This year marks the 50th anniversary of the first production of ultracold neutrons. They were actually discovered twice at nearly the same time during the cold war, in Dubna in the USSR and in Munich in the western world.

The research group Neutron and Quantum Physics of the Atominstitut wants to commemorate this event with a short correspondence article in Nature, which was be published on the 8th of August and can be found under https://rdcu.be/bNkHb, opens an external URL in a new window. The famous birthday song "Happy Birthday to you" was composed again, using only the acoustic transitions of the qBounce experiment. The frequencies used in this song are only dependant on the mass of the neutron, the acceleration of gravity and the Planck constant.

If the song is played next to a neutron, trapped in the gravitational potential of the earth, the associated Neutron density distributions change accordingly to the music.