Optical addressing, a technology to focus and align individual addressing beams onto quantum particles, needs integrated, miniatured, and flexible focusing optical elements to realize precise manipulation over quantum states of individual trapped ion or neutral atom. Existing technologies about optical addressing, are limited by the lack of scalability and face challenges in obtaining good focusing properties, such as diffraction-limited focusing spot size, low crosstalk, and high efficiency.

A Research group from Huazhong University of Science and Technology (HUST), China, payed their attension to  optical metalens as a solution to optical addressing, which is well known for their compact size, planar structure, and compatibility with CMOS processing. Their idea is to use the scalable metalens array consisting of periodical metalens molecules to focus the incident addressing beam array. In their design, each metalens molecule includes five metalenses spatially arranged in a “Z” shape with central symmetry, and each metalens is composed of nanopillars on an fused silica substrate. With a “Z” shaped metalens molecule incorporating both on-axis and off axis metalens, focused spot spacing can be much smaller than the spacing between two neighboring metalenses, even arbitrarily arranged focused spot array can be obtained by proper design. This design has distinct advantages for optical addressing applications, as spacing between trapped ions can be very compact, and more ions can be manipulated at a same time by just adding more metalens molecules.

Researchers successfully designed metalens arrays for x linearly polarized and left circularly polarized light respectively. The resuls show that they can focus collimated addressing beam array into a compact focused spot array with a uniform spot spacing of 5 μm, featuring a low crosstalk of less than 0.82%. 

Researchers believe that their design might be helpful to promote the development of integrated trapped-ion quantum computers and give some inspiration in the design of metalens for optical addressing applications.. The work entitled “Design of scalable metalens array for optical addressing” was published on Frontiers of Optoelectronics (published on August. 4, 2022).




Image: Design of Scalable metalens array for optical addressing.. (a) Individual metalens molecule including on-axis and off-axis metalens spatially arranged in a “Z” shape. (b) Scalable metalens array composed of several periods of metalens molecule. The obtained focused spot array is schematically shown in the black strip under the main figure


Reference: Tie Hu, Xing Feng, Zhenyu Yang, Ming Zhao. Design of scalable metalens array for optical addressing. Front. Optoelectron. 15, 32 (2022). https://doi.org/10.1007/s12200-022-00035-2