Probabilistic modeling over permutations using quantum computers

TL;DR

This paper introduces a quantum algorithm that leverages the quantum Fourier transform over the symmetric group to efficiently encode complex probabilistic models over permutations, enabling advanced machine learning applications.

Contribution

It presents a novel quantum algorithm that encodes intractable permutation-based probabilistic models into quantum states using non-Abelian Fourier transforms.

Findings

Quantum Fourier transform over the symmetric group enables efficient encoding of permutation models.

The approach can represent classically intractable probabilistic models.

Discussion of scalability and practical limitations of the quantum method.

Abstract

Quantum computers provide a super-exponential speedup for performing a Fourier transform over the symmetric group, an ability for which practical use cases have remained elusive so far. In this work, we leverage this ability to unlock spectral methods for machine learning over permutation-structured data, which appear in applications such as multi-object tracking and recommendation systems. It has been shown previously that a powerful way of building probabilistic models over permutations is to use the framework of non-Abelian harmonic analysis, as the model's group Fourier spectrum captures the interaction complexity: "low frequencies" correspond to low order correlations, and "high frequencies" to more complex ones. This can be used to construct a Markov chain model driven by alternating steps of diffusion (a group-equivariant convolution) and conditioning (a Bayesian update). However, this approach is computationally challenging and hence limited to simple approximations. Here we construct a quantum algorithm that encodes the exact probabilistic model -- a classically intractable object -- into the amplitudes of a quantum state by making use of the Quantum Fourier Transform (QFT) over the symmetric group. We discuss the scaling, limitations, and practical use of such an approach, which we envision to be a first step towards useful applications of non-Abelian QFTs.