Taking Pictures of Quantum Sound Waves

LV12662 - In quantum physics, all objects have a wavelike nature.  The more energy the object possesses, the faster its wave oscillates.  In this work, we study the particles of sound which exist in an ultra-cold gas called a Bose-Einstein condensate.  Previous works measured the energy of the sound particles, but did not observe the corresponding oscillations.  We look directly at these sound particles, and see that they indeed oscillate.  We are able to see the sound particles very clearly with the help of the surrounding Bose-Einstein condensate.  This occurs because the Bose-Einstein condensate is also governed by the laws of quantum physics, so it also acts like a wave.  The large wave of the Bose-Einstein condensate magnifies the small wave of the sound particle.  Upon studying the oscillations of the sound particles, we discovered a surprise.  The oscillation rate is smaller than expected.  This is because the long, narrow Bose-Einstein condensate acts as a flow channel, which only allows certain oscillation rates.  The smaller-than-expected rate implies that the speed of sound is slower than previously thought.  This implies that the Bose-Einstein condensate is less stable than was believed previously.