Exploiting symmetry in variational quantum machine learning
This work addresses a key bottleneck in variational quantum machine learning by providing guiding principles for model construction, which is incremental but domain-specific.
The authors tackled the problem of constructing suitable parametrizations for variational quantum machine learning by exploiting symmetries of the learning task, resulting in a substantial increase in generalization performance on two toy problems with non-trivial symmetries.
Variational quantum machine learning is an extensively studied application of near-term quantum computers. The success of variational quantum learning models crucially depends on finding a suitable parametrization of the model that encodes an inductive bias relevant to the learning task. However, precious little is known about guiding principles for the construction of suitable parametrizations. In this work, we holistically explore when and how symmetries of the learning problem can be exploited to construct quantum learning models with outcomes invariant under the symmetry of the learning task. Building on tools from representation theory, we show how a standard gateset can be transformed into an equivariant gateset that respects the symmetries of the problem at hand through a process of gate symmetrization. We benchmark the proposed methods on two toy problems that feature a non-trivial symmetry and observe a substantial increase in generalization performance. As our tools can also be applied in a straightforward way to other variational problems with symmetric structure, we show how equivariant gatesets can be used in variational quantum eigensolvers.