Measuring the Casimir energy in a superconducting cavity

Since its theoretical prediction in 1948, the Casimir effect has continued to attract considerable interest in the scientific community, with most studies focusing on calculating Casimir forces, which are attractive in the normal configuration of a metallic cavity. The question of the actual energy within Casimir cavities – the “Casimir energy” – has been less studied theoretically, and few measurements have been performed to detect it. Here we report on the theoretical understanding of a recent experimental realization. The experiment measures the change in critical temperature of a superconductor when it is introduced in a cavity with a conducting plate, due to the Casimir energy created in the cavity. The experiment shows a null result, which we justify theoretically. We also study how the change in critical temperature varies with the presence of a magnetic field as the system is taken across the superconducting transition, so as to be able to predict what changes in the experiment could have led to an observable result.