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Optics Letters

High-resolution trapped-ion fluorescence imaging via an integrated metalens

Pengcheng Zheng, Zerui Huang, Junxia Li, Ruxin Zhou, Peiliang Liu, Chaohong Lee

Published Sep 14, 2026• 0 citations
Publisher

Abstract

We demonstrate the first integration of a metalens inside the ultra-high-vacuum (UHV) chamber of an ion trap, enabling near-diffraction-limited imaging of trapped ions. A single trapped Yb + ion is laser-cooled close to the Lamb–Dicke regime to characterize the metalens performance, achieving a full-width at half-maximum (FWHM) of 1.16 ± 0.09 μm, which aligns closely with the Abbe diffraction limit of 1.15 μm and outperforms conventional external-cavity lenses (2.37 ± 0.12 μm) with the same numerical aperture. We further demonstrate near-diffraction-limited imaging of multi-ion systems over the accessible off-axis range. Our results establish the metalens as a superior optical element for ion fluorescence imaging, providing higher resolution for applications in ion position calibration, multi-qubit readout, and precision measurement. Furthermore, this miniaturized and integrable approach overcomes traditional optical constraints, delivering near-diffraction-limited imaging and advancing the development of compact ion trap platforms.

DOI
10.1364/ol.607181

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We demonstrate the first integration of a metalens inside the ultra-high-vacuum (UHV) chamber of an ion trap, enabling near-diffraction-limited imaging of trapped ions. A single trapped Yb + ion is laser-cooled close to the Lamb–Dicke regime to characterize the metalens performance, achieving a full-width at half-maximum (FWHM) of 1.16 ± 0.09 μm, which aligns closely with the Abbe diffraction limit of 1.15 μm and outperforms conventional external-cavity lenses (2.37 ± 0.12 μm) with the same numerical aperture. We further demonstrate near-diffraction-limited imaging of multi-ion systems over the accessible off-axis range. Our results establish the metalens as a superior optical element for ion fluorescence imaging, providing higher resolution for applications in ion position calibration, multi-qubit readout, and precision measurement. Furthermore, this miniaturized and integrable approach overcomes traditional optical constraints, delivering near-diffraction-limited imaging and advancing the development of compact ion trap platforms.
A scalable trapped-ion quantum computer demands efficient fluorescence collection from many readout zones distributed over a large chip area. We present a compact, monolithically integrated approach in which a metalens is fabricated on the backside of a surface-electrode ion trap to collect and collimate ion fluorescence. A 40 × 100 μm aperture formed in the trap’s ground electrode yields a simulated point-source solid-angle collection efficiency of 0.91% and a measured point-source detection efficiency of 0.58%. Expanding the aperture to 40 × 600 μm increases the simulated collection efficiency to 3.17%, comparable to a conventional objective with a numerical aperture of 0.35. An engineered undercut beneath the electrodes surrounding the aperture preserves the collection efficiency while increasing the ion-to-dielectric separation. By directly collimating fluorescence at the trap, the metalens eliminates the need for high numerical aperture objectives. Arrays of such readout zones enable scalable, high-fidelity parallel state detection in large-scale trapped-ion quantum computers.
A microfabricated phase Fresnel lens was used to image ytterbium ions trapped in a radio frequency Paul trap. The ions were laser cooled close to the Doppler limit on the 369.5 nm transition, reducing the ion motion so that each ion formed a near point source. By detecting the ion fluorescence on the same transition, near-diffraction-limited imaging with spot sizes of below 440 nm (FWHM) was achieved. To our knowledge, this is the first demonstration of wavelength-scale imaging of trapped ions and the highest imaging resolution ever achieved with atoms in free space.
The integration of optics for efficient light delivery and the collection of fluorescence from trapped ions in surface electrode ion traps is a key component to achieving scalability for quantum information processing.Diffractive optical elements (DOEs) present a promising approach as compared to bulk optics because of their small physical profile and their flexibility in tailoring the optical wavefront.The precise alignment of the optics for coupling fluorescence to and from the ions, however, poses a particular challenge.Excitation and manipulation of the ions requires a high degree of optical access, significantly restricting the area available for mounting components.The ion traps, DOEs, and other components are compact, constraining the manipulation of various elements.For efficient fluorescence collection from the ions the DOE must be have a large numerical aperture (NA), which results in greater sensitivity to misalignment.The ion traps are sensitive devices, a mechanical approach to alignment such as contacting the trap and using precision motors to back-off a set distance not only cannot achieve the desired alignment precision, but risks damage to the ion trap.We have developed a non-contact precision optical alignment technique.We use line foci produced by off-axis linear Fresnel zone plates (FZPs) projected on alignment targets etched in the top metal layer of the ion trap and demonstrate micron-level alignment accuracy.
The integration of optics for efficient light delivery and the collection of fluorescence from trapped ions in surface electrode ion traps is a key component to achieving scalability for quantum information processing. Diffractive optical elements (DOEs) present a promising approach as compared to bulk optics because of their small physical profile and their flexibility in tailoring the optical wavefront. The precise alignment of the optics for coupling fluorescence to and from the ions, however, poses a particular challenge. Excitation and manipulation of the ions requires a high degree of optical access, significantly restricting the area available for mounting components. The ion traps, DOEs, and other components are compact, constraining the manipulation of various elements. For efficient fluorescence collection from the ions the DOE must be have a large numerical aperture (NA), which results in greater sensitivity to misalignment. The ion traps are sensitive devices, a mechanical approach to alignment such as contacting the trap and using precision motors to back-off a set distance not only cannot achieve the desired alignment precision, but risks damage to the ion trap. We have developed a non-contact precision optical alignment technique. We use line foci produced by off-axis linear Fresnel zone plates (FZPs) projected on alignment targets etched in the top metal layer of the ion trap and demonstrate micron-level alignment accuracy.
Accurate measurements with implications in many branches of physics have been accessed using conventional techniques in Penning traps within a temperature regime where each eigenmotion of a charged particle is still a classical harmonic oscillator. Cooling the particle directly or indirectly with lasers allows reaching the quantum regime of each oscillator, controlling subtle effects in the precision frontier by detecting photons instead of electric currents. In this paper, we present a new in-vacuum optical system designed to detect 397-nm fluorescence photons from individual calcium ions and Coulomb crystals in a 7-T Penning trap. Based on the outcome of computer simulations, our design shows diffraction-limited performance. The system has been characterized using a single laser-cooled ion as a point-like source, reaching a final resolution of 3.69(3) μ m and 2.75(3) μ m for the trap’s axial and radial directions, respectively, after correcting aberrations.
Optical controls provided by lasers are the most important and essential techniques in trapped ion and cold atom systems. It is crucial to increase the optical accessibility of the setup to enhance these optical capabilities. Here, we present the design and construction of a new segmented-blade ion trap integrated with a compact glass vacuum cell, in place of the conventional bulky metal vacuum chamber. The distance between the ion and four outside surfaces of the glass cell is 15 mm, which enables us to install four high-numerical-aperture (NA) lenses (with two NA ⩽ 0.32 lenses and two NA ⩽ 0.66 lenses) in two orthogonal transverse directions, while leaving enough space for laser beams in the oblique and longitudinal directions. The high optical accessibility in multiple directions allows the application of small laser spots for addressable Raman operations, programmable optical tweezer arrays, and efficient fluorescence collection simultaneously. We have successfully loaded and cooled a string of 174Yb+ and 171Yb+ ions in the trap, which verifies the trapping stability. This compact high-optical-access trap setup not only can be used as an extendable module for quantum information processing but also facilitates experimental studies on quantum chemistry in a cold hybrid ion-atom system.