A Single-mode Phononic Wire*

Photons and electrons transmit information to form complex systems and networks. Phonons on the other hand are often considered only as carriers of thermal energy. Nonetheless, their flow can also be molded in fabricated nanoscale circuits. We design and experimentally demonstrate wires, or waveguides, for phonons that transmit information with little loss or scattering across a chip. By patterning the surface of a silicon chip, we completely eliminate all but one channel of phonon conduction. At cryogenic (11 K) temperatures, we observe the emergence of low-loss (0.88 dB/cm) GHz standing waves in millimeter long phononic wires that we address and cool optically. We show optically induced damping of the wire modes, with readout cooperativities exceeding unity. In turn, sympathetic laser cooling of the waveguide is achieved, reaching occupancies approximately 3 dB below that of the intrinsic bath. Coherent transport and strong optical coupling to a phononic wire enables new phononic technologies to manipulate information and energy on a chip.