However, since this book is based on Zwiebach's popular MIT courses, there are several to access much of its core content and supplementary materials for free. 1. Access the Core Content via MIT OpenCourseWare (Free)

While searching for a "free download" of Barton Zwiebach’s Mastering Quantum Mechanics

The book is structured into three distinct parts designed to take a student from fundamental concepts to research-level tools: Part 1: Essentials

(to help decide if it’s worth buying):