Yiqi Wang

selected publications

1. arXiv

   Nonlinear Dynamics and Mechanical Frequency Combs with a Meissner-levitated Micromagnet

   Yiqi Wang*, Trisha Madhavan*, Vanessa Wachter*, J. DaLi Schaefer, and 5 more authors

   arXiv Sep 2026

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   Nonlinearities in multimode mechanical systems can give rise to rich dynamical phenomena with great potential for sensing applications and for future quantum experiments. We demonstrate that the coupled center-of-mass and rotational motion of a Meissner-levitated micromagnet offer a promising platform for nonlinear dynamics, combining low dissipation, magnetic tunability, strong intrinsic Duffing nonlinearities, and nonlinear intermodal couplings. We use this tunability to demonstrate the generation of a mechanical frequency comb in the micromagnet dynamics, realized by parametric excitation of two translational modes followed by cascaded nonlinear frequency mixing, which produces a phononic comb with tunable spacing. At large amplitudes, nonlinear coupling to a low-frequency librational mode of the magnet leads to parametric excitation and phase locking of that mode, generating a dense spectral fine structure at subharmonics of the drive. These results establish levitated micromagnets as a platform for nonlinear multimode mechanics, with potential applications in precision sensing and quantum-limited metrology.

   @article{Wang2026FrequencyComb,
     title = {Nonlinear Dynamics and Mechanical Frequency Combs with a Meissner-levitated Micromagnet},
     author = {Wang*, Yiqi and Madhavan*, Trisha and Wachter*, Vanessa and Schaefer, J. DaLi and NewRingeisen, Addison and Wei, Zhiyuan and Fung, Frankie and Stickler, Benjamin A. and Lukin, Mikhail D.},
     journal = {arXiv},
     year = {2026},
     month = sep,
     url = {https://doi.org/10.48550/arXiv.2609.11668},
   }

2. arXiv

   Exploring Dynamics of Individual Vortices in a Superconductor via a Levitated Magnetic Transducer

   Yiqi Wang*, Trisha Madhavan*, J. DaLi Schaefer, Addison NewRingeisen, and 2 more authors

   arXiv Jun 2026

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   Trapped vortices determine fundamental properties of superconductors and play an important role in many practical applications such as magnetic levitation, however their complex dynamics remain poorly understood. Here, we use the mechanical motion of micron-scale levitated magnetic particles to probe the dynamics of individual vortices. Specifically, we show that the dynamics of levitated magnets are strongly influenced by vortices trapped in the YBCO superconducting film. We observe random telegraph signals in the mechanical frequency, dissipation rate, and energy of levitated particles, which we attribute to random tunneling of individual vortices. The nonlinearity of vortex-defect interaction manifests as non-exponential decay in ringdown measurements, revealing a complex underlying potential landscape. Our results provide insights into elusive dissipation mechanisms in superconducting levitated systems, open new avenues for using levitated magnets as sensitive probes of static and dynamic properties of individual vortices in superconductors and their interactions with material disorder, and point toward novel routes for using magnetic particles as highly coherent mechanical transducers.

   @article{Wang2026Vortex,
     title = {Exploring Dynamics of Individual Vortices in a Superconductor via a Levitated Magnetic Transducer},
     author = {Wang*, Yiqi and Madhavan*, Trisha and Schaefer, J. DaLi and NewRingeisen, Addison and Fung, Frankie and Lukin, Mikhail D.},
     journal = {arXiv},
     year = {2026},
     month = jun,
     url = {https://doi.org/10.48550/arXiv.2606.27297},
   }

3. 

   Manipulating and Measuring States of a Superfluid Optomechanical Resonator in the Quantum Regime

   Yiqi Wang

   Dec 2023

   Abs Bib HTML PDF

   Quantum optomechanics describes utilizing optics to precisely manipulate and read out the motional degrees of freedom of a mechanical oscillator. If the mechanical oscillator is very weakly coupled to its environment, then the optomechanical interaction can be used to control the state of the mechanical oscillator in a quantum way. Applying these systems to advanced sensing techniques has inaugurated experiments on dark matter searches, gravitational wave detection, quantum gravitational phenomena tests, and sensing beyond the standard quantum limit. I am motivated by asking: “What is the largest and most tangible object to reveal purely quantum phenomena?” In addition, I seek to use mechanics to explore quantum-enhanced applications.In this thesis, I describe my work toward preparing quantum states of mechanical motion in a cavity optomechanical system. The system is a Fabry-Perot cavity that is filled ´ with superfluid helium. A density wave of the helium serves as the mechanical resonator, whose effective mass is ∼1 ng. The radiation pressure of the light is used as a gentle quantum “drumstick” to control the motion of the helium, while the helium, in exchange, imprints information about its motion on the emitted light. For such a large object, a myriad of different factors conspire to mask quantum effects. However, I can circumvent some of the obstacles by leveraging the material properties of superfluid helium and by using single-photon counting techniques.In the experiment, I manipulated and characterized the state of the mechanics through optomechanical coupling and by performing photon counting measurements on the scattered light. I measured this mechanical resonator’s second/third/fourth-order coherence functions while it was in a thermal state with less than three phonons. In addition, I drove this mechanical resonator to a nearly coherent state. The state had around two phonons’ worth of fluctuations while its amplitude corresponded to 4 × 104 phonons. More striking quantum effects are related to states that are excluded by classical theories. Following the DLCZ protocol, I conditionally prepared non-classical photon-phonon entangled states. Their photon-phonon coherences violated a classical bound set by Cauchy-Schwarz inequality with a four-sigma significance.I will also discuss our next steps using an even larger cavity to observe more macroscopic and more striking quantum features. Such a system shows prospects for dark matter detection, gravitational wave detection, and testing non-standard modified quantum theory.

