  Transformer-based models have achieved great success on sentence pair
modeling tasks, such as answer selection and natural language inference (NLI).
These models generally perform cross-attention over input pairs, leading to
prohibitive computational costs. Recent studies propose dual-encoder and late
interaction architectures for faster computation. However, the balance between
the expressive of cross-attention and computation speedup still needs better
coordinated. To this end, this paper introduces a novel paradigm MixEncoder for
efficient sentence pair modeling. MixEncoder involves a light-weight
cross-attention mechanism. It conducts query encoding only once while modeling
the query-candidate interaction in parallel. Extensive experiments conducted on
four tasks demonstrate that our MixEncoder can speed up sentence pairing by
over 113x while achieving comparable performance as the more expensive
cross-attention models.
