&Bullet; physics 14, s54
An experiment with a nanoscale clock confirms that the entropy of a clock increases per tick as the clock is made more precise.
Entropy generally increases with every tick of time, so it is natural for a timepiece to produce an increase in entropy during operation. Building on earlier work with quantum clocks, researchers are now showing that a simple classic clock – the ticks of which are the vibrations of a heat-driven, nanometer-thick membrane – generates more entropy with increasing precision  . The experiments open a new line to investigate how nanomachines can convert random input into useful work.
A clock is a machine and, like all machines, obeys the laws of thermodynamics. Previous studies have looked at quantum clocks and found a linear relationship between their accuracy and the entropy they create (see Viewpoint: The Thermodynamic Costs of Timekeeping). However, whether this relationship holds true for classic watches is uncertain as it is more difficult to track the energy in and out of these larger devices.
Natalia Ares of Oxford University, UK, and colleagues designed a classic clock with adjustable precision that allowed them to measure energy flows. Their system consisted of a silicon nitride membrane that was suspended over metal electrodes and formed a tiny cavity.
The researchers applied a noisy signal to the electrodes, causing the membrane to vibrate at a resonant frequency. A circuit connected to the cavity measured the membrane vibrations and registered a “tick” for each vibration cycle. By increasing the energy or “heat” in the input signal, the team was able to increase the vibration amplitude and thereby improve the precision of the membrane measurements. They found that the entropy costs – estimated by measuring the heat loss in the probe circuit – increased linearly with accuracy in accordance with the behavior of the quantum clock.
Michael Schirber is the corresponding editor for physics based in Lyon, France.
- A Pearson et al., “Measurement of the thermodynamic costs of time measurement” Phys. Rev. X.11021029 (2021).