publications

2023

1. 

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

   Yiqi Wang

   Dec 2023

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   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},
   }

2. 

   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

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   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},
   }

3. 

   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

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   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},
   }

2022

1. 

   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

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   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},
   }