sentences:  He was notable for his wide-ranging expertise in relating theory to experiment, and was involved in all major efforts to understand non-classical light.A seminal paper by Walls with his first graduate student Howard Carmichael, showed how to create antibunched light, in which photons arrive at regular intervals, rather than randomly.Walls was a pioneer in the study of ways that the particle-like nature of light (photons) could be controlled to make optical systems less susceptible to unwanted fluctuations, in particular by the use of squeezed light, a concept formulated by Carlton Caves.