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1. On-chip optical levitation with a metalens in vacuum

   https://doi.org/10.1364/OPTICA.438410  

   Shen, Kunhong; Duan, Yao; Ju, Peng; Xu, Zhujing; Chen, Xi; Zhang, Lidan; Ahn, Jonghoon; Ni, Xingjie; Li, Tongcang (October 2021, Optica)

   Optical levitation of dielectric particles in vacuum is a powerful technique for precision measurements, testing fundamental physics, and quantum information science. Conventional optical tweezers require bulky optical components for trapping and detection. Here, we design and fabricate an ultrathin dielectric metalens with a high numerical aperture of 0.88 at 1064 nm in vacuum. It consists of 500-nm-thick silicon nano-antennas, which are compatible with an ultrahigh vacuum. We demonstrate optical levitation of nanoparticles in vacuum with a single metalens. The trapping frequency can be tuned by changing the laser power and polarization. We also transfer a levitated nanoparticle between two separated optical tweezers. Optical levitation with an ultrathin metalens in vacuum provides opportunities for a wide range of applications including on-chip sensing. Such metalenses will also be useful for trapping ultracold atoms and molecules. 

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2. Optical trapping and manipulation for single-particle spectroscopy and microscopy

   https://doi.org/10.1063/5.0086328  

   Chen, Zhenzhen; Cai, Zhewei; Liu, Wenbo; Yan, Zijie (August 2022, The Journal of Chemical Physics)

   Optical tweezers can control the position and orientation of individual colloidal particles in solution. Such control is often desirable but challenging for single-particle spectroscopy and microscopy, especially at the nanoscale. Functional nanoparticles that are optically trapped and manipulated in a three-dimensional (3D) space can serve as freestanding nanoprobes, which provide unique prospects for sensing and mapping the surrounding environment of the nanoparticles and studying their interactions with biological systems. In this perspective, we will first describe the optical forces underlying the optical trapping and manipulation of microscopic particles, then review the combinations and applications of different spectroscopy and microscopy techniques with optical tweezers. Finally, we will discuss the challenges of performing spectroscopy and microscopy on single nanoparticles with optical tweezers, the possible routes to address these challenges, and the new opportunities that will arise. 

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3. A fully-integrated single-photon source based on single Rb atoms

   HICKMAN, Garrett; VOLLBRECHT, Cecilia; MEHLENBACHER, Brandon; Yu, ZHAONING; XIAO, Yuzhe; Goldsmith, RANDALL; KATS, Mikhail; SAFFMAN, Mark (May 2019, 50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting)

   We describe recent work towards a fully-integrated single-photon source based on the use of single atoms captured from a grating magneto-optical trap (GMOT). Single Rb atoms from a ber-coupled GMOT will be loaded into an optical dipole trap formed by light from an integrated polarization-maintaining (PM) ber. Trapped single atoms will be excited to the 2P1/2 state using resonant light. The resulting single-photon fluorescence will be collected through the same PM ber as is used for trapping, and routed to further experiments. We describe progress towards an intermediate imple- mentation incorporating integrated optical bers and free space light sources. The completed, fully-integrated single-photon source will have numerous applications in quantum communications and quantum information processing, and particularly in improvement of the performance of quantum key distribution systems. 

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4. Opto-thermoelectric speckle tweezers

   https://doi.org/10.1515/nanoph-2019-0530  

   Kotnala, Abhay; Kollipara, Pavana Siddhartha; Zheng, Yuebing (March 2020, Nanophotonics)

   Abstract Opto-thermoelectric tweezers present a new paradigm for optical trapping and manipulation of particles using low-power and simple optics. New real-life applications of opto-thermoelectric tweezers in areas such as biophysics, microfluidics, and nanomanufacturing will require them to have large-scale and high-throughput manipulation capabilities in complex environments. Here, we present opto-thermoelectric speckle tweezers, which use speckle field consisting of many randomly distributed thermal hotspots that arise from an optical speckle pattern to trap multiple particles over large areas. By further integrating the speckle tweezers with a microfluidic system, we experimentally demonstrate their application for size-based nanoparticle filtration. With their low-power operation, simplicity, and versatility, opto-thermoelectric speckle tweezers will broaden the applications of optical manipulation techniques. 

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5. Long-lived Bell states in an array of optical clock qubits

   https://doi.org/10.48550/arXiv.2111.14653  

   Schine, N.; Young, A.W.; Eckner, W.J.; Martin, M. J.; Kaufman, A. M. (July 2022, ArXivorg)

   The generation of long-lived entanglement on an optical clock transition is a key requirement to unlocking the promise of quantum metrology. Arrays of neutral atoms constitute a capable quantum platform for accessing such physics, where Rydberg-based interactions may generate entanglement between individually controlled and resolved atoms. To this end, we leverage the programmable state preparation afforded by optical tweezers along with the efficient strong confinement of a 3d optical lattice to prepare an ensemble of strontium atom pairs in their motional ground state. We engineer global single-qubit gates on the optical clock transition and two-qubit entangling gates via adiabatic Rydberg dressing, enabling the generation of Bell states, |ψ⟩=12√(|gg⟩+i|ee⟩), with a fidelity of F=92.8(2.0)%. For use in quantum metrology, it is furthermore critical that the resulting entanglement be long lived; we find that the coherence of the Bell state has a lifetime of τbc=4.2(6) s via parity correlations and simultaneous comparisons between entangled and unentangled ensembles. Such Bell states can be useful for enhancing metrological stability and bandwidth. Further rearrangement of hundreds of atoms into arbitrary configurations using optical tweezers will enable implementation of many-qubit gates and cluster state generation, as well as explorations of the transverse field Ising model and Hubbard models with entangled or finite-range-interacting tunnellers. 

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