# Phonon-mediated quantum state transfer and remote qubit entanglement

## TL;DR

This paper demonstrates the deterministic emission, capture, and transfer of surface acoustic wave phonons to entangle distant superconducting qubits, showcasing a promising quantum communication channel with high fidelity.

## Contribution

It introduces a method for phonon-mediated quantum state transfer and entanglement between superconducting qubits over a 2 mm acoustic channel.

## Key findings

- Achieved 67% quantum state transfer efficiency.
- Generated Bell pairs with 84% fidelity.
- Demonstrated phonon emission and re-capture over 500 ns delay.

## Abstract

Phonons, and in particular surface acoustic wave phonons, have been proposed as a means to coherently couple distant solid-state quantum systems. Recent experiments have shown that superconducting qubits can control and detect individual phonons in a resonant structure, enabling the coherent generation and measurement of complex stationary phonon states. Here, we report the deterministic emission and capture of itinerant surface acoustic wave phonons, enabling the quantum entanglement of two superconducting qubits. Using a 2 mm-long acoustic quantum communication channel, equivalent to a 500 ns delay line, we demonstrate the emission and re-capture of a phonon by one qubit; quantum state transfer between two qubits with a 67\% efficiency; and, by partial transfer of a phonon between two qubits, generation of an entangled Bell pair with a fidelity of $\mathcal{F}_B = 84 \pm 1$ %