In 1971, Zel’dovich predicted that quantum fluctuations and classical waves reflected from a rotating absorbing cylinder will gain energy and be amplified. This concept, which is a key step towards the understanding that black holes may amplify quantum fluctuations, has not been verified experimentally owing to the challenging experimental requirement that the cylinder rotation rate must be larger than the incoming wave frequency. Here, we demonstrate experimentally that these conditions can be satisfied with acoustic waves. We show that low-frequency acoustic modes with orbital angular momentum are transmitted through an absorbing rotating disk and amplified by up to 30% or more when the disk rotation rate satisfies the Zel’dovich condition. These experiments address an outstanding problem in fundamental physics and have implications for future research into the extraction of energy from rotating systems.

1971年，Zel'dovich预测从旋转的吸收圆柱体反射的量子涨落和经典波将获得能量并被放大。这个概念是通向理解黑洞可能会放大量子涨落的关键一步，由于具有挑战性的实验要求，即圆柱旋转速度必须大于入射波频率，因此尚未进行实验验证。在这里，我们通过实验证明，声波可以满足这些条件。我们表明，当圆盘转速满足Zel'dovich条件时，具有轨道角动量的低频声模将通过吸收性旋转圆盘传输并放大多达30％或更多。