Entanglement Devised Barren Plateau Mitigation

TL;DR

This paper identifies random entanglement as the cause of barren plateaus in quantum machine learning and introduces techniques to mitigate their effects, improving training accuracy in variational quantum algorithms.

Contribution

It provides a theoretical framework linking entanglement dynamics to barren plateaus and proposes practical methods to reduce entanglement for better quantum training performance.

Findings

Entanglement correlates with barren plateau formation.

Mitigation techniques improve training accuracy.

Entanglement control is key to effective quantum learning.

Abstract

Hybrid quantum-classical variational algorithms are one of the most propitious implementations of quantum computing on near-term devices, offering classical machine learning support to quantum scale solution spaces. However, numerous studies have demonstrated that the rate at which this space grows in qubit number could preclude learning in deep quantum circuits, a phenomenon known as barren plateaus. In this work, we implicate random entanglement as the source of barren plateaus and characterize them in terms of many-body entanglement dynamics, detailing their formation as a function of system size, circuit depth, and circuit connectivity. Using this comprehension of entanglement, we propose and demonstrate a number of barren plateau ameliorating techniques, including: initial partitioning of cost function and non-cost function registers, meta-learning of low-entanglement circuit initializations, selective inter-register interaction, entanglement regularization, the addition of Langevin noise, and rotation into preferred cost function eigenbases. We find that entanglement limiting, both automatic and engineered, is a hallmark of high-accuracy training, and emphasize that as learning is an iterative organization process while barren plateaus are a consequence of randomization, they are not necessarily unavoidable or inescapable. Our work forms both a theoretical characterization and a practical toolbox; first defining barren plateaus in terms of random entanglement and then employing this expertise to strategically combat them.