Quantum State Transfer Using Surface Acoustic Wave Phonons*

Heavily used in classical signal processing, surface acoustic waves (SAWs) have also been proposed as a means to couple distant solid-state quantum systems. Several groups have reported the coherent coupling of standing SAWs modes to superconducting qubits, opening the door to the control and detection of quantum phonon states. Here, we explore the coherent coupling of superconducting qubits to propagating SAWs. The experimental device comprises a 2-mm-long SAW resonator coupled to two xmon-style qubits. The resonator operates at 4 GHz and sustains 70 standing SAW modes with a free spectral range of 2 MHz. We demonstrate that each qubit reaches the strong multi-mode regime, where the coupling to one standing mode exceeds the resonator free spectral range. We show that in this regime, each qubit can launch a propagating SAW into the resonator and capture it at a later time, showing that the SAW resonator can act as an acoustic communication channel. We perform quantum state transfer as well as remote entanglement generation between the two qubits using this acoustic channel.