Qing-Feng Sun’s Research Group and Collaborators Achieve Orbital Hybridization in Artificial Atoms
Recently, Professor Qing-Feng Sun’s research group from Peking University, in collaboration with Professor Lin He’s research group from Beijing Normal University, has achieved orbital hybridization in artificial atoms for the first time. The related research, titled Orbital hybridization in graphene-based artificial atoms, was published online in Nature on February 26, 2025 [1].
Quantum dots, due to confinement effects, form bound states with different orbitals, which are similar to the orbitals of real atoms. Therefore, quantum dots are also referred to as artificial atoms and are used to simulate the characteristics of real atoms. In recent years, Professor Qing-Feng Sun’s group and Professor Lin He’s group have collaborated to obtain a series of important findings in confined graphene systems. They induced a continuous change of Berry phase and manipulated the valley degree of freedom in bilayer graphene quantum dots under an applied magnetic field [Phys. Rev. Lett. 124, 166801 (2020); Phys. Rev. Lett. 128, 206805 (2022)] [2, 3]. They also achieved the manipulation of valley states via pseudomagnetic and real magnetic fields in monolayer graphene [Phys. Rev. Lett. 129, 076802 (2022)] [4]. Furthermore, they show a single wavefront dislocation induced by orbital angular momentum in graphene with the asymmetric confining potential [Nat. Commun. 15, 3546 (2024)] [5]. They discovered the coexistence of atomic collapse state and whispering gallery mode in monolayer graphene quantum dots [Nat. Commun. 13, 1597 (2022)] [6], and further demonstrated the evolution from atomic collapse states, to molecular collapse states, and finally to whispering gallery mode in coupled quantum dots [Phys. Rev. Lett. 130, 076202 (2023)] [7]. Additionally, they systematically regulated the molecular state properties by continuously tuning the distance between two quantum dots [Nat. Commun. 15, 8786 (2024)] [8]. In addition, they also realized molecular states by introducing potential barriers in single quantum dots [ACS Nano 19, 1352 (2025)] [9].
Matter is composed of atoms. When atoms condense to form the matter, two crucial processes occur: one is the intraatomic orbital hybridization, and the other is the interatomic chemical bond. Artificial atoms (i.e., quantum dots) have been used to successfully simulate the formation of chemical bonds in real atoms. Including Qing-Feng Sun’s group and Lin He’s group, researchers have realized the artificial bonding and antibonding states by coupling quantum dots. But the other crucial process in real atoms, orbital hybridization, had not yet been simulated by artificial atoms.
To address this gap, Professor Qing-Feng Sun’s group developed the theory of orbital hybridization in artificial atoms, proposing that the anisotropic potential in artificial atoms can induce the hybridization between confined states of different orbitals with close energies. Specifically, they pointed out that by deforming the circular potential in graphene quantum dots into an elliptical potential, orbital hybridization would occur between the s orbital (orbital quantum number 0) and the d orbital (orbital quantum number 2), which recombine to form two hybridized states.
Fig. 1. Upper panels: The schematic plots of (a) unhybridized orbitals and (b) sp2 orbital hybridization in real atoms. Lower panels: The schematic plots of (c) circular potential and (d) elliptical potential in graphene-based artificial atoms.
Qing-Feng Sun’s group obtained the shape of these hybridized states (θ shape and rotated θ shape) through analytical derivations and numerical calculations. Lin He’s group experimentally probed the confined states in various quantum dots, directly observing the orbital hybridization features. The experimental and theoretical results mutually confirmed that orbital hybridization indeed occurred in elliptical graphene quantum dots. This hybridization is a recombination between the atomic collapse state and the whispering gallery mode, where the hybridized states contain both of their components. The atomic collapse is the phenomenon predicted in quantum electrodynamics, and the whispering gallery effect is an acoustic phenomenon. They were usually considered to have completely different physical mechanisms. However, this work reveals the profound connection between these two effects. In addition, as the anisotropy of the quantum dots gradually increases, the strength of hybridization gradually increases, and the energies of the two hybridized states gradually split. This behavior was confirmed both experimentally and theoretically.
Fig. 2. (a, b) Numerically calculated hybridized states (θ shape and rotated θ shape). (c, d) Experimentally observed hybridized states. (e) Hybridized states split in energy versus the deformation of quantum dot.
This research was published online in Nature on February 26, 2025 [1]. The PhD students Yue Mao (Peking University), Hui-Ying Ren (Beijing Normal University), and Xiao-Feng Zhou (Beijing Normal University) are the co-first authors of the paper. Professor Qing-Feng Sun (Peking University), Professor Lin He (Beijing Normal University), and postdoctoral researcher Ya-Ning Ren (Beijing Normal University) are the corresponding authors. The other collaborators include postdoctoral researcher Yu-Chen Zhuang (Peking University), PhD students Hao Sheng (Beijing Normal University) and Yun-Hao Xiao (Beijing Normal University). This work was financially supported by the National Key R and D Programme of China, the National Natural Science Foundation of China, the Innovation Programme for Quantum Science and Technology, ‘the Fundamental Research Funds for the Central Universities’, the China National Postdoctoral Program for Innovative Talents, and the China Postdoctoral Science Foundation.
References:
[1] https://www.nature.com/articles/s41586-025-08620-z
[2] https://doi.org/10.1103/PhysRevLett.124.166801
[3] https://doi.org/10.1103/PhysRevLett.128.206805
[4] https://doi.org/10.1103/PhysRevLett.129.076802
[5] https://doi.org/10.1038/s41467-024-47756-w
[6] https://doi.org/10.1038/s41467-022-29251-2
[7] https://doi.org/10.1103/PhysRevLett.130.076202