High-Q mechanical resonator and novel optomechanical devices
Cavity optomechanics explores how electromagnetic fields entwine with mechanical motion to create powerful tools for quantum information, ultra-sensitive sensing and fundamental physics. At the heart of these ambitions lie mechanical resonators whose energy lingers for as long as possible—resonators whose quality factors (Q) approach the limits set by Nature.
Our group designs and fabricates such resonators from three complementary material platforms:
• High-stress and ultra-low-loss silicon nitride (SiN) and silicon carbide (SiC) membranes,
• Stress engineered superconducting metals (Nb, Al, NbTiN),
• Thin-film piezoelectric and electro-opto crystals (AlN, GaAs, LiNbO3).
By sculpting phononic bandgaps around the mechanical modes, we have already reached quality factors above 10⁸. This record coherence has enabled demonstrations of motional ground-state cooling, long-lived storage of quantum states, and bidirectional microwave-to-optical conversion. Superconducting variants, meanwhile, yield large single-photon cooperativity and seamless integration with planar superconducting circuits. We are now pushing mechanical Q beyond 10⁹ and coherence times into the multi-second regime. Such devices will serve as universal transducers linking superconducting qubits to telecom photons, as memory elements for photonic cluster states, and as force sensors capable of weighing single nuclear spins.
参考文献：
1.Yulong Liu, Qichun Liu, Shuaipeng Wang, Zhen Chen, Mika A. Sillanpää*, and Tiefu Li#, Optomechanical Anti-Lasing with Infinite Group Delay at a Phase Singularity, Physic Review Letters 127, 273603 (2021).
DOI: https://doi.org/10.1103/PhysRevLett.127.273603
arXiv 链接： https://arxiv.org/pdf/2112.06521
2.Sishi Wu, Yulong Liu‡, Qichun Liu, Shuaipeng Wang, Zhen Chen, and Tiefu Li#, Hybridized frequency combs in multimode cavity electromechanical system, Physic Review Letters 128, 153901 (2022).
DOI: https://doi.org/10.1103/PhysRevLett.128.153901
arXiv: 链接：https://arxiv.org/pdf/2203.06536
3.Yulong Liu, Jingwei Zhou, Laure M. de Lépinay, and Mika A. Sillanpää#, Quantum backaction evading measurements of a silicon nitride membrane resonator, New Journal of Physics 24, 083043 (2022).
DOI: https://iopscience.iop.org/article/10.1088/1367-2630/ac88ef/meta
arXiv: 链接：https://arxiv.org/pdf/2201.11041v1
4.Yulong Liu‡, Qichun Liu, Huanying Sun, Mo Chen, Shuaipeng Wang, and Tiefu Li#, Coherent memory for microwave photons based on long-lived mechanical excitations, Nature: npj Quantum Information 9, 80 (2023).
DOI: https://www.nature.com/articles/s41534-023-00749-x
5.Yulong Liu‡, Huanying Sun, Qichun Liu, Haihua Wu, Mika A. Sillanpää, and Tiefu Li#,Degeneracy-breaking and long-lived multimode microwave electromechanical systems enabled by cubic silicon-carbide membrane crystals, Nature Communications 16, 1207 (2025).
DOI: https://www.nature.com/articles/s41467-025-56497-3
Quantum optics in ultrastrong coupled superconducting circuits
The field of ultrastrong coupling (USC) represents a groundbreaking regime in quantum light–matter interactions, where the coupling strength between photons and a material system becomes comparable to or even exceeds the system’s characteristic transition frequencies. In the USC regime, non-perturbative effects dominate, resulting in a ground state containing virtual excitations, a breakdown of excitation-number conservation, and the emergence of novel phenomena such as quantum vacuum radiation, enhanced nonlinear processes, and entanglement between light and matter even without real photons.
Research in USC not only deepens our understanding of quantum electrodynamics but also opens pathways toward innovative applications in quantum computing, sensing, and materials science. Our group specializes in quantum optics using ultrastrongly-coupled superconducting circuits. Such circuits provide an ideal platform for reaching the deep-strong coupling regime due to their design flexibility, high coupling strengths, and compatibility with integrated quantum technologies. In particular, flux qubits—featuring macroscopic persistent currents—enable extremely strong inductive coupling to superconducting resonators.
