Dependence of 3D Cavity Lifetime on Magnetic Field*

In 3D circuit quantum electrodynamics, 3D cavities are often used as storage for quantum information for their relatively long lifetimes. Nonetheless, it would be desirable to further extend the cavity lifetime by determining which of the various loss phenomena limits the cavity performance. One loss mechanism known to contribute loss to some systems [1] arises from trapped magnetic flux in the form of superconducting vortices. Indirect evidence from past experiments suggests that ambient magnetic field near the cavity suppresses its superconductivity and reduces its lifetime. To determine whether ambient magnetic field is limiting the 3D cavity lifetime, we study the dependence of 3D cavity lifetime on an externally applied magnetic field; additionally, we compare the performance of a coaxial stub 3D cavity with that of a rectangular 3D cavity. [1] C. Song, T.W. Heitmann, M.P. Defeo, K. Yu, R. Mcdermott, M. Neeley, J.M. Martinis, and B.L.T. Plourde, Physical Review B 79, (2009).