On-chip Levitated Spin-optomechanics

Researching with levitated particles has become a fascinating topic in recent years. Either optical trap or ion trap provides a contactless platform for studying fundamental and quantum physics, including ultrasensitive force and torque sensors, microscopic thermodynamics, spin-cooling of the motion, optomechanical coupling, and quantum ground-state cooling. The latter offers promising opportunities to detect quantum aspects of gravity and quantum macro-superposition.

In this thesis, we first propose and fabricate a thin flat metalens and experimentally trap a silica nanoparticle with it. Compared to a bulky conventional objective, a metalens is much smaller with a flexible design. A high numerical aperture (NA) of 0.88 is measured, corresponding to a full angular aperture is 123 deg. Moreover, a hollow metalens is presented with a higher trapping stability that traps a nanoparticle at 0.2 mTorr. Such thin flat metalenses with various designs can improve the integrity and save valuable space.

However, high laser power of optical levitation places rigorous requirements on the types of particles when pumping down to high vacuum. The rising temperature is destructive to the internal composition of a trapped particle. To address these issues, we design and implement a surface ion trap for those special particles, including diamond, rare earth iron oxide, and etc. Using the surface ion trap, we successfully levitate a nanodiamond in high vacuum. Meanwhile, the measured internal temperature is around 350 K and does not increase when the pressure is below 0.1 mTorr, which is moderate for performing spin readout and quantum control of Nitrogen Vacancy (NV) centers. By applying a rotating electric field, we drive the nanodiamond to rotate at frequencies up to 20 MHz, enabling a comprehensive investigation of the geometric phase induced by classical rotation. The spin properties of the levitated rotating nanodiamond, such as Rabi oscillation, spin echo, and Ramsey dephasing, are characterized through precise control of the pulse sequence.

Finally, a theoretical model utilizing periodic magnetic meta-structure to achieve diamagnetic levitation is proposed. The trapped object is massive (~100 mg), while the trapping frequency remains constant (~100 Hz), making it a promising candidate for a fast-response sensor with high sensitivity.