Quartz resonators at cryogenic temperatures: Noise and quality factor

Bulk acoustic wave quartz crystal resonators exhibit 1/f frequency noise. Some theories attempt to explain the origin of this flicker noise and relate the quality factor Q of the resonator to its noise level such that a high Q-factor is required to reach a low noise level. This point is confirmed by experience and justifies tests at very low temperature. Indeed, a few years ago, it had been shown that quartz losses (i.e 1/Q), dramatically decreased below 20 Kelvins. Experiments have been performed using a pulse tube cryocooler. Various power spectral densities of resonator noise are presented and discussed, depending on the experimental environment conditions, especially regarding vibrations and temperature fluctuations around 4K. Moreover, measurements had also been performed down to 20 mK by means of a dilution cryorefrigerator. Some resonance modes at more than 50 MHz exhibit outstanding Q-values greater than 1 billion. With such values, electromagnetic cooling techniques such as parametric cold damping or feedback cooling are achievable. Future suitable prospects are described.