RUI: Photons Acting Like Fermions: Search for Violations of the Spin Statistics Theorem Using Sr Atoms

California State University, East Bay Foundation, Inc., Hayward CA

Investigators

Abstract

Fundamental particles of nature can be characterized by their individual properties such as electric charge, mass, and spin. This last property, spin angular momentum, appears to determine whether a particle falls into one of two general categories. Particles with integer valued spin are called "bosons", and those with half-integer valued spin are called "fermions." The boson or fermion distinction has a remarkable effect on the statistical behavior of particle groups. For example, an unlimited number of bosons (such as photons) can occupy the same quantum state, but only a single fermion (such as an electron) can occupy a specific state.  These differences in properties result in vastly different macroscopic behaviors. The distinction between a boson an a fermion is important for the structure of the periodic table of the elements, the degree to which atoms interact with each other during collisions, and even the stability of matter in everyday objects. This research aims to answer the question: are there exceptions to the general rule which links spin to the characterization of a particle as a boson or fermion?  Researchers at California State University East Bay will probe the fundamental properties of light (a spin-1 particle) and explore whether it, a boson, ever exhibits any fermion-like behavior.  Such a discovery would provide a new direction for the theoretical development of the basic axioms of physics and supply an essential ingredient to a more fundamental view of the world. Experimental searches for violations of the spin statistics theorem (SST) test fundamental assumptions of quantum field theory, such as local Lorentz invariance.  For this research, researachers will constrain the SST-forbidden two-photon transition rate between the ground J=0 and excited J'=1 states in atomic strontium.  A two-photon transition between these two states would possess total angular momentum J=1, which is an exchange-antisymmetric (fermionic) state forbidden by the SST.  This new experimental search is motivated by an expected three orders of magnitude increase in sensitivity over previous searches.  This increase is made possible by using laser-cooled strontium atoms and separate detection and excitation regions, reducing the leading systematic effect, scattered light. This work will take place at an undergraduate institution and will directly engage undergraduate students in hands-on research.  This research program will especially benefit the diverse student body at California State University East Bay, where nearly two-thirds of students are women, over sixty percent are first-generation college students, and over seventy-five percent are underrepresented minorities.