Observation of the Fundamental Nyquist Noise Limit in an Ultra-High $Q$-Factor Cryogenic Bulk Acoustic Wave Cavity

Abstract

Thermal Nyquist noise fluctuations of high-$Q$ Bulk Acoustic Wave (BAW) cavities have been observed at cryogenic temperatures with a DC Superconducting Quantum Interference Device (SQUID) amplifier. High $Q$ modes with bandwidths of few tens of milliHz produce thermal fluctuations with a Signal-To-Noise ratio of up to 23dB. The estimated effective temperature from the Nyquist noise is in good agreement with the physical temperature of the device, confirming the validity of the equivalent circuit model and the non-existence of any excess resonator self-noise. The measurements also confirm that the quality factor remains extremely high ($Q>10^8$ at low order overtones) for very weak (thermal) system motion at low temperatures, when compared to values measured with relatively strong external excitation. This result represents an enabling step towards operating such a high-Q acoustic device at the standard quantum limit.

appears in Appl. Phys. Lett (2014)

References in corpus (2)

• Gain, directionality and noise in microwave SQUID amplifiers: Input-output approach
• Effects of Geometry on Near Quantum Ground State Behaviour of Phonon-Trapping Acoustic Cavities

Cited by in corpus (16)

• Challenges and Opportunities of Gravitational Wave Searches at MHz to GHz Frequencies
• Detecting High-Frequency Gravitational Waves with Microwave Cavities
• Rare Events Detected with a Bulk Acoustic Wave High Frequency Gravitational Wave Antenna
• MAGO2.0: Electromagnetic Cavities as Mechanical Bars for Gravitational Waves
• Hybrid quantum systems with trapped charged particles
• Challenges and Opportunities of Gravitational Wave Searches above 10 kHz
• Cavity Detection of Gravitational Waves: Where Do We Stand?
• Searching for High Frequency Gravitational Waves with Phonons
• The Multi-mode Acoustic Gravitational Wave Experiment: MAGE
• Improved constraints on minimum length models with a macroscopic low loss phonon cavity
• Gravitational Waves from Preheating in Inflation with Weyl Symmetry
• Temperature coefficients of crystalline-quartz elastic constants over the cryogenic range [4 K, 15 K]
• An array of bulk-acoustic-wave sensors as a high-frequency antenna for gravitational waves
• High-frequency gravitational waves from first-order phase transitions
• Experimental Limits on Planetary Mass Primordial Black Hole Mergers
• The Study of Thermal Fluctuations in Microwave and Mechanical Resonators