Single Artificial Atom SASER
Lasing - an effect of orthodox quantum mechanics - was discovered in 1955 and recognized by the Nobel Prize in 1964 due to its fundamentality. Nowadays, lasers and masers routinely work with electromagnetic waves and consist of a resonator with an active medium - usually a system of atoms with population inversion mechanism. Amazingly, quantum mechanics remains valid even when electromagnetic waves are replaced by vibrations of a crystal lattice, and, therefore, photons by phonons, even though are not fundamental particles. By implementing acoustic resonators coupled to an atom with a mechanism of population inversion, the lasing effect in sound can be achieved. In this paper, we demonstrate the single artificial atom SASER (Sound Amplification by Stimulated Emission of Radiation) action by utilizing a surface acoustic wave (SAW) resonator on quartz coupled to a deliberately designed superconducting three-level quantum system (artificial atom), in which population inversion is realized. The SASER operates in the ultrasound range at a frequency about 3 GHz. Acoustic-to-electric signals are converted via piezo-electric effect and the circuit elements; an artificial atom and input/outputs are coupled via the acoustic waves. We observe amplification of the waves and their strong self-emission with a significant narrowing of the linewidth. The phonon number generated in the system exceeds 90.