Chongfan Technology
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09
2025
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02
Rep. Prog. Phys. | New Breakthrough in Controlling Rydberg Interactions
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However, despite the strong interactions of high-excited Rydberg states, a significant challenge they face is their high sensitivity to external electric fields. The sensitivity of Rydberg states to electric fields increases with the seventh power of the principal quantum number, leading to high-excited states being easily disturbed by external electric fields, which can trigger decoherence phenomena. In contrast, Rydberg states with lower principal quantum numbers exhibit greater robustness to external electric fields, maintaining better quantum coherence, but their interactions are weaker, limiting their applications in quantum information processing.
Recently, the National Center for Precision Gravity Measurement and the School of Physics at Huazhong University of Science and TechnologyProfessor Li Lin's research groupcollaborated with the Beijing Institute of Automation Control EquipmentResearcher Chang Yueand the Institute of Theoretical Physics, Chinese Academy of SciencesResearcher Shi Tao, proposing and experimentally verifying a novel scheme for controlling Rydberg atomic interactions. By coupling Rydberg states of different parity, quantum control is achieved at the wave function level, successfully realizing a cross-order magnitude enhancement of interaction strength and significantly expanding the range of interactions. This method is particularly notable in low-excited Rydberg states, promising to enhance interaction strength while maintaining good quantum coherence.
The research results were published inReports on Progress in Physics, titled “Continuously tunable single-photon level nonlinearity with Rydberg state wave-function engineering.” The doctoral students from the School of Physics at Huazhong University of Science and TechnologyXu Biao,Ye Genshengand the Beijing Institute of Automation Control Equipment'sResearcher Chang Yueare the joint first authors of this work.Professor Li LinandResearcher Chang Yueare the corresponding authors. Major collaborators also includeResearcher Shi Taofrom the Institute of Theoretical Physics, Chinese Academy of Sciences. Huazhong University of Science and Technology is the primary completion unit. This work was supported by the National Key R&D Program of the Ministry of Science and Technology, the National Natural Science Foundation, and the National Major Scientific Infrastructure for Precision Gravity Measurement at Huazhong University of Science and Technology. It is reported that Professor Li Lin has been engaged in research related to Rydberg atomic quantum information since 2010. The research group has made significant experimental progress in high-quality single-photon sources based on Rydberg atoms and photonic quantum logic gates(Nature Communications, 13, 4454 (2022)), high-fidelity quantum entanglement operations(Nature Photonics, 17, 538 (2023)), and atomic array quantum information(arXiv:2410.15455 (2024)).
Interaction control based on Rydberg microwave-dressed states
To further promote the development of scalable photonic quantum information processing technology, it is necessary to achieve nonlinear effects at the single-photon level while also ensuring tunability. This tunability is crucial in quantum information processing as it enables robust and high-fidelity photonic quantum logic operations, which have profound implications for constructing large-scale photonic quantum information processing circuits. Additionally, precise control of the Hamiltonian of multiphoton interactions can provide possibilities for studying many-body photonic quantum states and exploring dynamic behaviors in quantum phase transitions.
The single-photon nonlinear effects mediated by Rydberg atoms can be adjusted by controlling the strength of the interactions between atoms, typically by changing the principal quantum number n to adjust the van der Waals interaction coefficientC6. However, simply adjusting nto change the interaction method not only fails to achieve continuous control of the interaction but also makes it difficult to dynamically control the interaction strength.
In this study, the research team proposed a novel scheme for controlling Rydberg atomic interactions. Unlike traditional methods, this scheme does not rely on a single Rydberg state but instead uses a tunable Rabi frequency and detuned microwave field to couple two Rydberg states with opposite parity, forming Rydberg microwave-dressed states. By adjusting the parameters of the microwave field, the wave function structure in the dressed state can be precisely controlled, thereby realizing the transformation of Rydberg interactions from the initial van der Waals form(~C6/R6)to a continuously tunable resonant dipole-dipole interaction form.(~C3/R3).
Since the dipole-dipole interaction scales withn4while the van der Waals interaction scales with n11, the microwave-dressed state scheme has significant advantages at low Rydberg states. The study shows that at a principal quantum number n of 47, the distance between Rydberg atomsR~20μmIn this case, by adjusting the detuning of the microwave field, continuous control of the interaction strength can be achieved over nearly three orders of magnitude. This new scheme provides a more flexible and efficient means to achieve fine control of Rydberg atom interactions and opens up new directions for the study and application of single-photon nonlinear effects.
Continuous two-dimensional control of single-photon level nonlinear effects
The interaction control scheme based on Rydberg microwave dressed states can be applied to accelerate quantum operations based on Rydberg decoherence mechanisms. Although this decoherence mechanism has been successfully applied to various optical quantum operations, low-n Rydberg states typically lead to insufficient interaction strength, requiring longer coherence times to complete quantum operations driven by decoherence mechanisms. To address this issue, the research team proposed a new scheme that effectively overcomes this challenge by enhancing the interaction strength by several orders of magnitude. The research shows that this scheme can significantly accelerate the generation of single-photon states at low principal quantum numbers.
The research team selected low-excitation Rydberg states with principal quantum number n~47, successfully enhancing the interaction strength by adjusting different excitation parameters and dressing parameters, significantly accelerating the quantum operation process. At the same time, the research team utilized the good interaction between Rydberg atoms and photons to extend this technology to the regulation of optical nonlinearity, achieving single-photon level nonlinear effects and allowing for continuous adjustment over a large dynamic range. For example, in experiments preparing high-quality Rydberg single photons, this technology achieved an operational speed increase of over 40 times.
In addition, another significant advantage of this scheme is its programmability. The scheme allows for real-time control of the wave function during the dynamical evolution process, thereby dynamically adjusting the time evolution of the system Hamiltonian. Within a single experimental sequence, researchers can adjust the intensity of single-photon nonlinearity by dynamically turning the microwave field on or off, a capability that cannot be achieved by traditional methods of adjusting the principal quantum number. Therefore, this scheme is not only suitable for dynamically controlling the wave function but also allows for flexible manipulation of the Hamiltonian, providing new avenues for realizing complex time-varying Hamiltonians.
Summary and Outlook
The research team proposed and validated a novel Rydberg interaction control scheme, achieving cross-order continuous adjustment of Rydberg interactions through precise control of the wave function of Rydberg microwave dressed states, filling the gap in the field of Rydberg quantum optics where continuous control of single-photon level nonlinear effects was not achievable. This research not only proposes a new technical path for interaction control of low-excitation Rydberg states, significantly enhancing the control capability of interactions, but also provides new possibilities for developing fast, high-fidelity, and high-depth quantum circuits. Considering that the operational speed of quantum logic gates in Rydberg quantum computing is inversely proportional to the strength of Rydberg interactions, this advancement also holds significant potential application value in the field of quantum computing. Given the unique advantages of Rydberg atoms in atomic-photon information conversion, the research results are expected to find practical applications in cutting-edge fields such as distributed quantum computing.
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