Research

1. Spin qubits in 2D materials

We are interested in quantum sensing and quantum information processing with color centers in 2D materials and diamonds. In particular, we investigate spin defects in hexagonal boron nitride (hBN). A monolayer hBN is similar to graphene, but is an insulator. An hBN electron spin qubit can be readily integrated with other 2D materials for quantum sensing, and coupled to photonic and plasmonic cavities for quantum communication.

Recently, we created boron vacancy spin defects in hBN with femtosecond laser writing and ion implantation, and demonstrated high-contrast plasmon-enhanced shallow spin defects in hexagonal boron nitride [Nano Letters, 21, 7708 (2021) ]. We studied their excited-state spin resonance [Nature Communications, 13, 3233 (2022) ], optically polarized nuclear spins in hBN, and demonstrated optically detected nuclear magnetic resonance with spin defects in hBN for the first time [Nature Materials 21, 1024 (2022)]. Our work provides new opportunities for quantum sensing and quantum information processing with spin qubits in 2D van der Waals materials.

2. Levitated optomechanics

Levitated optomechanics has great potentials in precision measurements, thermodynamics, macroscopic quantum mechanics, and quantum sensing. Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. 

In the past few years, we have demonstrated electron spin control of optically levitated nanodiamonds in vacuum [Nature Communications 7, 12550 (2016)], observed torsional vibration of a levitated nanodiamond [Phys. Rev. Lett. 117, 123604 (2016)], invented an optically levitated Cavendish torsion balance and created the world's fastest nanorotor (beyond 60 billion rpm) at the time [Phys. Rev. Lett., 121, 033603 (2018)]. Our work on ultrafast nanorotor was selected as one of the APS Physics Highlights of the Year of 2018. Recently, we demonstrated the world's most sensitive torque detector that has a sensitivity of 10^(−27) N m Hz^(−1/2) at room temperature [Nature Nanotechnology, 15, 89 (2020)]. We also demonstrated optical levitation of a nanoparticle in a vacuum with a single ultrathin metalens [Optica, 8, 1359 (2021) ], which will be useful for portative sensing and quantum information science.

3. Quantum biological and chemical sensing

We are interested in using spin defects in solids for biological and chemical sensing. Paramagnetic ions and radicals play essential roles in biology and medicine, but detecting them requires highly sensitive and ambient-operable sensors. Recently, we showed that spin qubits in hexagonal boron nitride (hBN), a layered van der Waals (vdW) material, can efficiently detect paramagnetic spins in liquids at nanoscales. We detected paramagnetic ions in water using spin relaxation measurements, with a sensitivity of about 10–18 mol/Hz1/2 for Gd3+ ions [ACS Photonics 10, 2894 (2023)]. Previously, we have invented axial plane optical microscopy [Scientific Reports, 4, 7253 (2014)] and demonstrated axial plane single-molecule super-resolution microscopy of whole cells [Biomedical Optics Express, 11, 461 (2020)].