Zhujing Xu
Harvard University
zxu2@g.harvard.edu
Bio
Zhujing Xu received her B.S. in Physics from University of Science and Technology of China in 2016. After that, she joined Prof. Tongcang LiÕs group at Purdue University and received her Ph.D. in Physics in 2022. During her Ph.D., she has worked on optomechanics and solid-state spins. Her thesis work focused on building Casimir devices and realizing quantum vacuum mediated energy transfer between mechanical oscillators. Currently, she is a Harvard Quantum Initiative (HQI) postdoctoral fellow working in Prof. Marko LoncaråÕs group at Harvard University. She is working on probing spin-phonon interactions in diamonds and building integrated phononic circuits.
Areas of Research
- Photonics and Quantum Technologies
Phonon transport across vacuum and across solid-state spins
Phnonic devices are crucial in classical information processing. The slower speed and reduced losses of acoustic waves open the opportunity for realizing compact and efficient components for delaying, filtering, and storing memory. Besides, phononic devices are capable of coupling to many systems, including superconducting qubits, optical photons, and solid-state defects. Advancing the ability to control phonon propagation is a key step toward developing larger-scale phononic circuits and hybrid quantum systems. In the first part, I will talk about phonon transport by quantum vacuum fluctuations. Random quantum vacuum fluctuations exist everywhere, and they lead to the Casimir interaction between macroscopic bodies. The Casimir effect can dominate the interaction between microstructures at small separations and hence a device that can leverage the Casimir force is in demand. Phonons normally can not transport in vacuum except utilizing quantum vacuum fluctuations. In the talk, I will present the first experimental demonstration of quantum vacuum-mediated non-reciprocal phonon energy transfer between two micromechanical oscillations, revealing a new mechanism for controlling phonon transfer in vacuum. Besides, I will introduce the first observation of Casimir interaction between three cantilevers. We built a unique three-body Casimir device that can switch and amplify phonon energy transfer by quantum vacuum fluctuations. In the second part, I will introduce the spin-phonon interactions in diamonds. The negatively charged SiV in diamond has a remarkably high strain susceptibility, and its spin levels can be coherently driven by resonant surface acoustic wave (SAW) so it is one of the best candidates for realizing phononic quantum devices. I will talk about the experimental efforts in enhancing spin-phonon interaction by engineering the local density of states with SAW cavity. Besides, I will introduce the experimental efforts of realizing integrated phononic circuits by thin-film lithium niobate on sapphire.