Quantum machine learning with adaptive linear optics
This work sets explicit limits on the parameters for which a quantum advantage can be expected in machine learning with adaptive linear optics, which is important for researchers developing quantum machine learning algorithms.
This paper explores supervised learning algorithms utilizing quantum devices for prediction or kernel computation via Boson Sampling architectures with adaptive measurements. The authors derive classical simulation algorithms for these tasks, establishing limits on quantum advantage based on the number of adaptive measurements and input photons, showing that these cannot be simultaneously small compared to the number of modes.
We study supervised learning algorithms in which a quantum device is used to perform a computational subroutine - either for prediction via probability estimation, or to compute a kernel via estimation of quantum states overlap. We design implementations of these quantum subroutines using Boson Sampling architectures in linear optics, supplemented by adaptive measurements. We then challenge these quantum algorithms by deriving classical simulation algorithms for the tasks of output probability estimation and overlap estimation. We obtain different classical simulability regimes for these two computational tasks in terms of the number of adaptive measurements and input photons. In both cases, our results set explicit limits to the range of parameters for which a quantum advantage can be envisaged with adaptive linear optics compared to classical machine learning algorithms: we show that the number of input photons and the number of adaptive measurements cannot be simultaneously small compared to the number of modes. Interestingly, our analysis leaves open the possibility of a near-term quantum advantage with a single adaptive measurement.