with minimized resource requirements, resolving the contradiction between reliability and complexity.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12361312B2Encoder, calculating device, and encoding method

Publication Date: 2025.07.15 KK TOSHIBA

AI summary

An encoder includes a first element part and a controller. The first element part includes a first qubit, a second qubit coupleable with the first qubit, a third qubit coupleable with the second qubit, a fourth qubit coupleable with the third qubit, a fifth qubit coupleable with the fourth qubit, a sixth qubit coupleable with the fifth qubit, a seventh qubit coupleable with the sixth qubit, an eighth qubit coupleable with the seventh qubit, and a ninth qubit coupleable with the eighth qubit. The controller is configured to perform a first control. The first control includes encoding a surface code having a code distance of 3.