Breaking a Classical Barrier for Classifying Arbitrary Test Examples in the Quantum Model

Abstract

A new model for adversarial robustness was introduced by Goldwasser et al. in [GKKM20]. In this model the authors present a selective and transductive learning algorithm which guarantees a low test error and low rejection rate wrt to the original distribution. Moreover, a lower bound in terms of the VC-dimension, the standard risk and the number of samples is derived. We show that this lower bound can be broken in the quantum world. We consider a new model, influenced by the quantum PAC-learning model introduced by [BJ95], and similar in spirit to the one in [GKKM20]. In this model we give an interactive protocol between the learner and the adversary (at test-time) that guarantees robustness. This protocol, when applied, breaks the lower bound from [GKKM20]. From the technical perspective, our protocol is inspired by recent advances in delegation of quantum computation, e.g. [Mah18]. But in order to be applicable to our task, we extend the delegation protocol to enable a new feature, e.g. by extending delegation of decision problems, i.e. BQP, to sampling problems with adversarially chosen inputs.