Quantum Semi-Random Forests for Qubit-Efficient Recommender Systems

First and second authors contributed equally to this work Abstract --Modern recommenders describe each item with hundreds of sparse semantic tags, yet most quantum pipelines still map one qubit per tag, demanding well beyond one hundred qubits, far out of reach for current noisy-intermediate-scale quantum (NISQ) devices and prone to deep, error-amplifying circuits. We close this gap with a three-stage hybrid machine learning algorithm that compresses tag profiles, optimizes feature selection under a fixed qubit budget via QAOA, and scores recommendations with a Quantum semi-Random Forest (QsRF) built on just five qubits, while performing similarly to the state-of-the-art methods. Leveraging SVD sketching and k-means, we learn a 1 000-atom dictionary ( >97 % variance), then solve a 20 20 QUBO via depth-3 QAOA to select 5 atoms. A 100-tree QsRF trained on these codes matches full-feature baselines on ICM-150/500. To compress this combinatorial explosion, recent hybrid pipelines formulate feature selection as a Q uadratic U nconstrained Binary O ptimisation (QUBO) and delegate the search to quantum annealers [1], [2] or shallow gate-based circuits [3].