   @phdthesis{Yiqi2024Manipulating,
     author = {Wang, Yiqi},
     year = {2023},
     month = dec,
     title = {Manipulating and Measuring States of a Superfluid Optomechanical Resonator in the Quantum Regime},
     journal = {ProQuest Dissertations and Theses},
     pages = {278},
     note = {Copyright - Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works; Last updated - 2024-02-16},
     keywords = {Optomechanics; Photon statistics; Superfluid helium; Quantum states; Quantum physics; Acoustics; Low temperature physics; 0986:Acoustics; 0599:Quantum physics; 0598:Low Temperature Physics},
     isbn = {9798381438017},
     language = {English},
     url = {http://search.proquest.com.ezp-prod1.hul.harvard.edu/dissertations-theses/manipulating-measuring-states-superfluid/docview/2921076179/se-2},
   }

4. 

   A proposal for detecting the spin of a single electron in superfluid helium

   Jinyong Ma, Yogesh SS Patil, Jiaxin Yu, Yiqi Wang, and 1 more author

   arXiv Aug 2023

   Abs arXiv Bib HTML PDF

   The electron bubble in superfluid helium has two degrees of freedom that may offer exceptionally low dissipation:the electron’s spin and the bubble’s motion. If these degrees of freedom can be read out and controlled with sufficient sensitivity, they would provide a novel platform for realizing a range of quantum technologies and for exploring open questions in the physics of superfluid helium. Here we propose a practical scheme for accomplishing this by trapping an electron bubble inside a superfluid-filled opto-acoustic cavity.

   @article{Ma2023ElectronBubble,
     title = {A proposal for detecting the spin of a single electron in superfluid helium},
     author = {Ma, Jinyong and Patil, Yogesh SS and Yu, Jiaxin and Wang, Yiqi and Harris, J. G. E.},
     journal = {arXiv},
     year = {2023},
     month = aug,
     url = {https://doi.org/10.48550/arXiv.2308.07174},
   }

5. 

   Superfluid Helium Drops Levitated in High Vacuum

   C. D. Brown, Y. Wang, M. Namazi, G. I. Harris, and 2 more authors

   Physical Review Letters May 2023

   Abs arXiv Bib HTML PDF

   We demonstrate the trapping of millimeter-scale superfluid helium drops in high vacuum. The drops are sufficiently isolated that they remain trapped indefinitely, cool by evaporation to 330 mK, and exhibit mechanical damping that is limited by internal processes. The drops are also shown to host optical whispering gallery modes. The approach described here combines the advantages of multiple techniques, and should offer access to new experimental regimes of cold chemistry, superfluid physics, and optomechanics.

   @article{Brown2023Superfluid,
     title = {Superfluid Helium Drops Levitated in High Vacuum},
     author = {Brown, C. D. and Wang, Y. and Namazi, M. and Harris, G. I. and Uysal, M. T. and Harris, J. G. E.},
     journal = {Physical Review Letters},
     volume = {130},
     issue = {21},
     pages = {216001},
     numpages = {5},
     year = {2023},
     publisher = {American Physical Society},
     month = may,
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.130.216001},
   }

6. 

   Measuring High-Order Phonon Correlations in an Optomechanical Resonator

   Yogesh SS Patil, Jiaxin Yu, Sean Frazier, Yiqi Wang, and 4 more authors

   Physical Review Letters May 2022

   Abs arXiv Bib HTML PDF

   We use single photon detectors to probe the motional state of a superfluid 4-Helium resonator of mass around 1 ng. The arrival times of Stokes and anti-Stokes photons (scattered by the resonator’s acoustic mode) are used to measure the resonator’s phonon coherences up to the fourth order. By postselecting on photon detection events, we also measure coherences in the resonator when less than 3 phonons have been added or subtracted. These measurements are found to be consistent with predictions that assume the acoustic mode to be in thermal equilibrium with a bath through a Markovian coupling.

   @article{patil2022measuring,
     title = {Measuring High-Order Phonon Correlations in an Optomechanical Resonator},
     author = {Patil, Yogesh SS and Yu, Jiaxin and Frazier, Sean and Wang, Yiqi and Johnson, Kale and Fox, Jared and Reichel, Jakob and Harris, Jack GE},
     journal = {Physical Review Letters},
     volume = {128},
     number = {18},
     pages = {183601},
     year = {2022},
     publisher = {APS},
     url = {https://doi.org/10.1103/PhysRevLett.128.183601},
   }