Single Crystal Sapphire at milli-Kelvin Temperatures: Observation of Electromagnetically Induced Thermal Bistability in High Q-factor Whispering Gallery Modes

Abstract

Resonance modes in single crystal sapphire ($\alpha$-Al${}_2$O${}_3$) exhibit extremely high electrical and mechanical Q-factors ($\approx 10^9$ at 4K), which are important characteristics for electromechanical experiments at the quantum limit. We report the first cooldown of a bulk sapphire sample below superfluid liquid helium temperature (1.6K) to as low as 25mK. The electromagnetic properties were characterised at microwave frequencies, and we report the first observation of electromagnetically induced thermal bistability in whispering gallery modes due to the material $T^3$ dependence on thermal conductivity and the ultra-low dielectric loss tangent. We identify "magic temperatures" between 80 to 2100 mK, the lowest ever measured, at which the onset of bistability is suppressed and the frequency-temperature dependence is annulled. These phenomena at low temperatures make sapphire suitable for quantum metrology and ultra-stable clock applications, including the possible realization of the first quantum limited sapphire clock.

5 pages, 4 figures

References in corpus (3)

• A widely tunable parametric amplifier based on a SQUID array resonator
• Cryogenic sapphire oscillator with exceptionally high long-term frequency stability
• Measurement of fundamental thermal noise limit in a cryogenic sapphire frequency standard using bimodal maser oscillations

Cited by in corpus (9)

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• Towards achieving strong coupling in 3D-cavity with solid state spin resonance
• Hybrid Electron Spin Resonance and Whispering Gallery Mode Resonance Spectroscopy of Fe3+ in Sapphire
• Controlling the Frequency-Temperature Sensitivity of a Cryogenic Sapphire Maser Frequency Standard by Manipulating Fe3+ Spins in the Sapphire Lattice
• Time-resolved and Superradiantly Amplified Unruh Effect
• Jump Chaotic Behaviour of Ultra Low Loss Bulk Acoustic Wave Cavities
• Determination of Niobium Cavity Magnetic Field Screening via a Dispersively Hybridized Magnonic Sensor
• Towards Photonics Enabled Quantum Metrology of Temperature, Pressure and Vacuum
• Developing Microwave Photonic Temperature Sensors