A team of physicists led by Niels Otterstrom cooled free phonons — quasi-particles that reflect the character of atomic oscillations in a solid. They managed to achieve a temperature difference of 30 degrees Celsius.
This is the first time that scientists have managed to cool the sound wave in practice. Prior to this, a similar procedure was performed using optomechanical cavities, which limits the use of laser cooling. By cooling phonons directly, it is possible to obtain the so-called compressed quantum states, which are used to detect gravitational waves.
In order to achieve this result, physicists for a long time selected the necessary configuration of waves that would ensure the maximum interaction between laser photons and phonons in a sound wave. Scientists also developed a detailed sound wave model and theoretically substantiated the process of its cooling.
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