High-Q Nano Beam | Yiqi Wang

Since 2023 August, I have joined the NVs-mechanics project with graduate students Frankie Fung (BA, UChicago ‘18), DaLi Schaefer (BA, UMich ‘18) and Trisha Madhavan (BA, Princeton ‘21).

Interfacing spins and mechanical degrees of freedom allows for a variety of applications and experimental observations. For example, one can deterministically entangle pairs of spins through their coherent coupling with the dynamics of a resonator, even for large spin-spin distance separations and thermal resonator states. Additionally, the resonator could be cooled close to the quantum ground state by bringing a strongly coupled bath of spins into resonance, introducing the possibility of single phonon experiments and quantum state preparation of a mesoscopic object.

In our lab, we are pursuing strong, coherent coupling of Nitrogen Vacancy (NV) center spin qubits in diamond, to mechanical resonators via a magnetic field gradient. One setup we use in the lab consists of silicon nitride nanobeams with a magnet placed at the center. These resonators can be fabricated in a scalable way with several resonators per chip. Frequencies are typically ~ 1 MHz with quality factors of ~ 10^7. The diamonds are on the AFM tips, which allows us to bring an NV arbitrarily close to the magnet.

The previous work of this setup was lead by Mikhail Lukin and Jack Harris with Shimon Kolkowitz, Ania Jayich, Emma Rosenfeld, Jan Gieseler. See the following papers for details:

Kolkowitz, Shimon, et al. “Coherent sensing of a mechanical resonator with a single-spin qubit.” Science 335.6076 (2012): 1603-1606.
Bennett, S. D., et al. “Measuring mechanical motion with a single spin.” New Journal of Physics 14.12 (2012): 125004.
Rabl, Peter, et al. “Strong magnetic coupling between an electronic spin qubit and a mechanical resonator.”Physical Review B 79.4 (2009): 041302.

Based on this system, we are aiming to reach strong coherent coupling between a single spin and a single phonon. See the our recent work towards this goal:

Fung, F., et al. “Programmable Quantum Processors based on Spin Qubits with Mechanically-Mediated Interactions and Transport.” arXiv:2307.12193 (2023).

Now we are collabrating with Simon Groblaecher (TU Delft) to have their high-Q low-frequency hierarchical tensile structural mechanical resonators. See the following papers for details:

Guo, Jingkun, and Simon Groblacher. “Integrated optical-readout of a high-Q mechanical out-of-plane mode.” Light: Science & Applications 11.1 (2022): 282.
Bereyhi, Mohammad J., et al. “Hierarchical tensile structures with ultralow mechanical dissipation.” Nature Communications 13.1 (2022): 3097.

Based on this design, we have achived a magnet attached mechancal resonator with Q>10^7. We are currently working on realizing a stable and small seperation between the magnet and the NV towards the desired strong coupling.