PRL cover! CSU team makes another important progress
Recently, Prof. Guo Guoping and Prof. Cao Gang from the team of Academician Guo Guangcan of the University of Science and Technology of China (USTC), in collaboration with Senior Researcher Sigmund Kohler of the Institute of Materials Science, Madrid, and Hongyuan Quantum Computing Ltd. have experimentally and theoretically investigated non-dispersive coupled driven quantum dot-microwave resonant cavity hybridization systems, and developed and validated a response-theoretic method that can be applied to systems with different coupling strengths and multiple quantum bits. The research results were published on June 9, 2012 as the cover story of the paper.
The research results were published as a cover article in Physical Review Letters, a leading international physics journal, on June 9.
This time, Sisi Gu, a PhD student at the Key Laboratory of Quantum Information, CAS, was the first author of the paper, and Guoping Guo, Gang Cao and Sigmund Koller at the Institute of Materials Science, Madrid, were the co-corresponding authors. The work was funded by the Ministry of Science and Technology and the National Natural Science Foundation of China.
Semiconductor quantum dots (QDs) coupled to superconducting cavities provide a platform to study and exploit light-matter interactions, which have great potential for applications in solid-state quantum information processing. Since the coupling strength between cavities and quantum bits determines the speed of gate operation and information exchange, the development of cQED setups with strong interactions is of high interest. Experimental advances in QD-based cQEDs (e.g., high-impedance superconducting cavities) greatly increase the coupling strength and allow a systematic study of the Jaynes-Cummings model, the quantum Rabi (Rabi) model, and the physics of topologies.
In addition, it provides a direct path to integrate multiple quantum bits.
Strong periodic driving (STRONG) is a powerful and widely used tool in quantum control, quantum simulation and system characterization. The study of the corresponding Floquet dynamics is crucial for understanding such strongly driven systems and provides a solid foundation for further improvements in practical applications.
However, the weak coupling regime, which is the focus of most existing experimental and theoretical work, cannot meet the emerging need for large coupling strengths for coherent quantum information exchange and scalable quantum networks; the dynamics of driven multi-qubit-cavity systems (MQCS) remains a problem.
In the previous work (Science Bulletin 66, 332-338 (2021)), the group realized the strong coupling of quantum dot-microwave resonant cavity hybrid system with the help of high-impedance superconducting microwave resonant cavity. Based on this, this group further investigated the dynamics of the strongly coupled hybridized system under periodic driving.
Specifically, the team demonstrated a strongly driven hybrid system consisting of two spatially separated GaAs quantum dots coupled to a superconducting NbTiN cavity.
Benefiting from the enhanced coupling strength of the high-impedance cavity, the system works beyond the scope of existing theory. The team says, "In contrast to these theories that treat DQD as a relatively independent strongly driven system with weak coupling strength, here we further develop a generalized theory by considering the Floquet state of the fully hybrid system. In doing so, we treat the cavity as part of the central driving system, which provides a method that applies to arbitrarily strong DQD-cavity coupling and also captures the cavity-mediated interactions between different DQDs."
The Landau-Zener-St¨uckelberg-Majorana (LZSM) interference pattern and splitting (splitting) driving the single DQD-cavity setup, as well as the expanded splitting of the double DQD-cavity system, were observed in the cavity transport at the time of the experiment.
-- At a quantitative level, the team has also demonstrated excellent agreement between calculated and measured LZSM patterns in cases where the limitations of the former approach become apparent.
Further, the article states, "We have analyzed these results and reproduced them well with our model."
Figure (a) shows a half-wavelength superconducting NbTiN transmission cavity containing two DQDs separated by a distance of about 670 µm. the DQDs are formed in a GaAs/AlGaAs quantum well with gates [inset]. The occupancy numbers (mj , nj ) in the DQDj are controlled by the gate voltages VBRj and VBLj as shown in figures (b) and (c).
Figure (b) shows the interference pattern calculated under the set parameters. It is streaked in accordance with the resonance condition, but for some values of the driving parameters, the theoretical prediction of the transmission is considerably more than unity (red area, marked with arrows), which may indicate the presence of a laser. However, the opposite is the case here, where the DQD coupling strength to the cavity exceeds the linear response limit. In addition, the cavity-mediated interactions between the DQDs are neglected. To overcome these drawbacks, the team developed a response-theoretic approach for driving quantum bits, where the cavity is considered as part of the central system. Figure (c) illustrates this idea of single DQD coupling to the cavity, which will allow the team to deal with setups with arbitrarily strong DQD-cavity coupling.
Spectral measurement results.
These experimental and theoretical studies provide a new perspective for understanding quantum dot-resonant cavity hybridization systems driven by periodicity. At the same time, the theoretical approach developed and verified in this work is well generalized and scalable, not only for hybridized systems with different coupling strengths, but also to more bits, and may be applied to other physical systems as well.
Reference links:
[1] http://news.ustc.edu.cn/info/1055/83582.htm
[2]https://arxiv.org/pdf/2212.10212.pdf
[3]https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.233602
