Theres a lot of interesting physics to be found if you subject an atom to an electric or magnetic field. This chapter explores this physics. It covers the Stark effect and the Zeeman effect and Rabi oscillations. it also looks at what happens when coherent states of photons in a cavity interact with atoms.

Jane Dewey (1900−1976) was the only woman in a group that John Slater described as the lucky generation of US physicists: those born near the beginning of the twentieth century and who spent time in Europe, learning with the leading quantum physicists of the era. After completing a PhD at the Massachusetts Institute of Technology in 1925, Dewey went to Niels Bohr’s Institute for Theoretical Physics in Copenhagen. She worked on the Stark effect in helium, a key test of the recently formulated quantum mechanics. Bohr praised her skills in a fellowship application, and Karl Compton later supported her (unsuccessful) efforts to land a permanent job. Although Dewey did pioneering work in the field of quantum optics, the conditions she encountered made it difficult for her to continue on this research path. Her promising abilities did not translate into a successful academic career as they did for many of the men of the lucky generation. Perhaps she was not lucky enough. Or was luck conditional on being a man? This chapter argues that subtle – yet, structural – gender discriminatory practices contributed to her gradual exclusion from physics research, and ultimately from academia.

Laura M. Chalk (later, Laura Rowles, 1904−1996) was the first woman to complete a PhD in physics at McGill University in Montreal, Canada. Her doctoral research on the quantum phenomenon called the Stark effect, under the supervision of J. Stuart Foster, produced the earliest experimental test of Erwin Schrödinger’s wave mechanics. After a brief stint as a postdoctoral fellow at King’s College London, she chose to return home and dedicate herself to teaching and marriage. This paper aims to fully recover Chalk’s work and explore why the Foster−Chalk experiment was overlooked in physics historiography. It considers the Stark effect’s significance in quantum physics and the impact of gender on her personal trajectory. Shaped by personal choice, systemic discrimination, and acceptance of societal norms, Chalk Rowles’ story highlights the paradoxes faced by women in a culturally disembodied yet male-dominated field, and reflects broader themes of gender and identity in the history of women in physics.

We learn how to use perturbation theory to solve more realistic problems that do not admit exact solutions. We learn degenerate and nondegenerate perturbation theory and apply them to a variety of problems, including spin magnetic moments in magnetic fields and the Stark effect in hydrogen.