Studying Qubit Interactions with Multimode Cavities Using QuTiP

TL;DR

This paper uses QuTiP to simulate complex qubit-cavity interactions, replicating experimental results and exploring effects of coupling strength, multiple cavities, and thermal losses in quantum systems.

Contribution

It develops simulation techniques for multi-mode qubit-cavity systems and validates them against experimental data, highlighting the advantages of multiple cavities for energy transfer.

Findings

Stronger couplings increase eigen-mode separation.

Multiple cavities improve energy transfer efficiency.

Simulation results closely match experimental data.

Abstract

The project uses QuTiP, a quantum computing framework, to simulate interactions between two-qubits coupled with each other via three resonators. The main aim of this project is to build machinery of techniques to understand complex qubit-cavity interactions using QuTiP's functionalities. The system simulated mimics the one constructed by McKay et. al. (M15) and the results of the simulations closely agree with M15's experimental results. The effect of the coupling strength between the qubits and the cavities is studied. It was observed that stronger couplings generated larger separations between the eigen-modes. Studies involving resonance were used to construct the iSWAP gate, a universal quantum logic gate. This study showed the importance of external thermal losses due to cavity dissipation, and qubit decay and dephasing. The Landau-Zener model was tested for the case of multiple crossing; the model motivated the comparison of three scenarios where the 2 qubits were coupled via 1 cavity, 3 cavities, and 6 cavities. The study concluded that having multiple modes, which is a consequence of having multiple cavities, is advantageous for transferring energy from the qubit to the cavity. Finally, the ac-Stark shift was measured in the system and its dynamics showed excellent agreement with the experimental results obtained by M15.