Researchers Model Driven Light-matter Interactions, Accurately Capturing Key Dynamics across Platforms

Accurate modelling of how light interacts with matter underpins many emerging technologies, including those employing artificial atoms to store information and manipulate quantum states. Martin Jirlow, Kunal Helambe, and Axel M. Eriksson, along with colleagues at Chalmers University of Technology, address a significant challenge in this field: the difficulty of precisely describing systems subjected to complex, multi-tone drives. The team develops a new, effective Hamiltonian, a mathematical framework, that focuses on the slowly changing aspects of these interactions, providing a more accurate and broadly applicable model across various platforms. This advancement allows for quantitative prediction of experimental results, as demonstrated by its successful reproduction of key phenomena like ac Stark shifts and two-mode squeezing in circuit QED systems, ultimately offering a powerful tool for engineering quantum interactions in future processing technologies.

Driven Qubit-Cavity Interactions and Accurate Modeling

Accurate modeling of driven light-matter interactions is essential for developing quantum technologies, where both natural and artificial atoms are used to store and process quantum information, mediate interactions between different types of waves, and enable advanced quantum functionalities. Precisely describing these interactions underpins the development of robust and scalable quantum systems, particularly those employing superconducting qubits and microwave cavities. Current theoretical approaches often rely on approximations that become inadequate when dealing with strong driving fields or complex system parameters, limiting the fidelity of simulations and the predictability of experimental outcomes. Therefore, a more comprehensive and accurate theoretical framework is needed to facilitate the design of improved quantum devices.

This work addresses these challenges by presenting a derivation of an effective Hamiltonian for an off-resonantly driven qubit-cavity system that systematically incorporates higher-order terms. The method involves a canonical transformation to a rotating frame, followed by a perturbative expansion of the Hamiltonian in powers of the driving field amplitude. By retaining terms up to second order in the expansion, the resulting effective Hamiltonian accurately captures the effects of strong driving and significant qubit-cavity coupling. The objective is to provide a theoretical tool that enables more accurate simulations and predictions for a wide range of experimental scenarios, ultimately contributing to the advancement of quantum technologies.

Nonlinear operations are fundamental to quantum information processing, but theoretical descriptions become challenging in systems subject to multi-tone drives. Researchers derive an effective Hamiltonian that retains slowly rotating terms, providing a general framework for accurately describing driven dynamics across various platforms. Validation of this model, specifically within circuit QED, demonstrates its ability to quantitatively reproduce experimentally measured ac Stark shifts and capture key interactions like two-mode squeezing and beam-splitting. The results establish a broadly applicable tool to engineer driven interactions in quantum information processing platforms.

Higher Order Terms Validate Strong Coupling Model

This supplementary material provides detailed support for the claims made in the main paper, demonstrating the importance of including higher-order terms in the effective Hamiltonian when modeling strong coupling between a qubit and a cavity, particularly at small detunings. The conventional displaced-frame approach fails to accurately capture the observed behaviour, while the more complete model aligns much better with experimental results. The material also validates the model’s predictions for cavity Stark shifts, demonstrating that a more complete theoretical description is necessary for accurate modelling. The material lists the specific numerical values used for the system parameters in the simulations, allowing for reproducibility of the results. Simulation results for the qubit population during a two-mode squeezing transition are presented, comparing the predictions of the conventional approach and the more complete model against experimental data. The more complete model provides a much better match to the experimental data, especially for lower photon number states, highlighting the importance of including higher-order terms when dealing with strong coupling and small detunings.

Driven Interactions, Accurate Quantum Modelling Demonstrated

This research presents a new theoretical framework for accurately modeling the interaction between light and matter when driven by multiple tones. The team developed an effective Hamiltonian that focuses on slowly rotating terms, offering a more precise description of driven dynamics across various platforms. The significance of this work lies in providing a broadly applicable tool for engineering driven interactions in quantum processing systems, potentially leading to advancements in quantum technologies. The model addresses limitations found in existing approaches, particularly when dealing with multi-tone drives where conventional methods struggle to align with experimental data. While the model accurately predicts Stark shifts, minor discrepancies remain compared to experimental results. Future research could focus on incorporating additional effects or exploring the model’s applicability to other physical platforms beyond circuit QED, potentially refining its accuracy and expanding its utility in the field of quantum information processing.