Superconducting radio frequency cavities with seconds of photon lifetime in quantum regime

Superconducting radio frequency (SRF) cavities developed for accelerators are the highest quality factor (Q) man-made oscillators with record Q > 4e11, whereas Q~3e10 is a routine operation. Adopted for quantum regime, SRF cavities offer a route for multifold increase in photon lifetimes for applications in quantum computing and fundamental physics searches such as dark photons and axions. Initial demonstrations showed that the quantum regime lifetimes of tens of milliseconds can be achieved for SRF cavities "as-is", limited by the two-level-system (TLS) dissipation [1,2].

In this contribution we present the recent advancements [2] in the quantum regime performance of SRF cavities enabled by applying combined materials science investigations and vacuum heat treatments. We demonstrate the mitigation of the TLS dissipation and achievement of the 0.5 seconds of photon lifetime for 5 GHz and 2 seconds for 1.3 GHz cavities. Such cavities are currently being employed for several QIS type and fundamental physics applications such as dark photon searches, which we will summarize briefly as well.

[1] A. Romanenko and D. I. Schuster, Phys. Rev. Lett. 119, 264801 (2017)
[2] A. Romanenko, R. Pilipenko, S. Zorzetti, D. Frolov, M. Awida, S. Posen, A. Grassellino, arXiv:1810.03703