Quantum-to-Classical Transition In Quantum Acoustic Dynamics

Quantum acoustodynamics(QAD)mainly studies the interaction between acoustic waves or phonons and quantum systems.It opens up a new research field of quantum optics phenomena with acoustic systems.We use a system formed by capacitive coupling of Surface Acoustic Wave Resonator(SAW Resonator)and superconducting qubits to study how the coupled system evolves from the quantum regime to the classical regime with the increasing of effective temperature.In this way,the limits of quantum-classical transitions in quantum acoustic dynamics are explored details.This thesis is elaborated from the following aspects:First of all,The thesis studies the interaction between the SAW Resonator and the superconducting qubits.We characterize the samples mounted at the mixing chamber of the dilution refrigerator with base temperature?16mK.The energy structures of coupled system are measured through the spectrum versus biased flux.The probing power in the surface acoustic wave Resonator is calibrated using the AC-Stark effect.In the experiment,we observed a clear anti-cross structure,that is,Vacuum Rabi Splitting.when the superconducting qubit is resonant with the SAW resonator with the applied probing power is sufficiently low to keep the average number of phonons inside the resonator less than one.It proves that the coupling system works in the strong coupling regime.Next,we study the quantum-to-classical transition in QAD.In the experiment,thermal noise was introduced by changing the temperature of the mixing chamber of dilution refrigerator.with the influence of thermal phonons on the interaction between the superconducting qubits and the surface acoustic wave resonator,we observed that the anti-cross structure changes with temperature.In theory,we can simulate well with our experimental data by solving the coupled system master equation with Qutip softwave package based on Python.We found that when the thermal fluctuations come from system effective temperature compared to the characteristic energy hf of the coupled system is very low,that is,T(27)hfk_B?149mK,the coupled system works in the quantum regime,and the vacuum Rabi splitting is clearly observed When the system effective tempeature is very high,that is,T(29)hfk_B?149mK,the vacuum Rabi splitting is disappeared,and the coupled system works in the classical regime.WhenT?hfk_B?149mK,the vacuum Rabi splitting gradually disappears,and the quantum-to-classical transition is happening.