Pontryagin Maximum Principle for Rydberg-blockaded state-to-state transfers: A semi-analytic approach

TL;DR

This paper develops a semi-analytic method based on Pontryagin Maximum Principle for designing time-optimal control protocols in Rydberg-blockaded quantum systems, applicable to multi-qubit operations.

Contribution

It introduces a formalism that combines analytic and numerical techniques to find high-fidelity, time-optimal controls for multi-qubit Rydberg systems, including classification of extremals.

Findings

Classification of extremals for two-qubit control problems

Establishment of a correspondence between laser detuning and classical particle motion

A semi-analytic formulation that enhances control optimization

Abstract

We study time-optimal state-to-state control for two- and multi-qubit operations motivated by neutral-atom quantum processors within the Rydberg blockade regime. Block-diagonalization of the Hamiltonian simplifies the dynamics and enables the application of a semi-analytic approach to the Pontryagin Maximum Principle to derive optimal laser controls. We provide a general formalism for $N$ qubits. For $N=2$ qubits, we classify normal and abnormal extremals, showcasing examples where abnormal solutions are either absent or suboptimal. For normal extremals, we establish a correspondence between the laser detuning from atomic transitions and the motion of a classical particle in a quartic potential, yielding a reduced, semi-analytic formulation of the control problem. Combining PMP-based insights with numerical optimization, our approach bridges analytic and computational methods for high-fidelity, time-optimal control.