A B- in a physics course, particularly quantum mechanics, can negatively impact chances when applying for math PhD programs, though the extent varies based on the focus of the program. For applied mathematics, the grade may carry more weight than for theoretical areas like set theory or mathematical logic, where it is less relevant. Retaking the course and earning an A can improve prospects, but the original grade will still be visible on the transcript. Alternatively, taking a graduate-level quantum course might also demonstrate improvement, though it could be a significant workload for a subject outside the main area of study. Overall, while a B- is not ideal, it is not a dealbreaker, especially for mid-tier schools.
