Bose-Einstein condensation, originally predicted in 1924 by S. Bose and A. Einstein, refers to a quantum configuration at low temperatures in which a large portion (the condensate fraction) of particles collapse into the ground state. Figure 1 shows the phenomena in Rb-87, a less complicated system that superfluid 4He, but the first experimental evidence of BEC .
A superfluid is described as a phase of matter with zero viscosity, infinite conductivity, quantized vortices, and zero entropy. It is also characterized by the Cooper pairing of atoms and not electrons. It is generally accepted that superfluidity exhibited in Helium-4 is a consequence of composite boson exhibiting behavior that is associated with Bose-Einstein condensation.
It has been proposed that experiments observing the transmission characteristics of a slab of Helium-4 superfluid that is subjected to a pulse of Helium-4 vapor. Figure 3 shows the set-up of our experimental cell. In the current experiment, we use a fiber optic cable to heat a slab of Helium-4 superfluid, which results in a pulse of vapor. This pulse of vapor is then allowed to impinge on the bottom of a slab of suspended Helium-4 atoms. The resultant atomic flux is then observed on a series of superconducting bolometers, which allow us to see the energy levels of transmitted Helium-4 atoms. Bolometers are essential for the detection system in this experiment because they are designed to function at the low temperatures needed to carry out this experiment, and allow for detection speeds on the order of 1 μs.
Our experiment aims at pinning down Helium-4 superfluid as a Bose-Einstein condensate by observing the transmission characteristics of a Helium-4 superfluid slab. The purpose of my research was to understand and test the detection system being used to measure these transmission characteristics.