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We propose different implementations of hybrid transfer learning, but we focus mainly on the paradigm in which a pre-trained classical network is modified and augmented by a final variational quantum circuit. This approach is particularly attractive in the current era of intermediate-scale quantum technology since it allows to optimally pre-process high dimensional data (e.g., images) with any state-of-the-art classical network and to embed a select set of highly informative features into a quantum processor. We present several proof-of-concept examples of the convenient application of quantum transfer learning for image recognition and quantum state classification. We use the cross-platform software library PennyLane to experimentally test a high-resolution image classifier with two different quantum computers, respectively provided by IBM and Rigetti.<\/jats:p>","DOI":"10.22331\/q-2020-10-09-340","type":"journal-article","created":{"date-parts":[[2020,10,9]],"date-time":"2020-10-09T10:01:12Z","timestamp":1602237672000},"page":"340","source":"Crossref","is-referenced-by-count":336,"title":["Transfer learning in hybrid classical-quantum neural networks"],"prefix":"10.22331","volume":"4","author":[{"given":"Andrea","family":"Mari","sequence":"first","affiliation":[{"name":"Xanadu, 777 Bay Street, Toronto, Ontario, Canada."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thomas R.","family":"Bromley","sequence":"additional","affiliation":[{"name":"Xanadu, 777 Bay Street, Toronto, Ontario, Canada."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Josh","family":"Izaac","sequence":"additional","affiliation":[{"name":"Xanadu, 777 Bay Street, Toronto, Ontario, Canada."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maria","family":"Schuld","sequence":"additional","affiliation":[{"name":"Xanadu, 777 Bay Street, Toronto, Ontario, Canada."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nathan","family":"Killoran","sequence":"additional","affiliation":[{"name":"Xanadu, 777 Bay Street, Toronto, Ontario, Canada."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"9598","published-online":{"date-parts":[[2020,10,9]]},"reference":[{"key":"0","unstructured":"Sasank Chilamkurthy, PyTorch transfer learning tutorial. https:\/\/pytorch.org\/tutorials\/beginner\/transfer_learning_tutorial.html. 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