Figures are from Nat. Rev. Phys. 1, 19 (2019) and Rev. Mod. Phys. 91, 025005 (2019).
参考文献：
1.Shuaipeng Wang, Alberto Mercurio, Alessandro Ridolfo, Yuqing Wang, Mo Chen, Wenyan Wang, Yulong Liu, Huanying Sun, Tiefu Li*, Franco Nori, Salvatore Savasta†, and Jianqiang You‡, Strong coupling between a single-photon and a two-photon Fock state, Nature Communications, in press (2025).
DOI: https://arxiv.org/abs/2401.02738
2. Jia-Cheng Tang, Jin Zhao*, Haitao Yang, Junlong Tian, Pinghua Tang, Shuai-Peng Wang†, Lucas Lamata‡, and Jie Peng§, Deterministic two-photon controlled-Z gate with the two-photon quantum Rabi model, Physical Review A 111, 052601 (2025).
DOI: https://doi.org/10.1103/PhysRevA.111.052601
3. Shuai-Peng Wang, Alessandro Ridolfo, Tiefu Li†, Salvatore Savasta‡, Franco Nori*, Yasunobu Nakamura, and Jianqiang You§, Probing the symmetry breaking of a light--matter system by an ancillary qubit, Nature Communications 14, 4397 (2023).
DOI: https://www.nature.com/articles/s41467-023-40097-0
Cryo-CMOS for scalable quantum information processing
Cryo-CMOS circuits operating below 4K represent the most promising solution for controlling large-scale quantum computing systems. They can replace the current bulky and complex room-temperature control systems and can even be integrated directly with quantum chips at ultra-low temperature.
Our group focuses on developing cryo-CMOS circuits for the control and readout of superconducting transmon processors. The control chip includes dedicated XY and Z driver modules for qubits, with the XY driver capable of controlling multiple qubits simultaneously through frequency division multiplexing. The readout chip supports high-fidelity single-shot measurement of more than four qubits.
参考文献：
1.Yanshu Guo, Qichun Liu, Yaoyu Li , Wenqiang Huang, Tian Tian, Siqi Zhang, Nan Wu, Songyao Tan, Ning Deng, Zhihua Wang, Hanjun Jiang, Tiefu Li, Yuanjin Zheng, A Polar-Modulation-Based Cryogenic Transmon Qubit State Controller in 28 nm Bulk CMOS for Superconducting Quantum Computing. Journal of Solid-State Circuits, vol. 58, no. 11, pp. 3060-3073, Nov. 2023.
DOI: https://ieeexplore.ieee.org/abstract/document/10263624
2.Yanshu Guo, Qichun Liu, Wenqiang Huang, Yaoyu Li, Tian Tian, Nan Wu, Siqi Zhang, Tiefu Li, Zhihua Wang, Ning Deng, Yuanjin Zheng, Hanjun Jiang, A Cryo-CMOS Quantum Computing Unit Interface Chipset in 28nm Bulk CMOS with Phase-Detection Based Readout and Phase-Shifter Based Pulse Generation, 2024 IEEE International Solid-State Circuits Conference (ISSCC), San Francisco, CA, USA, 2024, pp. 476-478.
DOI: https://ieeexplore.ieee.org/document/10454392
Quantum Interface and distributed quantum computing
Distributed quantum computing (DQC) is essential for overcoming the limitations of single-node quantum processors, such as restricted qubit counts and coherence times, by interconnecting multiple quantum devices into scalable networks. An efficient quantum interface for transferring between microwave and optical photons is necessary for this process. This microwave-optical transduction is critical for distributed quantum computing, enabling scalable entanglement distribution and fault-tolerant interconnects between heterogeneous quantum processors.
This research focuses on developing a hybrid quantum interface that leverages cavity optomechanics for effective microwave-to-optical photon conversion. By integrating a Fabry-Pérot cavity with a high-Q mechanical membrane resonator and a superconducting microwave cavity, the dual coupling of the membrane to both the optical mode of the Fabry-Pérot cavity and the microwave mode of the superconducting cavity enables efficient quantum state transfer. The proposed architecture facilitates modular quantum hardware integration, enhancing computational power and error resilience—key steps toward realizing a global quantum internet and commercially viable quantum technologies.
