Abstract
Very high quality factor superconducting radio frequency cavities developed for accelerators can enable fundamental physics searches with orders of magnitude higher sensitivity, as well as offer a path to a 1000-fold increase in the achievable coherence times for cavity-stored quantum states in the 3D circuit QED architecture. Here we report the first measurements of multiple accelerator cavities of $f_0=$1.3, 2.6, 5 GHz resonant frequencies down to temperatures of about 10~mK and field levels down to a few photons, which reveal record high photon lifetimes up to 2 seconds, while also further exposing the role of the two level systems (TLS) in the niobium oxide. We also demonstrate how the TLS contribution can be greatly suppressed by the vacuum heat treatments at 340-450$^\circ$C.
Highlights
Superconducting radio-frequency (SRF) cavities in particle accelerators routinely achieve [1,2] very high quality factors Q > 1010–1011 corresponding to photon lifetimes τ as long as tens of seconds
Recent investigations [8] have revealed that the twolevel systems (TLS) residing inside niobium oxide may play a significant role in the low-field performance of SRF cavities, similar to two-dimensional (2D) resonators [9,10]
Our results demonstrate that SRF cavities can serve as a very long coherence platform for, e.g., 3D circuit QED and quantum memory [4,11] applications, as well as for various fundamental physics experiments, such as dark photon or axion searches [5,6,7]
Summary
Superconducting radio-frequency (SRF) cavities in particle accelerators routinely achieve [1,2] very high quality factors Q > 1010–1011 corresponding to photon lifetimes τ as long as tens of seconds These are much higher than the highest Q ∼ 108 reported in various quantum regime studies [3,4] with τ ∼ 1 ms. We achieve very long photon lifetimes of more than 2 s, and observe a Q decrease when going from previously explored temperatures of 1.3 K or above down to below 20 mK This is a direct study of the TLS in 3D Nb resonators in the quantum regime, as well as a demonstration of the drastic TLS-induced dissipation decrease associated with the oxide removal. Our results demonstrate that SRF cavities can serve as a very long coherence platform for, e.g., 3D circuit QED and quantum memory [4,11] applications, as well as for various fundamental physics experiments, such as dark photon or axion searches [5,6,7]
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