High Q-factor sapphire whispering gallery mode microwave resonator at single photon energies and millikelvin temperatures

Abstract

The microwave properties of a crystalline sapphire dielectric whispering gallery mode resonator have been measured at very low excitation strength (E/ ω ≈ 1) and low temperatures (T ≈ 30 mK). The measurements were sensitive enough to observe saturation due to a highly detuned electron spin resonance, which limited the loss tangent of the material to about 2 × 10 −8 measured at 13.868 and 13.259 GHz. Small power dependent frequency shifts were also measured which correspond to an added magnetic susceptibility of order 10 −9 . This work shows that quantum limited microwave resonators with Q-factors > 10 8 are possible with the implementation of a sapphire whispering gallery mode system.

High-Cooperativity Cavity QED with Magnons at Microwave Frequencies

“…Because of comparatively high cavity losses, the system demonstrates no nonlinear effects around the working incident power. The number of cavity photons is estimated to be less than 15 on resonance from the known incident power to the cavity, coupling, and Q factor [54,55]. …”

The 3D split-ring cavity lattice: a new metastructure for engineering arrays of coupled microwave harmonic oscillators

“…Also, high quality factors > Q 10 8 have been demonstrated for superconducting re-entrant-type resonators [8]. These 3D closed cavities outperform all known 2D structures popular in circuit quantum electrodynamics (cQED) [17] with the reported value only bettered by cryogenic dielectric resonators at low temperatures [18] and the best acoustical systems [12,13]. The functionality of the linear 3D split-ring metamaterial can be extended by the addition of nonlinear or parametric elements: for example, the 3D split ring cavity lattice could be used for cQED experiments by incorporating Josephson junctions.…”

Superconducting Resonators Based on TiN/Tapering/NbN/Tapering/TiN Heterostructures

“…Fortunately, the critical field can be significantly enhanced by using thin films [19] with the film plane kept parallel to the external magnetic field B 0 . [22] C-cut sapphire wafers were used as the substrate due to its high dielectric constant (%11.5), and its extremely low loss-tangent (%10 À8 at low temperature) [23] to minimize energy loss into the substrates. Epitaxial films, free from structural defects, with smooth and clean surfaces/interfaces are most desired for the application of superconducting resonators.…”