Quantum versus Classical Regime in Circuit Quantum Acoustodynamics

TL;DR

This paper experimentally investigates a circuit quantum acoustodynamics system, demonstrating strong coupling, control of microwave photon propagation by phonons, and observing a quantum-to-classical transition influenced by temperature.

Contribution

It provides the first experimental observation of the quantum-to-classical transition in a circuit quantum acoustodynamics system, linking temperature effects to spectral changes and system behavior.

Findings

Strong coupling confirmed by vacuum Rabi splitting

Microwave photon control via phonons demonstrated

Quantum-to-classical transition observed around crossover temperature

Abstract

We experimentally study a circuit quantum acoustodynamics system, which consists of a superconducting artificial atom, coupled to both a two-dimensional surface acoustic wave resonator and a one-dimensional microwave transmission line. The strong coupling between the artificial atom and the acoustic wave resonator is confirmed by the observation of the vacuum Rabi splitting at the base temperature of dilution refrigerator. We show that the propagation of microwave photons in the microwave transmission line can be controlled by a few phonons in the acoustic wave resonator. Furthermore, we demonstrate the temperature effect on the measurements of the Rabi splitting and temperature induced transitions from high excited dressed states. We find that the spectrum structure of two-peak for the Rabi splitting becomes into those of several peaks, and gradually disappears with the increase of the environmental temperature $T$. The quantum-to-classical transition is observed around the crossover temperature $T_{c}$, which is determined via the thermal fluctuation energy $k_{B}T$ and the characteristic energy level spacing of the coupled system. Experimental results agree well with the theoretical simulations via the master equation of the coupled system at different effective temperatures.