Quantum Phononics: From Principles to Engineering

Phonons, the vibrational quanta of substances, are of fundamental importance in chemical physics, condensed matter physics, materials science, and quantum science and technology. Manipulating phonons with electron-phonon coupling and spin-phonon coupling to realize charge transfer, energy transport, and spin control has many applications such as photodetectors, electroluminescence, heat engines, and spin-dependent solid-state quantum computation. With technological advancement, the investigation of the quantum nature of phonons is rapidly growing, leading to the recent fast development of "quantum phononics". This emerging field places greater emphasis on the wavefunction rather than the energy spectrum of phonons. In this Perspective, we focus on some important concepts and intriguing properties of quantum phononics, including the phonon coherence state, the squeezed state, the entangled state, quantum acoustics, and intrinsic phonon spin. We review the recent developments and applications of these quantum properties of phonons. With the superiority of low noise and good coherence, these nonclassical phonon states can be widely used for quantum state manipulation. Finally, we point out several potential research directions in quantum phononics.