Quantum Memory Refresh Using LDPC Syndrome Measurements
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Solution Overview
Problem
Quantum memory systems face high rates of error due to decoherence and processing issues, leading to loss of fidelity in stored quantum states, which existing error correction methods are unable to effectively address.
Innovation Solution
A memory system comprising a qubit array that uses a quantum stabilizer code and a low-density parity-check (LDPC) error-correction code to detect and correct errors through a quantum-state-refresh module, which performs redundant measurements and applies error-correction algorithms to maintain high fidelity of entangled qubit states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If quantum states are stored in quantum memory for extended periods, then the duration of storage is improved, but the fidelity of quantum states deteriorates due to decoherence and processing errors
Solution Approach 1:
The patent applies preliminary action by performing error correction before the quantum state fidelity deteriorates completely. The quantum-state-refresh module continuously monitors and corrects errors in entangled qubit states during storage, preventing cumulative decoherence damage. The LDPC code is pre-configured with optimal density parameters to provide proactive error protection throughout the storage duration.
Solution Approach 2:
The patent implements feedback through the quantum-state-refresh module that continuously measures syndrome values using redundant measurements based on LDPC codes. When errors are detected in the entangled qubit states, the system automatically applies corrective operations and refreshes the quantum states, creating a closed-loop feedback mechanism that maintains fidelity over extended storage periods.
2Reliability
If redundant measurements are performed to detect errors in quantum states, then the reliability of error detection is improved, but the complexity of the measurement system increases
Solution Approach 1:
The patent applies parameter changes by optimizing the density parameter of the LDPC code to balance error detection reliability with measurement system complexity. The low-density parity-check structure uses a specific density range (0.01 < density < 0.1) that provides sufficient redundant measurements for reliable error detection while keeping the number of measurement operations and system complexity manageable.
Solution Approach 2:
The patent segments the error detection process into multiple independent syndrome measurements using the LDPC code structure. Instead of a single complex measurement, the system performs multiple simpler redundant measurements of syndrome values, each measuring different aspects of the quantum state. This segmentation allows reliable error detection through accumulated information while keeping individual measurement operations simple and manageable.
3Manufacturing precision
If LDPC error-correction codes with optimized density are used, then the manufacturing precision of the code structure is improved, but the device complexity increases due to sparse matrix operations
Solution Approach 1:
The patent applies parameter changes by precisely controlling the density parameter of the LDPC code within the optimal range of 0.01 < density < 0.1. This parameter optimization ensures that the sparse matrix has enough non-zero elements to provide accurate error correction capability while maintaining sufficient zeros to reduce computational complexity. The EXIT-function analysis is used to determine the precise density parameter that achieves the desired manufacturing precision of the code structure.
Solution Approach 2:
The patent applies the porous materials principle by utilizing the sparse structure of the LDPC code, where most matrix elements are zero (empty spaces) with only a small fraction being non-zero. This sparsity allows the system to achieve high manufacturing precision in code structure while reducing device complexity, as the zero elements require no physical implementation and only the non-zero elements need to be implemented in hardware, significantly reducing the number of required components and operations.
Data Source
AI summary
A memory system comprising a qubit array configured to store therein and read one or more entangled qubit states encoded using a quantum stabilizer code. The quantum-memory system further comprises a quantum-state-refresh module configured to change an entangled qubit state in the qubit array when an error is detected therein. The quantum-state-refresh module is configured to detect an error by performing a redundant measurement of a set of syndrome values corresponding to the quantum stabilizer code, with the redundant measurement being based on a block error-correction code. In one embodiment, the block error-correction code is a low-density generator-matrix code or a low-density parity-check code constructed using an EXIT-function optimization method.