参考文献：
1.Wenlong Li, Huanying Sun, Yulong Liu*, Tiefu Li†, and Re-Bing Wu‡, Flying-Qubit Control: Basics, Progress, and Outlook, Advanced Devices & Instrumentation 5, 0059 (2024).
DOI: https://spj.science.org/doi/10.34133/adi.0059
2.Huanying Sun, Yulong Liu*, and Tiefu Li‡, Application perspective of cavity optomechanical system, Frontiers in Quantum Science and Technology 1, 09 (2023).
DOI: https://doi.org/10.3389/frqst.2022.1091691
3.Huanying Sun, Zilong Zhang, Yulong Liu, Guo Chen, Tiefu Li†, Meiyong Liao‡, Diamond MEMS: From Classical to Quantum, Advanced Quantum Technologies 6, 2300189 (2023).
DOI: https://doi.org/10.1002/qute.202300189
4.Huanying Sun, Yanlin Chen, Qichun Liu, Haihua Wu, Yuqing Wang, Tiefu Li*, Yulong Liu†, Superior Frequency Stability and Long-Lived State-Swapping in Cubic-SiC Mechanical Mode Pairs, arXiv:2507.05646 (2025).
DOI: arxiv.org/pdf/2507.05646
Massive mechanical resonators for gravity-quantum interfaces
Traditionally, effects of quantum gravity were expected only at Planck scales—extremely high energies and tiny length scales that are far beyond current experiments. Massive quantum systems, such as cavity optomechanics, provide a unique platform to probe the long-sought connection between quantum mechanics and gravity. It has become possible to prepare massive objects in nearly quantum states inside the laboratory. These systems open a new regime where gravity can be sourced and probed directly by quantum matter, offering tabletop tests that complement accelerator-based and cosmological approaches.
We focuses on developing optomechanical platforms with massive resonators, realized through gold spheres that serve as source and test masses. Specifically, we employ high-stress membrane-based microwave cavity optomechanical systems to control spheres of significant mass. This setup enables ultra-sensitive measurements of the tiny gravitational attraction between two nearby spheres, thereby testing the validity of Newton’s law of gravitation at small mass and length scales.
Beyond precision force measurements, the system can be prepared into non-classical motional states, where both gravitational and quantum effects are simultaneously relevant. This allows us to investigate whether gravity can generate quantum features such as motion correlation, squeezing, or entanglement between the spheres. Such experiments would provide direct evidence on whether the gravitational field exhibits genuinely quantum behavior.
参考文献：
1.Yulong Liu, Jay Mummery, Jingwei Zhou, and Mika A. Sillanpää*, Gravitational Forces Between Nonclassical Mechanical Oscillators, Physical Review Applied 15, 034004 (2021).
DOI: https://doi.org/10.1103/PhysRevApplied.15.034004
2.Ziqian Tang, Hanyu Xue, Zizhao Han, Zikuan Kan, Zeji Li, and Yulong Liu*, Optimal form factors for experimental proposals on gravity-induced entanglement, Physical Review D 112, 042004 (2025).
DOI: https://doi.org/10.1103/jznw-q3q8
3.Ziqian Tang, Wenlong Li, Huanying Sun, Xiaoxia Cai, Tiefu Li, Yulong Liu*, Cavity Optomechanical Probe of Gravity Between Massive Mechanical Oscillators, arXiv:2506.13398 (2025).
DOI: https://arxiv.org/abs/2506.13398
4.Ewa Rej, Richa Cutting, Joe Depellette, Debopam Datta, Nils Tiencken, Joonas Govenius, Visa Vesterinen, Yulong Liu, and Mika A. Sillanpää*, Near-ground-state cooling in electromechanics using measurement-based feedback and a Josephson traveling-wave parametric amplifier, Physical Review Applied 23, 034009 (2025).
DOI: https://doi.org/10.1103/PhysRevApplied.23.034009
