Nonappearance of Vortices in Fast Mechanical Expansions of Liquid ${}^4\mathrm{He}$ through the Lambda Transition

A new experiment has been performed to study the formation of topological defects (quantized vortices) during rapid quenches of liquid ${}^4\mathrm{He}$ through the superfluid transition, with particular care taken to minimize vortex creation via conventional hydrodynamic flow processes. It is found that the generated vortices, if any, are being produced at densities at least 2 orders of magnitude less than might be expected on the basis of the Kibble-Zurek mechanism.