SQO-LSTM: a single quantum-output long short-term memory for classification tasks
摘要
Quantum long short-term memory (QLSTM) networks have gained attention for sequential modeling tasks but suffer from inconsistent implementations, particularly regarding the number of variational quantum circuits (VQCs) used (4, 5, or 6) without a well-defined rationale. This lack of standardization limits their efficiency, especially on near-term quantum devices (NISQ). We introduce the Single Quantum-Output LSTM (SQO-LSTM), an optimized QLSTM architecture that consolidates multiple VQCs into a single quantum module, reducing complexity while maintaining performance. This design minimizes quantum resource usage, making it more suitable for current NISQ devices. SQO-LSTM was evaluated on 20 diverse text classification datasets (binary and multi-class). These datasets span linguistic diversity (English and Spanish), various levels of structural complexity, and different sequence lengths. Our experimental findings demonstrate a clear quantum advantage: SQO-LSTM showing consistent improvements over classical and QLSTM baselines under identical experimental settings, where it surpasses the 4-VQC QLSTM by 10–20% on challenging datasets such as RP and MILK, while significantly reducing training times. Moreover, we explored different classical-quantum layer configurations and ansatz choices, finding that the Bi-Ansatz structure optimally improves accuracy (e.g., RP dataset: 76%