  Contrastive learning has become a new paradigm for unsupervised sentence
embeddings. Previous studies focus on instance-wise contrastive learning,
attempting to construct positive pairs with textual data augmentation. In this
paper, we propose a novel Contrastive learning method with Prompt-derived
Virtual semantic Prototypes (ConPVP). Specifically, with the help of prompts,
we construct virtual semantic prototypes to each instance, and derive negative
prototypes by using the negative form of the prompts. Using a prototypical
contrastive loss, we enforce the anchor sentence embedding to be close to its
corresponding semantic prototypes, and far apart from the negative prototypes
as well as the prototypes of other sentences. Extensive experimental results on
semantic textual similarity, transfer, and clustering tasks demonstrate the
effectiveness of our proposed model compared to strong baselines. Code is
available at https://github.com/lemon0830/promptCSE.
