Integrated photonics in surface-electrode ion trap chips

Short answer: Integrated photonics puts the waveguides and grating couplers that deliver laser light inside a surface-electrode ion trap chip, replacing free-space optics. A 2016 paper reports waveguide-based ion addressing in a trap chip, a 2020 Nature paper reports delivery of all wavelengths needed to control strontium ion qubits, and a 2025 paper proposes a design for addressing three ions. These are laboratory demonstrations and a simulation-based design.

The problem

The 2020 Nature authors say monolithic integration of control technologies is a promising route to quantum computers and portable quantum sensors. They say current trapped-ion implementations rely on free-space optics for ion control, which limits portability and scalability. The 2025 paper says conventional free-space optics face challenges in alignment stability and scalability as the number of qubits increases.

2016: waveguides and grating couplers in the trap

A 2016 paper (hosted by MIT) demonstrates lithographically defined nanophotonic waveguide devices for light routing and ion addressing integrated within a surface-electrode trap chip. Focusing grating couplers emit light through openings in the trap electrodes to ions trapped 50 micrometres above the chip, and the authors perform coherent operations on the optical qubit transition in individual strontium-88 ions. They report a diffraction-limited spot with a 2 micrometre 1/e squared radius along the trap axis, and crosstalk errors between 10 to the minus 2 and 4 times 10 to the minus 4 at distances of 7.5 to 15 micrometres from the beam centre. They say the planar fabrication and stable alignment give a path toward the optical systems needed for large-scale trapped-ion quantum information processing.

2020: all wavelengths, delivered by fibre

The 2020 Nature paper demonstrates a surface-electrode ion-trap chip with integrated waveguides and grating couplers that delivers all the wavelengths needed for ionization, cooling, coherent operations and state preparation and detection of strontium ion qubits. Light from violet to infrared is coupled onto the chip through an optical-fibre array, which the authors say creates an inherently stable optical path. They use it to demonstrate qubit coherence resilient to platform vibrations, and describe the work as a key advance toward portable trapped-ion sensors and clocks and toward individual control of larger numbers of ions.

2025: a multimode design for three ions

The 2025 paper proposes a design for a multimode photonic circuit integrated with a surface-electrode trap. A focusing grating coupler emits multimode light through electrode openings to ions trapped 68 micrometres above the chip, and can address three closely positioned ions. Simulations show diffraction-limited spots with a 4.3 micrometre beam waist along the trap axis and 2.2 micrometres perpendicular to it. Controlled interference of two modes gives crosstalk of minus 20 dB to minus 30 dB at ion separations of 5 to 8 micrometres when addressing ions individually, and down to minus 60 dB when two of the three are addressed together. The authors add that higher-order modes might offer a new way to drive spin-motion coupling transitions.

Limits

The 2016 and 2020 results are experiments on single ions or small numbers of ions. The 2025 results are simulations of a proposed design, and the authors call it a viable path to large-scale systems, which is a claim about the future. None of the three papers reports a large processor built this way.

FAQ

Why integrate optics into the trap chip?

The authors say free-space optics limit portability and scalability, and that integrated optics give a stable optical path.

Which wavelengths were delivered in 2020?

All wavelengths needed for ionization, cooling, coherent operations and state preparation and detection of strontium ion qubits, from violet to infrared.

How well can individual ions be addressed?

The 2016 paper measured crosstalk errors of 10 to the minus 2 to 4 times 10 to the minus 4 at 7.5 to 15 micrometres. The 2025 paper simulates minus 20 to minus 30 dB crosstalk at 5 to 8 micrometre spacing.

Is the 2025 design built?

The paper presents it as a proposal supported by simulations.

Was vibration a problem?

The 2020 authors report qubit coherence that is resilient to platform vibrations with fibre-to-chip delivery.